The Caenorhabditis elegans rol-6 gene, which interacts with the sqt-1 collagen gene to determine organismal morphology, encodes a collagen

Protein phosphatase 2A cooperates with the autophagy-related kinase UNC-51 to regulate axon guidance in Caenorhabditis elegans

UNC-51 is a serine/threonine protein kinase conserved from yeast to humans. The yeast homolog Atg1 regulates autophagy (catabolic membrane trafficking) required for surviving starvation. In C. elegans, UNC-51 regulates the axon guidance of many neurons by a different mechanism than it and its homologs use for autophagy. UNC-51 regulates the subcellular localization (trafficking) of UNC-5, a receptor for the axon guidance molecule UNC-6/Netrin; however, the molecular details of the role for UNC-51 are largely unknown. Here, we report that UNC-51 physically interacts with LET-92, the catalytic subunit of serine/threonine protein phosphatase 2A (PP2A-C), which plays important roles in many cellular functions. A low allelic dose of LET-92 partially suppressed axon guidance defects of weak, but not severe, unc-51 mutants, and a low allelic dose of PP2A regulatory subunits A (PAA-1/PP2A-A) and B (SUR-6/PP2A-B) partially enhanced the weak unc-51 mutants. We also found that LET-92 can work cell-non-autonomously on axon guidance in neurons, and that LET-92 colocalized with UNC-51 in neurons. In addition, PP2A dephosphorylated phosphoproteins that had been phosphorylated by UNC-51. These results suggest that, by forming a complex, PP2A cooperates with UNC-51 to regulate axon guidance by regulating phosphorylation. This is the first report of a serine/threonine protein phosphatase functioning in axon guidance in vivo.

Vectors for co-expression of two genes in Caenorhabditis elegans

To meet the increasing need of simultaneously co-expressing two different genes in the same cell of transgenic Caenorhabditis elegans, here, we report the establishment of dicistronic vectors that contain an intercistronic region (ICR) of the C. elegans operon, CEOP5428. In these vectors, a green fluorescence protein (GFP) and a red FP (RFP) genes were placed in the first and second cistrons, respectively, which were separated by the ICR. Driven by the fibrillarin (fib-1) or myo-2 promoter, the GFP- and RFP-fusion proteins were consistently co-expressed in the entire worm cells or in the pharynx muscle cells of the transgenic worms, respectively. Our work demonstrates that ICR-containing dicistronic vectors could be developed into versatile co-expression systems in C. elegans for functional analysis of genes of interest.

Structural and functional characterisation of the fork head transcription factor-encoding gene, Hc-daf-16, from the parasitic nematode Haemonchus contortus (Strongylida)

Despite their phylogenetic diversity, parasitic nematodes share attributes of longevity and developmental arrest (=hypobiosis) with free-living nematodes at key points in their life cycles, particularly in larval stages responsible for establishing infection in the host. Insulin-like signalling plays crucial roles in the regulation of life span and arrest (=dauer formation) in the free-living nematode, Caenorhabditis elegans. Insulin-like signalling in C. elegans negatively regulates the fork head boxO (FoxO) transcription factor encoded by daf-16, which is linked to initiating a dauer-specific pattern of gene expression. Orthologues of daf-16 have been identified in several species of parasitic nematode. Although function has been demonstrated for an orthologue from the parasitic nematode Strongyloides stercoralis (Rhabditida), the functional capabilities of homologues/orthologues in bursate nematodes (Strongylida) are unknown. In the present study, we used a genomic approach to determine the structures of two complete daf-16 orthologues (designated Hc-daf-16.1 and Hc-daf-16.2) and their transcripts in the parasitic nematode Haemonchus contortus, and assessed their function(s) using C. elegans as a genetic surrogate. Unlike the multiple isoforms of Ce-DAF-16 and Ss-DAF-16, which are encoded by a single gene and produced by alternative splicing, mRNAs encoding the proteins Hc-DAF-16.1 and Hc-DAF-16.2 are transcribed from separate and distinct loci. Both orthologues are transcribed in all developmental stages and both sexes of H. contortus, and the inferred proteins (603 and 556 amino acids) each contain a characteristic, highly conserved fork head domain. In spite of distinct differences in genomic organisation compared with orthologues in C. elegans and S. stercoralis, genetic complementation studies demonstrated here that Hc-daf-16.2, but not Hc-daf-16.1, could restore daf-16 function to a C. elegans strain carrying a null mutation at this locus. These findings are consistent with previous results for S. stercoralis and demonstrate functional conservation of the daf-16b orthologue between key parasitic nematodes from two different taxonomic orders and C. elegans. We conclude from these experiments that the fork head transcription factor DAF-16 and, by inference, other insulin-like signalling elements, are conserved in H. contortus, a parasitic nematode of paramount economic importance. We demonstrate that functionality is sufficiently conserved in Hc-DAF-16.2 that it can replace Ce-DAF-16 in promoting dauer arrest in C. elegans.

The BCL-2-like protein CED-9 of C. elegans promotes FZO-1/Mfn1,2- and EAT-3/Opa1-dependent mitochondrial fusion

The mammalian dynamin-related guanosine triphosphatases Mfn1,2 and Opa1 are required for mitochondrial fusion. However, how their activities are controlled and coordinated is largely unknown. We present data that implicate the BCL-2–like protein CED-9 in the control of mitochondrial fusion in Caenorhabditis elegans. We demonstrate that CED-9 can promote complete mitochondrial fusion of both the outer and inner mitochondrial membrane. We also show that this fusion is dependent on the C. elegans Mfn1,2 homologue FZO-1 and the C. elegans Opa1 homologue EAT-3. Furthermore, we show that CED-9 physically interacts with FZO-1 in vivo and that the ability of CED-9 to interact with FZO-1 is important for its ability to cause mitochondrial fusion. CED-9–induced mitochondrial fusion is not required for the maintenance of mitochondrial morphology during embryogenesis or in muscle cells, at least under normal conditions and in the absence of stress. Therefore, we propose that the BCL-2–like CED-9 acts through FZO-1/Mfn1,2 and EAT-3/Opa1 to promote mitochondrial fusion in response to specific cellular signals.

Functional genomics of hsp-90 in parasitic and free-living nematodes

Heat shock protein 90 (Hsp-90) is a highly conserved essential protein in eukaryotes. Here we describe the molecular characterisation of hsp-90 from three nematodes, the free-living Caenorhabditis elegans (Ce) and the parasitic worms Brugia pahangi (Bp) and Haemonchus contortus (Hc). These molecules were functionally characterised by rescue of a Ce-daf-21 (hsp-90) null mutant. Our results show a gradient of rescue: the C. elegans endogenous gene provided full rescue of the daf-21 mutant, while Hc-hsp-90 provided partial rescue. In contrast, no rescue could be obtained using a variety of Bp-hsp-90 constructs, despite the fact that Bp-hsp-90 was transcribed and translated in the mutant worms. daf-21 RNA interference (RNAi) experiments were carried out to determine whether knock-down of the endogenous daf-21 mRNA in N2 worms could be complemented by expression of either parasite gene. However neither parasite gene could rescue the daf-21 (RNAi) phenotypes. These results indicate that factors other than the level of sequence identity are important for determining whether parasite genes can functionally complement in C. elegans.

Dopamine counteracts octopamine signalling in a neural circuit mediating food response in C. elegans

Animals assess food availability in their environment by sensory perception and respond to the absence of food by changing hormone and neurotransmitter signals. However, it is largely unknown how the absence of food is perceived at the level of functional neurocircuitry. In Caenorhabditis elegans, octopamine is released from the RIC neurons in the absence of food and activates the cyclic AMP response element binding protein in the cholinergic SIA neurons. In contrast, dopamine is released from dopaminergic neurons only in the presence of food. Here, we show that dopamine suppresses octopamine signalling through two D2-like dopamine receptors and the G protein Gi/o. The D2-like receptors work in both the octopaminergic neurons and the octopamine-responding SIA neurons, suggesting that dopamine suppresses octopamine release as well as octopamine-mediated downstream signalling. Our results show that C. elegans detects the absence of food by using a small neural circuit composed of three neuron types in which octopaminergic signalling is activated by the cessation of dopamine signalling.

Caenorhabditis elegans genomic response to soil bacteria predicts environment-specific genetic effects on life history traits

With the post-genomic era came a dramatic increase in high-throughput technologies, of which transcriptional profiling by microarrays was one of the most popular. One application of this technology is to identify genes that are differentially expressed in response to different environmental conditions. These experiments are constructed under the assumption that the differentially expressed genes are functionally important in the environment where they are induced. However, whether differential expression is predictive of functional importance has yet to be tested. Here we have addressed this expectation by employing Caenorhabditis elegans as a model for the interaction of native soil nematode taxa and soil bacteria. Using transcriptional profiling, we identified candidate genes regulated in response to different bacteria isolated in association with grassland nematodes or from grassland soils. Many of the regulated candidate genes are predicted to affect metabolism and innate immunity suggesting similar genes could influence nematode community dynamics in natural systems. Using mutations that inactivate 21 of the identified genes, we showed that most contribute to lifespan and/or fitness in a given bacterial environment. Although these bacteria may not be natural food sources for C. elegans, we show that changes in food source, as can occur in environmental disturbance, can have a large effect on gene expression, with important consequences for fitness. Moreover, we used regression analysis to demonstrate that for many genes the degree of differential gene expression between two bacterial environments predicted the magnitude of the effect of the loss of gene function on life history traits in those environments.

Transcriptional profiling is often used to identify genes that are differentially regulated in response to different environments. These experiments assume that genes differentially expressed in response to different environments are functionally important and, furthermore, that the degree of differential gene expression is predictive of the magnitude of functional importance. In genetic experiments, function is inferred from analyzing the phenotypes of removing, reducing or altering gene function. However, to date, there has not been a specific test of how well the degree of differential gene expression between two (or more) environments is predictive of gene function. Here we identified C. elegans genes that were differentially expressed in response to different bacterial environments and determined the phenotypic differences of life history traits between these environments using mutant strains that compromised gene function. We found that differential gene expression is indeed predictive of functional importance of the identified genes in different environments. This observation has important implications for interpreting the results of transcriptional profiling experiments of populations of organisms in their native environments, where in many cases the genetic tools to disrupt gene function have not yet been fully developed or interfering with gene functions in nature may not be feasible.

CRIP homologues maintain apical cytoskeleton to regulate tubule size in C. elegans

Maintenance of the shape and diameter of biological tubules is a critical task in the development and physiology of all metazoan organisms. We have cloned the exc-9 gene of Caenorhabditis elegans, which regulates the diameter of the single-cell excretory canal tubules. exc-9 encodes a homologue of the highly expressed mammalian intestinal LIM-domain protein CRIP, whose function has not previously been determined. A second well-conserved CRIP homologue functions in multiple valves of C. elegans. EXC-9 shows genetic interactions with other EXC proteins, including the EXC-5 guanine exchange factor that regulates CDC-42 activity. EXC-9 and its nematode homologue act in polarized epithelial cells that must maintain great flexibility at their apical surface; our results suggest that CRIPs function to maintain cytoskeletal flexibility at the apical surface.

Transgenesis and neuronal ablation in parasitic nematodes: revolutionary new tools to dissect host-parasite interactions

Ease of experimental gene transfer into viral and prokaryotic pathogens has made transgenesis a powerful tool for investigating the interactions of these pathogens with the host immune system. Recent advances have made this approach feasible for more complex protozoan parasites. By contrast, the lack of a system for heritable transgenesis in parasitic nematodes has hampered progress toward understanding the development of nematode-specific cellular responses. Recently, however, significant strides towards such a system have been made in several parasitic nematodes, and the possible applications of these in immunological research should now be contemplated. In addition, methods for targeted cell ablation have been successfully adapted from Caenorhabditis elegans methodology and applied to studies of neurobiology and behaviour in Strongyloides stercoralis. Together, these new technical developments offer exciting new tools to interrogate multiple aspects of the host-parasite interaction following nematode infection.

Strongyloides stercoralis: cell- and tissue-specific transgene expression and co-transformation with vector constructs incorporating a common multifunctional 3' UTR

Transgenesis is a valuable methodology for studying gene expression patterns and gene function. It has recently become available for research on some parasitic nematodes, including Strongyloides stercoralis. Previously, we described a vector construct, comprising the promoter and 3' UTR of the S. stercoralis gene Ss era-1 that gives expression of GFP in intestinal cells of developing F1 progeny. In the present study, we identified three new S. stercoralis promoters, which, in combination with the Ss era-1 3' UTR, can drive expression of GFP or the red fluorescent protein, mRFPmars, in tissue-specific fashion. These include Ss act-2, which drives expression in body wall muscle cells, Ss gpa-3, which drives expression in amphidial and phasmidial neurons and Ss rps-21, which drives ubiquitous expression in F1 transformants and in the gonads of microinjected P0 female worms. Concomitant microinjection of vectors containing GFP and mRFPmars gave dually transformed F1 progeny, suggesting that these constructs could be used as co-injection markers for other transgenes of interest. We have developed a vector "toolkit" for S. stercoralis including constructs with the Ss era-1 3' UTR and each of the promoters described above.

Insulin signaling and the heat shock response modulate protein homeostasis in the Caenorhabditis elegans intestine during infection

During infection, damage can occur to the host as an outcome of both pathogen virulence mechanisms and host defense strategies. Using aggregation of a model polyglutamine-containing protein as an indicator in Caenorhabditis elegans, we show that protein damage occurs specifically at the site of the host-pathogen interaction, the intestine, in response to various bacterial pathogens. We demonstrate that the insulin signaling pathway and the heat shock transcription factor (HSF-1) influence the amount of aggregation that occurs, in addition to heat shock proteins and oxidative stress enzymes. We also show that addition of the antioxidants epigallocatechin gallate and alpha-lipoic acid reduces polyglutamine aggregation. The influence of oxidative stress enzymes and exogenous antioxidants on protein aggregation suggests that reactive oxygen species produced by the host are a source of protein damage during infection. We propose a model in which heat shock proteins and oxidative stress enzymes regulated by insulin signaling and HSF-1 are required for tissue protection during infection, to minimize the effects of protein damage occurring as a result of host-pathogen interactions.

C. elegans orthologs of components of the RB tumor suppressor complex have distinct pro-apoptotic functions

To obtain insight into the role of the retinoblastoma susceptibility gene (Rb; also known as Rb1) in apoptosis, we analyzed Caenorhabditis elegans mutants lacking a functional lin-35 RB gene. We found that the loss of lin-35 function results in a decrease in constitutive germ cell apoptosis. We present evidence that lin-35 promotes germ cell apoptosis by repressing the expression of ced-9, an anti-apoptotic C. elegans gene that is orthologous to the human proto-oncogene BCL2. Furthermore, we show that the genes dpl-1 DP, efl-1 E2F and efl-2 E2F also promote constitutive germ cell apoptosis. However, in contrast to lin-35, dpl-1 (and probably also efl-1 and efl-2) promotes germ cell apoptosis by inducing the expression of the pro-apoptotic genes ced-4 and ced-3, which encode an APAF1-like adaptor protein and a pro-caspase, respectively. Based on these results, we propose that C. elegans orthologs of components of the RB tumor suppressor complex have distinct pro-apoptotic functions in the germ line and that the transcriptional regulation of components of the central apoptosis machinery is a critical determinant of constitutive germ cell apoptosis in C. elegans. Finally, we demonstrate that lin-35, dpl-1 and efl-2, but not efl-1, function either downstream of or in parallel to cep-1 p53 (also known as TP53) and egl-1 BH3-only to cause DNA damage-induced germ cell apoptosis. Our results have implications for the general mechanisms through which RB-like proteins control gene expression, the role of RB-, DP- and E2F-like proteins in apoptosis, and the regulation of apoptosis.

Expression and purification of an active cysteine protease of Haemonchus contortus using Caenorhabditis elegans

Many proteolytic enzymes of parasitic nematodes have been identified as possible targets of control. Testing these as vaccine or drug targets is often difficult due to the problems of expressing proteases in a correctly folded, active form in standard expression systems. In an effort to overcome these difficulties we have tested Caenorhabditis elegans as an expression system for a Haemonchus contortus cathepsin L cysteine protease, Hc-CPL-1. Recombinant Hc-CPL-1 with a polyhistidine tag added to the C-terminal was expressed in an active and glycosylated form in C. elegans. Optimal expression was obtained expressing Hc-cpl-1 under control of the promoter of the homologous C. elegans cpl-1 gene. The recombinant protein was purified from liquid cultures by nickel chelation chromatography in sufficient amounts for vaccination studies to be carried out. This study provides proof of principle that active, post-translationally modified parasitic nematode proteases can be expressed in C. elegans and this approach can be extended for expression of known protective antigens.

Transcriptional repressor and activator activities of SMA-9 contribute differentially to BMP-related signaling outputs

In the nematode Caenorhabditis elegans, the BMP-related growth factor DBL-1 regulates body size and male tail morphogenesis via a conserved receptor/Smad signaling pathway. Smads are transcription factors, but rely on transcription cofactors for appropriate regulation of target genes in response to TGF-beta- and BMP-related signals. In the DBL-1 pathway, sma-9 encodes multiple zinc finger transcription factors homologous to Drosophila Schnurri, which functions in Dpp/BMP signaling. We have studied the molecular functions of SMA-9 as a model for transcription cofactor-dependent regulation of gene expression. Using SMA-9 fusions to known transcriptional activators and repressors, we demonstrate that SMA-9 acts primarily as a transcriptional repressor in body size regulation in vivo. In contrast, both activator and repressor functions contribute to male tail patterning. We further show that different SMA-9 regions have intrinsic repressor and activator activities using a yeast transcription assay. We use microarray analysis to identify transcriptional target genes in body size regulation. Consistent with the importance of repression in mediating body size regulation, we find more repressed genes than activated genes in this pool. Finally, we identify five transcriptional targets with body size and/or male tail patterning phenotypes, including transcription factors related to Runx and fos and signaling molecules related to hedgehog and patched. Our results thus suggest that SMA-9 products function differentially as transcriptional repressors and activators in DBL-1/BMP pathway regulated body size and male tail morphogenesis.

The frataxin-encoding operon of Caenorhabditis elegans shows complex structure and regulation

The genome of the nematode Caenorhabditis elegans is unusual among eukaryotes, in that it contains operons. Approximately 15% of genes in the worm are clustered into groups of between two and eight genes, which are under the control of shared regulatory sequences. Polycistronic transcripts from such operons are trans-spliced, during transcription, to produce mature monocistronic messengers. The C. elegans frataxin gene, frh-1, is encoded in the operon CEOP2232. This is one of the largest operons identified thus far in the C. elegans genome. Here we describe in detail the structure of all of the coding units within this operon. The operon is composed of eight genes of a diverse nature, organized in a complex structure. We have produced transgenic strains carrying fusions between gfp and a number of genes from the operon. These constructs show complex differential expression patterns that suggest the presence of internal promoters and regulatory sequences in the operon. This organization would permit both coordinated expression and differential expression of the components of the CEOP2232 operon. The heterogeneity of the genes, and their complex expression patterns, suggests that the clustering of CEOP2232 is not due to a need for synchronized expression of genes involved in the same physiological pathway.

Characterization of STIP, a multi-domain nuclear protein, highly conserved in metazoans, and essential for embryogenesis in Caenorhabditis elegans

We report here the identification and characterization of STIP, a multi-domain nuclear protein that contains a G-patch, a coiled-coil, and several short tryptophan-tryptophan repeats highly conserved in metazoan species. To analyze their functional role in vivo, we cloned nematode stip-1 genes and determined the spatiotemporal pattern of Caenorhabditis elegans STIP-1 protein. RNA analyses and Western blots revealed that stip-1 mRNA was produced via trans-splicing and translated as a 95-kDa protein. Using reporter constructs, we found STIP-1 to be expressed at all developmental stages and in many tissue/cell types including worm oocyte nuclei. We found that STIP-1 is targeted to the nucleus and forms large polymers with a rod-like shape when expressed in mammalian cells. Using deletion mutants, we mapped the regions of STIP-1 involved in nuclear import and polymer assembly. We further showed that knockdown of C. elegans stip-1 by RNA interference arrested development and resulted in morphologic abnormalities around the 16-cell stage followed by 100% lethality, suggesting its essential role in worm embryogenesis. Importantly, the embryonic lethal phenotype could be faithfully rescued with Drosophila and human genes via transgenic expression. Our data provide the first direct evidence that STIP have a conserved essential nuclear function across metazoans from worms to humans.

Expression of gamma-tubulin during the development of nematode Caenorhabditis elegans

Gamma-tubulin is a centrosomal protein found in microtubule organizing centres (MTOCs) in cells from many different organisms, and has several properties, which makes it a candidate for both the initiation of microtubule assembly and anchorage. Gamma-tubulin is encoded by a single gene tbg-1 in Caenorhabditis elegans. In this paper tbg-1 was studied to understand the essential role of gamma-tubulin in C. elegans. Essential role of tbg-1 expression was confirmed by the disruption of the gene expression by gamma-tubulin anti-sense RNA production in vivo under the heat shock promoter that caused lethality in the nematodes. Expression of tbg-1 deduced from Northern blot analysis during the development revealed differential expression in different developmental stages. Using tbg-1::lacZ fusion gene expression studies in the germ line transformed worms, it was further revealed that gamma-tubulin expression was observed through out the development from embryonic and post-embryonic stages.

Caenorhabditis elegans in the study of SMN-interacting proteins: a role for SMI-1, an orthologue of human Gemin2 and the identification of novel components of the SMN complex

Spinal muscular atrophy is a common neuromuscular disorder caused by mutations in the survival motor neuron (SMN) gene. In mammals, SMN is tightly associated with Gemin2. To gain further insight into the functions of SMN and Gemin2, we have cloned and sequenced smi-1 (Survival of Motor neuron-Interacting protein 1), a C. elegans homologue of the human Gemin2 gene. We show that the SMI-1 expression pattern and RNA interference phenotype show considerable overlap with that previously reported for SMN-1. Finally, we demonstrate that the SMN-1 and SMI-1 proteins directly interact. Having demonstrated the utility of the C. elegans genetic model for investigating genes encoding SMN-interacting proteins, we have undertaken a yeast two-hybrid screen of a C. elegans cDNA library to identify novel proteins that interact with SMN-1. We show the direct interaction of SMN-1 with nine novel proteins, several of which may be involved in RNA metabolism.

Deleted in cancer 1 (DICE1) is an essential protein controlling the topology of the inner mitochondrial membrane in C. elegans

DICE1 (deleted in cancer 1), first identified in human lung carcinoma cell lines, is a candidate tumor suppressor, but the details of its activity remain largely unknown. We have found that RNA interference of its C. elegans homolog (DIC-1) produced inviable embryos with increased apoptosis, cavities in cells and abnormal morphogenesis. In the dic-1(RNAi) germ line, ced-3-dependent apoptosis increased, and cell cavities appeared at the late-pachytene/oogenic stage,leading to defective oogenesis. Immunofluorescence microscopy of DIC-1 revealed its ubiquitous expression in the form of cytoplasmic foci, and cryoelectron microscopy narrowed down the location of the foci to the inner membrane of mitochondria. After dic-1 RNAi, mitochondria had an irregular morphology and contained numerous internal vesicles. Homozygous embryos from a heterozygous dic-1 mother arrested at the L3 larval stage, in agreement with the essential role of DIC-1 in mitochondria. In summary, C. elegans DIC-1 plays a crucial role in the formation of normal morphology of the mitochondrial cristae/inner membrane. Our results suggest that human DICE1 may have several functions in multiple intracellular locations.

The Caenorhabditis elegans CPI-2a cystatin-like inhibitor has an essential regulatory role during oogenesis and fertilization

In the present study, we characterized a sterile cpi-2a(ok1256) deletion mutant in Caenorhabditis elegans and showed that CPI-2a has an essential regulatory role during oogenesis and fertilization. We have also shown that the CPI2a inhibitor and both Ce-CPL-1 and Ce-CPZ-1 enzymes are present in the myoepithelial sheath surrounding germ cells, oocytes, and embryos as well as in the yolk granules within normal oocytes. Staining of mutant worms with anti-yolk protein antibodies has indicted that the proteins are not present in the mature oocytes. Moreover, green fluorescent protein expression was absence or reduced in cpi-2a/yp170:gfp mutant oocytes, although it was expressed in one of the successfully developed embryos. Based on these results, we hypothesize that the sterility in cpi-2a(ok1256) mutant worms is potentially caused by two possible mechanisms: 1) defects in the uptake and/or processing of yolk proteins by the growing oocytes and 2) indirect induction of defects in cell-cell signaling that is critical for promoting germ line development, oocyte maturation, ovulation, and fertilization. A defect in any of these processes would have detrimental effects on the development of normal embryos and consequently normal production of progenies as we observed in cpi-2a mutant worms. This is the first study that demonstrates the expression of cysteine proteases and their endogenous inhibitor in the gonadal sheath cells surrounding germ cells and oocytes, which indirectly have established their potential involvement in proteolytic processing of molecules within the gonadal sheath cells, such as components of the extracellular matrix or the cytoskeletal proteins, which are essential for proper cell-cell signaling activities of the gonadal sheath cells during normal maturation and ovulation processes.

SER-1, a Caenorhabditis elegans 5-HT2-like receptor, and a multi-PDZ domain containing protein (MPZ-1) interact in vulval muscle to facilitate serotonin-stimulated egg-laying

Serotonin (5-HT) stimulation of egg-laying in Caenorhabditis elegans is abolished in ser-1 (ok345) animals and is rescued by ser-1 expression in vulval muscle. A PDZ binding motif (ETFL) at the SER-1 C-terminus is not essential for rescue, but facilitates SER-1 signaling. SER-1 binds specifically to PDZ domain 10 of the multi-PDZ domain protein, MPZ-1, based on GST pulldown and co-immunoprecipitation. mpz-1 is expressed in about 60 neurons and body wall and vulval muscles. In neurons, GFP-tagged MPZ-1 is punctate and colocalizes with the synaptic marker, synaptobrevin. The expression patterns of ser-1 and mpz-1 overlap in 3 pairs of neurons and vulval muscle. In addition, MPZ-1 also interacts with other GPCRs with acidic amino acids in the -3 position of their PDZ binding motifs. mpz-1 RNAi reduces 5-HT stimulated egg-laying in wild type animals and in ser-1 mutants rescued by muscle expression of SER-1. In contrast, mpz-1 RNAi has no effect on 5-HT stimulated egg-laying in ser-1 mutants rescued by expression of a truncated SER-1 that lacks the C-terminal PDZ binding motif. The overexpression of MPZ-1 PDZ domain 10 also inhibits 5-HT stimulated egg-laying. These studies suggest that the SER-1/MPZ-1 interaction facilitates SER-1 mediated signaling.

The fork head transcription factor FKTF-1b from Strongyloides stercoralis restores DAF-16 developmental function to mutant Caenorhabditis elegans

The purpose of this study was to determine whether Strongyloides stercoralis FKTF-1, a transcription factor of the FOXO/FKH family and the likely output of insulin/IGF signal transduction in that parasite, has the same or similar developmental regulatory capabilities as DAF-16, its structural ortholog in Caenorhabditis elegans. To this end, both splice variants of the fktf-1 message were expressed under the control of the daf-16alpha promoter in C. elegans carrying loss of function mutations in both daf-2 (the insulin/IGF receptor kinase) and daf-16. Under well-fed culture conditions the majority (91%) of untransformed daf-2; daf-16 double mutants developed via the continuous reproductive cycle, whereas under the same conditions 100% of daf-2 single mutants formed dauers. Transgenic daf-2; daf-16 individuals expressing fktf-1b showed a reversal of the double mutant phenotype with 75% of the population forming dauers under well-fed conditions. This phenotype was even more pronounced than that of daf-2; daf-16 mutants transformed with a homologous rescuing construct, daf-16alpha::daf-16a (56% dauers under well fed conditions), indicating that S. stercoralis fktf-1b can almost fully rescue loss-of-function mutants in C. elegans daf-16. By contrast, daf-2; daf-16 mutants expressing S. stercoralis fktf-1a, encoding the second splice variant of FKTF-1, showed a predominantly continuous pattern of development identical to that of the parental double mutant stock. This indicates that, unlike FKTF-1b, the S. stercoralis transcription factor FKTF-1a cannot trigger the shift to dauer-specific gene expression in C. elegans.

Reduction of Caenorhabditis elegans frataxin increases sensitivity to oxidative stress, reduces lifespan, and causes lethality in a mitochondrial complex II mutant

Friedreich ataxia is an autosomal recessive neurological disorder caused by deficiency of the mitochondrial protein frataxin. Studies in patient cells, mouse knockout animals, and Saccharomyces cerevisiae models have suggested several hypotheses on the frataxin function, but the full physiology of frataxin in mitochondria has not been well established yet. We have characterized the genomic structure of frh-1, the Caenorhabditis elegans frataxin gene, and we have developed a transient knockdown model of C. elegans frataxin deficiency by RNA interference. frh-1(RNAi) worms show a consistent pleiotropic phenotype that includes slow growth, lethargic behavior, egg laying defects, reduced brood size, abnormal pharyngeal pumping, and altered defecation. Lifespan is significantly reduced, and worms have increased sensitivity to oxidative stress that, in turn, might explain the reduction of longevity of the worms. We also demonstrate synthetic genetic interaction between frh-1 and mev-1, the gene encoding the succinate dehydrogenase cytochrome b subunit of complex II in mitochondria, suggesting a possible role of the C. elegans frataxin in the electron transport chain; thus, the respiratory chain might be involved in the pathogenesis of the disease. We propose that this C. elegans model may be a useful biological tool for drug screening in Friedreich ataxia.

Requirement of tyrosylprotein sulfotransferase-A for proper cuticle formation in the nematode C. elegans

Tyrosine O-sulfation is one of the post-translational modification processes that occur to membrane proteins and secreted proteins in eukaryotes. Tyrosylprotein sulfotransferase (TPST) is responsible for this modification, and in this report, we describe the expression pattern and the biological role of TPST-A in the nematode Caenorhabditis elegans. We found that TPST-A was mainly expressed in the hypodermis, especially in the seam cells. Reduction of TPST-A activity by RNAi caused severe defects in cuticle formation, indicating that TPST-A is involved in the cuticle formation in the nematode. We found that RNAi of TPST-A suppressed the roller phenotype caused by mutations in the rol-6 collagen gene, suggesting that sulfation of collagen proteins may be important for proper organization of the extracellular cuticle matrix. The TPST-A RNAi significantly decreased the dityrosine level in the worms, raising the possibility that the sulfation process may be a pre-requisite for the collagen tyrosine cross-linking.

Metalloproteases with EGF, CUB, and thrombospondin-1 domains function in molting of Caenorhabditis elegans

Functional analysis using RNAi was performed on eleven genes for metalloproteases of the M12A family in Caenorhabditis elegans and the interference of the C17G1.6 gene (nas-37) was found to cause incomplete molting. The RNAi of the C26C6.3 gene (nas-36) also caused a similar molting defect but not so severely as that of the nas-37 gene. Both the genes encode an astacin-like metalloprotease with an epidermal growth factor (EGF)-like domain, a CUB domain, and a thrombospondin-1 domain, in this order. The promoter-driven green fluorescent protein (GFP) expression analysis suggested that they are expressed in hypodermal cells throughout the larval stages and in the vulva of adult animals. In the genetic background of rde-1(ne219), where RNAi does not work, the molting defect caused by the nas-37 interference was observed when the transgenic wild-type rde-1 gene was expressed under the control of the dpy-7 promoter, known to be active in the hypodermal cells, but not under the control of the myo-3 promoter, active in the muscular cells. Therefore these proteases are thought to be secreted by the hypodermal cells and to participate in shedding of old cuticles.

FLR-4, a novel serine/threonine protein kinase, regulates defecation rhythm in Caenorhabditis elegans

The defecation behavior of the nematode Caenorhabditis elegans is controlled by a 45-s ultradian rhythm. An essential component of the clock that regulates the rhythm is the inositol trisphosphate receptor in the intestine, but other components remain to be discovered. Here, we show that the flr-4 gene, whose mutants exhibit very short defecation cycle periods, encodes a novel serine/threonine protein kinase with a carboxyl terminal hydrophobic region. The expression of functional flr-4::GFP was detected in the intestine, part of pharyngeal muscles and a pair of neurons, but expression of flr-4 in the intestine was sufficient for the wild-type phenotype. Furthermore, laser killing of the flr-4-expressing neurons did not change the defecation phenotypes of wild-type and flr-4 mutant animals. Temperature-shift experiments with a temperature-sensitive flr-4 mutant suggested that FLR-4 acts in a cell-functional rather than developmental aspect in the regulation of defecation rhythms. The function of FLR-4 was impaired by missense mutations in the kinase domain and near the hydrophobic region, where the latter allele seemed to be a weak antimorph. Thus, a novel protein kinase with a unique structural feature acts in the intestine to increase the length of defecation cycle periods.

Ethanol-response genes and their regulation analyzed by a microarray and comparative genomic approach in the nematode Caenorhabditis elegans

The nematode shows responses to acute ethanol exposure that are similar to those observed in humans, mice, and Drosophila, namely hyperactivity followed by uncoordination and sedation. We used in this report the nematode Caenorhabditis elegans as a model system to identify and characterize the genes that are affected by ethanol exposure and to link those genes functionally into an ethanol-induced gene network. By analyzing the expression profiles of all C. elegans ORFs using microarrays, we identified 230 genes affected by ethanol. While the ethanol response of some of the identified genes was significant at early time points, that of the majority was at late time points, indicating that the genes in the latter case might represent the physiological consequence of the ethanol exposure. We further characterized the early response genes that may represent those involved directly in the ethanol response. These genes included many heat shock protein genes, indicating that high concentration of ethanol acts as a strong stress to the animal. Interestingly, we identified two non-heat-shock protein genes that were specifically responsive to ethanol. glr-2 was the only glutamate receptor gene to be induced by ethanol. T28C12.4, which encodes a protein with limited homology to human neuroligin, was also specific to ethanol stress. Finally, by analyzing the promoter regions of the early response genes, we identified a regulatory element, TCTGCGTCTCT, that was necessary for the expression of subsets of ethanol response genes.

Whole-genome analysis of temporal gene expression during foregut development

We have investigated the cis-regulatory network that mediates temporal gene expression during organogenesis. Previous studies demonstrated that the organ selector gene pha-4/FoxA is critical to establish the onset of transcription of Caenorhabditis elegans foregut (pharynx) genes. Here, we discover additional cis-regulatory elements that function in combination with PHA-4. We use a computational approach to identify candidate cis-regulatory sites for genes activated either early or late during pharyngeal development. Analysis of natural or synthetic promoters reveals that six of these sites function in vivo. The newly discovered temporal elements, together with predicted PHA-4 sites, account for the onset of expression of roughly half of the pharyngeal genes examined. Moreover, combinations of temporal elements and PHA-4 sites can be used in genome-wide searches to predict pharyngeal genes, with more than 85% accuracy for their onset of expression. These findings suggest a regulatory code for temporal gene expression during foregut development and provide a means to predict gene expression patterns based solely on genomic sequence.

Caenorhabditis elegans-based screen identifies Salmonella virulence factors required for conserved host-pathogen interactions

A Caenorhabditis elegans-Salmonella enterica host-pathogen model was used to identify both novel and previously known S. enterica virulence factors (HilA, HilD, InvH, SptP, RhuM, Spi4-F, PipA, VsdA, RepC, Sb25, RfaL, GmhA, LeuO, CstA, and RecC), including several related to the type III secretion system (TTSS) encoded in Salmonella pathogenicity island 1 (SPI-1). Mutants corresponding to presumptive novel virulence-related genes exhibited diminished ability to invade epithelial cells and/or to induce polymorphonuclear leukocyte migration in a tissue culture model of mammalian enteropathogenesis. When expressed in C. elegans intestinal cells, the S. enterica TTSS-exported effector protein SptP inhibited a conserved p38 MAPK signaling pathway and suppressed the diminished pathogenicity phenotype of an S. enterica sptP mutant. These results show that C. elegans is an attractive model to study the interaction between Salmonella effector proteins and components of the innate immune response, in part because there is a remarkable overlap between Salmonella virulence factors required for human and nematode pathogenesis.

The Caenorhabditis elegans Cathepsin Z-like Cysteine Protease, Ce-CPZ-1, Has a Multifunctional Role during the Worms' Development

We have analyzed the expression and function of Cecpz-1, a Caenorhabditis elegans cathepsin Z-like cysteine protease gene, during development of the worm. The cpz-1 gene is expressed in various hypodermal cells of all developmental stages and is specifically expressed in the gonads and the pharynx of adult worms. Disruption of cpz-1 function by RNA interference or cpz-1(ok497) deletion mutant suggests that cpz-1 has a role in the molting pathways. The presence of the native CPZ-1 protein in the hypodermis/cuticle of larval and adult stages and along the length of the pharynx of adult worms, as well as the cyclic expression of the transcript during larval development, supports such function. We hypothesize that the CPZ-1 enzyme functions directly as a proteolytic enzyme degrading cuticular proteins before ecdysis and/or indirectly by processing other proteins such as proenzymes and/or other proteins that have an essential role during molting. Notably, an impressive level of the CPZ-1 native protein is present in both the new and the old cuticles during larval molting, in particular in the regions that are degraded prior to shedding and ecdysis. The similar localization of the related Onchocerca volvulus cathepsin Z protein suggests that the function of CPZ-1 during molting might be conserved in other nematodes. Based on the cpz-1 RNA interference and cpz-1 (ok497) deletion mutant phenotypes, it appears that cpz-1 have additional roles during morphogenesis. Deletion of cpz-1 coding sequence or inhibition of cpz-1 function by RNA interference also caused morphological defects in the head or tail region of larvae, improperly developed gonad in adult worms and embryonic lethality. The CPZ-1 native protein in these affected regions may have a role in the cuticular and the basement membrane extracellular matrix assembly process. The present findings have defined a critical role for cathepsin Z in nematode biology.

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.

Deficiency of Caenorhabditis elegans RecQ5 homologue reduces life span and increases sensitivity to ionizing radiation

Gene expression and RNA interference phenotypes were investigated for a Caenorhabditis elegans homologue (Ce-RCQ-5) of human RecQ5 protein. Expression of the mRNA was observed by in situ hybridization from earliest embryogenesis and gradually decreased during late embryogenesis. Ce-RCQ-5 was immuno-localized in the nuclei of embryos, germ cells, and oocytes and also in the nuclei of various somatic cells of larvae and adults. Despite ubiquitous expression in postembryonic cells, RCQ-5 protein expression was highest in intestinal cells, which was confirmed by tagging the gene expression with green fluorescence protein. When endogenous Ce-rcq-5 gene expression was inhibited by RNA interference, no clear phenotypes were observed during development. However, C. elegans life span was reduced by 37% due to RNA interference of rcq-5 gene, suggesting its possible role in maintenance of genomic stability, as has been ascribed to other RecQ family DNA helicases. In addition, C. elegans became significantly more sensitive to ionizing radiation after inhibition of rcq-5 gene expression, indicating an involvement of C. elegans RCQ-5 in a cellular response to DNA damage, possibly in DNA repair.

SER-7b, a constitutively active Galphas coupled 5-HT7-like receptor expressed in the Caenorhabditis elegans M4 pharyngeal motorneuron

Serotonin plays a key role in the regulation of pharyngeal pumping in nematodes. We have isolated a Caenorhabditis elegans cDNA (C09B7.1b, ser-7b) with greatest identity to the 5-HT7 receptor family. Membranes from COS-7 cells expressing SER-7b exhibit saturable [3H]-LSD binding (Kd = 45 nm) that is inhibited by serotonin (5-HT) and tryptamine, but not by other physiological biogenic amines. Expression of SER-7b in COS-7 cells results in dramatic increase in basal cAMP levels over untransfected cells that is dependent on expression level. 5-HT further elevates cAMP levels in a dose-dependent manner (pEC50 = 7.5 +/- 0.5). Mammalian 5-HT7 receptor inverse agonists reduce constitutive activity, with methiothepin the most potent (pIC50 = 7.8 +/- 0.1). Ser-7::GFP transcriptional fusions reveal that SER-7b appears to be expressed solely in the M4 pharyngeal motorneuron after hatching. This is the first report of a Galphas coupled biogenic amine receptor in nematodes and the localization of SER-7b in the M4 pharyngeal motorneuron suggests that SER-7b may play a role in the regulation of pharyngeal pumping.

M142.2 (cut-6), a novel Caenorhabditis elegans matrix gene important for dauer body shape

The cuticle of the nematode Caenorhabditis elegans is a collagenous extracellular matrix which forms the exoskeleton and defines the shape of the worm. We have characterized the C. elegans gene M142.2, and we show that this is a developmentally regulated gene important for cuticle structure. Transgenic worms expressing M142.2 promoter fused to green fluorescent protein showed that M142.2 is expressed in late embryos and L2d predauers, in the hypodermal cells which synthesize the cuticle. The same temporal pattern was seen by RT-PCR using RNA purified from specific developmental stages. A recombinant fragment of M142.2 was expressed in Escherichia coli and used to raise an antiserum. Immunohistochemistry using the antiserum localized M142.2 to the periphery of the alae of L1 and dauers, forming two longitudinal ribbons over the hypodermal cells. Loss-of-function of M142.2 by RNAi resulted in a novel phenotype: dumpy dauers which lacked alae. M142.2 therefore plays a major role in the assembly of the alae and the morphology of the dauer cuticle; because of its similarity to the other cut genes of the cuticle, we have named the gene cut-6.

Expression of the C. elegans labial orthologue ceh-13 during male tail morphogenesis

Hox genes are transcriptional regulators of metazoan body regionalization along the anteroposterior axis that act by specifying positional identity in differentiating cells. ceh-13, the labial orthologue in Caenorhabditis elegans, is expressed both during embryogenesis and post- embryonic development. Using GFP reporter analysis and immunocytochemistry, we discovered a spatiotemporal pattern of gene expression in the male tail during the L3 and L4 larval stages that is TGF-beta pathway-dependent. Analysis of reporter activity in transgenic animals identified a distinct promoter region driving male tail-specific ceh-13 expression. We also report the interspecies conservation of sequence motifs within this region and speculate that, in the course of evolutionary diversification, ceh-13 may have acquired new functionality while conserving its homeotic role.

The maintenance of neuromuscular function requires UBC-25 in Caenorhabditis elegans

Caenorhabditis elegans gene ubc-25 encodes a novel type of an E2 ubiquitin transferase domain (UBCc) protein, which is highly conserved in multicellular animals, but which is not present in the genomes of fungi or plants. To identify the cellular localization of UBC-25 during the development of C. elegans, we used a ubc-25::gfp reporter gene construct. These experiments showed that ubc-25 expression starts during embryogenesis and that it is restricted to neurons and muscle cells in all later stages of development as well as in adult animals. RNA interference with ubc-25 caused late-onset paralysis of most muscular functions such as locomotion, egg laying, and defecation. We therefore propose that ubc-25 in C. elegans is required for the maintenance (homeostasis) of neuromuscular functions by contributing to a tissue specific protein modification pathway, and we speculate that the adult onset phenotype results from the accumulation of target proteins which fail to be degraded.

The role of the ELAV homologue EXC-7 in the development of the Caenorhabditis elegans excretory canals

The exc mutations of Caenorhabditis elegans alter the position and shape of the apical cytoskeleton in polarized epithelial cells. Mutants in exc-7 form small cysts throughout the tubular excretory canals that regulate organismal osmolarity. We have cloned the exc-7 gene, the closest nematode homologue to the neural RNA-binding protein ELAV. EXC-7 is expressed in the canal for a short time midway through embryogenesis. Cysts in exc-7 mutants do not develop until several hours later, beginning at the time of hatching. We find that the first larval period is when the canal completes the majority of its outgrowth, and adds new apical cytoskeleton at a rapid rate. Ultrastructural studies show that exc-7 mutant defects resemble loss of beta(H)-spectrin (encoded by sma-1) at the distal ends of the excretory canals. In addition, exc-7 mutants exhibit synergistic excretory canal defects with mutations in sma-1, and EXC-7 binds sma-1 mRNA. These data imply that EXC-7 protein may affect expression of sma-1 and other genes to effect proper development of the excretory canals.

UNC-5 function requires phosphorylation of cytoplasmic tyrosine 482, but its UNC-40-independent functions also require a region between the ZU-5 and death domains

Members of the UNC-5 protein family are transmembrane receptors for UNC-6/netrin guidance cues. To analyze the functional roles of different UNC-5 domains, we sequenced mutations in seven severe and three weak alleles of unc-5 in Caenorhabditis elegans. Four severe alleles contain nonsense mutations. Two weak alleles are truncations of the cytodomain, but one is a missense mutation in an extracellular immunoglobulin domain. To survey the function of different regions of UNC-5, wild-type and mutant unc-5::HA transgenes were tested for their ability to rescue the unc-5(e53) null mutant. Our data reveal partial functional requirements for the extracellular domains and identify a portion of the cytoplasmic juxtamembrane (JM) region as essential for rescue of migrations. When nine cytodomain tyrosines, including seven in the JM region, are mutated to phenylalanine, UNC-5 function and tyrosine phosphorylation are largely compromised. When F482 in the JM region of the mutant protein is reverted to tyrosine, UNC-5 tyrosine phosphorylation and in vivo function are largely recovered, suggesting that Y482 phosphorylation is critical to UNC-5 function in vivo. Our data also show that part of the ZU-5 motif is required for UNC-40-independent signaling of UNC-5.

Abundant larval transcript-1 and -2 genes from Brugia malayi: diversity of genomic environments but conservation of 5' promoter sequences functional in Caenorhabditis elegans

The genomic organisation of two abundant larval transcript (alt) genes from the filarial nematode Brugia malayi has been defined. The products of these genes are 78% identical in amino acid sequence, and are highly expressed in a stage-specific manner by mosquito-borne infective larvae. alt-1 is present as two near-identical copies organised in an inverted repeat of approximately 7.6 kb, occupying a total of 16 kb of the genome. alt-2 is a single-copy gene at a different locus to alt-1. The two alt-1 genes (alt-1.1 and -1.2) are 99.7% identical in coding sequence and 99.5% in intronic sequences. Both alt-1 and -2 contain 3 introns, and the third intron of alt-2 exhibits a size polymorphism evident in different individual parasites from the laboratory-maintained strain. Genomic sequence up- and down-stream from alt-1.1/1.2 (26 and 6 kb, respectively) and alt-2 (6 and 4 kb, respectively) show that neither gene is in a multiple array or an operon. Most notably, the neighbouring genes of alt-1 and -2 show no similarity to each other, or to the genes flanking the distant alt homologue in Caenorhabditis elegans. Despite this diversity in flanking genes, the 5' UTR tracts extending some 800 bp upstream of each B. malayi alt gene show a high degree of similarity (overall 59% identity with tracts of 77-86% identity). Surmising that this region may contain conserved promoter elements, constructs containing the B. malayi alt 5' UTR with or without coding sequence were made fused to beta-galactosidase reporter protein. These constructs were injected into the syncytical gonad of C. elegans and progeny stained for beta-gal expression. Our results show relatively strong expression in the gut cells of C. elegans for both alt-1 and -2 constructs, commencing in larval worms and continuing into adulthood. Moreover, expression was enhanced when constructs contained segments of alt-1 coding and intronic sequence in addition to the 5' UTR. We conclude that the high level of alt transcription in filarial L3s is not due to expression from a multi-copy gene family but to a set of strong promoter elements shared between the two alt genes.

Expression profiles of the essential intermediate filament (IF) protein A2 and the IF protein C2 in the nematode Caenorhabditis elegans

The multigene family of intermediate filament (IF) proteins in Caenorhabditis elegans covers 11 members of which four (A1-3, B1) are essential for development. Suppression of a fifth gene (C2) results in a dumpy phenotype. Expression patterns of three essential genes (A1, A3, B1) were already reported. To begin to analyze the two remaining RNAi phenotypes we followed the expression of the A2 and C2 proteins. Expression of A2 mRNA starts in larval stage L1 and continues in the adult. Transgenic A2 promoter/gfp larvae strongly display GFP in the main body hypodermis but not in seam cells. This pattern and the muscle displacement/paralysis induced by RNAi silencing are consistent with the role of this protein in keeping the correct hypodermis/muscle relationship during development. IF protein C2 occurs in the cytoplasm and desmosomes of intestinal cells and in pharynx desmosomes. Expression of C2 starts in the late embryo and persists in all further stages.

The NHX family of Na+-H+ exchangers in Caenorhabditis elegans

Na+-H+ exchangers prevent cellular acidification by catalyzing the electroneutral exchange of extracellular sodium for an intracellular proton. To date, seven Na+-H+ exchangers have been identified in mammals, and although several members of this family have been extensively studied and characterized, it is clear that there are major gaps in our understanding with respect to the remaining family members. To initiate the study of Na+-H+ exchangers in a genomically defined and genetically tractable model system, we have cloned the complete cDNAs and analyzed splice site variation for nine putative homologs from the nematode Caenorhabditis elegans, which we have called NHX-1 through -9. The expression patterns and cellular distributions of the NHX proteins were determined using transcriptional and translational promoter-transgene fusion constructs to green fluorescent protein. Four of the putative exchangers were expressed at the cell surface, whereas five of the exchangers were associated with the membranes of intracellular organelles. Individual isoforms were expressed exclusively in the intestine, seam cells, hypodermal cells of the main body syncytium, and the excretory cell, all of which are polarized epithelial cells, suggesting a role for these proteins in epithelial membrane transport processes in the nematode. Other isoforms were found to express either ubiquitously or in a pan-neural pattern, suggesting a more conserved role in cell pH regulation or neuronal function. Finally, we show that recombinant NHX-4, the ubiquitous nematode Na+-H+ exchanger, mediates Na+-dependent pH recovery after intracellular acidification. NHX-4 has a K(a) for Na+ of approximately 32 mm, is not Cl- -dependent, and is relatively insensitive to the amiloride analog EIPA.

A novel linker histone-like protein is associated with cytoplasmic filaments inCaenorhabditis elegans

The histone H1 complement of Caenorhabditis elegans contains a single unusual protein, H1.X. Although H1.X possesses the globular domain and the canonical three-domain structure of linker histones, the amino acid composition of H1.X is distinctly different from conventional linker histones in both terminal domains. We have characterized H1.X in C. elegans by antibody labeling, green fluorescent protein fusion protein expression and RNA interference. Unlike normal linker histones, H1.X is a cytoplasmic as well as a nuclear protein and is not associated with chromosomes. H1.X is most prominently expressed in the marginal cells of the pharynx and is associated with a peculiar cytoplasmic cytoskeletal structure therein, the tonofilaments. Additionally H1.X::GFP is expressed in the cytoplasm of body and vulva muscle cells, neurons, excretory cells and in the nucleoli of embryonic blastomeres and adult gut cells. RNA interference with H1.X results in uncoordinated and egg laying defective animals, as well as in a longitudinally enlarged pharynx. These phenotypes indicate a cytoplasmic role of H1.X in muscle growth and muscle function.

Egg shell collagen formation in Caenorhabditis elegans involves a novel prolyl 4-hydroxylase expressed in spermatheca and embryos and possessing many unique properties

The collagen prolyl 4-hydroxylases (EC ) play a critical role in the synthesis of all collagens. The enzymes from all vertebrate species studied are alpha(2)beta(2) tetramers, in which the beta subunit is identical to protein disulfide isomerase (PDI). Two isoforms of the catalytic alpha subunit, PHY-1 and PHY-2, have previously been characterized from Caenorhabditis elegans. We report here on the cloning and characterization of a third C. elegans alpha subunit isoform, PHY-3. It is much shorter than the previously characterized vertebrate and C. elegans alpha subunits and shows 23-30% amino acid sequence identity to PHY-1 and PHY-2 within the catalytic C-terminal region. Recombinant PHY-3 coexpressed in insect cells with a C. elegans PDI isoform that does not associate with PHY-1 was found to be an active prolyl 4-hydroxylase. The phy-3 gene consists of five exons, and its expression pattern differs distinctly from the hypodermally expressed phy-1 and phy-2 in that it is expressed in embryos, late larval stages, and adult nematodes, expression in the latter being restricted to the spermatheca. Nematodes homozygous for a phy-3 deletion are phenotypically of the wild type and fertile, but the 4-hydroxyproline content of phy-3(-/-) early embryos was reduced by about 90%. PHY-3 is thus likely to be involved in the synthesis of collagens in early embryos, probably of those in the egg shell.

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.

Spermiogenesis initiation in Caenorhabditis elegans involves a casein kinase 1 encoded by the spe-6 gene

Immature spermatids from Caenorhabditis elegans are stimulated by an external activation signal to reorganize their membranes and cytoskeleton to form crawling spermatozoa. This rapid maturation, termed spermiogenesis, occurs without any new gene expression. To better understand this signal transduction pathway, we isolated suppressors of a mutation in the spe-27 gene, which is part of the pathway. The suppressors bypass the requirement for spe-27, as well as three other genes that act in this pathway, spe-8, spe-12, and spe-29. Eighteen of the suppressor mutations are new alleles of spe-6, a previously identified gene required for an early stage of spermatogenesis. The original spe-6 mutations are loss-of-function alleles that prevent major sperm protein (MSP) assembly in the fibrous bodies of spermatocytes and arrest development in meiosis. We have isolated the spe-6 gene and find that it encodes a predicted protein-serine/threonine kinase in the casein kinase 1 family. The suppressor mutations appear to be reduction-of-function alleles. We propose a model whereby SPE-6, in addition to its early role in spermatocyte development, inhibits spermiogenesis until the activation signal is received. The activation signal is transduced through SPE-8, SPE-12, SPE-27, and SPE-29 to relieve SPE-6 repression, thus triggering the formation of crawling spermatozoa.

Cathepsin L is essential for embryogenesis and development of Caenorhabditis elegans

Cysteine proteases play critical biological roles in both intracellular and extracellular processes. We characterized Ce-cpl-1, a Caenorhabditis elegans cathepsin L-like cysteine protease. RNA interference with Ce-cpl-1 activity resulted in embryonic lethality and a transient delayed growth of larvae to egg producing adults, suggesting an essential role for cpl-1 during embryogenesis, and most likely during post-embryonic development. Cpl-1 gene (Ce-cpl-1:lacZ) is widely expressed in the intestine and hypodermal cells of transgenic worms, while the fusion protein (Ce-CPL-1::GFP) was expressed in the hypodermis, pharynx, and gonad. The CPL-1 native protein accumulates in early to late stage embryos and becomes highly concentrated in gut cells during late embryonic development. CPL-1 is also present near the periphery of the eggshell as well as in the cuticle of larval stages suggesting that it may function not only in embryogenesis but also in further development of the worm. Although the precise role of Ce-CPL-1 during embryogenesis is not yet clear it could be involved in the processing of nutrients responsible for synthesis and/or in the degradation of eggshell. Moreover, an increase in the cpl-1 mRNA is seen in the intermolt period approximately 4 h prior to each molt. During this process Ce-CPL-1 may act as a proteolytic enzyme in the processing/degradation of cuticular or other proteins. Similar localization of a related cathepsin L in the filarial nematode Onchocerca volvulus, eggshell and cuticle, suggests that some of the Ce-CPL-1 function during development may be conserved in other parasitic nematodes.