Caenorhabditis elegans sqt-3 mutants have mutations in the col-1 collagen gene

Nanoscale patterning of collagens in C. elegans apical extracellular matrix

Apical extracellular matrices (aECMs) are complex extracellular compartments that form important interfaces between animals and their environment. In the adult C. elegans cuticle, layers are connected by regularly spaced columnar structures known as struts. Defects in struts result in swelling of the fluid-filled medial cuticle layer ('blistering', Bli). Here we show that three cuticle collagens BLI-1, BLI-2, and BLI-6, play key roles in struts. BLI-1 and BLI-2 are essential for strut formation whereas activating mutations in BLI-6 disrupt strut formation. BLI-1, BLI-2, and BLI-6 precisely colocalize to arrays of puncta in the adult cuticle, corresponding to struts, initially deposited in diffuse stripes adjacent to cuticle furrows. They eventually exhibit tube-like morphology, with the basal ends of BLI-containing struts contact regularly spaced holes in the cuticle. Genetic interaction studies indicate that BLI strut patterning involves interactions with other cuticle components. Our results reveal strut formation as a tractable example of precise aECM patterning at the nanoscale.

Molecular Characterization and Virus-Induced Gene Silencing of a Collagen Gene, Me-col-1, in Root-Knot Nematode Meloidogyne enterolobii

Meloidogyne enterolobii, a highly pathogenic root-knot nematode species, causes serious damage to agricultural production worldwide. Collagen is an important part of the nematode epidermis, which is crucial for nematode shape maintenance, motility, and reproduction. In this study, we report that a novel collagen gene, Me-col-1, from the highly pathogenic root-knot nematode species Meloidogyne enterolobi was required for the egg formation of this pathogen. Me-col-1 encodes a protein with the size of 35 kDa, which is closely related to collagen found in other nematodes. Real-time PCR assays showed that the expression of Me-col-1 was highest in eggs and lowest in pre-parasitic second-stage juveniles (preJ2). Interestingly, knockdown of Me-col-1 did not compromise the survival rate of preJ2 but significantly reduced the egg production and consequentially caused 35.79% lower multiplication rate (Pf/Pi) compared with control. Our study provides valuable information for better understanding the function of collagen genes in the nematode life cycle, which can be used in the development of effective approaches for nematode control.

The Ancestral Caenorhabditis elegans Cuticle Suppresses rol-1

Genetic background commonly modifies the effects of mutations. We discovered that worms mutant for the canonical rol-1 gene, identified by Brenner in 1974, do not roll in the genetic background of the wild strain CB4856. Using linkage mapping, association analysis and gene editing, we determined that N2 carries an insertion in the collagen gene col-182 that acts as a recessive enhancer of rol-1 rolling. From population and comparative genomics, we infer the insertion is derived in N2 and related laboratory lines, likely arising during the domestication of Caenorhabditis elegans, and breaking a conserved protein. The ancestral version of col-182 also modifies the phenotypes of four other classical cuticle mutant alleles, and the effects of natural genetic variation on worm shape and locomotion. These results underscore the importance of genetic background and the serendipity of Brenner's choice of strain.

Game of Tissues: How the Epidermis Thrones C. elegans Shape

The versatility of epithelial cell structure is universally exploited by organisms in multiple contexts. Epithelial cells can establish diverse polarized axes within their tridimensional structure which enables them to flexibly communicate with their neighbors in a 360° range. Hence, these cells are central to multicellularity, and participate in diverse biological processes such as organismal development, growth or immune response and their misfunction ultimately impacts disease. During the development of an organism, the first task epidermal cells must complete is the formation of a continuous sheet, which initiates its own morphogenic process. In this review, we will focus on the C. elegans embryonic epithelial morphogenesis. We will describe how its formation, maturation, and spatial arrangements set the final shape of the nematode C. elegans. Special importance will be given to the tissue-tissue interactions, regulatory tissue-tissue feedback mechanisms and the players orchestrating the process.

The ortholog of the human proto-oncogene ROS1 is required for epithelial development in C. elegans

The orphan receptor ROS1 is a human proto-oncogene, mutations of which are found in an increasing number of cancers. Little is known about the role of ROS1, however in vertebrates it has been implicated in promoting differentiation programs in specialized epithelial tissues. In this study we show that the C. elegans ortholog of ROS1, the receptor tyrosine kinase ROL-3, has an essential role in orchestrating the morphogenesis and development of specialized epidermal tissues, highlighting a potentially conserved function in coordinating crosstalk between developing epithelial cells. We also provide evidence of a direct relationship between ROL-3, the mucin SRAP-1, and BCC-1, the homolog of mRNA regulating protein Bicaudal-C. This study answers a longstanding question as to the developmental function of ROL-3, identifies three new genes that are expressed and function in the developing epithelium of C. elegans, and introduces the nematode as a potentially powerful model system for investigating the increasingly important, yet poorly understood, human oncogene ROS1. genesis 51:545–561.

C. elegans ADAMTS ADT-2 regulates body size by modulating TGFβ signaling and cuticle collagen organization

Organismal growth and body size are influenced by both genetic and environmental factors. We have utilized the strong molecular genetic techniques available in the nematode Caenorhabditis elegans to identify genetic determinants of body size. In C. elegans, DBL-1, a member of the conserved family of secreted growth factors known as the Transforming Growth Factor β superfamily, is known to play a major role in growth control. The mechanisms by which other determinants of body size function, however, is less well understood. To identify additional genes involved in body size regulation, a genetic screen for small mutants was previously performed. One of the genes identified in that screen was sma-21. We now demonstrate that sma-21 encodes ADT-2, a member of the ADAMTS (a disintegrin and metalloprotease with thrombospondin motifs) family of secreted metalloproteases. ADAMTS proteins are believed to remodel the extracellular matrix and may modulate the activity of extracellular signals. Genetic interactions suggest that ADT-2 acts in parallel with or in multiple size regulatory pathways. We demonstrate that ADT-2 is required for normal levels of expression of a DBL-1-responsive transcriptional reporter. We further demonstrate that adt-2 regulatory sequences drive expression in glial-like and vulval cells, and that ADT-2 activity is required for normal cuticle collagen fibril organization. We therefore propose that ADT-2 regulates body size both by modulating TGFβ signaling activity and by maintaining normal cuticle structure.

Collagen processing and cuticle formation is catalysed by the astacin metalloprotease DPY-31 in free-living and parasitic nematodes

The exoskeleton or cuticle performs many key roles in the development and survival of all nematodes. This structure is predominantly collagenous in nature and requires numerous enzymes to properly fold, modify, process and cross-link these essential structural proteins. The cuticle structure and its collagen components are conserved throughout the nematode phylum but differ from the collagenous matrices found in vertebrates. This structure, its formation and the enzymology of nematode cuticle collagen biogenesis have been elucidated in the free-living nematode Caenorhabditis elegans. The dpy-31 gene in C. elegans encodes a procollagen C-terminal processing enzyme of the astacin metalloprotease or bone morphogenetic protein class that, when mutated, results in a temperature-sensitive lethal phenotype associated with cuticle defects. In this study, orthologues of this essential gene have been identified in the phylogenetically diverse parasitic nematodes Haemonchus contortus and Brugia malayi. The DPY-31 protein is expressed in the gut and secretory system of C. elegans, a location also confirmed when a B. malayi transcriptional dpy-31 promoter-reporter gene fusion was expressed in C. elegans. Functional conservation between the nematode enzymes was supported by the fact that heterologous expression of the H. contortus dpy-31 orthologue in a C. elegans dpy-31 mutant resulted in the full rescue of the mutant body form. This interspecies conservation was further established when the recombinant nematode enzymes were found to have a similar range of inhibitable protease activities. In addition, the recombinant DPY-31 enzymes from both H. contortus and B. malayi were shown to efficiently process the C. elegans cuticle collagen SQT-3 at the correct C-terminal procollagen processing site.

Requirement for the ERI/DICER complex in endogenous RNA interference and sperm development in Caenorhabditis elegans

Small regulatory RNAs are key regulators of gene expression. One class of small regulatory RNAs, termed the endogenous small interfering RNAs (endo siRNAs), is thought to negatively regulate cellular transcripts via an RNA interference (RNAi)-like mechanism termed endogenous RNAi (endo RNAi). A complex of proteins composed of ERI-1/3/5, RRF-3, and DICER (the ERI/DICER complex) mediates endo RNAi processes in Caenorhabditis elegans. We conducted a genetic screen to identify additional components of the endo RNAi machinery. Our screen recovered alleles of eri-9, which encodes a novel DICER-interacting protein, and a missense mutation within the helicase domain of DICER [DCR-1(G492R)]. ERI-9(-) and DCR-1(G492) animals exhibit defects in endo siRNA expression and a concomitant failure to regulate mRNAs that exhibit sequence homology to these endo siRNAs, indicating that ERI-9 and the DCR-1 helicase domain function in the C. elegans endo RNAi pathway. We define a subset of Eri mutant animals (including eri-1, rrf-3, eri-3, and dcr-1, but not eri-9 or ergo-1) that exhibit temperature-sensitive, sperm-specific sterility and defects in X chromosome segregation. Among these mutants we find multiple aberrations in sperm development beginning with cytokinesis and extending through terminal differentiation. These results identify novel components of the endo RNAi machinery, demonstrate differential requirements for the Eri factors in the sperm-producing germline, and begin to delineate the functional requirement for the ERI/DICER complex in sperm development.

The C terminus of collagen SQT-3 has complex and essential functions in nematode collagen assembly

The nematode exoskeleton is a multilayered structure secreted by the underlying hypodermal cells and mainly composed of small collagens, which are encoded by a large gene family. In previous work, we reported analysis of the C. elegans dpy-31 locus, encoding a hypodermally expressed zinc-metalloprotease of the BMP-1/TOLLOID family essential for viability and cuticle deposition. We have generated a large set of extragenic suppressors of dpy-31 lethality, most of which we show here to be allelic to the cuticle collagen genes sqt-3 and dpy-17. We analyzed the interaction among dpy-31, sqt-3, and dpy-17 using a SQT-3-specific antiserum, which was employed in immunofluorescence experiments. Our results support a role for DPY-31 in SQT-3 extracellular processing and suggest that the SQT-3 C-terminal nontrimeric region serves multiple roles during SQT-3 assembly. Different missense mutations of this region have diverse phenotypic consequences, including cold-sensitive lethality. Furthermore, the biochemical and genetic data indicate that the extracellular assemblies of DPY-17 and SQT-3 are interdependent, most likely because the collagens are incorporated into the same cuticular substructure. We find that absence of DPY-17 causes extensive intracellular retention of SQT-3, indicating that formation of the SQT-3-DPY-17 polymer could begin in the intracellular environment before secretion.

Gene interactions in Caenorhabditis elegans define DPY-31 as a candidate procollagen C-proteinase and SQT-3/ROL-4 as its predicted major target

Zinc metalloproteases of the BMP-1/TOLLOID family (also known as astacins) are extracellular enzymes involved in important developmental processes in metazoans. We report the characterization of the Caenorhabditis elegans gene dpy-31, which encodes the first essential astacin metalloprotease identified in this organism. Loss-of-function mutations in dpy-31 result in cuticle defects, abnormal morphology, and embryonic lethality, indicating that dpy-31 is required for formation of the collagenous exoskeleton. DPY-31 is widely expressed in the hypodermal cells, which are responsible for cuticle secretion. We have investigated the dpy-31 function through reversion analysis. While complete reversion can be obtained only by intragenic suppressors, reversion of the Dpy-31 lethal phenotype also can be caused by dominant extragenic suppressors. Nine extragenic suppressors carry mutations in the uniquely essential collagen gene sqt-3, which we show is the same gene as rol-4. Most mutations exhibit the unusual property of exclusively dominant suppression and all affect the sequence of the SQT-3 collagen C terminus. This suggests that DPY-31 is responsible for C-terminal proteolytic processing of collagen trimers and is therefore a structural and functional homolog of vertebrate BMP-1. The results also demonstrate the critical importance of the collagen C-terminal sequence, which is highly conserved among all 49 members of the SQT-3 subfamily.

Genetic analysis of lysosomal trafficking in Caenorhabditis elegans

The intestinal cells of Caenorhabditis elegans embryos contain prominent, birefringent gut granules that we show are lysosome-related organelles. Gut granules are labeled by lysosomal markers, and their formation is disrupted in embryos depleted of AP-3 subunits, VPS-16, and VPS-41. We define a class of gut granule loss (glo) mutants that are defective in gut granule biogenesis. We show that the glo-1 gene encodes a predicted Rab GTPase that localizes to lysosome-related gut granules in the intestine and that glo-4 encodes a possible GLO-1 guanine nucleotide exchange factor. These and other glo genes are homologous to genes implicated in the biogenesis of specialized, lysosome-related organelles such as melanosomes in mammals and pigment granules in Drosophila. The glo mutants thus provide a simple model system for the analysis of lysosome-related organelle biogenesis in animal cells.

A mutation in a cuticle collagen causes hypersensitivity to the endocrine disrupting chemical, bisphenol A, in Caenorhabditis elegans

A novel mutant gene, bis-1 (bisphenol A sensitive) has been isolated in the nematode, Caenorhabditis elegans, that affects the response to endocrine disrupting chemicals (EDC). The bis-1(nx3) allele is hypersensitive to bisphenol A (BPA), is allelic to a collagen gene (col-121), and is expressed in hypodermal cells. Among the collagen mutants so far studied, bis-1(nx3), dpy-2(e8), dpy-7(e88) and dpy-10(e128) showed BPA sensitivity. The isolated mutant may work as a useful tool for the assay of EDC toxicity since the physiological effect of the collagen mutation (glycine substitution) indicates an increased sensitivity to BPA.

Enzymes involved in the biogenesis of the nematode cuticle

Nematodes include species that are significant parasites of man, his domestic animals and crops, and cause chronic debilitating diseases in the developing world; such as lymphatic filariasis and river blindness caused by filarial species. Around one third of the World's population harbour parasitic nematodes; no vaccines exist for prevention of infection, limited effective drugs are available and drug resistance is an ever-increasing problem. A critical structure of the nematode is the protective cuticle, a collagen-rich extracellular matrix (ECM) that forms the exoskeleton, and is critical for viability. This resilient structure is synthesized sequentially five times during nematode development and offers protection from the environment, including the hosts' immune response. The detailed characterization of this complex structure; it's components, and the means by which they are synthesized, modified, processed and assembled will identify targets that may be exploited in the future control of parasitic nematodes. This review will focus on the nematode cuticle. This structure is predominantly composed of collagens, a class of proteins that are modified by a range of co- and post-translational modifications prior to assembly into higher order complexes or ECMs. The collagens and their associated enzymes have been comprehensively characterized in vertebrate systems and some of these studies will be addressed in this review. Conversely, the biosynthesis of this class of essential structural proteins has not been studied in such detail in the nematodes. As with all morphogenetic, functional and developmental studies in the Nematoda phylum, the free-living species Caenorhabditis elegans has proven to be invaluable in the characterization of the cuticle and the cuticle collagen gene family, and is now proving to be an excellent model in the study of cuticle collagen biosynthetic enzymes. This model system will be the main focus of this review.

Two sets of interacting collagens form functionally distinct substructures within a Caenorhabditis elegans extracellular matrix

A ubiquitous feature of collagens is protein interaction, the trimerization of monomers to form a triple helix followed by higher order interactions during the formation of the mature extracellular matrix. The Caenorhabditis elegans cuticle is a complex extracellular matrix consisting predominantly of cuticle collagens, which are encoded by a family of approximately 154 genes. We identify two discrete interacting sets of collagens and show that they form functionally distinct matrix substructures. We show that mutation in or RNA-mediated interference of a gene encoding a collagen belonging to one interacting set affects the assembly of other members of that set, but not those belonging to the other set. During cuticle synthesis, the collagen genes are expressed in a distinct temporal series, which we hypothesize exists to facilitate partner finding and the formation of appropriate interactions between encoded collagens. Consistent with this hypothesis, we find for the two identified interacting sets that the individual members of each set are temporally coexpressed, whereas the two sets are expressed approximately 2 h apart during matrix synthesis.

Caenorhabditis elegans exoskeleton collagen COL-19: an adult-specific marker for collagen modification and assembly, and the analysis of organismal morphology

The integral role that collagens play in the morphogenesis of the nematode exoskeleton or cuticle makes them a useful marker in the examination of the collagen synthesizing machinery. In this study, a green fluorescent protein-collagen fusion has been constructed by using the Caenorhabditis elegans adult-specific, hypodermally synthesized collagen COL-19. In wild-type nematodes, this collagen marker localized to the circumferential annular rings and the lateral trilaminar alae of the cuticle. Crosses carried out between a COL-19::GFP integrated strain and several morphologically mutant strains, including blister, dumpy, long, small, squat, and roller revealed significant COL-19 disruption that was predominantly strain-specific and provided a structural basis for the associated phenotypes. Disruption was most notable in the cuticle overlying the lateral seam cell syncytium, and confirmed the presence of two distinct forms of hypodermis, namely the circumferentially contracting lateral seam cells and the laterally contracting ventral-dorsal hypodermis. The effect of a single aberrant collagen being sufficient to mediate widespread collagen disruption was exemplified by the collagen mutant strain dpy-5 and its disrupted COL-19::GFP and DPY-7 collagen expression patterns. Through the disrupted pattern of COL-19 and DPY-7 in a thioredoxin mutant, dpy-11, and through RNA interference of a dual oxidase enzyme and a vesicular transport protein, we also show the efficacy of the COL-19::GFP strain as a marker for aberrant cuticle collagen synthesis and, thus, for the identification of factors involved in the construction of collagenous extracellular matrices.

The Caenorhabditis elegans ERp60 homolog protein disulfide isomerase-3 has disulfide isomerase and transglutaminase-like cross-linking activity and is involved in the maintenance of body morphology

A novel protein disulfide isomerase gene, pdi-3, was isolated from the nematode Caenorhabditis elegans. This gene encodes an enzyme related to the ERp60 class of thioredoxin proteins and was found to exhibit unusual enzymatic properties. Recombinant protein displayed both disulfide bond isomerase activity and calcium-dependent transglutaminase-like cross-linking activity. The pdi-3 transcript was developmentally constitutively expressed, and the encoded protein is present in many tissues including the gut and the hypodermis. The nematode hypodermis synthesizes the essential collagenous extracellular matrix (ECM) called the cuticle. Transcript disruption via double-stranded RNA interference resulted in dramatic and specific synthetic phenotypes in several C. elegans mutant alleles with weakened cuticles: sqt-3(e2117), dpy-18(e364, ok162, and bx26). These nematodes displayed severe dumpy phenotypes and disrupted lateral alae, a destabilized cuticle and abnormal male and hermaphrodite tail morphologies. These defects were confirmed to be consistent with hypodermal seam cell abnormalities and corresponded with the severe disruption of a cuticle collagen. Wild type nematodes did not exhibit observable morphological defects; however, cuticle collagen localization was mildly disrupted following pdi-3 RNA interference. The unusual thioredoxin enzyme, protein disulfide isomerase-3, may therefore play a role in ECM assembly. This enzyme is required for the proper maintenance of post-embryonic body shape in strains with a weakened cuticle, perhaps through ECM stabilization via cross-linking activity, disulfide isomerase protein folding activity, protein disulfide isomerase chaperone activity, or via multifunctional events.

Increased or decreased levels of Caenorhabditis elegans lon-3, a gene encoding a collagen, cause reciprocal changes in body length

Body length in C. elegans is regulated by a member of the TGFbeta family, DBL-1. Loss-of-function mutations in dbl-1, or in genes encoding components of the signaling pathway it activates, cause worms to be shorter than wild type and slightly thinner (Sma). Overexpression of dbl-1 confers the Lon phenotype characterized by an increase in body length. We show here that loss-of-function mutations in dbl-1 and lon-1, respectively, cause a decrease or increase in the ploidy of nuclei in the hypodermal syncytial cell, hyp7. To learn more about the regulation of body length in C. elegans we carried out a genetic screen for new mutations causing a Lon phenotype. We report here the cloning and characterization of lon-3. lon-3 is shown to encode a putative cuticle collagen that is expressed in hypodermal cells. We show that, whereas putative null mutations in lon-3 (or reduction of lon-3 activity by RNAi) causes a Lon phenotype, increasing lon-3 gene copy number causes a marked reduction in body length. Morphometric analyses indicate that the lon-3 loss-of-function phenotype resembles that caused by overexpression of dbl-1. Furthermore, phenotypes caused by defects in dbl-1 or lon-3 expression are in both cases suppressed by a null mutation in sqt-1, a second cuticle collagen gene. However, whereas loss of dbl-1 activity causes a reduction in hypodermal endoreduplication, the reduction in body length associated with overexpression of lon-3 occurs in the absence of defects in hypodermal ploidy.

The let-268 locus of Caenorhabditis elegans encodes a procollagen lysyl hydroxylase that is essential for type IV collagen secretion

Basement membranes are thin sheets of specialized extracellular matrix molecules that are important for supplying mechanical support and for providing an interactive surface for cell morphology. Prior to secretion and assembly, basement membrane molecules undergo intracellular processing, which is essential for their function. We have identified several mutations in a procollagen processing enzyme, lysyl hydroxylase (let-268). The Caenorhabditis elegans lysyl hydroxylase is highly similar to the vertebrate lysyl hydroxylase, containing all essential motifs required for enzymatic activity, and is the only lysyl hydroxylase found in the C. elegans sequenced genome. In the absence of C. elegans lysyl hydroxylase, type IV collagen is expressed; however, it is retained within the type IV collagen-producing cells. This observation indicates that in let-268 mutants the processing and secretion of type IV collagen is disrupted. Our examination of the body wall muscle in these mutant animals reveals normal myofilament assembly prior to contraction. However, once body wall muscle contraction commences the muscle cells separate from the underlying epidermal layer (the hypodermis) and the myofilaments become disorganized. These observations indicate that type IV collagen is required in the basement membrane for mechanical support and not for organogenesis of the body wall muscle.

dpy-18 encodes an alpha-subunit of prolyl-4-hydroxylase in caenorhabditis elegans

Collagen is an extracellular matrix (ECM) component encoded by a large multigene family in multicellular animals. Procollagen is post-translationally modified by prolyl-4-hydroxylase (EC 1.14.11.2) before secretion and participation in ECM formation. Therefore, collagen processing and regulation can be studied by examining this required interaction of prolyl-4-hydroxylase with procollagen. High-resolution polymorphism mapping was used to place the Caenorhabditis elegans dpy-18 gene on the physical map, and we show that it encodes a prolyl-4-hydroxylase alpha catalytic subunit. The Dpy phenotype of dpy-18(e364) amber mutants is more severe when this mutation is in trans to the noncomplementing deficiency tDf7, while the dpy-18(e499) deletion mutant exhibits the same phenotype as dpy-18(e499)/tDf7. Furthermore, dpy-18 RNA interference (RNAi) in wild-type worms results in Dpy progeny, while dpy-18 (RNAi) in dpy-18(e499) mutants does not alter the Dpy phenotype of their progeny. These observations suggest that the dpy-18 null phenotype is Dpy. A dpy-18::gfp promoter fusion construct is expressed throughout the hypodermis within the cells that abundantly produce the cuticle collagens, as well as in certain head and posterior neurons. While prolyl-4-hydroxylase has been studied extensively by biochemical techniques, this is the first report of a mutationally defined prolyl-4-hydroxylase in any animal.

Prolyl 4-hydroxylase is an essential procollagen-modifying enzyme required for exoskeleton formation and the maintenance of body shape in the nematode Caenorhabditis elegans

The multienzyme complex prolyl 4-hydroxylase catalyzes the hydroxylation of proline residues and acts as a chaperone during collagen synthesis in multicellular organisms. The beta subunit of this complex is identical to protein disulfide isomerase (PDI). The free-living nematode Caenorhabditis elegans is encased in a collagenous exoskeleton and represents an excellent model for the study of collagen biosynthesis and extracellular matrix formation. In this study, we examined prolyl 4-hydroxylase alpha-subunit (PHY; EC 1.14.11.2)- and beta-subunit (PDI; EC 5.3.4.1)-encoding genes with respect to their role in collagen modification and formation of the C. elegans exoskeleton. We identified genes encoding two PHYs and a single associated PDI and showed that all three are expressed in collagen-synthesizing ectodermal cells at times of maximal collagen synthesis. Disruption of the pdi gene via RNA interference resulted in embryonic lethality. Similarly, the combined phy genes are required for embryonic development. Interference with phy-1 resulted in a morphologically dumpy phenotype, which we determined to be identical to the uncharacterized dpy-18 locus. Two dpy-18 mutant strains were shown to have null alleles for phy-1 and to have a reduced hydroxyproline content in their exoskeleton collagens. This study demonstrates in vivo that this enzyme complex plays a central role in extracellular matrix formation and is essential for normal metazoan development.

A transmembrane guanylyl cyclase (DAF-11) and Hsp90 (DAF-21) regulate a common set of chemosensory behaviors in caenorhabditis elegans

Caenorhabditis elegans daf-11 and daf-21 mutants share defects in specific chemosensory responses mediated by several classes of sensory neurons, indicating that these two genes have closely related functions in an assortment of chemosensory pathways. We report that daf-11 encodes one of a large family of C. elegans transmembrane guanylyl cyclases (TM-GCs). The cyclic GMP analogue 8-bromo-cGMP rescues a sensory defect in both daf-11 and daf-21 mutants, supporting a role for DAF-11 guanylyl cyclase activity in this process and further suggesting that daf-21 acts at a similar step. daf-11::gfp fusions are expressed in five identified pairs of chemosensory neurons in a pattern consistent with most daf-11 mutant phenotypes. We also show that daf-21 encodes the heat-shock protein 90 (Hsp90), a chaperone with numerous specific protein targets. We show that the viable chemosensory-deficient daf-21 mutation is an unusual allele resulting from a single amino acid substitution and that the daf-21 null phenotype is early larval lethality. These results demonstrate that cGMP is a prominent second messenger in C. elegans chemosensory transduction and suggest a previously unknown role for Hsp90 in regulating cGMP levels.

Genetic requirements for inheritance of RNAi in C. elegans

In Caenorhabditis elegans, the introduction of double-stranded RNA triggers sequence-specific genetic interference (RNAi) that is transmitted to offspring. The inheritance properties associated with this phenomenon were examined. Transmission of the interference effect occurred through a dominant extragenic agent. The wild-type activities of the RNAi pathway genes rde-1 and rde-4 were required for the formation of this interfering agent but were not needed for interference thereafter. In contrast, the rde-2 and mut-7 genes were required downstream for interference. These findings provide evidence for germ line transmission of an extragenic sequence-specific silencing factor and implicate rde-1 and rde-4 in the formation of the inherited agent.

Cuticle collagen genes. Expression in Caenorhabditis elegans

Collagen is a structural protein used in the generation of a wide variety of animal extracellular matrices. The exoskeleton of the free-living nematode, Caenorhabditis elegans, is a complex collagen matrix that is tractable to genetic research. Mutations in individual cuticle collagen genes can cause exoskeletal defects that alter the shape of the animal. The complete sequence of the C. elegans genome indicates upwards of 150 distinct collagen genes that probably contribute to this structure. During the synthesis of this matrix, individual collagen genes are expressed in distinct temporal periods, which might facilitate the formation of specific interactions between distinct collagens.

Disruption of clh-1, a chloride channel gene, results in a wider body of Caenorhabditis elegans

We cloned the clh-1 gene coding for a putative ClC chloride channel in Caenorhabditis elegans. The gene product exhibited a high degree of homology with human ClC-1 and ClC-2. The clh-1 gene was predominantly expressed in the hypodermis, including seam cells. Null mutations of clh-1 caused a significantly wider body and an abnormal alae structure. High osmolarity in the culture medium restored the normal body width of the clh-1 mutants. These results suggest that the clh-1 gene contributes to maintenance of the body width through regulation of osmolarity.

The rde-1 gene, RNA interference, and transposon silencing in C. elegans

Double-stranded (ds) RNA can induce sequence-specific inhibition of gene function in several organisms. However, both the mechanism and the physiological role of the interference process remain mysterious. In order to study the interference process, we have selected C. elegans mutants resistant to dsRNA-mediated interference (RNAi). Two loci, rde-1 and rde-4, are defined by mutants strongly resistant to RNAi but with no obvious defects in growth or development. We show that rde-1 is a member of the piwi/sting/argonaute/zwille/eIF2C gene family conserved from plants to vertebrates. Interestingly, several, but not all, RNAi-deficient strains exhibit mobilization of the endogenous transposons. We discuss implications for the mechanism of RNAi and the possibility that one natural function of RNAi is transposon silencing.

Conservation of the Caenorhabditis elegans cuticle collagen gene col-12 in Caenorhabditis briggsae

The functional importance of the majority of Caenorhabditis elegans cuticle collagen genes is unknown. We have identified, cloned and sequenced the Caenorhabditis briggsae homologue of the C. elegans gene col-12, a cuticle collagen for which no mutants have yet been identified. Homology in the flanking sequence has allowed us to unambiguously identify this gene as the col-12 homologue, as opposed to some other closely related member of this large multigene family. The whole of the predicted polypeptide is highly conserved (94.9% identical), including those regions not yet shown by mutational analysis to be important for C. elegans cuticle collagen function. These include the whole of the N-terminal non-Gly-X-Y domain and the X and Y positions of the Gly-X-Y domain. This may be a consequence of the requirement of cuticle collagens to participate in intermolecular interactions throughout the full length of the polypeptide. There is increasing evidence to suggest that conservation between C. elegans and C. briggsae is confined to functionally significant sequence. Hence, the conservation of col-12 between these two species provides evidence that this member of the cuticle collagen family has a significant structural function.

The role of actin filaments in patterning the Caenorhabditis elegans cuticle

Nematodes are covered by a cuticle with a prominent pattern of circumferentially oriented, parallel furrows. We report here that the pattern of furrows on the first larval cuticle of Caenorhabditis elegans, which is secreted during embryogenesis, is coincident with a pattern of submembranous actin filament bundles in the epithelial cells that secrete the cuticle. We propose that the pattern of cortical actin filaments biases the growth of the epithelial cell membranes, creating a furrowed surface template for deposition of the first cuticle layer. This layer then detaches from the epithelial cell surface as additional, nonpatterned components of the cuticle are secreted. Furrows are present on the surfaces of each of the four larval cuticles in C. elegans and on the adult cuticle. We show that similar ordered arrays of actin filaments appear during each of the postembryonic molts when new cuticles are synthesized. Our analysis suggests that conditions or mutations that affect the pattern of cuticle furrows might cause primary defects in the cytoskeletal organization of the epithelial cells that secrete the cuticle.

Structure, function, and expression of SEL-1, a negative regulator of LIN-12 and GLP-1 in C. elegans

Previous work indicated that sel-1 functions as a negative regulator of lin-12 activity, and predicted that SEL-1 is a secreted or membrane associated protein. In this study, we describe cell ablation experiments that suggest sel-1 mutations elevate lin-12 activity cell autonomously. We also use transgenic approaches to demonstrate that the predicted signal sequence of SEL-1 can direct secretion and is important for function, while a C-terminal hydrophobic region is not required for SEL-1 function. In addition, by analyzing SEL-1 localization using specific antisera we find that SEL-1 is localized intracellularly, with a punctate staining pattern suggestive of membrane bound vesicles. We incorporate these observations, and new information about a related yeast gene, into a proposal for a possible mechanism for SEL-1 function in LIN-12 turnover.