Segregation during cleavage of a factor determining endodermal alkaline phosphatase development in ascidian embryos.

Localized alkaline phosphatase activity (EC 3.1.3.1) develops progressively in endodermal tissues of the presumptive digestive system in Ciona intestinalis embryos. It was first detected histochemically at late gastrulation, and a puromycin sensitivity period coincident with this time suggests that new alkaline phosphatase is synthesized. Embryos in which cell division was blocked with cytochalasin B at early cleavage stages up to the 64-cell stage, eventually differentiated strong alkaline phosphatase activity in certain cells at each cleavage-arrested stage. The maximum cell numbers and their positions were identical to those of the previously known endodermal cell lineage. Actinomycin D did not prevent development of endodermal alkaline phosphatase when administered from fertilization onwards, nor did other inhibitors of RNA synthesis (chromomycin A3, cordycepin, and daunomycin). There is probably a preformed maternal mRNA for endodermal alkaline phosphatase present in the unfertilizec Ciona egg. Either this RNA itself, or some related translation factor, is localized in the egg cytoplasm and segregated during early cleavages into the endodermal cell lineage of the embryo.