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[
WormBook,
2005]
Nervous systems are characterized by an astounding degree of cellular diversity. The nematode Caenorhabditis elegans has served as a valuable model system to define the genetic programs that serve to generate cellular diversity in the nervous system. This review discusses neuronal diversity in C. elegans and provides an overview of the molecular mechanisms that define and specify neuronal cell types in C. elegans.
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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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[
Adv Exp Med Biol,
2018]
Transcription factors of the Zic family play important roles during animal development, and their misregulation has been implicated in several human diseases. Zic proteins are present in nematodes, and their function has been mostly studied in the model organism C. elegans. C. elegans possesses only one Zic family member, REF-2. Functional studies have shown that this factor plays a key role during the development of the nervous system, epidermis, and excretory system. In addition, they have revealed that the C. elegans Zic protein acts as an atypical mediator of the Wnt/-catenin pathway. In other animals including vertebrates, Zic factors are also regulators of nervous system development and modulators of Wnt signaling, suggesting that these are evolutionary ancient functions of Zic proteins.
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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,
2005]
The most abundant synapses in the central nervous system of vertebrates are inhibitory synapses that use the neurotransmitter gamma-aminobutyric acid (GABA). GABA is also an important neurotransmitter in C. elegans; however, in contrast to vertebrates where GABA acts at synapses of the central nervous system, in nematodes GABA acts primarily at neuromuscular synapses. Specifically, GABA acts to relax the body muscles during locomotion and foraging and to contract the enteric muscles during defecation. The importance of this neurotransmitter for basic motor functions of the worm has facilitated the genetic analysis of proteins required for GABA function. Genetic screens have identified the GABA biosynthetic enzyme, the vesicular transporter, inhibitory and excitatory receptors, and a transcription factor required for the differentiation of GABA cell identity. The plasma membrane transporter and other GABA receptors have been identified by molecular criteria.
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[
1994]
The current interest in the nematode Caenorhabditis elegans began approximately 25 years ago when Sidney Brenner selected this species as the most suitable for studies of metazoan development and nervous system. The basis of this selection rested on the anatomical simplicity of nematodes, which nevertheless possess the major differentiated cell types of higher animals, and the tractability of C. elegans to the genetic approach. Over the past two decades or so, progress has been impressive: the cell lineage from egg to adult and the anatomy of the nervous system have been completely described, genetic investigations of numerous developmental problems are co-ordinated within a universally-agreed, systematic nomenclature, a physical map of the C. elegans genome is nearing completion and a project to sequence the entire genome is underway. Furthermore, the number of laboratories seeking to understand the mechanisms controlling animal development through genetic and molecular investigations of C. elegans is rising rapidly as the advantages of this organism become
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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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[
WormBook,
2005]
Ion channels are the "transistors" (electronic switches) of the brain that generate and propagate electrical signals in the aqueous environment of the brain and nervous system. Potassium channels are particularly important because, not only do they shape dynamic electrical signaling, they also set the resting potentials of almost all animal cells. Without them, animal life as we know it would not exist, much less higher brain function. Until the completion of the C. elegans genome sequencing project the size and diversity of the potassium channel extended gene family was not fully appreciated. Sequence data eventually revealed a total of approximately 70 genes encoding potassium channels out of the more than 19,000 genes in the genome. This seemed to be an unexpectedly high number of genes encoding potassium channels for an animal with a small nervous system of only 302 neurons. However, it became clear that potassium channels are expressed in all cell types, not only neurons, and that many cells express a complex palette of multiple potassium channels. All types of potassium channels found in C. elegans are conserved in mammals. Clearly, C. elegans is "simple" only in having a limited number of cells dedicated to each organ system; it is certainly not simple with respect to its biochemistry and cell physiology.
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[
2010]
Over 30 years ago, Nobel laureate Sydney Brenner recognized that an intellectually straightforward strategy to delineate the basic principles in neurobiology is to utilize a model organism with a nervous system that is simple enough to lend itself to anatomical, cellular, genetic, and molecular analysis, yet be complex enough that lessons learned in that organism would give us insight into general principles of neural function. The humble organism he chose, the nematode Caenorhabditis elegans, is now one of the most thoroughly characterized metazoans, particularly in terms of its nervous system. One of Brenner's motivations in adapting C. elegans as a model organism was to understand the totality of the molecular and cellular basis for the control of animal behavior (Brener 1988). In this chapter, we review what is arguably the best-studied aspect of C. elegans behavior: response to chemical stimuli. The C. elegans neurobiology literature can be intimidating for the uninitiated; we attempt to limit the use of "worm jargon" in this review. For a more C. elegans-centric review, we refer you to other excellent sources (Bargmann 2006).
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[
1993]
In the past 10 years, the remarkable discovery has been made that molecular mechanisms of development are conserved among all animals, and that many of the same molecular components appear in signal transduction pathways of all eukaryotes from yeast to man. This mechanistic conservation means that molecules can be studied in the organism in which their properties are most transparent; general principles or specific predictions made from work in one organism can subsequently be explored in other organisms. This chapter reviews aspects of nervous system development that have been studied using genetic approaches in two simple invertebrates, the fruit fly Drosophila melanogaster (herein referred to as Drosophila) and the soil nematode worm Caenorhabditis elegans (C. elegans). The nervous systems of both of these organisms are extremely simple compared to those of mammals....