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The apical extracellular matrix (aECM) of external epithelia often contains lipid-rich outer layers that contribute to permeability barrier function. The external aECM of nematodes is known as the cuticle and contains an external lipid-rich layer - the epicuticle. Epicuticlins are a family of tandem repeat cuticle proteins of unknown function. Here, we analyze the localization and function of the three C. elegans epicuticlins (EPIC proteins). EPIC-1 and EPIC-2 localize to the surface of the cuticle near the outer lipid layer, as well as to interfacial cuticles and adult-specific struts. EPIC-3 is expressed in dauer larvae and localizes to interfacial aECM in the buccal cavity. Skin wounding in the adult induces epic-3 expression, and EPIC proteins localize to wound sites. Null mutants lacking EPIC proteins are viable with reduced permeability barrier function and normal epicuticle lipid mobility. Loss of function in EPIC genes modifies the skin blistering phenotypes of Bli mutants and reduces survival after skin wounding. Our results suggest EPIC proteins define specific cortical compartments of the aECM and promote wound repair. [ABSTRACT FROM AUTHOR]

Some types of collagens, including transmembrane MACIT collagens and C. elegans cuticle collagens, are N-terminally cleaved at a dibasic site that resembles the consensus for furin or other proprotein convertases of the subtilisin/kexin (PCSK) family. Such cleavage may release transmembrane collagens from the plasma membrane and affect extracellular matrix assembly or structure. However, the functional consequences of such cleavage are unclear and evidence for the role of specific PCSKs is lacking. Here, we used endogenous collagen fusions to fluorescent proteins to visualize the secretion and assembly of the first collagen-based cuticle in C. elegans and then tested the role of the PCSK BLI-4 in these processes. Unexpectedly, we found that cuticle collagens SQT-3 and DPY-17 are secreted into the extraembryonic space several hours before cuticle matrix assembly. Furthermore, this early secretion depends on BLI-4/PCSK; in bli-4 and cleavage-site mutants, SQT-3 and DPY-17 are not efficiently secreted and instead form large intracellular puncta. Their later assembly into cuticle matrix is reduced but not entirely blocked. These data reveal a role for collagen N-terminal processing in intracellular trafficking and the control of matrix assembly in vivo. Our observations also prompt a revision of the classic model for C. elegans cuticle matrix assembly and the pre-cuticle-to-cuticle transition, suggesting that cuticle layer assembly proceeds via a series of regulated steps and not simply by sequential secretion and deposition. Author summary: Extracellular matrices coat cell surfaces to affect many aspects of animal biology. Collagens are among the most common constituents of such matrices and often form fibrillar- or mesh-like structures. It is important that these structures form only at the right time and place in the extracellular environment, and not prematurely during intracellular trafficking. Type I collagen matrix assembly typically occurs after proteolytic cleavage to remove both the N- and C-terminal ends of collagen molecules, and defects in this cleavage can cause a variety of human matrix disorders. Nevertheless, many questions remain about how N-terminal cleavage impacts collagen matrix assembly, particularly within other families of collagens that may be regulated differently than Type I collagen. The nematode Caenorhabditis elegans has an exoskeleton or cuticle that is composed of many collagens, and sequential secretion and membrane-proximal assembly of different collagens has been supposed to explain the eventual layered structure of the cuticle. Here we visualized tagged collagens during cuticle assembly and investigated the roles of N-terminal cleavage by characterizing mutants in the predicted collagen protease BLI-4 (a member of the furin/PCSK family) and also mutants in the predicted N-terminal cleavage sites within the tagged cuticle collagens. We observed that collagen secretion normally precedes cuticle matrix assembly by several hours, requiring a new way of thinking about cuticle layer formation. Furthermore, in both bli-4 mutants and N-terminal cleavage site mutants, collagens were not secreted efficiently and instead formed intracellular puncta. These data reveal an unexpected role for N-terminal cleavage in cuticle collagen secretion, which could be relevant to the cell biology of human matrix disorders. [ABSTRACT FROM AUTHOR]

Nematode molting is a remarkable process where animals must repeatedly build a new apical extracellular matrix (aECM) beneath a previously built aECM that is subsequently shed. The nuclear hormone receptor NHR-23 (also known as NR1F1) is an important regulator of C. elegans molting. NHR-23 expression oscillates in the epidermal epithelium, and soma-specific NHR-23 depletion causes severe developmental delay and death. Tissue-specific RNAi suggests that nhr-23 acts primarily in seam and hypodermal cells. NHR-23 coordinates the expression of factors involved in molting, lipid transport/metabolism and remodeling of the aECM. NHR-23 depletion causes dampened expression of a nas-37 promoter reporter and a loss of reporter oscillation. The cuticle collagen ROL-6 and zona pellucida protein NOAH-1 display aberrant annular localization and severe disorganization over the seam cells after NHR-23 depletion, while the expression of the adult-specific cuticle collagen BLI-1 is diminished and frequently found in patches. Consistent with these localization defects, the cuticle barrier is severely compromised when NHR-23 is depleted. Together, this work provides insight into how NHR-23 acts in the seam and hypodermal cells to coordinate aECM regeneration during development. [ABSTRACT FROM AUTHOR]

Semaphorins are extracellular proteins that regulate axon guidance and morphogenesis by interacting with a variety of cell surface receptors. Most semaphorins interact with plexin-containing receptor complexes, although some interact with non-plexin receptors. Class 2 semaphorins are secreted molecules that control axon guidance and epidermal morphogenesis in Drosophila and Caenorhabditis elegans. We show that the C. elegans class 2 semaphorin MAB-20 binds the plexin PLX-2. plx-2 mutations enhance the phenotypes of hypomorphic mab-20 alleles but not those of mab-20 null alleles, indicating that plx-2 and mab-20 act in a common pathway. Both mab-20 and plx-2 mutations affect epidermal morphogenesis during embryonic and in postembryonic development. In both contexts, plx-2 null mutant phenotypes are much less severe than mab-20 null phenotypes, indicating that PLX-2 is not essential for MAB-90 signaling. Mutations in the ephrin efn-4 do not synergize with mab-20, indicating that EFN-4 may act in MAB-90 signaling. EFN-4 and PLX-9 are coexpressed in the late embryonic epidermis where they play redundant roles in MAB-20-dependent cell sorting.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2006.02.036 Byline: Martin L. Hudson (a), Tarja Kinnunen (b), Hediye Nese Cinar (a), Andrew D. Chisholm (a) Keywords: Morphogenesis; Ephrin; Syndecan; Glypican; Kallmann syndrome; Anosmin; Heparan sulfate proteoglycan Abstract: The anosmin-1 protein family regulates cell migration, axon guidance, and branching, by mechanisms that are not well understood. We show that the C. elegans anosmin-1 ortholog KAL-1 promotes migrations of ventral neuroblasts prior to epidermal enclosure. KAL-1 does not modulate FGF signaling in neuroblast migration and acts in parallel to other neuroblast migration pathways. Defects in heparan sulfate (HS) synthesis or in specific HS modifications disrupt neuroblast migrations and affect the KAL-1 pathway. KAL-1 binds the cell surface HS proteoglycans syndecan/SDN-1 and glypican/GPN-1. This interaction is mediated via HS side chains and requires specific HS modifications. SDN-1 and GPN-1 are expressed in ventral neuroblasts and have redundant roles in KAL-1-dependent neuroblast migrations. Our findings suggest that KAL-1 interacts with multiple HSPGs to promote cell migration. Author Affiliation: (a) Department of Molecular, Cell, and Developmental Biology, Sinsheimer Laboratories, University of California, Santa Cruz, CA 95064, USA (b) School of Biological Sciences, University of Liverpool, Bioscience Building, Crown Street, Liverpool L69 7ZB, UK Article History: Received 20 December 2005; Revised 17 February 2006; Accepted 21 February 2006

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2005.08.011 Byline: Miwa Furuya (a), Hiroshi Qadota (a), Andrew D. Chisholm (b), Asako Sugimoto (a) Keywords: Caenorhabditis elegans; eyes absent; Eya; Pax6; Transcriptional regulation; Morphogenesis Abstract: eyes absent/Eya is a conserved transcriptional coactivator involved in development of various tissues and organs in arthropods and vertebrates. In Drosophila eye development, eya functions as part of the transcriptional regulatory network along with eyeless/Pax6, sine oculis/Six and dachshund/Dach. Here, we present the first functional study of the C. elegans Eya homolog, EYA-1. Loss of EYA-1 function by RNAi and deletion mutations resulted in early larval lethality with incomplete penetrance, associated with defects of differentiation and morphogenesis of several tissues and organs. In late embryogenesis, morphological defect in the head region, pharyngeal malformation and excess cell deaths in the anterior region were observed. Consistently, EYA-1 was expressed in the nuclei of a subset of anterior cells including pharyngeal and body wall muscle cells, starting from the morphogenesis stage in embryogenesis. Interestingly, eya-1 and pax-6/Pax6 mutants showed a strong genetic interaction for larval viability and embryonic anterior morphogenesis. Thus, eya-1 appears to play a partially redundant role with pax-6 during C. elegans embryogenesis. Author Affiliation: (a) Laboratory for Developmental Genomics, RIKEN Center for Developmental Biology, Kobe 650-0047, Japan (b) Sinsheimer Laboratories, Department of Molecular, Cellular and Developmental Biology, University of California, Santa Cruz, CA 95064, USA Article History: Received 26 May 2005; Revised 18 July 2005; Accepted 5 August 2005

RPM-1 that negatively regulates a p38 MAP kinase pathway composed of the dual leucine zipper-bearing MAPKKK DLK-1, the MAPKK MKK-4, and the p38 MAP kinase PMK-3, is reported. A presynaptic role of a previously unknown p38 MAP kinase cascade is revealed.

PAX-6 proteins are involved in eye and brain development in many animals. In the nematode Caenorhabditis elegans the pax-6 locus encodes multiple PAX-6 isoforms both with and without a paired domain. Mutations in the C. elegans pax-6 locus can be grouped into three classes. Mutations that affect paired domain-containing isoforms cause defects in epidermal morphogenesis, epidermal cell fates, and gonad cell migration and define the class I (vab-3) complementation group. The class II mutation mab-18(bx23) affects nonpaired domain-containing isoforms and transforms the fate of a sensory organ in the male tail. Class III mutations affect both paired domain and nonpaired domain isoforms; the most severe class III mutations are candidate null mutations in pax-6. Class III mutant phenotypes do Dot resemble a simple sum of class I and class I1 phenotypes. A comparison of class I and class III phenotypes indicates that PAX-6 isoforms can interact additively, synergistically, or antagonistically, depending on the cellular con text.

Cytoplasmic intermediate filaments (cIFs) are thought to provide mechanical strength to vertebrate cells; however, their function in invertebrates has been largely unexplored. The Caenorhabditis elegans genome encodes multiple cIFs. The C. elegans ifb-1 locus encodes two cIF isoforms, IFB-1A and IFB-1B, that differ in their head domains. We show that both IFB-1 isoforms are expressed in epidermal cells, within which they are localized to muscle-epidermal attachment structures. Reduction in IFB-1A function by mutation or RNA interference (RNAi) causes epidermal fragility, abnormal epidermal morphogenesis, and muscle detachment, consistent with IFB-1A providing mechanical strength to epidermal attachment structures. Reduction in IFB-1B function causes morphogenetic defects and defective outgrowth of the excretory cell. Reduction in function of both IFB-1 isoforms results in embryonic arrest due to muscle detachment and failure in epidermal cell elongation at the 2-fold stage. Two other cIFs, IFA-2 and IFA-3, are expressed in epidermal cells. We show that loss of function in IFA-3 results in defects in morphogenesis indistinguishable from those of embryos lacking ifb-1. In contrast, IFA-2 is not required for embryonic morphogenesis. Our data indicate that IFB-1 and IFA-3 are likely the major cIF isoforms in embryonic epidermal attachment structures. Keywords: C. elegans; Intermediate filament; IFB-1; IFA-3; Morphogenesis: Epidermis

Results demonstrate that ephrin VAB2/EFN-1 receptor, a component of the neurons, regulates epidermal morphogenesis in nematodes and serves as a ligand for VAB-1 receptor. VAB2 is expressed adjacent to VAB-1 in neurons and may partly function in a kinase-independent VAB-1 pathway.

The inositol triphosphate receptor, which regulates a 50-second behavioral rhythm in Caenorhabditis elegans, a nematode, is discussed. A study has shown that the defecation cycle, which is characterized by contraction of three distinct sets of muscles at 50 second intervals, is regulated by periodic calcium release mediated by the inositol trisphosphate receptor. The receptor is an essential timekeeper component for the cycle and represents a novel mechanism for control of behavioral rhythms.

Research was conducted to characterize genes associated with epidermal morphogenesis in Caenorhabditis elegans. Vab-1 mutants were isolated based on their morphogenetic defects in head epidermis while sequences of genomic DNAs from the mutants were amplified. Results showed that the null phenotype of vab-1 has a variable defect in epidermal morphogenesis. They also indicated that signaling through receptors and ligands was correlated in axon guidance and topographic mapping.

The animals belonging to vertebrate, insects and nematodes, in spite of the differences in the development of the head region, have the same type of gene that codes for the cells in the head region. Mutants in the vab-3 gene of the nematode, caenorhabditis elegans, exhibit defects in the development of the head region, indicating that the vab-3 gene is a part of the Pax-6 gene family. The Pax-6 genes are necessary for the development of the eye in vertebrates and drosophila also.

An investigation on clusters of Antennapedia class homobox (HOM-C) genes specify anteroposterior body pattern revealed that, besides the HOM-C genes of nematode Caenorhabditis elegans that specify positional identity, the other two genes also performed this function. Nematodes, anthropods and vertebrates have not stopped producing anteroposterior patterns in a basically conserved fashion, since the HOM-C emerged in a common ancestor.

A homobox gene lin-39, which is essential for the specification of cell fates inside the mid-body area of Caenorhabditis elegans, was characterized. In the mid-body cells and in the migrating nemoblast, lin-39 functions independent of the cell. Lin-39 encodes a protein having an Antennapedia class homodomain, which is placed in a homeotic gene cluster with mab-5 and egl-5, the two other regional homeotic genes.