Membrane extensions are associated with proper anterior migration of muscle cells during Caenorhabditis elegans embryogenesis

C. elegans body wall muscle is formed after a series of well-orchestrated steps. With the onset of specification embryonic muscle cells accumulate under the hypodermal seam cells at the left and right sides of the embryo. Shortly thereafter they begin to migrate dorsally and ventrally resting beneath the dorsal and ventral hypodermis eventually forming the four muscle quadrants present upon hatching. In this study we describe the plasma membrane dynamics of these migrating cells and observe the extension of filopodia and lamellipodia during dorso-ventral migration but not during the earlier stages of accumulation. We also describe an anterior migration event during embryonic muscle morphogenesis, whereby the anterior-most pair of cells in each of the four muscle quadrants extends long processes to the anterior tip of the developing embryo. Anteriormost muscle cells then follow these extensions into their final positions in the developing embryo. Using RNAi and mutant analysis, we have identified laminin as being involved in mediating the dorsal-ventral muscle migrations. Finally we show that the α-integrin INA-1, the ephrin VAB-2 and its receptor VAB-1 and the Robo receptor SAX-3 indirectly promote the proper extension of the ventral anterior muscle processes by organizing the embryonic neurons so as to provide a clear path for muscle membrane extension.     

CPNA-1, a copine domain protein,is located at integrin adhesion sites and is required for myofilament stability in Caenorhabditis elegans

We identify cpna-1 (F31D5.3) as a novel essential muscle gene in the nematode Caenorhabditis elegans. Antibodies specific to copine domain protein atypical-1 (CPNA-1), as well as a yellow fluorescent protein translational fusion, are localized to integrin attachment sites (M-lines and dense bodies) in the body-wall muscle of C. elegans. CPNA-1 contains an N-terminal predicted transmembrane domain and a C-terminal copine domain and binds to the M-line/dense body protein PAT-6 (actopaxin) and the M-line proteins UNC-89 (obscurin), LIM-9 (FHL), SCPL-1 (SCP), and UNC-96. Proper CPNA-1 localization is dependent upon PAT-6 in embryonic and adult muscle. Nematodes lacking cpna-1 arrest elongation at the twofold stage of embryogenesis and display disruption of the myofilament lattice. The thick-filament component myosin heavy chain MYO-3 and the M-line component UNC-89 are initially localized properly in cpna-1–null embryos. However, in these embryos, when contraction begins, MYO-3 and UNC-89 become mislocalized into large foci and animals die. We propose that CPNA-1 acts as a linker between an integrin-associated protein, PAT-6, and membrane-distal components of integrin adhesion complexes in the muscle of C. elegans.     

De Novo Identification of Single Nucleotide Mutations in Caenorhabditis elegans Using Array Comparative Genomic Hybridization

Array comparative genomic hybridization (aCGH) has been used primarily to detect copy-number variants between two genomes. Here we report using aCGH to detect single nucleotide mutations on oligonucleotide microarrays with overlapping 50-mer probes. This technique represents a powerful method for rapidly detecting novel homozygous single nucleotide mutations in any organism with a sequenced reference genome.     

Characterization of the astacin family of metalloproteases in <Emphasis Type="Italic">C. elegans</Emphasis>

Background  

Astacins are a large family of zinc metalloproteases found in bacteria and animals. They have diverse roles ranging from digestion of food to processing of extracellular matrix components. The C. elegans genome contains an unusually large number of astacins, of which the majority have not been functionally characterized yet.     

Whole-Genome Profiling of Mutagenesis in Caenorhabditis elegans

Deep sequencing offers an unprecedented view of an organism''s genome. We describe the spectrum of mutations induced by three commonly used mutagens: ethyl methanesulfonate (EMS), N-ethyl-N-nitrosourea (ENU), and ultraviolet trimethylpsoralen (UV/TMP) in the nematode Caenorhabditis elegans. Our analysis confirms the strong GC to AT transition bias of EMS. We found that ENU mainly produces A to T and T to A transversions, but also all possible transitions. We found no bias for any specific transition or transversion in the spectrum of UV/TMP-induced mutations. In 10 mutagenized strains we identified 2723 variants, of which 508 are expected to alter or disrupt gene function, including 21 nonsense mutations and 10 mutations predicted to affect mRNA splicing. This translates to an average of 50 informative mutations per strain. We also present evidence of genetic drift among laboratory wild-type strains derived from the Bristol N2 strain. We make several suggestions for best practice using massively parallel short read sequencing to ensure mutation detection.MUTAGENESIS and the screening for mutants have long been a key tool of the practicing geneticist. The early work of T. H. Morgan and his colleagues relied on recovery of spontaneous mutations, which was limiting for the study of inheritance due to their infrequent occurrence (Morganet al. 1922; also see Sturtevant 1965). The discovery by H. J. Muller and others that X rays cause mutations ushered in the era of inducing mutations (Muller 1927). There is a long history of studies on mutagen specificity, both in prokaryotes and in eukaryotes, and today many mutagens are utilized in a variety of model organisms. In this article we use whole-genome deep sequencing in the model organism Caenorhabditis elegans to explore the types and frequencies of mutations induced by various mutagens and to document the feasibility of global identification of mutations.The mutagenic properties of ethyl methanesulfonate (EMS) were first demonstrated using the T4 viral system (Loveless 1959). Soon after, Lewis and Bacher (1968) demonstrated how to administer EMS to Drosophila melanogaster to generate mutations, and later Sydney Brenner did the same for the nematode C. elegans (Brenner 1974). The now classic article by Coulondre and Miller (1977) demonstrated the types of nucleotide substitutions generated by EMS and confirmed earlier observations (Bautz and Freese 1960) concerning the strong bias for GC to AT transitions. Today, EMS is still the most powerful and popular mutagen used by researchers studying D. melanogaster and C. elegans. Purely on the basis of genetic inference, when used at a concentration of 50 mm, EMS is calculated to induce ∼20 function-affecting variant alleles in C. elegans strains derived using this mutagen (Greenwald and Horvitz 1982; Anderson 1995).The chemical N-ethyl-N-nitrosourea (ENU) has been used as a mutagen since the 1970s but came to prominence when it was demonstrated to be the most effective chemical mutagen in mice (Russell et al. 1979). Today it is still the chemical mutagen of choice for this organism (Anderson 2000; Acevedo-Arozena et al. 2008). ENU has also been used for C. elegans mutagenesis (De Stasio et al. 1997). Although it appears to have different biases with regard to gene targets and base changes relative to EMS, the background mutational load after ENU mutagenesis has not been fully characterized (De Stasio and Dorman 2001).The chemical 4,5′,8-trimethylpsoralen is a crosslinking agent that is activated by near ultraviolet light. Studies in Escherichia coli have shown that it causes both single-base changes and deletions (Piette et al. 1985; Sladek et al. 1989). C. elegans researchers became interested in the potential of ultraviolet trimethylpsoralen (UV/TMP) to generate deletions in worms after the first deletions in this organism were isolated using this mutagen (Yandell et al. 1994). UV/TMP is now a major reagent in the arsenal of the C. elegans knockout consortium laboratories (Barstead and Moerman 2006). As a tool for generating deletions in eukaryotes it is quite useful but, outside of studies on prokaryotes, little else is known about the spectrum of mutagenic effects caused by UV/TMP.Massively parallel short read sequencing technologies offer unprecedented opportunities to study the complete genetic complement of an individual organism (Hillier et al. 2008). For genetic model systems the impact of this technology extends to the identification and correlation of induced mutations with selected phenotypes (Sarin et al. 2008). Several of the technological and bioinformatic issues that arise with next generation sequencing have already been addressed for the nematode C. elegans (Hillier et al. 2008; Sarin et al. 2008; Shen et al. 2008; Rose et al. 2010). Still, it is not clear how deeply one must sequence to confidently identify a relevant variant allele in a target mutant strain. Also of importance are questions concerning mutagen choice and dosage as they relate to the rate of induction of new mutations and background mutational load. We have undertaken the following study on mutagenesis and mutation detection to establish the parameters necessary to exploit next generation sequencing technologies for C. elegans genetics. For the first time we offer a whole-genome direct measure of mutation spectrum and background load for EMS, ENU, and UV/TMP. Readers interested in whole-genome sequencing of EMS mutagenized strains in C. elegans should also see the accompanying article in this issue by Sarin et al. (2010). In our study we also measured the single-nucleotide variation among currently used wild-type strains. In addition, we measured sequence read depth of all sequence and coding sequence and from this we make a recommendation of average genome coverage to ensure the correct identification of the causative mutation. We also examined the issue of false positive and false negative calls and make recommendations to eliminate most false positives without losing bona fide mutations.     

The UNC-112 gene in Caenorhabditis elegans encodes a novel component of cell-matrix adhesion structures required for integrin localization in the muscle cell membrane

Embryos homozygous for mutations in the unc-52, pat-2, pat-3, and unc-112 genes of C. elegans exhibit a similar Pat phenotype. Myosin and actin are not organized into sarcomeres in the body wall muscle cells of these mutants, and dense body and M-line components fail to assemble. The unc-52 (perlecan), pat-2 (alpha-integrin), and pat-3 (beta-integrin) genes encode ECM or transmembrane proteins found at the cell-matrix adhesion sites of both dense bodies and M-lines. This study describes the identification of the unc-112 gene product, a novel, membrane-associated, intracellular protein that colocalizes with integrin at cell-matrix adhesion complexes. The 720-amino acid UNC-112 protein is homologous to Mig-2, a human protein of unknown function. These two proteins share a region of homology with talin and members of the FERM superfamily of proteins.We have determined that a functional UNC-112::GFP fusion protein colocalizes with PAT-3/beta-integrin in both adult and embryonic body wall muscle. We also have determined that UNC-112 is required to organize PAT-3/beta-integrin after it is integrated into the basal cell membrane, but is not required to organize UNC-52/perlecan in the basement membrane, nor for DEB-1/vinculin to localize with PAT-3/beta-integrin. Furthermore, UNC-112 requires the presence of UNC-52/perlecan and PAT-3/beta-integrin, but not DEB-1/vinculin to become localized to the muscle cell membrane.     

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.     

Parabutoporin--an antibiotic peptide from scorpion venom--can both induce activation and inhibition of granulocyte cell functions

Parabutoporin (PP) affects motility and NADPH oxidase activity in normal human polymorphonuclear neutrophils and in granulocytic HL-60 cells. These PP-induced interactions utilize a Rac activation pathway. PP induces chemotaxis of neutrophils and HL-60 cells via a pertussis toxin-sensitive way, thus using trimeric G-proteins. The enhanced chemotaxis is also apparent in undifferentiated HL-60 cells which lack functional formyl peptide receptors. On the other hand, PP strongly reduces the superoxide production by the NADPH oxidase complex after either PMA or fMLP activation of granulocytes. These combined results strongly suggest a direct activation of G-proteins and subsequent Rac activation as the basis for the observed effects. The unexpected inhibitory effect of PP, despite Rac activation, on superoxide production in granulocytes is explained by the direct interaction of membrane localized PP which prevents the formation of a functional NADPH oxidase complex.