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The embryonic cell lineage of Caenorhabditis elegans has been traced from zygote to newly hatched larva, with the result that the entire cell lineage of this organism is now known. During embryogenesis 671 cells are generated; in the hermaphrodite 113 of these (in the male 111) undergo programmed death and the remainder either differentiate terminally or become postembryonic blast cells. The embryonic lineage is highly invariant, as are the fates of the cells to which it gives rise. In spite of the fixed relationship between cell ancestry and cell fate, the correlation between them lacks much obvious pattern. Thus, although most neurons arise from the embryonic ectoderm, some are produced by the mesoderm and a few are sisters to muscles; again, lineal boundaries do not necessarily coincide with functional boundaries. Nevertheless, cell ablation experiments (as well as previous cell isolation experiments) demonstrate substantial cell autonomy in at least some sections of embryogenesis. We conclude that the cell lineage itself, complex as it is, plays an important role in determining cell fate. We discuss the origin of the repeat units (partial segments) in the body wall, the generation of the various orders of symmetry, the analysis of the lineage in terms of sublineages, and evolutionary implications.
Contents. Introduction. Materials, methods, and background information. Culture. General biology. Light microscopy. Electron microscopy. Strategy of observation. Reliability. Nomenclature. Results and comments. General description. Invariance. Cell divisions and cell movement. The founder cells. Gastrulation. Later cell movements. Migrations. Programmed cell death. Other nematode species. Tissue description. Hypodermis. Excretory system. Nervous system. Mesoderm (excluding the pharynx). Alimentary tract. Gonad. Cell interaction experiments. Early ablations. Body muscle from C and D. MS lineage. AB lineage. Other late ablations. Summary. Discussion. Invariance, cell autonomy, and cell interaction. Embryonic germ layers and cell fate. Lineal boundaries and functional boundaries. Segments. Sublineages. Programmed cell death and sexual dimorphism. Rotational symmetry. Symmetry and asymmetry. Conclusion.
Adapted by Yusuf KARABEY for WORMATLAS, 2003