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[
WormBook,
2007]
The intestine is one of the major organs in C. elegans and is largely responsible for food digestion and assimilation as well as the synthesis and storage of macromolecules. In addition, the intestine is emerging as a powerful experimental system in which to study such universal biological phenomena as vesicular trafficking, biochemical clocks, stress responses and aging. The present chapter describes some of these many and varied properties of the C. elegans intestine: the embryonic cell lineage, intestine morphogenesis, structure and physiology of the intestinal cell and, finally, the transcription factor network controlling intestine development and function.
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[
WormBook,
2005]
Nematodes are the most abundant type of animal on earth, and live in hot springs, polar ice, soil, fresh and salt water, and as parasites of plants, vertebrates, insects, and other nematodes. This extraordinary ability to adapt, which hints at an underlying genetic plasticity, has long fascinated biologists. The fully sequenced genomes of Caenorhabditis elegans and Caenorhabditis briggsae, and ongoing sequencing projects for eight other nematodes, provide an exciting opportunity to investigate the genomic changes that have enabled nematodes to invade many different habitats. Analyses of the C. elegans and C. briggsae genomes suggest that these include major changes in gene content; as well as in chromosome number, structure and size. Here I discuss how the data set of ten genomes will be ideal for tackling questions about nematode evolution, as well as questions relevant to all eukaryotes.
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[
WormBook,
2005]
The regulation of transcription in C. elegans shares many similarities to transcription in other organisms. The details of how specific transcription factors bind to target promoters and act as either activators or repressors are still being examined in many cases, but an increasing number of factors and their binding sites are being characterized. This chapter reviews the general concepts that have emerged with regards to promoter function in C. elegans. Included are the methods that have been successfully employed as well as limitations encountered to date. Specific cis-acting promoter elements from
myo-2 ,
hlh-1 and
lin-26 are discussed as examples of complex promoters regulated by multiple sequence elements. In addition, examples of organ-, tissue-, and cell type-specific mechanisms for generating spatial specificity in gene expression are discussed.
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[
WormBook,
2006]
Wild C. elegans and other nematodes live in dirt and eat bacteria, relying on mechanoreceptor neurons (MRNs) to detect collisions with soil particles and other animals as well as forces generated by their own movement. MRNs may also help animals detect bacterial food sources. Hermaphrodites and males have 22 putative MRNs; males have an additional 46 MRNs, most, if not all of which are needed for mating. This chapter reviews key aspects of C. elegans mechanosensation, including MRN anatomy, what is known about their contributions to behavior as well as the neural circuits linking MRNs to movement. Emerging models of the mechanisms used to convert mechanical energy into electrical signals are also discussed. Prospects for future research include expanding our understanding of the molecular basis of mechanotransduction and how activation of MRNs guides and modulates behavior.
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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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[
WormBook,
2005]
A wide variety of bacterial pathogens, as well as several fungi, kill C. elegans or produce non-lethal disease symptoms. This allows the nematode to be used as a simple, tractable model host for infectious disease. Human pathogens that affect C. elegans include Gram-negative bacteria of genera Burkholderia, Pseudomonas, Salmonella, Serratia and Yersinia; Gram-positive bacteria Enterococcus, Staphylococcus and Streptococcus; and the fungus Cryptococcus neoformans. Microbes that are not pathogenic to mammals, such as the insect pathogen Bacillus thuringiensis and the nematode-specific Microbacterium nematophilum, are also studied with C. elegans. Many of the pathogens investigated colonize the C. elegans intestine, and pathology is usually quantified as decreased lifespan of the nematode. A few microbes adhere to the nematode cuticle, while others produce toxins that kill C. elegans without a requirement for whole, live pathogen cells to contact the worm. The rapid growth and short generation time of C. elegans permit extensive screens for mutant pathogens with diminished killing, and some of the factors identified in these screens have been shown to play roles in mammalian infections. Genetic screens for toxin-resistant C. elegans mutants have identified host pathways exploited by bacterial toxins.
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[
Genetics,
2019]
Males of <i>Caenorhabditis elegans</i> provide a crucial practical tool in the laboratory, but, as the rarer and more finicky sex, have not enjoyed the same depth of research attention as hermaphrodites. Males, however, have attracted the attention of evolutionary biologists who are exploiting the <i>C. elegans</i> system to test longstanding hypotheses about sexual selection, sexual conflict, transitions in reproductive mode, and genome evolution, as well as to make new discoveries about <i>Caenorhabditis</i> organismal biology. Here, we review the evolutionary concepts and data informed by study of males of <i>C. elegans</i> and other <i>Caenorhabditis</i> We give special attention to the important role of sperm cells as a mediator of inter-male competition and male-female conflict that has led to drastic trait divergence across species, despite exceptional phenotypic conservation in many other morphological features. We discuss the evolutionary forces important in the origins of reproductive mode transitions from males being common (gonochorism: females and males) to rare (androdioecy: hermaphrodites and males) and the factors that modulate male frequency in extant androdioecious populations, including the potential influence of selective interference, host-pathogen coevolution, and mutation accumulation. Further, we summarize the consequences of males being common <i>vs</i> rare for adaptation and for trait divergence, trait degradation, and trait dimorphism between the sexes, as well as for molecular evolution of the genome, at both micro-evolutionary and macro-evolutionary timescales. We conclude that <i>C. elegans</i> male biology remains underexploited and that future studies leveraging its extensive experimental resources are poised to discover novel biology and to inform profound questions about animal function and evolution.
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[
Genetics,
2022]
The nematode Caenorhabditis elegans has shed light on many aspects of eukaryotic biology, including genetics, development, cell biology, and genomics. A major factor in the success of C. elegans as a model organism has been the availability, since the late 1990s, of an essentially gap-free and well-annotated nuclear genome sequence, divided among 6 chromosomes. In this review, we discuss the structure, function, and biology of C. elegans chromosomes and then provide a general perspective on chromosome biology in other diverse nematode species. We highlight malleable chromosome features including centromeres, telomeres, and repetitive elements, as well as the remarkable process of programmed DNA elimination (historically described as chromatin diminution) that induces loss of portions of the genome in somatic cells of a handful of nematode species. An exciting future prospect is that nematode species may enable experimental approaches to study chromosome features and to test models of chromosome evolution. In the long term, fundamental insights regarding how speciation is integrated with chromosome biology may be revealed.
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[
WormBook,
2010]
An understanding of evolution at the molecular level requires the simultaneous consideration of the 5 fundamental evolutionary processes: mutation, recombination, natural selection, genetic drift, and population dynamic effects. Experimental, comparative genomic, and population genetic work in C. elegans has greatly expanded our understanding of these core processes, as well as of C. elegans biology. This chapter presents a brief overview of some of the most salient features of molecular evolution elucidated by the C. elegans system.
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[
WormBook,
2005]
The morphogenesis of the C. elegans embryo is largely controlled by the development of the epidermis, also known as the hypodermis, a single epithelial layer that surrounds the animal. Morphogenesis of the epidermis involves cell-cell interactions with internal tissues, such as the developing nervous system and musculature. Genetic analysis of mutants with aberrant epidermal morphology has defined multiple steps in epidermal morphogenesis. In the wild type, epidermal cells are generated on the dorsal side of the embryo among the progeny of four early embryonic blastomeres. Specification of epidermal fate is regulated by a hierarchy of transcription factors. After specification, dorsal epidermal cells rearrange, a process known as dorsal intercalation. Most epidermal cells fuse to generate multinucleate syncytia. The dorsally located epidermal sheet undergoes epiboly to enclose the rest of the embryo in a process known as ventral enclosure; this movement requires both an intact epidermal layer and substrate neuroblasts. At least three distinct types of cellular behavior underlie the enclosure of different regions of the epidermis. Following enclosure, the epidermis elongates, a process driven by coordinated cell shape changes. Epidermal actin microfilaments, microtubules, and intermediate filaments all play roles in elongation, as do body wall muscles. The final shape of the epidermis is maintained by the collagenous exoskeleton, secreted by the apical surface of the epidermis.