CiteULike: lisa1's library [404 articles]

The lens-regenerating competence in the outer cornea and epidermis of larval Xenopus laevis is related to pax6 expression

Gargioli — 2008-04-26T08:32:31-00:00

Journal of Anatomy, Vol. 212, No. 5. (May 2008), pp. 612-620.

After lentectomy, larval Xenopus laevis can regenerate a new lens by transdifferentiation of the outer cornea and pericorneal epidermis (lentogenic area). This process is promoted by retinal factor(s) accumulated into the vitreous chamber. To understand the molecular basis of the lens-regenerating competence (i.e. the capacity to respond to the retinal factor forming a new lens) in the outer cornea and epidermis, we analysed the expression of otx2, pax6, sox3, pitx3, prox1, betaB1-cry (genes all involved in lens development) by Real-time RT-PCR in the cornea and epidermis fragments dissected from donor larvae. The same fragments were also implanted into the vitreous chamber of host larvae to ascertain their lens-regenerating competence using specific anti-lens antibodies. The results demonstrate that there is a tight correlation between lens-regenerating competence and pax6 expression. In fact, (1) pax6 is the only one of the aforesaid genes to be expressed in the lentogenic area; (2) pax6 expression is absent in head epidermis outside the lentogenic area and in flank epidermis, both incapable of transdifferentiating into lens after implantation into the vitreous chamber; (3) in larvae that have undergone eye transplantation under the head or flank epidermis, pax6 re-expression was observed only in the head epidermis covering the transplanted eye. This is consistent with the fact that only the head epidermis reacquires the lens-regenerating competence after eye transplantation, forming a lens following implantation into the vitreous chamber; and (4) in larvae that have undergone removal of the eye, the epidermis covering the orbit maintained pax6 expression. This is consistent with the fact that after the eye enucleation the lentogenic area maintains the lens-regenerating competence, giving rise to a lens after implantation into the vitreous chamber. Moreover, we observed that misexpression of pax6 is sufficient to promote the acquisition of the lens-regenerating competence in flank epidermis. In fact, flank epidermis fragments dissected from pax6 RNA injected embryos could form lenses when implanted into the vitreous chamber. The data indicate for the first time that pax6 is a pivotal factor of lens-regenerating competence in the outer cornea and epidermis of larval X. laevis.

The optic vesicle promotes cornea to lens transdifferentiation in larval Xenopus laevis

Cannata — 2008-04-26T08:32:31-00:00

Journal of Anatomy, Vol. 212, No. 5. (May 2008), pp. 621-626.

The outer cornea and pericorneal epidermis (lentogenic area) of larval Xenopus laevis are the only epidermal regions competent to regenerate a lens under the influence of the retinal inducer. However, the head epidermis of the lentogenic area can acquire the lens-regenerating competence following transplantation of an eye beneath it. In this paper we demonstrate that both the outer cornea and the head epidermis covering a transplanted eye are capable of responding not only to the retinal inducer of the larval eye but also to the inductive action of the embryonic optic vesicle by synthesizing crystallins. As the optic vesicle is a very weak lens inductor, which promotes crystallin synthesis only on the lens biased ectoderm of the embryo, these results indicate that the lens-forming competence in the outer cornea and epidermis of larval X. laevis corresponds to the persistence and acquisition of a condition similar to that of the embryonic biased ectoderm.

Identifying Autism Loci and Genes by Tracing Recent Shared Ancestry

Eric Morrow — 2008-07-11T15:08:30-00:00

Science, Vol. 321, No. 5886. (11 July 2008), pp. 218-223.

To find inherited causes of autism-spectrum disorders, we studied families in which parents share ancestors, enhancing the role of inherited factors. We mapped several loci, some containing large, inherited, homozygous deletions that are likely mutations. The largest deletions implicated genes, including PCDH10 (protocadherin 10) and DIA1 (deleted in autism1, or c3orf58), whose level of expression changes in response to neuronal activity, a marker of genes involved in synaptic changes that underlie learning. A subset of genes, including NHE9 (Na+/H+ exchanger 9), showed additional potential mutations in patients with unrelated parents. Our findings highlight the utility of "homozygosity mapping" in heterogeneous disorders like autism but also suggest that defective regulation of gene expression after neural activity may be a mechanism common to seemingly diverse autism mutations. 10.1126/science.1157657

Amphibian Cell Culture: Permanent Cell Line from the Bullfrog (Rana catesbeiana)

Ken Wolf — 2008-07-02T16:33:42-00:00

Science, Vol. 144, No. 3626. (26 June 1964), pp. 1578-1580.

A line of fibroblast cells has been established from tongue tissue of the bullfrog (Rana catesbeiana). The cells are near-triploid and were subcultured 57 times during the 22/3 years of their existence. Some of their characteristics are described. 10.1126/science.144.3626.1578

Identification of genes associated with regenerative success of Xenopus laevis hindlimbs

Esther Pearl — 2008-06-24T10:44:52-00:00

BMC Developmental Biology, Vol. 8 (23 June 2008), 66.

ABSTRACT: BACKGROUND: Epimorphic regeneration is the process by which complete regeneration of a complex structure such as a limb occurs through production of a proliferating blastema. This type of regeneration is rare among vertebrates but does occur in the African clawed frog Xenopus laevis, traditionally a model organism for the study of early development. Xenopus tadpoles can regenerate their tails, limb buds and the lens of the eye, although the ability of the latter two organs to regenerate diminishes with advancing developmental stage. Using a heat shock inducible transgene that remains silent unless activated, we have established a stable line of transgenic Xenopus (strain N1) in which the BMP inhibitor Noggin can be over-expressed at any time during development. Activation of this transgene blocks regeneration of the tail and limb of Xenopus tadpoles. RESULTS: In the current study, we have taken advantage of the N1 transgenic line to directly compare morphology and gene expression in same stage regenerating vs. BMP signalling deficient, non-regenerating hindlimb buds. The wound epithelium of N1 transgenic hindlimb buds, which forms over the cut surface of the limb bud after amputation, does not transition normally into the distal thickened apical epithelial cap. Furthermore, the underlying mesenchyme remains rounded and does not expand to form a cone shaped blastema, a normal feature of successful regeneration. Using Affymetrix Gene Chip analysis, we have identified genes linked to regenerative success downstream of BMP signalling, including the BMP inhibitor Gremlin and the stress protein Hsp60 (no blastema in zebrafish). Gene Ontology analysis showed that genes involved in embryonic development and growth are significantly over-represented in regenerating early hindlimb buds and that successful regeneration in the Xenopus hindlimb depends on induction of stress response pathways. CONCLUSION: N1 transgenic hindlimbs, which do not regenerate, do not form an apical epithelial cap or cone shaped blastema following amputation. Comparison of gene expression in stage matched N1 vs. wild type hindlimb buds has revealed several new targets for regeneration research.

FGF-Dependent Mechanosensory Organ Patterning in Zebrafish

Alex Nechiporuk — 2008-06-27T19:42:58-00:00

Science, Vol. 320, No. 5884. (27 June 2008), pp. 1774-1777.

During development, organ primordia reorganize to form repeated functional units. In zebrafish (Danio rerio), mechanosensory organs called neuromasts are deposited at regular intervals by the migrating posterior lateral line (pLL) primordium. The pLL primordium is organized into polarized rosettes representing proto-neuromasts, each with a central atoh1a-positive focus of mechanosensory precursors. We show that rosettes form cyclically from a progenitor pool at the leading zone of the primordium as neuromasts are deposited from the trailing region. fgf3/10 signals localized to the leading zone are required for rosette formation, atoh1a expression, and primordium migration. We propose that the fibroblast growth factor (FGF) source controls primordium organization, which, in turn, regulates the periodicity of neuromast deposition. This previously unrecognized mechanism may be applicable to understanding segmentation and morphogenesis in other organ systems. 10.1126/science.1156547

Proliferating Cells Express mRNAs with Shortened 3' Untranslated Regions and Fewer MicroRNA Target Sites

Rickard Sandberg — 2008-06-20T15:33:43-00:00

Science, Vol. 320, No. 5883. (20 June 2008), pp. 1643-1647.

Messenger RNA (mRNA) stability, localization, and translation are largely determined by sequences in the 3' untranslated region (3'UTR). We found a conserved increase in expression of mRNAs terminating at upstream polyadenylation sites after activation of primary murine CD4+ T lymphocytes. This program, resulting in shorter 3'UTRs, is a characteristic of gene expression during immune cell activation and correlates with proliferation across diverse cell types and tissues. Forced expression of full-length 3'UTRs conferred reduced protein expression. In some cases the reduction in protein expression could be reversed by deletion of predicted microRNA target sites in the variably included region. Our data indicate that gene expression is coordinately regulated, such that states of increased proliferation are associated with widespread reductions in the 3'UTR-based regulatory capacity of mRNAs. 10.1126/science.1155390

Insertion of a Pax6 Consensus Binding Site into the alphaA-Crystallin Promoter Acts as a Lens Epithelial Cell Enhancer in Transgenic Mice

Haotian Zhao — 2008-05-23T17:57:59-00:00

Invest. Ophthalmol. Vis. Sci., Vol. 45, No. 6. (1 June 2004), pp. 1930-1939.

PURPOSE. Although the murine alphaA-crystallin promoter is the most commonly used promoter for achieving transgene expression in the developing lens, this promoter directs transgene expression efficiently only in lens fiber cells. The purpose of the present study was to generate promoters capable of directing transgene expression to the entire lens but not to the corneal epithelium. METHODS. Transgenic mice were generated with fragments of the murine alphaA- and alphaB-crystallin promoters, as well as with an alphaA-crystallin promoter engineered with the insertion of a Pax6 consensus binding site driving either human growth hormone (hGH) or Cre recombinase genes. hGH expression was evaluated by in situ hybridization and immunohistochemistry. Cre expression was revealed by x-gal staining after crossing Cre transgenic mice with a Cre reporter strain. RESULTS. Within the lens, the -214/+38 alphaB-crystallin promoter fragment directed transgene expression in the lens epithelium, but not in fiber cells. The native -282/+43 alphaA-crystallin promoter drove transgene expression in the lens fiber cells of several independent lines of transgenic mice, but none of these mice demonstrated significant transgene expression in the lens epithelium. In contrast, the insertion of a 32-bp sequence containing a Pax6 consensus binding site into the -282/+43 alphaA-crystallin promoter reproducibly led to transgene expression in the lens epithelium as well as the lens fiber cells. CONCLUSIONS. The inclusion of a Pax6 consensus binding site within the -282/+43 alphaA-crystallin promoter enhances the ability of this promoter to drive transgene expression in the lens epithelium. 10.1167/iovs.03-0856

Generation of transparency and cellular organization in lens explants

Michael O'Connor — 2008-05-23T15:25:48-00:00

Experimental Eye Research, Vol. 86, No. 5. (May 2008), pp. 734-745.

The lens grows via the proliferation and differentiation of lens epithelial cells into lens fibres. This differentiation process, thought to be controlled by factors present in the vitreous fluid, generates tightly-packed, parallel-aligned fibre cells that confer transparency to the lens. Using lens epithelial-cell explants we examined how explant orientation and growth factor treatment can affect cellular arrangement and explant transparency. Fibre cell differentiation was induced in lens explants by culturing cells with fibroblast growth factor (FGF) or bovine vitreous. Cell shape and arrangement was investigated using confocal microscopy, electron microscopy, immunofluorescence and in situ hybridization. Explant transparency was measured using light microscopy. Confocal microscopy demonstrated that explant orientation determined cellular arrangement, irrespective of the differentiation stimuli used. In explants where epithelial cells were confined between their normal basement membrane (the lens capsule) and the base of the culture dish, the cells became elongated, thin and parallel-aligned. In contrast, in explants cultured with cells directly exposed to the culture media the cells appeared to be shorter, globular and haphazardly arranged. FGF initiated the differentiation of most lens epithelial cells; however, abnormal cellular morphologies developed with subsequent culture of the cells. As a result, the transparency of these explants decreased with prolonged culture. Interestingly, explants cultured with vitreous (i) did not develop abnormal cellular morphologies, (ii) contained two distinct cell types (retained epithelial cells and newly differentiated fibre cells) and (iii) remained transparent throughout the lengthy culture period. In summary, we have developed a culture system that generates a transparent tissue with a cellular arrangement resembling that of the lens in vivo. We have shown that while FGF and vitreous initiate differentiation within this system, better maintenance of fibre cell integrity, more appropriate regulation of molecular events, and better maintenance of explant transparency was achieved in the presence of vitreous. This system offers an opportunity to further investigate the process of lens fibre cell differentiation as well as a means of better identifying the factors that contribute to the development of tissue transparency in vitro.

Fibroblast growth factor receptor signaling is essential for lens fiber cell differentiation.

Haotian Zhao — 2008-05-22T18:48:47-00:00

Developmental biology (28 March 2008)

The vertebrate lens provides an excellent model to study the mechanisms that regulate terminal differentiation. Although fibroblast growth factors (FGFs) are thought to be important for lens cell differentiation, it is unclear which FGF receptors mediate these processes during different stages of lens development. Deletion of three FGF receptors (Fgfr1-3) early in lens development demonstrated that expression of only a single allele of Fgfr2 or Fgfr3 was sufficient for grossly normal lens development, while mice possessing only a single Fgfr1 allele developed cataracts and microphthalmia. Profound defects were observed in lenses lacking all three Fgfrs. These included lack of fiber cell elongation, abnormal proliferation in prospective lens fiber cells, reduced expression of the cell cycle inhibitors p27(kip1) and p57(kip2), increased apoptosis and aberrant or reduced expression of Prox1, Pax6, c-Maf, E-cadherin and alpha-, beta- and gamma-crystallins. Therefore, while signaling by FGF receptors is essential for lens fiber differentiation, different FGF receptors function redundantly.

Heparin-induced oligomerization of FGF molecules is responsible for FGF receptor dimerization, activation, and cell proliferation

T Spivak-Kroizman — 2008-05-22T16:23:41-00:00

Cell, Vol. 79, No. 6. (16 December 1994), pp. 1015-1024.

Heparin is required for fibroblast growth factor (FGF) stimulation of biological responses. Using isothermal titration calorimetry, we show that acidic FGF (aFGF) forms a 1:1 complex with the soluble extracellular domain of FGF receptor (FGFR). Heparin exerts its effect by binding to many molecules of aFGF. The resulting aFGF-heparin complex can bind to several receptor molecules, leading to FGFR dimerization. In two cell lines lacking endogenous heparan sulfate, exogenous heparin is required for FGFR dimerization, tyrosine kinase activation, c-fos mRNA transcription, and cell proliferation. Moreover, a synthetic heparin analog that binds monovalently to aFGF blocks FGFR dimerization, activation, and signaling via FGFR. We propose that heparin causes oligomerization of aFGF such that its binding to FGFR results in dimerization and activation. This represents a novel mechanism for transmembrane signaling and may account for the action of many heparin-bound growth factors.

A stem batrachian from the Early Permian of Texas and the origin of frogs and salamanders

Jason Anderson — 2008-05-21T21:58:26-00:00

Nature, Vol. 453, No. 7194. (22 May 2008), pp. 515-518.

Wound repair and regeneration

Geoffrey Gurtner — 2008-05-15T23:29:38-00:00

Nature, Vol. 453, No. 7193. (14 May 2008), pp. 314-321.

Structural interactions of fibroblast growth factor receptor with its ligands

Deborah Stauber — 2008-05-15T22:28:48-00:00

Proceedings of the National Academy of Sciences, Vol. 97, No. 1. (4 January 2000), pp. 49-54.

10.1073/pnas.97.1.49

Eye drop delivery of nano-polymeric micelle formulated genes with cornea-specific promoters.

YC Tong — 2008-05-14T16:13:50-00:00

The journal of gene medicine, Vol. 9, No. 11. (November 2007), pp. 956-966.

BACKGROUND: This study evaluates the eye drop delivery of genes with cornea-specific promoters, i.e., keratin 12 (K12) and keratocan (Kera3.2) promoters, by non-ionic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) polymeric micelles (PM) to mouse and rabbit eyes, and investigates the underlying mechanisms. METHODS: Three PM-formulated plasmids (pCMV-Lac Z, pK12-Lac Z and pKera3.2-Lac Z) containing the Lac Z gene for beta-galactosidase (beta-Gal) whose expression was driven by the promoter of either the cytomegalovirus early gene, the keratin 12 gene or the keratocan gene, were characterized by critical micelle concentration (CMC), dynamic light scattering (DLS), and atomic force microscopy (AFM). Transgene expression in ocular tissue after gene delivery was analyzed by 5-bromo-4-chloro-3-indolyl-beta-D-galactoside (X-Gal) color staining, 1,2-dioxetane beta-Gal enzymatic activity measurement, and real-time polymerase chain reaction (PCR) analysis. The delivery mechanisms of plasmid-PM on mouse and rabbit corneas were evaluated by EDTA and RGD (arginine-glycine-aspartic acid) peptide. RESULTS: The sizes of the three plasmid-PM complexes were around 150-200 nm with unimodal distribution. Enhanced stability was found for three plasmid-PM formulations after DNase I treatment. After six doses of eye drop delivery of pK12-Lac Z-PM three times a day, beta-Gal activity was significantly increased in both mouse and rabbit corneas. Stroma-specific Lac Z expression was only found in pKera3.2-Lac Z-PM-treated animals with pretreatment by 5 mM EDTA, an opener of junctions. Lac Z gene expression in both pK12-Lac Z-PM and pKera3.2-Lac Z-PM delivery groups was decreased by RGD peptide pretreatment. CONCLUSIONS: Cornea epithelium- and stroma-specific gene expression could be achieved using cornea-specific promoters of keratin 12 and keratocan genes, and the gene was delivered with PM formulation through non-invasive, eye drop in mice and rabbits. The transfection mechanism of plasmid-PM may involve endocytosis and particle size dependent paracellular transport.

Cornea-specific expression of K12 keratin during mouse development.

CY Liu — 2008-05-14T15:51:44-00:00

Current eye research, Vol. 12, No. 11. (November 1993), pp. 963-974.

The full-length cDNA of mouse K12 keratin was characterized by sequencing overlapping cDNA clones isolated from a mouse cornea cDNA library. Using Northern blot hybridization, the radio-labeled cDNA hybridized to a 1.9 kb mRNA from adult cornea, but not from other mouse tissues including snout, esophagus, tongue, and skin. During mouse development, corneas do not express K12 mRNA until 4 days postnatal when the epithelium begins to stratify as judged by Northern blot and in situ hybridization. In situ hybridization with 3H-labeled cDNA probe and immunohistochemical studies with antibodies against a synthetic oligo-peptide deduced from rabbit K12 cDNA demonstrate that this mouse K12 keratin is expressed in all cell layers of adult corneal epithelium, and the suprabasal layers, but not the basal layer of the limbal epithelium. Epidermal growth factor (EGF) has been shown to promote epithelium stratification of cultured chicken and human corneas in vitro. To examine whether EGF can promote K12 expression, EGF was administered to neonatal mice. The results indicate that EGF retards K12 expression by corneal epithelial cells, even though it promotes corneal epithelial stratification during mouse development. Taken together, our results demonstrate that the expression of K12 keratin is cornea-specific, differentiation-dependent, and developmentally regulated.

Appearance of the keratin pair K3/K12 during embryonic and adult corneal epithelial differentiation in the chick and in the rabbit.

C Chaloin-Dufau — 2008-05-14T15:41:14-00:00

Cell differentiation and development : the official journal of the International Society of Developmental Biologists, Vol. 32, No. 2. (1 December 1990), pp. 97-108.

Sequential expression of the K3/K12 keratin pair was studied during epithelial corneal differentiation, using monoclonal antibodies coupled with electrophoretic analysis. In the chick embryo, K12 appears on day 12, while K3 is present at least from day 11. By contrast, in the rabbit embryo, the expression of K12 (at 17 days) precedes that of K3 (at 21 days). In the adult rabbit, K3 is expressed without K12 in part of the limbus. Thus, within the corneal-type keratin pair, either the acidic or the basic partner appears first, according to the developmental stage or the species.

Crystal Structures of Two FGF-FGFR Complexes Reveal the Determinants of Ligand-Receptor Specificity

Alexander Plotnikov — 2008-05-13T16:07:02-00:00

Cell, Vol. 101, No. 4. (12 May 2000), pp. 413-424.

To elucidate the structural determinants governing specificity in fibroblast growth factor (FGF) signaling, we have determined the crystal structures of FGF1 and FGF2 complexed with the ligand binding domains (immunoglobulin-like domains 2 [D2] and 3 [D3]) of FGF receptor 1 (FGFR1) and FGFR2, respectively. Highly conserved FGF-D2 and FGF-linker (between D2-D3) interfaces define a general binding site for all FGF-FGFR complexes. Specificity is achieved through interactions between the N-terminal and central regions of FGFs and two loop regions in D3 that are subject to alternative splicing. These structures provide a molecular basis for FGF1 as a universal FGFR ligand and for modulation of FGF-FGFR specificity through primary sequence variations and alternative splicing.

The hedgehog pathway is a modulator of retina regeneration

Jason Spence — 2008-05-13T15:43:50-00:00

Development, Vol. 131, No. 18. (15 September 2004), pp. 4607-4621.

The embryonic chick has the ability to regenerate its retina after it has been completely removed. Here, we provide a detailed characterization of retina regeneration in the embryonic chick at the cellular level. Retina regeneration can occur in two distinct manners. The first is via transdifferentiation, which is induced by members of the Fibroblast growth factor (Fgf) family. The second type of retinal regeneration occurs from the anterior margin of the eye, near the ciliary body (CB) and ciliary marginal zone (CMZ). We show that regeneration from the CB/CMZ is the result of proliferating stem/progenitor cells. This type of regeneration is also stimulated by Fgf2, but we show that it can be activated by Sonic hedgehog (Shh) overexpression when no ectopic Fgf2 is present. Shh-stimulated activation of CB/CMZ regeneration is inhibited by the Fgf receptor (Fgfr) antagonist, PD173074. This indicates that Shh-induced regeneration acts through the Fgf signaling pathway. In addition, we show that the hedgehog (Hh) pathway plays a role in maintenance of the retina pigmented epithelium (RPE), as ectopic Shh expression inhibits transdifferentiation and Hh inhibition increases the transdifferentiation domain. Ectopic Shh expression in the regenerating retina also results in a decrease in the number of ganglion cells present and an increase in apoptosis mostly in the presumptive ganglion cell layer (GCL). However, Hh inhibition increases the number of ganglion cells but does not have an effect on cell death. Taken together, our results suggest that the hedgehog pathway is an important modulator of retina regeneration. 10.1242/dev.01298

Mind Bomb Is a Ubiquitin Ligase that Is Essential for Efficient Activation of Notch Signaling by Delta

Motoyuki Itoh — 2008-05-08T15:33:58-00:00

Developmental Cell, Vol. 4, No. 1. (January 2003), pp. 67-82.

Lateral inhibition, mediated by Notch signaling, leads to the selection of cells that are permitted to become neurons within domains defined by proneural gene expression. Reduced lateral inhibition in zebrafish mib mutant embryos permits too many neural progenitors to differentiate as neurons. Positional cloning of mib revealed that it is a gene in the Notch pathway that encodes a RING ubiquitin ligase. Mib interacts with the intracellular domain of Delta to promote its ubiquitylation and internalization. Cell transplantation studies suggest that mib function is essential in the signaling cell for efficient activation of Notch in neighboring cells. These observations support a model for Notch activation where the Delta-Notch interaction is followed by endocytosis of Delta and transendocytosis of the Notch extracellular domain by the signaling cell. This facilitates intramembranous cleavage of the remaining Notch receptor, release of the Notch intracellular fragment, and activation of target genes in neighboring cells.

Fibroblast growth factor receptors regulate the ability for hindlimb regeneration in Xenopus laevis

Christopher D'Jamoos — 2008-05-05T17:04:34-00:00

Wound Repair and Regeneration, Vol. 6, No. 4. (1998), pp. S-388-S-397.

During outgrowth of the developing limb, signals from the apical ectodermal ridge, such as fibroblast growth factors, are paramount for limb patterning. Similarly, fibroblast growth factor molecules and their receptors are synthesized in the wound epithelium of the regenerating limb blastema, implicating an analogous function to limb development. To address this issue further and to understand the role of fibroblast growth factor receptor signaling in limb regeneration, we have examined the expression patterns of x-fibroblast growth factor receptors-1, -2, -3, -4a, and -4b in Xenopus laevis. This amphibian model provides a system in which both regenerating (premetamorphic; tadpole or larva stage) and nonregenerating (postmetamorphic; froglet stage) hindlimbs can be studied. In premetamorphic hindlimbs (stage 53), all of the receptors were expressed in the wound epithelium and the underlying mesenchyme. In postmetamorphic limbs (stage 61), however, transcripts for x-fibroblast growth factor receptors-1 and -2 were absent from the wound epithelium. The expression results for x-fibroblast growth factor receptors-1 and -2 were corroborated at the protein level by employing specific antibodies. Thus, it appears that expression of both fibroblast growth factor receptors-1 and -2 is associated with the ability for limb regeneration. The role of these receptors in regeneration was further investigated by using specific inhibitors to fibroblast growth factor receptors during premetamorphic hindlimb regeneration. These compounds inhibited the normal limb outgrowth and resulted, in the majority of the cases, in outgrowths of cones or spikes reminiscent of growth that is seen in amputated postmetamorphic limbs. Thus, fibroblast growth factor receptors-1 and -2 expression and function should be regarded as paramount for the ability of limb regeneration in Xenopus.

Ocular surface tissue morphogenesis in normal and disease states revealed by genetically modified mice.

WW Kao — 2008-05-02T22:06:24-00:00

Cornea, Vol. 25, No. 10 Suppl 1. (December 2006)

Many transgenic and knockout mice exhibit pathogenic processes resembling human ocular surface diseases. Thus, the clinical manifestations of mouse lines can provide clues for identifying heritable human diseases of unknown etiology. However, mouse lines using conventional techniques of transgenesis and gene targeting often exhibit embryonic lethality and congenital defects, which preclude the use of such mouse models to study acquired ocular surface tissue diseases. These difficulties can be in part overcome by preparing mouse lines of inducible transgene expression, tissue-specific gene ablation, and inducible tissue-specific gene ablation. Conditional transgenic mouse lines live normally until administration of doxycycline and hormones that induce expression of the transgene and ablation of gene of interest. Toward this goal, we prepared 2 groups of genetically modified mouse lines: (1) transgenesis using keratocan promoter was used to create Kera-rtTA mice (doxycycline-inducible mice) and Cre-LoxP system (ie, Kera-Cre mice; conditional gene ablation in neural crest cell lineage and adult stromal keratocyte) and Kera-CrePR mice (RU-486 inducible); and (2) knock-in strategies were used to create Krt12-rtTA mice (doxycycline inducible), Krt12-Cre mice (conditional ablation in corneal epithelium), and Krt12rtTA-tet-O-Cre mice (doxycycline-inducible corneal epithelium-specific gene ablation). Using these mouse lines, we showed that transforming growth factor (TGF)-beta2 is essential for eye morphogenesis, TGF-alpha is a morphogen for eyelid formation, and lumican is a matrikine that has multiple regulatory functions on cell activities (eg, migration proliferation and gene expression) besides serving as a regulatory molecule of collagen fibrillogenesis. These mouse lines can also be used as models for development of therapeutic treatment regimens of ocular surface diseases using gene therapy and stem cell strategies.

Role that phosphorylation of GSK3 plays in insulin and Wnt signalling defined by knockin analysis

Edward Mcmanus — 2005-03-24T21:43:02-00:00

The EMBO Journal, Vol. aop, No. current. (24 March 2005)

Phosphorylation by p38 MAPK as an Alternative Pathway for GSK3beta Inactivation

Tina Thornton — 2008-05-02T15:08:25-00:00

Science, Vol. 320, No. 5876. (2 May 2008), pp. 667-670.

Glycogen synthase kinase 3 (GSK3) is involved in metabolism, neurodegeneration, and cancer. Inhibition of GSK3 activity is the primary mechanism that regulates this widely expressed active kinase. Although the protein kinase Akt inhibits GSK3 by phosphorylation at the N terminus, preventing Akt-mediated phosphorylation does not affect the cell-survival pathway activated through the GSK3 substrate -catenin. Here, we show that p38 mitogen-activated protein kinase (MAPK) also inactivates GSK3 by direct phosphorylation at its C terminus, and this inactivation can lead to an accumulation of -catenin. p38 MAPK-mediated phosphorylation of GSK3 occurs primarily in the brain and thymocytes. Activation of -catenin-mediated signaling through GSK3 inhibition provides a potential mechanism for p38 MAPK-mediated survival in specific tissues. 10.1126/science.1156037

Structural Basis for FGF Receptor Dimerization and Activation

Alexander Plotnikov — 2008-05-01T16:01:33-00:00

Cell, Vol. 98, No. 5. (3 September 1999), pp. 641-650.

The crystal structure of FGF2 bound to a naturally occurring variant of FGF receptor 1 (FGFR1) consisting of immunoglobulin-like domains 2 (D2) and 3 (D3) has been determined at 2.8 Å resolution. Two FGF2:FGFR1 complexes form a 2-fold symmetric dimer. Within each complex, FGF2 interacts extensively with D2 and D3 as well as with the linker between the two domains. The dimer is stabilized by interactions between FGF2 and D2 of the adjoining complex and by a direct interaction between D2 of each receptor. A positively charged canyon formed by a cluster of exposed basic residues likely represents the heparin-binding site. A general model for FGF- and heparin-induced FGFR dimerization is inferred from the crystal structure, unifying a wealth of biochemical data.

Melanopsin cells are the principal conduits for rod–cone input to non-image-forming vision

Ali Güler — 2008-04-24T18:14:00-00:00

Nature (23 April 2008)

Heparin Structure and Interactions with Basic Fibroblast Growth Factor

S Faham — 2008-04-28T22:06:18-00:00

Science, Vol. 271, No. 5252. (23 February 1996), pp. 1116-1120.

10.1126/science.271.5252.1116

Rare Structural Variants Disrupt Multiple Genes in Neurodevelopmental Pathways in Schizophrenia

Tom Walsh — 2008-03-28T13:34:50-00:00

Science (27 March 2008), 1155174.

Schizophrenia is a devastating neurodevelopmental disorder whose genetic influences remain elusive. We hypothesize that individually rare structural variants contribute to the illness. Microdeletions and microduplications >100 kb were identified by microarray comparative genomic hybridization (CGH) of genomic DNA from 150 individuals with schizophrenia and 268 ancestry-matched controls. All variants were validated by high-resolution platforms. Novel deletions and duplications of genes were present in 5% of controls versus 15% of cases (P = 0.0008) and 20% of young onset cases (P = 0.0001). The association was independently replicated in patients with childhood-onset schizophrenia compared to their parents (P = 0.03). Mutations in cases disrupted genes disproportionately from signaling networks controlling neurodevelopment, including neuregulin and glutamate pathways. These results suggest that multiple, individually rare mutations impacting genes in neurodevelopmental pathways contribute to schizophrenia. 10.1126/science.1155174

Lens regeneration in Xenopus is not a mere repeat of lens development, with respect to crystallin gene expression

Nobuhiko Mizuno — 2008-04-28T16:54:51-00:00

Differentiation, Vol. 64, No. 3. (1999), pp. 143-149.

Abstract The spatio-temporal expression of three crystallin genes (alphaA, betaB1 and gamma) in lenses of Xenopus laevis was studied by in situ hybridization to compare the process of lens formation in embryonic development with that of lens regeneration from cornea that occurs in the tadpole. During embryonic lens development, all three crystallin transcripts were initially detected at the same stage of lens placode formation, and subsequently their signals became restricted to the presumptive lens fiber region. At later stages, the three crystallin genes were expressed in primary and secondary lens fibers, but not in lens epithelium. During lens regeneration, alphaA- and betaB1-crystallin signals were first detected in the presumptive lens fiber region of the lens vesicle. The expression of gamma-crystallin, however, appeared later than the other two crystallin genes and was detected only in morphologically discernible lens fibers. In the later stages of lens regeneration, expression of these crystallins was observed only in the lens fiber region, similar to embryonic lens development. These results reveal that lens regeneration from the inner layer of the outer cornea is not simply a repetition of embryonic lens development, when examined at the level of crystallin gene transcription.

Heparin is required for cell-free binding of basic fibroblast growth factor to a soluble receptor and for mitogenesis in whole cells.

DM Ornitz — 2008-04-24T20:11:36-00:00

Molecular and cellular biology, Vol. 12, No. 1. (January 1992), pp. 240-247.

Heparin is required for the binding of basic fibroblast growth factor (bFGF) to high-affinity receptors on cells deficient in cell surface heparan sulfate proteoglycan. So that this heparin requirement could be evaluated in the absence of other cell surface molecules, we designed a simple assay based on a genetically engineered soluble form of murine FGF receptor 1 (mFR1) tagged with placental alkaline phosphatase. Using this assay, we showed that FGF-receptor binding has an absolute requirement for heparin. By using a cytokine-dependent lymphoid cell line engineered to express mFR1, we also showed that FGF-induced mitogenic activity is heparin dependent. Furthermore, we tested a series of small heparin oligosaccharides of defined lengths for their abilities to support bFGF-receptor binding and biologic activity. We found that a heparin oligosaccharide with as few as eight sugar residues is sufficient to support these activities. We also demonstrated that heparin facilitates FGF dimerization, a property that may be important for receptor activation.

Quantitative Analysis of mRNA Levels in Xenopus Embryos by Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR)

Oliver Steinbach — 2008-04-22T18:37:26-00:00

Molecular Methods in Developmental Biology (1999), pp. 41-56.

Over the last few years, RT-PCR (1,2) has become a widely accepted method for quantitation of steady-state mRNA levels, particularly in Xenopus. Its unmatched sensitivity and swiftness allows for a high sample throughput with minimal amounts of starting material—considerable advantages over the conventional methods of Northern blotting or RNase protection. Initially, the use of RT-PCR for quantitative analysis was viewed skeptically. This was based on the concern that minor differences in the reaction conditions between samples would erratically influence the exponential rate of PCR amplification; therefore, results would be skewed a priori. This theoretical concern has turned out to be irrelevant for most applications.

Inhibition of protein tyrosine kinase activity disrupts early retinal development

Ming Li — 2008-04-18T20:08:54-00:00

Developmental Biology, Vol. 266, No. 1. (1 February 2004), pp. 209-221.

In the present study, we have investigated the role of tyrosine kinase activity during early retinal development in Xenopus laevis. The protein tyrosine kinase (PTK) inhibitors lavendustin A and genistein were used to determine the possible role of tyrosine kinase activity during retinal development in vivo and in vitro. Application of the inhibitors to early embryonic retina disrupted the pattern of lamination in the developing retina. The plexiform layers were severely disorganized or were no longer apparent, and photoreceptor morphogenesis was disrupted. Immunocytochemical analysis verified the presence of focal adhesions in dissociated retinal neuroepithelial cells isolated from St 25 embryos. Application of the PTK inhibitors blocked focal adhesion assembly in these primary cultured cells. To further investigate the regulation of focal adhesions by PTK activity, we examined the effect of lavendustin A on cultured XR1 glial cells. Lavendustin A produced a dose-dependent decrease in the proportion of XR1 cells displaying focal adhesions. Taken together, these results suggest that tyrosine kinase activity is essential for regulating neuroepithelial cell adhesion, migration and morphogenesis during retinal development. Furthermore, the disruption of retinal development may, in part, be due to the inhibition of integrin-mediated signaling.

Integration of growth and specification in chick wing digit-patterning

Matthew Towers — 2008-03-21T04:33:18-00:00

Nature (19 March 2008)

Relationships between eye factors and lens-forming transformations in the cornea and pericorneal epidermis of larval Xenopus laevis.

L Bosco — 2008-04-14T22:38:58-00:00

The Journal of experimental zoology, Vol. 209, No. 2. (August 1979), pp. 261-282.

Larval Xenopus laevis at stage 56 (Nieuwkoop and Faber, '56) were subjected to various types of lentectomy: (1) simple lentectomy, from the pupillary space after incision of outer and inner cornea; (2) lentectomy from the dorsal region of the eye; (3) lentectomy from the dorsal region of the eye and simultaneous incision of the outer cornea; (4) lentectomy from the dorsal region of the eye and simultaneous incision of the outer and inner cornea. The results obtained show that the outer cornea underwent lens-forming transformations only when the inner cornea had been incised, thus permitting outer cornea (Experiments I-IV). No lens regeneration occurred when the inner cornea was left intact (Experiments II, III). It was concluded that the factor(s) allowing the lens-forming transformations of the outer cornea is not an aspecific nutritional factor(s) but a more specific factor(s) that cannot reach the outer cornea when the inner cornea is intact. Therefore, the absence of the lens and sufficient nutrient available to the outer cornea are not enough to allow lens regeneration from the outer cornea. When lens removal was carried out through the dorsal part of the eye (Experiments III-IV) the lens regenerated from the pericorneal epidermis of this region in a large number of cases.

WNT/Frizzled signaling in eye development and disease.

RU de Iongh — 2008-04-14T15:25:42-00:00

Frontiers in bioscience : a journal and virtual library, Vol. 11 (2006), pp. 2442-2464.

The canonical Wnt/Fzd signaling pathway is highly conserved among various species. Increasing evidence is accumulating for non-canonical Wnt signaling pathways, analogous to those discovered in Drosophila, being operative in vertebrates. Similarly, the networks of genes involved in eye development show significant conservation during evolution. The amenability of Drosophila for genetic manipulation and analysis of ocular phenotypes has delivered a great deal of information about the roles of the Wnt/Fzd signaling pathways at various stages of ocular development and growth, particularly in regulating the formation and size of the eye field, cell proliferation, polarity and differentiation. In addition to the numerous recent studies that have identified the expression of various components of these signaling pathways in the developing vertebrate eye, functional studies have revealed significant parallels in the way that Wnt/Fz signals regulate the formation of the vertebrate eye field and also the proliferation and differentiation of cells, particularly in the lens and retina. Significant advances have also recently been made in identifying mutations in these signaling pathways that underlie or contribute to various ocular diseases such as exudative vitreoretinopathy, retinal degenerations, cataract, ocular tumors and various congenital ocular malformations. Combined with the mechanistic studies in vertebrate and invertebrate models, these studies point to important functional roles for Wnt/Fzd pathways in the human eye. Further investigation of how these pathways function during eye development and growth may yield important insights into novel therapeutic approaches to treat or prevent diseases that cause blindness.

Molecular adapters in Fc(epsilon)RI signaling and the allergic response.

J Rivera — 2008-04-13T20:46:21-00:00

Current opinion in immunology, Vol. 14, No. 6. (December 2002), pp. 688-693.

IgE-dependent activation of mast cells is central to the allergic response. The engagement of IgE-occupied receptors initiates a series of molecular events that cause the release of preformed, and de novo synthesis of, allergic mediators. Recent investigations demonstrate a critical role for non-enzymatic proteins that facilitate the activation and coordination of biochemical signals required for mast cell activation. Among these LAT, SLP-76 and Gab2 are critically important as adapters that facilitate events initiated by IgE receptor-dependent activation of Src family protein tyrosine kinases, Lyn and Fyn. An evaluation of the role of these adapters points to complementary but independent steps in early signaling and the possibility that preference for one or another adaptor complex may result in selective mast cell responses.

The paradoxical pro- and anti-apoptotic actions of GSK3 in the intrinsic and extrinsic apoptosis signaling pathways

Eleonore Beurel — 2008-04-10T22:33:53-00:00

Progress in Neurobiology, Vol. 79, No. 4. (July 2006), pp. 173-189.

Few things can be considered to be more important to a cell than its threshold for apoptotic cell death, which can be modulated up or down, but rarely in both directions, by a single enzyme. Therefore, it came as quite a surprise to find that one enzyme, glycogen synthase kinase-3 (GSK3), has the perplexing capacity to either increase or decrease the apoptotic threshold. These apparently paradoxical effects now are known to be due to GSK3 oppositely regulating the two major apoptotic signaling pathways. GSK3 promotes cell death caused by the mitochondrial intrinsic apoptotic pathway, but inhibits the death receptor-mediated extrinsic apoptotic signaling pathway. Intrinsic apoptotic signaling, activated by cell damage, is promoted by GSK3 by facilitation of signals that cause disruption of mitochondria and by regulation of transcription factors that control the expression of anti- or pro-apoptotic proteins. The extrinsic apoptotic pathway entails extracellular ligands stimulating cell-surface death receptors that initiate apoptosis by activating caspase-8, and this early step in extrinsic apoptotic signaling is inhibited by GSK3. Thus, GSK3 modulates key steps in each of the two major pathways of apoptosis, but in opposite directions. Consequently, inhibitors of GSK3 provide protection from intrinsic apoptosis signaling but potentiate extrinsic apoptosis signaling. Studies of this eccentric ability of GSK3 to oppositely influence two types of apoptotic signaling have shed light on important regulatory mechanisms in apoptosis and provide the foundation for designing the rational use of GSK3 inhibitors for therapeutic interventions.

Cross-talk of WNT and FGF signaling pathways at GSK3β to regulate β-catenin and SNAIL signaling cascades

Masuko Katoh — 2008-04-10T22:26:48-00:00

Cancer Biology & Therapy, Vol. 5, No. 9. (September 2006), pp. 1059-1064.

WNT and FGF signaling pathways cross-talk during a variety of cellular processes, such as human colorectal carcinogenesis, mouse mammary tumor virus (MMTV)-induced carcinogenesis, E2A-Pbx-induced leukemogenesis, early embryogenesis, body-axis formation, limb-bud formation, and neurogenesis. Canonical WNT signals are transduced through Frizzled receptor and LRP5/6 co-receptor to downregulate GSK3ß (GSK3B) activity not depending on Ser 9 phosphorylation. FGF signals are transduced through FGF receptor to the FRS2-GRB2-GAB1-PI3K-AKT signaling cascade to downregulate GSK3ß activity depending on Ser 9 phosphorylation. Because GSK3ß-dependent phosphorylation of ß-catenin and SNAIL leads to FBXW1 (ßTRCP)-mediated ubiquitination and degradation, GSK3ß downregulation results in the stabilization and the nuclear accumulation of ß-catenin and SNAIL. Nuclear ß-catenin is complexed with TCF/LEF, Legless (BCL9 or BCL9L) and PYGO (PYGO1 or PYGO2) to activate transcription of CCND1, MYC, FGF18 and FGF20 genes for the cell-fate determination. Nuclear SNAIL represses transcription of CDH1 gene, encoding E-cadherin, to induce the epithelial-mesenchymal transition (EMT). Mammary carcinogenesis in MMTV-Wnt1 transgenic mice is accelerated by MMTV infection due to MMTV integration around Fgf3-Fgf4 or Fgf8 loci, and mammary carcinogenesis in MMTV-Fgf3 transgenic mice due to MMTV integration around Wnt1-Wnt10b locus. Co-activation of WNT and FGF signaling pathways in tumors leads to more malignant phenotypes. Single nucleotide polymorphism (SNP) and copy number polymorphism (CNP) of WNT and FGF signaling molecules could be utilized as screening method of cancer predisposition. cDNA-PCR, microarray or ELISA reflecting aberrant activation of WNT and FGF signaling pathways could be developed as novel cancer-related biomarkers for diagnosis, prognosis, and therapy. Cocktail therapy using WNT and FGF inhibitors, such as small-molecule compounds and human neutralizing antibodies, should be developed to increase the efficacy of chemotherapy through the inhibition of recurrence by destructing cancer stem cells.

GSK3 at the edge: regulation of developmental specification and cell polarization.

L Kim — 2008-04-10T22:15:38-00:00

Current drug targets, Vol. 7, No. 11. (November 2006), pp. 1411-1419.

GSK3 is a multifunctional protein kinase that is pivotal for the regulation of metabolism, the cytoskeleton, and gene expression. Multicellular eukaryotes utilize GSK3 as a molecular switch to specify distinct cell fates, but also to organize these cells spatially within the developing organism. We discuss the central role of GSK3 in control of the Wnt, Hedgehog, cAMP (in Dictyostelium), and other signaling pathways, but also focus on significant new evidence that GSK3 is required to establish cell polarity.

AKT/PKB signaling: navigating downstream.

BD Manning — 2007-07-14T11:47:15-00:00

Cell, Vol. 129, No. 7. (29 June 2007), pp. 1261-1274.

The serine/threonine kinase Akt, also known as protein kinase B (PKB), is a central node in cell signaling downstream of growth factors, cytokines, and other cellular stimuli. Aberrant loss or gain of Akt activation underlies the pathophysiological properties of a variety of complex diseases, including type-2 diabetes and cancer. Here, we review the molecular properties of Akt and the approaches used to characterize its true cellular targets. In addition, we discuss those Akt substrates that are most likely to contribute to the diverse cellular roles of Akt, which include cell survival, growth, proliferation, angiogenesis, metabolism, and migration.

Cellular signaling by fibroblast growth factor receptors

VP Eswarakumar — 2008-04-09T22:48:18-00:00

Cytokine & Growth Factor Reviews, Vol. 16, No. 2. (April 2005), pp. 139-149.

The 22 members of the fibroblast growth factor (FGF) family of growth factors mediate their cellular responses by binding to and activating the different isoforms encoded by the four receptor tyrosine kinases (RTKs) designated FGFR1, FGFR2, FGFR3 and FGFR4. Unlike other growth factors, FGFs act in concert with heparin or heparan sulfate proteoglycan (HSPG) to activate FGFRs and to induce the pleiotropic responses that lead to the variety of cellular responses induced by this large family of growth factors. A variety of human skeletal dysplasias have been linked to specific point mutations in FGFR1, FGFR2 and FGFR3 leading to severe impairment in cranial, digital and skeletal development. Gain of function mutations in FGFRs were also identified in a variety of human cancers such as myeloproliferative syndromes, lymphomas, prostate and breast cancers as well as other malignant diseases. The binding of FGF and HSPG to the extracellular ligand domain of FGFR induces receptor dimerization, activation and autophosphorylation of multiple tyrosine residues in the cytoplasmic domain of the receptor molecule. A variety of signaling proteins are phosphorylated in response to FGF stimulation including Shc, phospholipase-C[gamma], STAT1, Gab1 and FRS2[alpha] leading to stimulation of intracellular signaling pathways that control cell proliferation, cell differentiation, cell migration, cell survival and cell shape. The docking proteins FRS2[alpha] and FRS2[beta] are major mediators of the Ras/MAPK and PI-3 kinase/Akt signaling pathways as well as negative feedback mechanisms that fine-tune the signal that is initiated at the cell surface following FGFR stimulation.

Notch Signaling: Cell Fate Control and Signal Integration in Development

Spyros Artavanis-Tsakonas — 2008-04-08T15:34:20-00:00

Science, Vol. 284, No. 5415. (30 April 1999), pp. 770-776.

10.1126/science.284.5415.770

Xenopus, An Ideal Vertebrate System for Studies of Eye Development and Regeneration

JJ Henry — 2008-04-03T19:34:56-00:00

(2008)

PKB/AKT: functional insights from genetic models.

MP Scheid — 2008-04-03T17:12:05-00:00

Nature reviews. Molecular cell biology, Vol. 2, No. 10. (October 2001), pp. 760-768.

Since its discovery 10 years ago, the potential functions of protein kinase B (PKB)/AKT have been catalogued with increasing efficiency. The physiological relevance of some of the proposed mechanisms by which PKB/AKT mediates many of its effects has been questioned, and recent work using new reagents and approaches has revealed some cracks in our understanding of this important molecule, and also hinted that these effects may involve other players.

TreeView: an application to display phylogenetic trees on personal computers.

RD Page — 2008-04-03T13:18:59-00:00

Computer applications in the biosciences: CABIOS, Vol. 12, No. 4. (August 1996), pp. 357-358.

Clustal W and Clustal X version 2.0

MA Larkin — 2007-11-17T21:15:47-00:00

Bioinformatics, Vol. 23, No. 21. (1 November 2007), pp. 2947-2948.

Summary: The Clustal W and Clustal X multiple sequence alignment programs have been completely rewritten in C++. This will facilitate the further development of the alignment algorithms in the future and has allowed proper porting of the programs to the latest versions of Linux, Macintosh and Windows operating systems. Availability: The programs can be run on-line from the EBI web server: http://www.ebi.ac.uk/tools/clustalw2. The source code and executables for Windows, Linux and Macintosh computers are available from the EBI ftp site ftp://ftp.ebi.ac.uk/pub/software/clustalw2/ Contact: clustalw@ucd.ie 10.1093/bioinformatics/btm404

Fibroblast Growth Factor (FGF) 3 from Xenopus laevis (XFGF3) Binds with High Affinity to FGF Receptor 2

Marc Mathieu — 2008-04-03T02:39:27-00:00

J. Biol. Chem., Vol. 270, No. 12. (24 March 1995), pp. 6779-6787.

ABSTRACTWe demonstrate that purified fibroblast growth factor (FGF) 3 from Xenopus laevis (XFGF3) activates the mitogen-activated protein kinase pathway and induces DNA synthesis in quiescent cells. To characterize the high affinity cell surface receptors that mediate these responses, the ligand binding domains of different FGF receptors (FGFR) were expressed on COS-1 cells, and their affinity for XFGF3 was determined. Unlabeled XFGF3 efficiently competed with [IMG]_24879_tex2html_wrap1053.gif">I-FGF1 for binding to the IIIb and IIIc isoforms of FGFR2, giving 50% displacement (ID[IMG]_24879_tex2html_wrap807.gif">) at 0.3-0.8 nM. Higher XFGF3 concentrations were needed to displace [IMG]_24879_tex2html_wrap1053.gif">I-FGF1 from FGFR3 and FGFR1 (ID[IMG]_24879_tex2html_wrap807.gif"> [IMG]_24879_tex2html_wrap809.gif"> 4 and 21 nM, respectively), indicating that XFGF3 has a lower affinity for these receptors. No association of XFGF3 with FGFR4 was found using this assay. FGFR2 isoforms isolated from both mouse and Xenopus showed similar high affinity binding of XFGF3 as determined by direct binding assays (K[IMG]_24879_tex2html_wrap811.gif"> values in the range of 0.2-0.6 nM). These results indicate that the binding specificity of XFGF3 is different from that of other FGFs, and identifies FGFR2 as its high affinity receptor. 10.1074/jbc.270.12.6779

Signaling specificities of fibroblast growth factor receptors in early Xenopus embryo

M Umbhauer — 2008-04-02T23:17:48-00:00

J Cell Sci, Vol. 113, No. 16. (15 August 2000), pp. 2865-2875.

Normal table of Xenopus laevis (Daudin)

PD Nieuwkoop — 2008-04-02T21:21:36-00:00

(1956)

Secreted Frizzled-related proteins: searching for relationships and patterns

Steve Jones — 2008-04-02T16:19:42-00:00

BioEssays, Vol. 24, No. 9. (2002), pp. 811-820.

Secreted Frizzled-related proteins (SFRPs) are modulators of the intermeshing pathways in which signals are transduced by Wnt ligands through Frizzled (Fz) membrane receptors. The Wnt networks influence biological processes ranging from developmental cell fate, cell polarity and adhesion to tumorigenesis and apoptosis. In the five or six years since their discovery, the SFRPs have emerged as dynamically expressed proteins able to bind both Wnts and Fz, with distinctive structural properties in which cysteine-rich domains from Fz- and from netrin-like proteins are juxtaposed. The abundant expression of SFRP genes in the early embryo, altered expression patterns in disease states, and potential significance in the evolution of the vertebrate body plan, make these intriguing molecules relevant to investigations in diverse fields of biology and biomedical sciences. BioEssays 24:811-820, 2002. © 2002 Wiley Periodicals, Inc.