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[
1983]
More than 100 years ago, early European embryologists had posed the two central questions of animal development: First, how is the sameness of cells and organisms maintained during development and reproduction, and what factors transmit this hereditary information? Second, how do the cells of an embryo become different; what factors dictate that a particular cell at a particular time and position becomes committed to a particular developmental pathway? In the intervening century, we have largely answered the first question, acquiring extensive information about the genetic machinery and how it works. By contrast, we have gained little new understanding of the epigenetic process responsible for temporal and positional control of cell determination in embryos. How this process operates remains a central problem of contemporary
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[
1981]
A neuron can be characterized by its morphology, transmitter (s?), receptor(s) and the nature of its synaptic contacts (chemical or electrical; excitatory or inhibitory; number and distribution of synapses; identity of the cells to which it is presynaptic or postsynaptic). It is clear that according to such criteria nervous sytems consist of neurons of many distinct types. The origin of neuronal diversity is unknown. Both how such diversity is generated during development and how the relevant developmental programme is encoded in the genome remain to
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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,
2007]
The non-motile cilium, once believed to be a vestigial cellular structure, is now increasingly associated with the ability of a wide variety of cells and organisms to sense their chemical and physical environments. With its limited number of sensory cilia and diverse behavioral repertoire, C. elegans has emerged as a powerful experimental system for studying how cilia are formed, function, and ultimately modulate complex behaviors. Here, we discuss the biogenesis, distribution, structures, composition and general functions of C. elegans cilia. We also briefly highlight how C. elegans is being used to provide molecular insights into various human ciliopathies, including Polycystic Kidney Disease and Bardet-Biedl Syndrome.
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[
WormBook,
2005]
Mutations in many genes can result in a similar phenotype. Finding a number of mutants with the same phenotype tells you little about how many genes you are dealing with, and how mutable those genes are until you can assign those mutations to genetic loci. The genetic assay for gene assignment is called the complementation test. The simplicity and robustness of this test makes it a fundamental genetic tool for gene assignment. However, there are occasional unexpected outcomes from this test that bear explanation. This chapter reviews the complementation test and its various outcomes, highlighting relatively rare but nonetheless interesting exceptions such as intragenic complementation and non-allelic non-complementation.
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[
Methods Mol Biol,
2013]
The nematode Caenorhabditis elegans secretes a family of water-soluble small molecules, known as the ascarosides, into its environment and uses these ascarosides in chemical communication. The ascarosides are derivatives of the 3,6-dideoxysugar ascarylose, modified with different fatty acid-derived side chains. C. elegans uses specific ascarosides, which are together known as the dauer pheromone, to trigger entry into the stress-resistant dauer larval stage. In addition, C. elegans uses specific ascarosides to control certain behaviors, including mating attraction, aggregation, and avoidance. Although in general the concentration of the ascarosides in the environment increases with population density, C. elegans can vary the types and amounts of ascarosides that it secretes depending on the culture conditions under which it has been grown and its developmental history. Here, we describe how to grow high-density worm cultures and the bacterial food for those cultures, as well as how to extract the culture medium to generate a crude pheromone extract. Then, we discuss how to analyze the types and amounts of ascarosides in that extract using mass spectrometry and NMR spectroscopy.
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[
WormBook,
2005]
Asymmetric cell divisions play an important role in generating diversity during metazoan development. In the early C. elegans embryo, a series of asymmetric divisions are crucial for establishing the three principal axes of the body plan (AP, DV, LR) and for segregating determinants that specify cell fates. In this review, we focus on events in the one-cell embryo that result in the establishment of the AP axis and the first asymmetric division. We first describe how the sperm-derived centrosome initiates movements of the cortical actomyosin network that result in the polarized distribution of PAR proteins. We then briefly discuss how components acting downstream of the PAR proteins mediate unequal segregation of cell fate determinants to the anterior blastomere AB and the posterior blastomere P 1 . We also review how a heterotrimeric G protein pathway generates cortically based pulling forces acting on astral microtubules, thus mediating centrosome and spindle positioning in response to AP polarity cues. In addition, we briefly highlight events involved in establishing the DV and LR axes. The DV axis is established at the four-cell stage, following specific cell-cell interactions that occur between P 2 and EMS , the two daughters of P 1 , as well as between P 2 and ABp , a daughter of AB . The LR axis is established shortly thereafter by the division pattern of ABa and ABp . We conclude by mentioning how findings made in early C. elegans embryos are relevant to understanding asymmetric cell division and pattern formation across metazoan evolution.
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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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[
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.
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[
Methods Cell Biol,
1995]
This chapter has two aims. First, we describe one method, the electropharyngeogram (EPG), insufficient detail that a Caenorhabditis elegans researcher unfamiliar with electrophysiological methods could set up the apparatus and get useful results. Second, we describe more generally for researchers familiar with electrophysiological methods how they may be applied to C. elegans. We do not describe methods for electrophysiological investigation of C. elegans sperm.