Cell fate specification by localized cytoplasmic determinants and cell interactions in ascidian embryos.

Tadpole larvae of ascidians show the basic body plan of chordates. An ascidian larva consists of only a few types of cells and has a relatively small number of cells. Cell lineages are invariant among individuals and have been described in detail. These advantages facilitate the analysis of how the fate of each blastomere becomes specified during development. Over a century of research on ascidian embryogenesis has uncovered many interesting features concerning cellular mechanisms responsible for the fate specification. During embryogenesis, the developmental fate of a blastomere is specified by one of three different mechanisms: localized maternal cytoplasmic determinants, inductive interactions, or lateral inhibition in an equivalence cell group.