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[
Chromosomes Today,
2004]
C. elegans meiotic chromosomes do not require meiotic double-stranded DNAbreaks for synaptonemal complex formation. However, homologues must share a cisactingregion, the so-called HRR, to become synapsed. To achive orderly segregation at thefirst and second meiotic divisions, C. elegans chromosomes must transform from theirmitotic holocentric to monocentric organization. Here we address issues concerning thenature of the HRR and the selection of the meiotic kinetochore site.
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[
1978]
A small sightless worm crawling among particles of soil and decaying vegetation must have a variety of chemical senses to locate bacteria for food and to avoid poisons and predators. What chemicals are sensed? How many different kinds of receptor molecules are there? On which neurons are the receptors located? How sensitive are these neurons? How is the detection of a chemical communicated to the worm's central nervous system and converted into a behavioral response? All of these questions have been addressed in studies of the soil nematode Caenorhabditis elegans. This organism has recently become the subject of intensive genetic, behavioral and anatomical studies. The behavior that has been examined in most detail is chemotaxis. This chapter will review what is known about C. elegans chemotaxis and will present a number of new observations. The results will be interpreted in terms of a specific model of chemoreceptor function. The problem of analysis of central nervous system processing of chemosensory neuron information will be discussed briefly.
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[
1990]
Sex determination in the C. elegans germ line addresses two major problems of biological control. First, any regulation that directs male or female development in all tissues must rely on tissue-specific controls to specify a particular pathway of differentiation (e.g., sperm or oocyte) in a single tissue. The C. elegans germ line provides several technical advantages for analyzing sex determination in a single tissue, including powerful genetic selections (Kimble, 1988) and ease of micro-injection (Kimble et al., 1982). Second, the self-fertility of the C. elegans hermaphrodite depends upon its transient production of sperm in an otherwise female animal. Analysis of sex determination in the hermaphrodite germ line should therefore shed light on the evolution of hermaphrodites from females. Here, we review our efforts towards identifying the regulatory elements that control the C. elegans hermaphrodite germ line to produce sperm and
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[
1975]
Much of the discussion in this symposium has addressed the question of how a single cell differentiates into two different daughter cells. Considerable effort is being made to understand the ability of cells to regulate protein synthesis either by temporal regulation at the level of the genome or through the inherent order of assembly of macromolecules, as is seen in the case of T4 bacteriophage late functions. We now turn to consideration of the genetic control of development in an organism which is complex relative to those prokaryotes and unicellular eukaryotes which have been discussed so far. Studies on the development of prokaryotes or simple eukaryotes rely upon the extensive knowledge of how genes are replicated, transcribed, and translated as deciphered over the past 15 years of molecular biology. An alternative approach is required in studying an organism with several cell types and asymmetries in which there is complex development. I have chosen the small nematode Caenorhabditis elegans for studying genetic control of development because it lends itself to detailed morphological studies and because its genetics is now well defined through the elegant work of Brenner......
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[
Methods Cell Biol,
1995]
In studying embryos of many species, methods of fragmenting and culturing embryonic tissues or cells have been useful for addressing questions of blastomere autonomy in early and later embryogenesis, for exposure to drugs or other agents that perturb specific processes, and for direct labeling of DNA or RNA. For Caenorhabditis elegans workers, the small size of the embryo and the impermeability of the chitinous eggshell and inner vitelline membrane have made such experiments difficult. A method of permeabilization and blastomere isolation, a culture system that will support further cellular development and differentiation, and assay methods for assaying the degree of development and its relative normality after experimental manipulation are minimal requirements for a satisfactory C. elegans embryonic culture system. Methods of isolating early blastomeres have included crushing of the eggshell and extrusion, laser ablation of neighboring blastomeres within an itact eggshell, laser puncturing of the eggshell producing extrusion, and digestion of the eggshell followed by shearing or manual stripping of the vitelline membrane. This last method is described in detail below. Permeabilization of complete embryos can be achieved by the same methods; in addition, one-cell embryos within the shell can be permeabilized to certain drugs such as cytochalasin D by gentle pressure on an overlying
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[
1998]
The free-living nematode Caenorhabditis elegans has emerged rapidly as an organism with which to study many basic biological phenomena, particularly those related to development. This can ben evidenced numerically in many ways; for example, the number of presentations at the biennial C. elegans meeting has increased over sevenfold, from 80 in 1979 to 569 in 1995. In addition to numerous review articles, several books are devoted to this nematode, its attributes and various foci of interest. The three preliminary attributes that have rendered C. elegans a popular model system are overviewed briefly in the following three sections. The attributes that have rendered C. elegans popular with developmental biologists have also been exploited to examine specific areas in radiation biology, DNA repair, and mutagenesis. Several of the basic DNA repair pathways operative in C. elegans have been elucidated. Also, a number of biological end points such as survival and mutagenesis, have been examined so as to address the various mechanisms by which C. elegans accommodates DNA damage. Central to these efforts has been the isolation and characterization of radiation-sensitive (rad) mutants that modify various biological responses. In particular, these studies provide insights into damage processing, particularly as related to development and aging.
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[
1983]
In the preparation of this review, I have made the basic assumption that the desire of the reader is to understand the biological basis of organismic aging. Given this premise, the organism of choice should be one that offers the most immediate hope of arriving at such an understanding. An ideal organism should have a short lifespan; be inexpensive to maintain; be experimentally malleable by a variety of techniques including molecular, morphological, genetic, and biological approaches; and be the object of study in a sufficient number of different laboratories to assure the accumulation of a critical mass of data. The nematode, Caenorhabditis elegans, admirably fulfills all of these basic requirememts. Researchers in the field of aging are faced with a large number of different theories which purport to explain the molecular basis of organismic aging. There are two major reasons for this proliferation of theoretical views. First, aging is an extremely complex phenomenon involving changes in a number of different physiological systems; these physiological changes are often detected, but proof that any one of the changes is responsible for aging is lacking. Second, the focus of a great deal of the research in the field has not been so much on understanding the biological basis of the entire aging process as on understanding one or another of the consequences of this process, particularly in humans and other mammals. The mammalian model systems may often be quite inappropriate for addressing the more basic, long-term questions about the
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[
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.
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[
WormBook,
2006]
C. elegans occurs in two natural sexes, the XX hermaphrodite and the XO male, which differ extensively in anatomy, physiology, and behavior. All somatic differences between the sexes result from the differential activity of a global sex determination regulatory pathway. This pathway also controls X chromosome dosage compensation, which is coordinated with sex determination by the action of the three SDC proteins. The SDC proteins control somatic and germline sex by transcriptional repression of the
her-1 gene. HER-1 is a secreted protein that controls a regulatory module consisting of a transmembrane receptor, TRA-2 , three intracellular FEM proteins, and the zinc finger transcription factor TRA-1 . The molecular workings of this regulatory module are still being elucidated. Similarity of TRA-2 to patched receptors and of TRA-1 to GLI proteins suggests that parts of the global pathway originally derived from a Hedgehog signaling pathway. TRA-1 controls all aspects of somatic sexual differentiation, presumably by regulating a variety of tissue- and cell-specific downstream targets, including the cell death regulator EGL-1 and the male sexual regulator MAB-3 . Sex determination evolves rapidly, and conservation of sexual regulators between phyla has been elusive. An apparent exception involves DM domain proteins, including MAB-3 , which control sexual differentiation in nematodes, arthropods, and vertebrates. Important issues needing more study include the detailed molecular mechanisms of the global pathway, the identities of additional sexual regulators acting in the global pathway and downstream of TRA-1 , and the evolutionary history of the sex determination pathway. Recently developed genetic and genomic technologies and comparative studies in divergent species have begun to address these issues.
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[
Methods Cell Biol,
1995]
The clone-based physical map of the 100-Mb Caenorhabditis elegans genome has evolved over a number of years. Although the detection of clone overlaps and construction of the map have of necessity been carried out centrally, it has been essentially a community project. Without the provision of cloned markers and relevant map information by the C. elegans community as a whole, the map would lack the genetic anchor points and coherent structure that make it a viable entity. Currently, the map consists of 13 mapped contigs totaling in excess of 95 Mb and 2 significant unmapped contigs totaling 1.3 Mb. Telomeric clones are not yet in place. The map carries 600 physically mapped loci, of which 262 have genetic map data. With one exception, the physical extents of the remaining gaps are not known. The exception is the remaining gap on linkage group (LG) II. This has been shown to be bridged by a 225-kb Sse83871 fragment. Because the clones constituting the map are a central resource, there is essentially no necessity for individuals to construct cosmid and yeast artificial chromosome (YAC) libraries. Consequently, such protocols are not included here. Similarly, protocols for clone fingerprinting, which forms the basis of the determination of cosmid overlaps and the mapping of clones received from outside sources and has to be a centralized operation, and YAC linkage are not give here. What follows is essentially a "user's guide" to the physical map. Details of map construction are given where required for interpretation of the map as distributed. The physical mapping has been a collaboration between the MRC Laboratory of Molecular Biology, Cambridge, United Kingdom (now at The Sanger Centre, Cambridge, UK) and Washington University School of Medicine, St. Louis, Missouri. Inquiries regarding map interpretation, information, and materials should be addressed to alan@sanger.ac.uk or rw@nematode.wustl.edu.