5 Cell Lineage

Abstract

I. INTRODUCTION
The cell lineage of an organism is a description of the route by which all the cells of the adult are derived from the zygote. We use the term to imply a precise knowledge of both division pattern and cell fate. The somatic cell lineage of Caenorhabditis elegans is largely invariant and is known in its entirety, as is the postembryonic somatic cell lineage of the related nematode Panagrellus redivivus. The postembryonic germ cell lineage is a general proliferation under the control of the somatic cells of the gonad (see Chapter 7) and is probably indeterminate.

What is the point of knowing the cell lineage? First, it provides us with a concise description of the development of the wild-type animal, in which both the detailed pattern of cell fates and the ancestral relationships between tissues are precisely defined. Second, it is a basis for the analysis of development in individuals made defective by experimental intervention or mutation and for comparison with other species.

Because of its relative invariance, cell lineage occupies a special place in C. elegans research. It is similarly important in the study of various other organisms and has been extensively explored in the leech (Stent and Weisblat 1982). Cell lineage probably plays a major role in the development of insect nervous systems (Taghert et al. 1984), though apparently not in the determination of photoreceptors (Lawrence and Green 1979). On the other hand, in the development of many larger organisms, the behavior of cell groups seems...