Neuronal leucine-rich repeat 6 (XlNLRR-6) is required for late lens and retina development in Xenopus laevis

Understanding cornea homeostasis and wound healing using a novel model of stem cell deficiency in Xenopus

Limbal Stem Cell Deficiency (LSCD) is a painful and debilitating disease that results from damage or loss of the Corneal Epithelial Stem Cells (CESCs). Therapies have been developed to treat LSCD by utilizing epithelial stem cell transplants. However, effective repair and recovery depends on many factors, such as the source and concentration of donor stem cells, and the proper conditions to support these transplanted cells. We do not yet fully understand how CESCs heal wounds or how transplanted CESCs are able to restore transparency in LSCD patients. A major hurdle has been the lack of vertebrate models to study CESCs. Here we utilized a short treatment with Psoralen AMT (a DNA cross-linker), immediately followed by UV treatment (PUV treatment), to establish a novel frog model that recapitulates the characteristics of cornea stem cell deficiency, such as pigment cell invasion from the periphery, corneal opacity, and neovascularization. These PUV treated whole corneas do not regain transparency. Moreover, PUV treatment leads to appearance of the Tcf7l2 labeled subset of apical skin cells in the cornea region. PUV treatment also results in increased cell death, immediately following treatment, with pyknosis as a primary mechanism. Furthermore, we show that PUV treatment causes depletion of p63 expressing basal epithelial cells, and can stimulate mitosis in the remaining cells in the cornea region. To study the response of CESCs, we created localized PUV damage by focusing the UV radiation on one half of the cornea. These cases initially develop localized stem cell deficiency characteristics on the treated side. The localized PUV treatment is also capable of stimulating some mitosis in the untreated (control) half of those corneas. Unlike the whole treated corneas, the treated half is ultimately able to recover and corneal transparency is restored. Our study provides insight into the response of cornea cells following stem cell depletion, and establishes Xenopus as a suitable model for studying CESCs, stem cell deficiency, and other cornea diseases. This model will also be valuable for understanding the nature of transplanted CESCs, which will lead to progress in the development of therapeutics for LSCD.

RNA helicase Mov10 is essential for gastrulation and central nervous system development

BACKGROUND

Mov10 is an RNA helicase that modulates access of Argonaute 2 to microRNA recognition elements in mRNAs. We examined the role of Mov10 in Xenopus laevis development and show a critical role for Mov10 in gastrulation and in the development of the central nervous system (CNS).

RESULTS

Knockdown of maternal Mov10 in Xenopus embryos using a translation blocking morpholino led to defects in gastrulation and the development of notochord and paraxial mesoderm, and a failure to neurulate. RNA sequencing of the Mov10 knockdown embryos showed significant upregulation of many mRNAs when compared with controls at stage 10.5 (including those related to the cytoskeleton, adhesion, and extracellular matrix, which are involved in those morphogenetic processes). Additionally, the degradation of the miR-427 target mRNA, cyclin A1, was delayed in the Mov10 knockdowns. These defects suggest that Mov10's role in miRNA-mediated regulation of the maternal to zygotic transition could lead to pleiotropic effects that cause the gastrulation defects. Additionally, the knockdown of zygotic Mov10 showed that it was necessary for normal head, eye, and brain development in Xenopus consistent with a recent study in the mouse.

CONCLUSIONS

Mov10 is essential for gastrulation and normal CNS development. Developmental Dynamics 247:660-671, 2018. © 2017 Wiley Periodicals, Inc.

The lens regenerative competency of limbal vs. central regions of mature Xenopus cornea epithelium

The frog, Xenopus laevis, is capable of completely regenerating a lens from the cornea epithelium. Because this ability appears to be limited to the larval stages of Xenopus, virtually all the work to understand the mechanisms regulating this process has been limited to pre-metamorphic tadpoles. It has been reported that the post-metamorphic cornea is competent to regenerate under experimental conditions, despite the fact that the in vivo capacity to regenerate is lost; however, that work didn't examine the regenerative potential of different regions of the cornea. A new model suggests that cornea-lens regeneration in Xenopus may be driven by oligopotent stem cells, and not by transdifferentiation of mature cornea cells. We investigated the regenerative potential of the limbal region in post-metamorphic cornea, where the stem cells of the cornea are thought to reside. Using EdU (5-Ethynyl-2'-deoxyuridine), we identified long-term label retaining cells in the basal cells of peripheral post-metamorphic Xenopus cornea, consistent with slow-cycling stem cells of the limbus that have been described in other vertebrates. Using this data to identify putative stem cells of the limbal region in Xenopus, we tested the regenerative competency of limbal regions and central cornea. These regions showed a similarly high ability for the cells of the basal epithelium to express lens proteins when cultured in proximity to larval retina. Thus, the regenerative competency in the post-metamorphic cornea is not restricted to stem cells of the limbal region, but also occurs in the transit amplifying cells throughout the basal layer of the cornea epithelium.

Report of leucine-rich repeats (LRRs) from Scylla serrata: Ontogeny, molecular cloning, characterization and expression analysis following ligand stimulation, and upon bacterial and viral infections

Leucine-rich repeat (LRR) proteins are present in all living organisms, and their participation in signal transduction and defense mechanisms has been elucidated in humans and mosquitoes. LRRs possibly involve in protein-protein interactions also and show differential expression pattern upon challenge with pathogens. In the present study, a new LRR gene was identified in mud crab, Scylla serrata. LRR gene mRNA levels in different developmental stages and various tissues of S. serrata were analysed. Further, the response of the gene against different ligands, Gram-negative bacterium, and white spot syndrome virus (WSSV) was investigated in vitro and in vivo. Full-length cDNA sequence of S. serrata LRR (SsLRR) was found to be 2290 nucleotide long with an open reading frame of 1893bp. SsLRR encodes for a protein containing 630 deduced amino acids with 17 conserved LRR domains and exhibits significant similarity with crustacean LRRs so that these could be clustered into a branch in the phylogenetic tree. SsLRR mRNA transcripts were detected in all the developmental stages (egg, Zoea1-5, megalopa and crab instar), haemocytes and various tissues such as, stomach, gill, muscle, hepatopancreas, hematopoietic organ, heart, epithelial layer and testis by reverse-transcriptase PCR. SsLRR transcripts in cultured haemocytes showed a 2-fold increase in expression at 1.5 and 12h upon Poly I:C induction. WSSV challenge resulted in significant early up-regulation at 3h in-vitro and late up-regulation at 72h in-vivo. Peptidoglycan (PGN)-induction resulted in marginal up-regulation of SsLRR at timepoints, 6, 12 and 24h (fold change below 1.5) and no significant change in the expression at early timepoints. LPS-stimulation, on the other hand, showed either down-regulation or normal level of expression at all timepoints. However, a delayed 5-fold up-regulation was observed in vivo against Vibrio parahaemolyticus infection at 72hpi. The constitutive expression of the LRR gene in all the early life-stages, and its response to various ligands and to viral challenge suggest the possible role of the LRR in immune defense in mud crab. The result provides additional information which would help in future studies in understanding the innate immune pathways in crustaceans.

Caenorhabditis elegans PAQR-2 and IGLR-2 Protect against Glucose Toxicity by Modulating Membrane Lipid Composition

In spite of the worldwide impact of diabetes on human health, the mechanisms behind glucose toxicity remain elusive. Here we show that C. elegans mutants lacking paqr-2, the worm homolog of the adiponectin receptors AdipoR1/2, or its newly identified functional partner iglr-2, are glucose intolerant and die in the presence of as little as 20 mM glucose. Using FRAP (Fluorescence Recovery After Photobleaching) on living worms, we found that cultivation in the presence of glucose causes a decrease in membrane fluidity in paqr-2 and iglr-2 mutants and that genetic suppressors of this sensitivity act to restore membrane fluidity by promoting fatty acid desaturation. The essential roles of paqr-2 and iglr-2 in the presence of glucose are completely independent from daf-2 and daf-16, the C. elegans homologs of the insulin receptor and its downstream target FoxO, respectively. Using bimolecular fluorescence complementation, we also show that PAQR-2 and IGLR-2 interact on plasma membranes and thus may act together as a fluidity sensor that controls membrane lipid composition.

Expression pattern of leucine-rich repeat neuronal protein 4 in adult mouse dorsal root ganglia

A member of leucine-rich repeat neuronal protein family, leucine-rich repeat neuronal protein 4 (Lrrn4), is a type I transmembrane protein. Previously, we have reported that Lrrn4 is expressed in various regions of the central nervous system (CNS) and involved in the memory retention. However, little is known about the role of Lrrn4 in the peripheral nervous system (PNS). Northern blot analysis revealed that Lrrn4 mRNA was expressed predominantly in the dorsal root ganglia (DRGs) with low levels in some regions of the CNS. To identify Lrrn4-expressing cells in the DRGs, we performed in situ hybridization histochemistry and LacZ staining in Lrrn4-heterozygous (Lrrn4+/-) mice generated by the replacement of Lrrn4 gene with β-galactosidase gene. In the adult DRGs, 8% of total DRG neurons contained Lrrn4 mRNA, which was exclusively expressed in the small-sized neurons. LacZ staining combined with immunohistochemistry revealed that approximately 42% and 58% of Lrrn4-positive neurons contained receptor tyrosine kinase A (TrkA)- and Ret-immunoreactivity, respectively. After sciatic nerve axotomy, the expression of Lrrn4 mRNA was reduced in injured side of the DRGs. Thus, Lrrn4 is expressed in a subset of nociceptive neurons and might contribute to the maintenance of nociceptive circuits.

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.

A cell surface interaction network of neural leucine-rich repeat receptors

A network of Zebrafish extracellular neuroreceptor interactions are revealed using AVEXIS, a highly stringent interaction assay.

Background

The vast number of precise intercellular connections within vertebrate nervous systems is only partly explained by the comparatively few known extracellular guidance cues. Large families of neural orphan receptor proteins have been identified and are likely to contribute to these recognition processes but due to the technical difficulty in identifying novel extracellular interactions of membrane-embedded proteins, their ligands remain unknown.

Results

To identify novel neural recognition signals, we performed a large systematic protein interaction screen using an assay capable of detecting low affinity extracellular protein interactions between the ectodomains of 150 zebrafish receptor proteins containing leucine-rich-repeat and/or immunoglobulin superfamily domains. We screened 7,592 interactions to construct a network of 34 cell surface receptor-ligand pairs that included orphan receptor subfamilies such as the Lrrtms, Lrrns and Elfns but also novel ligands for known receptors such as Robos and Unc5b. A quantitative biochemical analysis of a subnetwork involving the Unc5b and three Flrt receptors revealed a surprising quantitative variation in receptor binding strengths. Paired spatiotemporal gene expression patterns revealed dynamic neural receptor recognition maps within the developing nervous system, providing biological support for the network and revealing likely functions.

Conclusions

This integrated interaction and expression network provides a rich source of novel neural recognition pathways and highlights the importance of quantitative systematic extracellular protein interaction screens to mechanistically explain neural wiring patterns.

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.

Analysis of Lrrn1 expression and its relationship to neuromeric boundaries during chick neural development

Background

The Drosophila leucine-rich repeat proteins Tartan (TRN) and Capricious (CAPS) mediate cell affinity differences during compartition of the wing imaginal disc. This study aims to identify and characterize the expression of a chick orthologue of TRN/CAPS and examine its potential function in relation to compartment boundaries in the vertebrate central nervous system.

Results

We identified a complementary DNA clone encoding Leucine-rich repeat neuronal 1 (Lrrn1), a single-pass transmembrane protein with 12 extracellular leucine-rich repeats most closely related to TRN/CAPS. Lrrn1 is dynamically expressed during chick development, being initially localized to the neural plate and tube, where it is restricted to the ventricular layer. It becomes downregulated in boundaries following their formation. In the mid-diencephalon, Lrrn1 expression prefigures the position of the anterior boundary of the zona limitans intrathalamica (ZLI). It becomes progressively downregulated from the presumptive ZLI just before the onset of expression of the signalling molecule Sonic hedgehog (Shh) within the ZLI. In the hindbrain, downregulation at rhombomere boundaries correlates with the emergence of specialized boundary cell populations, in which it is subsequently reactivated. Immunocolocalization studies confirm that Lrrn1 protein is endocytosed from the plasma membrane and is a component of the endosomal system, being concentrated within the early endosomal compartment.

Conclusion

Chick Lrrn1 is expressed in ventricular layer neuroepithelial cells and is downregulated at boundary regions, where neurogenesis is known to be delayed, or inhibited. The timing of Lrrn1 downregulation correlates closely with the activation of signaling molecule expression at these boundaries. This expression is consistent with the emergence of secondary organizer properties at boundaries and its endosomal localisation suggests that Lrrn1 may regulate the subcellular localisation of specific components of signalling or cell-cell recognition pathways in neuroepithelial cells.