-
[
1990]
Three DNA repair systems (photoreactivation, excision repair and post-replication repair) exist in most organisms. Their status has been examined in the nematode C. elegans. This metazoan is deficient in photoreactivation but possesses efficient excision and post-replication repair systems. The stage-specific variations in hypersensitivity displayed by radiation-sensitive (rad) mutants, as well as the stage-specific excision-repair deficiency displayed by
rad-3, indicate that DNA repair is developmentally regulated in this popular model system. In addition, various data suggest that C. elegans may possess novel
-
[
2013]
C. elegans germline stem cells are a particularly simple system for analysis of stem cell regulation. Their well-defined mesenchymal niche consists of a single cell, the Distal Tip Cell, which uses Notch signaling to maintain a pool of germline stem cells. Downstream of Notch signaling a post-transcriptional regulatory network dictates self-renewal or differentiation. The major self-renewal hub of that network is FBF, a conserved RNA-binding protein and conserved stem cell regulator. FBF represses mRNAs encoding key regulators of germline differentiation (entry into the meiotic cell cycle, sperm or oocyte specification) as well as established regulators of somatic differentiation. Transcriptional and post-transcriptional mechanisms also control totipotency in the C. elegans germline. The key C. elegans GSC regulators are conserved broadly, making this system a paradigm for stem cell regulation.
-
[
1979]
In many invertebrates, cell lineages are apparently invariant from individual to individual. A given precursor cell follows a specific pattern of cell divisions, and its descendants follow fates that correspond to their respective positions in the lineage tree. Such a reproducible sequence of events provides an excellent system for studying how cells come to pursue particular fates during development. We have been interested to know if a cell's fate is specified by factors intrinsic to the cell, or if it is influenced by interactions between the cell and its environment. C. elegans is a particularly suitable organism for lineage studies because it is transparent throughout its life cycle, and because it consists of relatively few cells. Furthermore, C. elegans is a favorable organism for genetics, so the control of cell lineages can be studied by characterizing mutations that are defective in known lineages. The cell lineages of C. elegans have been described in the embryo to the 182 cell stage and after hatching. Approximately 50 cells resume divisions post-embyronically. In the somatic tissues, the number of cells (or nuclei) is increased from about 550 to about 950 in hermaphrodites and to about 1025 in males. These post-embryonic lineages are essentially invariant from worm to worm. As the worm enlarges and matures sexually, cells (or nuclei) are added to previously existing tissues (hypodermis, muscle, gut, and nervous system), and structures necessary for reproduction are elaborated. The latter include a gonad in both sexes, a vulva in hermaphrodites, and a tail specialized for copulation in males. This paper summarizes the results of laser ablation experiments performed on cells in the post-embryonic lineages of C. elegans. In particular, we focus on those experiments that demonstrate a regulative capacity in the cells of this predominantly invariant system. The post-embyronic lineages have the practical advantage for these studies that they can be traced by direct observation of the cells as they divide and assume their final fate. The regulative response, therefore, can be described at a level of cellular detail that has not been possible in other deletion studies. Our aim in performing these experiments is to infer how cells are controlled during normal development from their behavior in
-
[
WormBook,
2005]
Synaptogenesis is a process involving the formation of a neurotransmitter release site in the presynaptic neuron and a receptive field at the postsynaptic partners, and the precise alignment of pre- and post-synaptic specializations. In C. elegans synapses are found as en passant axonal swellings along the nerve processes. Genetic screens using a synaptic vesicle-associated GFP marker have identified key players in synaptic target recognition and organization of the presynaptic terminals. Importantly, the functions of most genes are evolutionarily conserved. Further studies using a combination of genetic modifier screens and reverse genetics have begun to reveal the underlying signaling pathways.
-
[
Methods Cell Biol,
1995]
The genetics of Caenorhabditis elegans provides a convenient experimental entry point into many developmental processes and a powerful tool that can be exploited to characterize interactions among a set of genes regulating a particular pathway. Eventually, though, the study of developmental processes becomes a molecular study of gene regulation. At this level, the determination of the on/off state of a gene requires an understanding of not only its transcriptional state, but also post-transcriptional, translational, and post-translational control mechanisms. Although the vertebrate literature is rich in details of factors that influence these regulatory processes, relatively few of the factors responsible for gene expression in the nematode C. elegans have been characterized. This lag in knowledge reflects both the relatively recent arrival of C. elegans on the list of experimental systems, as well as its general unsuitability for biochemistry. There are no tissue culture cell lines established from C. elegans, and it is difficult to isolate, in large amounts, any homogeneous cell type. Moreover, the impermeable eggshell encasing the embryo and the cuticle encasing the worm make pharmacological studies in intact animals difficult and tedious. Grim as this sounds, progress has been made in C. elegans in the field of gene expression. The sensitivity of techniques has improved and the available molecular tool kit has expanded. The study of individual genes has provided descriptions of several regulatory processes, some general and some gene specific. Our current level of understanding of gene regulation is sufficient to say that C. elegans appears, in general, to be a typical eukaryote. As such, C. elegans is amenable to many of the standard analytical approaches used in other developmental systems. The purpose of this chapter is to review our current state of knowledge of transcription and translation in C. elegans (for a review
-
[
WormBook,
2005]
Alternative splicing is a common mechanism for the generation of multiple isoforms of proteins. It can function to expand the proteome of an organism and can serve as a way to turn off gene expression post-transcriptionally. This review focuses on splicing and its regulation in C. elegans. The fully-sequenced C. elegans genome combined with its elegant genetics offers unique advantages for exploring alternative splicing regulation in metazoans. The topics covered in this review include constitutive splicing factors, identification of alternatively spliced genes, examples of alternative splicing in C. elegans, and alternative splicing regulation. Key genes whose regulated alternative splicing are reviewed include
let-2 ,
unc-32 ,
unc-52 ,
egl-15 and
xol-1 . Factors involved in alternative splicing that are discussed include
mec-8 ,
smu-1 ,
smu-2 ,
fox-1 ,
exc-7 and
unc-75 .
-
[
WormBook,
2007]
The nematode cuticle is an extremely flexible and resilient exoskeleton that permits locomotion via attachment to muscle, confers environmental protection and allows growth by molting. It is synthesised five times, once in the embryo and subsequently at the end of each larval stage prior to molting. It is a highly structured extra-cellular matrix (ECM), composed predominantly of cross-linked collagens, additional insoluble proteins termed cuticlins, associated glycoproteins and lipids. The cuticle collagens are encoded by a large gene family that are subject to strict patterns of temporal regulation. Cuticle collagen biosynthesis involves numerous co- and post-translational modification, processing, secretion and cross-linking steps that in turn are catalysed by specific enzymes and chaperones. Mutations in individual collagen genes and their biosynthetic pathway components can result in a range of defects from abnormal morphology (dumpy and blister) to embryonic and larval death, confirming an essential role for this structure and highlighting its potential as an ECM experimental model system.
-
[
2006]
RNA interference (RNAi) describes a conserved biological response to double-stranded RNA (dsRNA) resulting in the degradation of homologous messenger RNA. In the last few years, this process of sequence-specific, post-transcriptional gene silencing has become a key technique for rapidly assessing gene function in species ranging from plants to mammals. Fire et al. provided the first insight into the RNAi mechanism by identifying dsRNA as the trigger of RNAi in Caenorhabditis elegans in 1998 [1]. However, a similar gene-silencing phenomenon was reported in earlier studies in both plants and Neurospora [2,3]. The basic RNAi response starts with long dsRNA being processed into small interfering RNAs (siRNAs) by a ribonuclease (RNase) III enzyme, Dicer. Next, the siRNA is incorporated into the RNA-induced silencing complex (RISC). For target RNA recognition to occur, the siRNA duplex must be unwound, allowing binding of one siRNA strand to the target mRNA. This is followed by RISC cleavage of the homologous mRNA. Recent work has shown that the RNAi machinery is also involved in antiviral responses, transposon silencing, development and heterochromatin formation [4].
-
[
WormBook,
2006]
The DNA in eukaryotes is wrapped around a histone octamer core, together comprising the main subunit of chromatin, the nucleosome. Modifications of the nucleosomal histones in the genome correlate with the ability or inability of chromatin to form higher order structures, that in turn influence gene activity. The genome in primordial germ cells in early C. elegans germ cells carries a unique pattern of histone modifications that correlate with transcriptional repression in these cells, and aspects of this chromatin regulation are conserved in Drosophila. Loss of repression causes sterility in the adults, suggesting that chromatin-based repression is essential for germ line maintenance. The post-embryonic germ line also exhibits unique and dynamic aspects of chromatin regulation, with chromosome-wide regulation particularly evident on the X chromosome. Several properties of X-specific chromatin assembly are also sex-specific. These properties appear to be responding to the meiotic pairing status of the X chromosome, rather than the sex of the germ cells. Finally, gamete-specific chromatin regulation during gametogenesis impacts on X chromatin assembly in the offspring, leading to an apparent sperm-imprinted X inactivation in the early embryo. Other potential roles for germline-specific modes of chromatin assembly in genome regulation and protection are discussed.
-
[
WormBook,
2008]
The role of neuropeptides in modulating behavior is slowly being elucidated. With the sequencing of the C. elegans genome, the extent of the neuropeptide genes in C. elegans can be determined. To date, 113 neuropeptide genes encoding over 250 distinct neuropeptides have been identified. Of these, 40 genes encode insulin-like peptides, 31 genes encode FMRFamide-related peptides, and 42 genes encode non-insulin, non-FMRFamide-related neuropeptides. As in other systems, C. elegans neuropeptides are derived from precursor molecules that must be post-translationally processed to yield the active peptides. These precursor molecules contain a single peptide, multiple copies of a single peptide, multiple distinct peptides, or any combination thereof. The neuropeptide genes are expressed extensively throughout the nervous system, including in sensory, motor, and interneurons. In addition, some of the genes are also expressed in non-neuronal tissues, such as the somatic gonad, intestine, and vulval hypodermis. To address the effects of neuropeptides on C. elegans behavior, animals in which the different neuropeptide genes are inactivated or overexpressed are being isolated. In a complementary approach the receptors to which the neuropeptides bind are also being identified and examined. Among the knockout animals analyzed thus far, defects in locomotion, dauer formation, egg laying, ethanol response, and social behavior have been reported. These data suggest that neuropeptides have a modulatory role in many, if not all, behaviors in C. elegans.