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Riddle DL, Blumenthal T, Meyer BJ, et al., editors. C. elegans II. 2nd edition. Cold Spring Harbor (NY): Cold Spring Harbor Laboratory Press; 1997.

Cover of C. elegans II

C. elegans II. 2nd edition.

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Section IIntroduction

Classical studies in embryology showed that in certain animals, the descent, or lineage, of cells was correlated strictly with cell fate; these animals were described as having a determinate, autonomous, or mosaic mode of development. Nematodes like Caenorhabditis elegans have an invariant lineage and have been a paradigm of the determinate mode. Results from experiments on C. elegans in the 1980s were, and remain, consistent with the classical notion that some specification of cell fates in nematodes occurs autonomously (Laufer et al. 1980; Cowan and McIntosh 1985; Edgar and McGhee 1986; Schierenberg 1988). For example, it was shown that certain cleavage-arrested blastomeres are nevertheless able to undergo tissue-specific differentiation. However, as described in this chapter, a large number of cell-cell interactions have now been identified in the C. elegans embryo. The invariant lineage of the embryo may result largely from the fact that invariant cleavage patterns set up reproducible patterns of cell-cell interactions.

Table 1. Localization of gene products described in this chapter.

Table 1

Localization of gene products described in this chapter.

All of C. elegans embryogenesis occurs within a transparent egg shell; the egg measures about 50 μm in length and 30 μm in diameter. The small size of the egg and the small number of cells at hatching (55) have made it possible to observe with the light microscope the pattern of cell cleavage and differentiation of all cells in the living embryo. A major conclusion from these studies is that this pattern, or lineage, is largely invariant between different embryos. Thus, it has been possible to construct a single diagram representing the entire cell lineage of the C. elegans embryo (Deppe et al. 1978; Sulston et al. 1983).

During the first four cleavages of the embryo, five cells, or blastomeres, are produced that generate distinct sets of somatic tissues. These blastomeres, called AB, MS, E, C, and D, often are referred to as somatic founder cells. The sister of D is the P4 blastomere and is the precursor of the germ line (Fig. 1). We will discuss embryogenesis by focusing on how the fates of the individual founder cells are specified and by describing how P4 becomes the germ-line precursor.

Copyright © 1997, Cold Spring Harbor Laboratory Press.
Bookshelf ID: NBK20121


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