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Unformatted text preview: The nematode Caenorhabditis elegans, one of the simplest multicellular organisms, lives in soils worldwide and feeds on soil bacteria. Adults are about 1 mm in length and contain an invariant number of somatic cells ( Fig. C.1 ). The mature “female,” which is actually a hermaphrodite able to produce both eggs and sperm, has precisely 959 somatic cells that arose from progenitor cells by a reproducible pattern of cell division. The mature male, which produces sperm and has genitalia that enable it to mate with the hermaphrodite, includes precisely 1031 somatic cells that also arose by a reproducible pattern of cell division. C. elegans has a short life cycle and an enormous reproductive capacity, progressing in just three days from the fertilized egg of one generation to between 250 and 1000 fer- tilized eggs of the next generation. It is transparent at all stages, so that investigators can use the light microscope to track development at the cellular level throughout the life cycle. Its small size and small cell number, precisely reproducible and viewable cellular composition, short life cycle, and capacity for prolific reproduction make C. elegans an ideal subject for the genetic analysis of development. The fact that the genome for C. elegans was sequenced in 1998 makes it an even more appeal- ing organism to study. Although C. elegans and most other free-living species of nematodes are gen- erally beneficial, they are related to nematodes that parasitize animals and plants, causing human disease and agricultural damage. Knowledge gained from the study of C. elegans will help combat these problems. Three unifying themes surface in our discussion of C. elegans. First, the invari- ance of cell number and fates forms the basis of many experimental protocols used to study nematode development. Second, the invariant specification of cellular divisions and fates depends on a varied palette of developmental strategies. These include the segregation of particular molecules to particular daughter cells at divi- sion, inductive signals sent from one cell to influence the development of an adja- cent cell, signal transduction pathways within each cell that respond to the arrival of an inductive signal, and a genetically determined program that causes the death of specific cells. Third, genetic studies on the development of C. elegans reveal the simultaneous conservation and innovation of evolution. Because the nematode exhibits many features of development, physiology, and behavior found in other com- plex animals such as Drosophila and humans, studies of C. elegans can help eluci- date developmental pathways and genes conserved throughout animal evolution. But because other features of C. elegans development, such as the invariant spatial and temporal pattern of cell positions, divisions, and fates, are quite different from those found in more complex animals, studies of C. elegans provide a comparative coun- terpoint that deepens our understanding of the full range of genetic controls over...
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This note was uploaded on 04/03/2012 for the course BSCI 410 taught by Professor Staff during the Spring '08 term at Maryland.
- Spring '08