Abstract

Development of the nematode Caenorhabditis elegans has been described completely on a cell‐by‐cell basis. In an invariant pattern five somatic founder cells and the primordial germ cell are generated within the first hour after the onset of cleavage. Using a laser microbeam for manipulation of individual blastomers several aspects of early embryogenesis have been investigated, including the expression of cellular polarity, the localization of lineage‐specific cleavage potential, the necessity for early cell–cell interaction, and the control of differential cell‐cycle timing. The experiments demonstrate the central importance of a correct partitioning of cytoplasmic components during early embryogenesis and suggest a stepwise, binary segregation mechanism associated with the unequal cleavages in the germline.