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[
WormBook,
2005]
Early development of many species depends on the temporal and spatial control of maternal gene products. This review discusses the control of maternal mRNAs that encode regulators of C. elegans embryogenesis. In the C. elegans embryo, maternal mRNA regulation is crucial to the patterning of early cell fates. Translational control of key mRNAs spatially organizes cell signaling pathways, localizes transcription factor activities, and controls germ cell precursor development. From the few mRNAs studied thus far, some themes are beginning to emerge. Control of maternal mRNA translation begins in the hermaphrodite germ line. Distinct regulatory systems keep mRNAs silent during different stages of oogenesis, and lead to precise temporal and spatial patterns of translation in the embryo. In the embryo, cell polarity factors control the localization of translational regulators. Each maternal mRNA contains multiple elements in its 3'' untranslated region (3'' UTR) that specify the timing and localization of translation. A relatively small number of RNA-binding proteins likely control many mRNAs through these 3'' UTR elements. Therefore, the combination of RNA elements and the regulatory complexes recruited to them specify unique patterns of translation for different mRNAs. The mechanisms of translational control are only beginning to be explored, but are likely to regulate diverse developmental and cellular events in metazoans.
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[
WormBook,
2006]
Small GTPases of the Ras superfamily are key regulators of diverse cellular and developmental events, including differentiation, cell division, vesicle transport, nuclear assembly, and control of the cytoskeleton. The C. elegans genome encodes 56 members of the major Ras GTPase subfamilies, including the Ras/Ral/Rap family, the Rho family, the Rab family, Ran, and the Arf/Sar family. Studies in C. elegans have shown that Ras/Rap family members control cell fate specification and differentiation; Rho GTPases control morphogenesis and actin dynamics, including axon pathfinding and cell migration; Rab GTPases control synaptic vesicle trafficking and release and gene expression responses in innate immunity; the Ran GTPase controls nuclear import/export, nuclear reassembly after mitosis, and kinetechore association with microtubules; and Arf/Sar GTPases control morphogenesis and microtubule organization and possibly cilia development. Functions for many of the small GTPases remain to be discovered, and continuing studies in C. elegans will elucidate the roles of these molecules in animal development.
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[
WormBook,
2005]
C. elegans hermaphrodites are self-fertile, and their rate and temporal pattern of egg-laying are modulated by diverse environmental cues. Egg-laying behavior has served as an important phenotypic assay for the genetic dissection of neuronal signal transduction mechanisms. This chapter reviews our current understanding of the neuronal and neurochemical mechanisms underlying the control of egg-laying in C. elegans. The roles of specific neurons in the egg-laying motor circuit, which release multiple neurotramsmitters affecting distinct parameters of egg-laying muscle activity, and the possible mechanisms for sensory control of egg-laying behavior, are discussed.
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[
1987]
Mutations in genes that control developmental patterns undoubtedly underlie evolutionary change in development. The elucidation of the precise genetic basis of evolutionary change requires the identification and genetic analysis of key genes that control normal developmental patterns of an organism ("developmental control genes"), the analysis of the precise nature of developmental differences between that organism and its related species, and the determination of what changes in these developmental control genes actually cause the observed evolutionary developmental differences. Nematodes offer an excellent opportunity to study the roles of developmental control genes in evolutionary change. The simple anatomy and rapid life cycle of the nematode Caenorhabditis elegans has allowed a detailed analysis of its wild-type development. As a result, the complete cell lineage of C. elegans has been elucidated. This lineage is nearly invariant in the wild type; each cell is formed after a defined lineage history and at a specific time during development. Thus, the developmental defects of mutants can be accurately determined at the level of the fates expressed by specific cells at specific times in development. Through genetic analyses of C. elegans developmental mutants, genes have been identified that play crucial roles in specifying and expressing the normal developmental program. If these genes code for developmental control processes common to different nematode species, then mutations of these genes might underlie interspecific developmental change. Other nematode species can be isolated from the wild and cultured in the laboratory with ease. The relatively simple cellular anatomy of nematodes allows the direct comparison of cell lineages between different species on the level of individual cells and cell divisions. If genes affecting development in C. elegans play evolutionary roles, then developmental differences between species should emerge that parallel, or even are identical to, mutationally induced changes in C. elegans. It should eventually be possible to test directly which genes are responsible for certain evolutionary differences in development by altering
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[
WormBook,
2007]
Heterorhabditis bacteriophora is an entomopathogenic nematode (EPN) mutually associated with the enteric bacterium, Photorhabdus luminescens, used globally for the biological control of insects. Much of the previous research concerning H. bacteriophora has dealt with applied aspects related to biological control. However, H. bacteriophora is an excellent model to investigate fundamental processes such as parasitism and mutualism in addition to its comparative value to Caenorhabditis elegans. In June 2005, H. bacteriophora was targeted by NHGRI for a high quality genome sequence. This chapter summarizes the biology of H. bacteriophora in common and distinct from C. elegans, as well as the status of the genome project.
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[
1988]
The development of a multicellular organism from a single-celled egg involves the coordinated control of many cells and tissues. How are cells specified to develop as one cell type rather than another, in one position rather than another, and at one time rather than another? What is the molecular basis of the spatial and temporal cues necessary to direct development of the organism? The information for this developmental feat is stored in the egg-either in its genome or in products of the maternal genome contributed to that cell. Developmental genetics provides a powerful way to investigate that information. The nematode, Caenorhabditis elegans, has proven to be an excellent model organism for analysis of the genes that control development...
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[
1992]
Caenorhabditis elegans is a small soil nematode which is currently being extensively studied to discern general principles of how genes control development. The short life cycle, ability to culture in quantities sufficient for biochemical work, well-developed genetics, small cell number for a rather sophisticated animal, and rapidly increasing possibilities for molecular genetics are features that make this species a very productive system
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[
Adv Exp Med Biol,
2010]
Nematode neuropeptide systems comprise an exceptionally complex array of approximately 250 peptidic signaling molecules that operate within a structurally simple nervous system of approximately 300 neurons. A relatively complete picture of the neuropeptide complement is available for Caenorhabditis elegans, with 30 flp, 38 ins and 43 nlp genes having been documented; accumulating evidence indicates similar complexity in parasitic nematodes from clades I, III, IV and V. In contrast, the picture for parasitic platyhelminths is less clear, with the limited peptide sequence data available providing concrete evidence for only FMRFamide-like peptide (FLP) and neuropeptide F (NPF) signaling systems, each of which only comprises one or two peptides. With the completion of the Schmidtea meditteranea and Schistosoma mansoni genome projects and expressed sequence tag datasets for other flatworm parasites becoming available, the time is ripe for a detailed reanalysis ofneuropeptide signalingin flatworms. Although the actual neuropeptides provide limited obvious value as targets for chemotherapeutic-based control strategies, they do highlight the signaling systems present in these helminths and provide tools for the discovery of more amenable targets such as neuropeptide receptors or neuropeptide processing enzymes. Also, they offer opportunities to evaluate the potential of their associated signaling pathways as targets through RNA interference (RNAi)-based, target validation strategies. Currently, within both helminth phyla, theflp signaling systems appear to merit further investigation as they are intrinsically linked with motor function, a proven target for successful anti-parasitics; it is clear that some nematode NLPs also play a role in motor function and could have similar appeal. At this time, it is unclear if flatworm NPF and nematode INS peptides operate in pathways that have utility for parasite control. Clearly, RNAi-based validation could be a starting point for scoring potential target pathways within neuropeptide signaling for parasiticide discovery programs. Also, recent successes in the application of in planta-based RNAi control strategies for plant parasitic nematodes reveal a strategy whereby neuropeptide encoding genes could become targets for parasite control. The possibility of developing these approaches for the control of animal and human parasites is intriguing, but will require significant advances in the delivery of RNAi-triggers.
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[
WormBook,
2005]
Cell-division control affects many aspects of development. Caenorhabditis elegans cell-cycle genes have been identified over the past decade, including at least two distinct Cyclin-Dependent Kinases (CDKs), their cyclin partners, positive and negative regulators, and downstream targets. The balance between CDK activation and inactivation determines whether cells proceed through G 1 into S phase, and from G 2 to M, through regulatory mechanisms that are conserved in more complex eukaryotes. The challenge is to expand our understanding of the basic cell cycle into a comprehensive regulatory network that incorporates environmental factors and coordinates cell division with growth, differentiation and tissue formation during development. Results from several studies indicate a critical role for CKI-1 , a CDK inhibitor of the Cip/Kip family, in the temporal control of cell division, potentially acting downstream of heterochronic genes and dauer regulatory pathways.
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[
WormBook,
2006]
Receptor Tyrosine Kinase (RTK)/Ras GTPase/MAP kinase (MAPK) signaling pathways are used repeatedly during metazoan development to control many different biological processes. In the nematode Caenorhabditis elegans , two different RTKs ( LET-23 /EGFR and EGL-15 /FGFR) are known to stimulate LET-60 /Ras and a MAPK cascade consisting of the kinases LIN-45 /Raf, MEK-2 /MEK and MPK-1 /ERK. This Ras/MAPK cascade is required for multiple developmental events, including induction of vulval, uterine, spicule, P12 and excretory duct cell fates, control of sex myoblast migration and axon guidance, and promotion of germline meiosis. Studies in C. elegans have provided much insight into the basic framework of this RTK/Ras/MAPK signaling pathway, its regulation, how it elicits cell-type specific responses, and how it interacts with other signaling pathways such as the Wnt and Notch pathways.