FGF signaling is required for lens regeneration in Xenopus laevis.

In species of the frog genus Xenopus, lens regeneration occurs through a process of transdifferentiation, in which cornea epithelial cells presumably undergo dedifferentiation and subsequently redifferentiate to form a new lens. Experimental studies have shown that the retina provides the key signal required to trigger this process once the original lens is removed. A previous study showed that addition of an exogenous fibroblast growth factor (i.e., FGF1 protein) could initiate transdifferentiation of cornea epithelial cells in culture. To determine the role of FGF signaling in X. laevis lens regeneration, we have examined the presence of specific FGFs and their receptors (FGFRs) during this process and evaluated the necessity of FGFR signaling. Reverse transcriptase-polymerase chain reaction analyses reveal that a number of FGF family members are expressed in cornea epithelium and retinal tissues both before and during the process of lens regeneration. Of these, FGF1, FGF8, and FGF9 are expressed principally in retinal tissue and not in the cornea epithelium. Hence, these ligands could represent key signaling factors originating from the retina that trigger regeneration. The results of experiments using an in vitro eye culture system and an FGFR inhibitor (SU5402) suggest that FGFR signaling is required for lens regeneration in Xenopus.

The G-protein-coupled receptor, GPR84, is important for eye development in Xenopus laevis.

G-protein-coupled receptors (GPCRs) represent diverse, multifamily groups of cell signaling receptors involved in many cellular processes. We identified Xenopus laevis GPR84 as a member of the A18 subfamily of GPCRs. During development, GPR84 is detected in the embryonic lens placode, differentiating lens fiber cells, retina, and cornea. Anti-sense morpholino oligonucleotide-mediated knockdown and RNA rescue experiments demonstrate GPR84's importance in lens, cornea, and retinal development. Examination of cell proliferation using an antibody against histone H3 S10P reveals significant increases in the lens and retina following GPR84 knockdown. Additionally, there was also an increase in apoptosis in the retina and lens, as revealed by TUNEL assay. Reciprocal transplantation of the presumptive lens ectoderm between uninjected controls and morpholino-injected embryos demonstrates that GPR84 is necessary in the retina for proper development of the retina, as well as other eye tissues including the lens and cornea.

Differential localization of mRNAs during early development in the mollusc, Crepidula fornicata.

Certain mRNAs have been shown to be segregated in different cells in various metazoan embryos. These events represent aspects of autonomous mechanisms that establish particular embryonic cell fates and axial properties associated with asymmetric cell divisions. The spiralian lophotrochozoans (which include molluscs, annelids, nemerteans, gnathostomulids, dicyemid mesozoans, entoprocts, and platyhelminthes) exhibit a highly conserved pattern of early development that involves stereotypical, asymmetric cell divisions (termed "spiral cleavage"). Recently, it was demonstrated that various mRNAs are dynamically localized to the centrosomes in specific cells during early development in the gastropod mollusc, Ilyanassa obsoleta. During subsequent cell divisions, these messages become segregated in particular daughter cells, and it has been proposed that these events distinguish the developmental potential of these cells within the early embryo of I. obsoleta. The molecular mechanisms underlying these events, however, are still unknown. Here we show for the first time in another spiralian lophotrochozoan (the gastropod Crepidula fornicata) that similar patterns of mRNA localization take place during early development. To characterize the transcriptome of early development, and identify candidate genes for the expression analyses, high-throughput sequencing was carried out, via GS FLX Titanium 454 pyrosequencing. The annotated sequences have been made available as a resource for the scientific community (www.life.illinoi.edu/henry/crepidula_databases.html). Presumably, specific proteins associated with centrosomes may be important for these mRNA localization events. In silico sequence comparisons with known centriolar/centrosomal, ciliary/basal body proteomes shows that a large number of those proteins are represented in the collection of expressed sequence tags of C. fornicata annotated in this study. These data should be useful for future studies of the role of specific mRNAs in controlling cell fate and axial specification in the spiralian Lophotrochozoa, and for dissecting the underlying molecular mechanisms that accomplish these events.

Gene expression profiles of lens regeneration and development in Xenopus laevis.

Seven hundred and thirty-four unique genes were recovered from a cDNA library enriched for genes up-regulated during the process of lens regeneration in the frog Xenopus laevis. The sequences represent transcription factors, proteins involved in RNA synthesis/processing, components of prominent cell signaling pathways, genes involved in protein processing, transport, and degradation (e.g., the ubiquitin/proteasome pathway), matrix metalloproteases (MMPs), as well as many other proteins. The findings implicate specific signal transduction pathways in the process of lens regeneration, including the FGF, TGF-beta, MAPK, Retinoic acid, Wnt, and hedgehog signaling pathways, which are known to play important roles in eye/lens development and regeneration in various systems. In situ hybridization revealed that the majority of genes recovered are expressed during embryogenesis, including in eye tissues. Several novel genes specifically expressed in lenses were identified. The suite of genes was compared to those up-regulated in other regenerating tissues/organisms, and a small degree of overlap was detected.

Conformational transition associated with E1-E2 interaction in small ubiquitin-like modifications.

Ubiquitin-like modifications regulate nearly every aspect of cellular functions. A key step in these modifications is the recognition of the carrier enzyme (E2) by the activating enzyme (E1). In this study, we have found that a critical E2-binding surface on the E1 of the small ubiquitin-like modifier has unusually high populations in both ordered and disordered states. Upon binding the E2, the disordered state is converted to the ordered state, which resembles the structure of the bound conformation, providing a mechanism to resolve the "Levinthal Paradox" search problem in a folding-upon-binding process. The significance of the folding-unfolding equilibrium is shown by the loss of functions of the mutations that shift the equilibrium to the folded state. This study highlights the importance of conformational flexibility in the molecular recognition event.

Psf2 plays important roles in normal eye development in Xenopus laevis.

PURPOSE: Psf2 (partner of Sld5 2) represents a member of the GINS (go, ichi, ni, san) heterotetramer [1] and functions in DNA replication as a "sliding clamp." Previous in situ hybridization analyses revealed that Psf2 is expressed during embryonic development in a tissue-specific manner, including the optic cup (retina) and the lens [2]. This article provides an analysis of Psf2 function during eye development in Xenopus laevis. METHODS: A morpholino targeted to Psf2 mRNA was designed to knockdown Psf2 translation and was injected into specific embryonic cells during early cleavage stages in the frog, Xenopus laevis. Injected embryos were assayed for specific defects in morphology, cell proliferation, and apoptosis. Synthetic Psf2 RNA was also co-injected with the morpholino to rescue morpholino-mediated developmental defects. It is well known that reciprocal inductive interactions control the development of the optic cup and lens. Therefore, control- and morpholino-injected embryos were used for reciprocal transplantation experiments to distinguish the intrinsic role of Psf2 in the development of the optic cup (retina) versus the lens. RESULTS: Morpholino-mediated knockdown of Psf2 expression resulted in dosage-dependent phenotypes, which included microphthalmia, incomplete closure of the ventral retinal fissure, and retinal and lens dysgenesis. Defects were also observed in other embryonic tissues that normally express Psf2 including the pharyngeal arches and the otic vesicle, although other tissues that express Psf2 were not found to be grossly defective. Eye defects could be rescued by co-injection of synthetic Psf2 RNA. Examination of cell proliferation via an antibody against phospho-histone H3 S10P revealed no significant differences in the retina and lens following Psf2 knockdown. However, there was a significant increase in the level of apoptosis in retinal as well as forebrain tissues, as revealed by TUNEL (terminal deoxynucleotide transferase dUTP nick end labeling) assay. CONCLUSIONS: The results demonstrate intrinsic roles for Psf2 in both retinal and to a lesser extent, lens tissues. Observed lens defects can mainly be attributed to deficiencies in retinal development and consequently the late phase of lens induction, which involves instructive cues from the optic cup. Developmental defects were not observed in all tissues that express Psf2, which could be related to differences in the translation of Psf2 or redundant effects of related factors such as proliferating cell nuclear antigen (PCNA).

NvMap: automated analysis of NMR chemical shift perturbation data.

UNLABELLED: NMR chemical shift perturbation experiments are widely used to define binding sites in biomolecular complexes. Especially in the case of high throughput screening of ligands, rapid analysis of NMR spectra is essential. NvMap extends NMRViewJ and provides a means for rapid assignments and book-keeping of NMR titration spectra. Our module offers options to analyze multiple titration spectra both separately and sequentially, where the sequential spectra are analyzed either two at a time or all simultaneously. The first option is suitable for slow or intermediate exchange rates between free and bound proteins. The latter option is particularly useful for fast exchange situations and can compensate for the lack of indicators for overlapped peaks. Our module also provides a simple user interface to automate the analysis process from dataset to peak list. We demonstrate the effectiveness of our program using NMR spectra of SUMO in complexes with three different peptides. AVAILABILITY: NvMap is available on the web at http://www.cityofhope.org/Researchers/ChenYuan/NvMap/ Supplemental information: Manual pages and test spectra will be available on the web at the above site.