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[
WormBook,
2005]
The features that differentiate the C. elegans male from the hermaphrodite arise during postembryonic development. The major male mating structures, consisting of the blunt tail with fan and rays, the hook, the spicules and proctodeum, and the thin body, form just before the last larval molt. Male and hermaphrodite embryogenesis are similar but some essential male cell fates are already established at hatching. The male mating structures arise from three important sets of male-specific blast cells. These cells generate a total of 205 male-specific somatic cells, including 89 neurons, 36 neuronal support cells, 41 muscles, 23 cells involved in differentiating the hindgut, and 16 hypodermal cells associated with mating structures. Genetic and molecular studies have identified many genes required for male development, most of which also function in the hermaphrodite. Cell-cell interactions play a role in patterning all three of the generative tissues. Male-specific neurons, including sensory neurons of the rays, hook, post-cloacal sensilla, and spicules, differentiate at the end of the last larval stage and send out axons to make connections into the existing neuropil, greatly enlarging the posterior ganglia. The hindgut is highly differentiated to accommodate the spicules and the joining of the reproductive tract to the cloaca. A complex male-specific program generates many new muscles for copulation. The cell lineage and genetic program that gives rise to the one-armed male gonad appears to be a variation on that of the hermaphrodite.
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[
WormBook,
2006]
Spermatogenesis creates functional sperm from an initially undifferentiated germ cell. In the nematode Caenorhabditis elegans, both males and hermaphrodites engage in spermatogenesis. The hermaphrodite germ line, like that of the male, initiates spermatogenesis during the L4 larval stage. The hermaphrodite germ line differs from that of the male because it ceases spermatogenesis and switches to oogenesis during the adult stage. Each hermaphrodite stores her sperm and uses them to fertilize her oocytes. Many mutants have been identified where hermaphrodite self-fertility is disrupted. If such a self-sterile hermaphrodite is mated to a wild-type male, mutant hermaphrodites that either lack sperm or contain defective sperm will produce outcross progeny. Easily implemented tests are then applied to identify the subset of these mutants that produce defective sperm. Currently, more than 44 genes are known that are required for normal spermatogenesis. This chapter discusses the 25 best-understood genes that affect spermatogenesis and mutants are grouped based on the cellular structure or process that is affected. C. elegans spermatozoa lack an acrosome and a flagellum, which are organelles found in the spermatozoa produced by most other species. Like other nematodes, C. elegans spermatozoa move by crawling using a single pseudopod. Wild-type spermatogenesis and its defects in mutants can be studied in vivo because the animal is transparent and in vitro because a simple, chemically defined medium that supports development has been discovered. Unlike nearly all other C. elegans cells, homogeneous sperm can be obtained in sufficient quantities to permit biochemical analyses.
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[
1982]
Caenorhabditis elegans is a free-living, nonparasitic nematode. It is a self-fertilizing hermaphrodite. Males arise spontaneously by nondisjunction of X-chromosomes. Of all eukaryotic organisms C. elegans has probably been most extensively studied at the cellular level. Within 12 hours the fertilized egg develops into a young larva with 558 nuclei (560 in the male). During postembryonic development the animal proceeds through four larval stages increasing its number of nuclei to 959 (1,031 in the male) plus some 2,000 germ cells (about 1,000 in the male). The cell lineages from fertilization to adulthood have been completely analyzed in living embryos and animals. This and its well-established genetics (more than 300 genes have been mapped on the six linkage groups) make it a suitable model organism to study problems of gene action and development. Various techniques have been used to interfere with normal development (including laser-induced cell ablations) and to analyze development on the subcellular level (including recombinant DNA technology). The characteristic features of rigidly determined development, the low cell number, and the knowledge of cellular events should make it possible to identify molecular action in situ and relate it to the structure and
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[
WormBook,
2007]
Acetylcholine is the major excitatory neurotransmitter at nematode neuromuscular junctions, and more than a third of the cells in the C. elegans nervous system release acetylcholine. Through a combination of forward genetics, drug-resistance selections, and genomic analysis, mutants have been identified for all of the steps specifically required for cholinergic function. These include two enzymes, two transporters, and a bewildering assortment of receptors. Cholinergic transmission is involved, directly or indirectly, in many C. elegans behaviors, including locomotion, egg laying, feeding, and male mating.
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[
WormBook,
2007]
Strongyloides is a genus of parasitic nematodes, which, unusually, has a free-living adult generation. Here we introduce the biology of this genus, especially the fascinating, but complex, life-cycle together with an overview of the taxonomy, morphology, genetics and genomics of this genus.
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[
2017]
Since their discovery in late 1970, transient receptor potential (TRP) channels have been implicated in a variety of cellular and physiological functions (Minke, 2010). The superfamily of TRP channels consists of nearly 30 members that are organized into seven major subgroups based on their specific function and sequence similarities (Owsianik et al., 2006; Ramsey et al., 2006). With the exception of TRPN channels that are only found in invertebrates and fish, mammalian genomes contain representatives of all six subfamilies: (1) TRPV (vanilloid); (2) TRPC (canonical); (3) TRPM (melastatin); (4) TRPA (ankyrin); (5) TRPML (mucolipin); and (6) TRPP (polycystin). TRP channels play crucial regulatory roles in many physiological processes, including those associated with reproductive tissues. As calcium-permeable cation channels that respond to a variety of signals (Clapham et al., 2003; Wu et al., 2010), TRP channels exert their role as sensory detectors in both male and female gametes, and play regulatory functions in germ cell development and maturation. Recent evidence obtained from Caenorhabditis elegans studies point to the importance of these proteins during fertilization where certain sperm TRP channels could migrate from a spermatozoon into an egg to ensure successful fertilization and embryo development. In this chapter we discuss how TRP channels can regulate both female and male fertility in different species and their specific roles.
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[
WormBook,
2005]
The C. elegans germ line proliferates from one primordial germ cell (PGC) set aside in the early embryo to over a thousand cells in the adult. Most germline proliferation is controlled by the somatic distal tip cell, which provides a stem cell niche at the distal end of the adult gonad. The distal tip cell signals to the germ line via the Notch signaling pathway, which in turn controls a network of RNA regulators. The FBF-1 and FBF-2 RNA-binding proteins promote continued mitoses in germ cells located close to the distal tip cell, while the GLD-1 , GLD-2 , GLD-3 , and NOS-3 RNA regulators promote entry into meiosis as germ cells leave the stem cell niche. In addition to these key regulators, many other genes affect germline proliferation.
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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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[
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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[
WormBook,
2005]
The knowledge about C. elegans provides a paradigm for comparative studies. Nematodes are very attractive in evolutionary developmental biology given the species richness of the phylum and the easiness with which several of these species can be cultured under laboratory conditions. Embryonic, gonad, vulva and male tail development were studied and compared in nematodes of five different families, providing a detailed picture of evolutionary changes in development. In particular, vulva development has been studied in great detail and substantial differences in the cellular, genetic and molecular mechanisms have been observed between C. elegans and other nematodes. For example, vulva induction relies on the single anchor cell in C. elegans, whereas a variety of different cellular mechanisms are used in related species. In recent years, a few species have been developed as satellite systems for detailed genetic and molecular studies, such as Oscheius tipulae and Pristionchus pacificus.