Temporal and spatial expression of embryonic alkaline phosphatase activity in the surf clam, Spisula solidissima

The temporal appearance and spatial distribution of alkaline phosphatase (EC 3.1.3.1) have been examined during the development of the surf clam, Spisula solidissima. Enzyme activity was detectable at low levels from fertilization onward with a sharp linear increase in activity occurring at the trochophore stage, 14 h post-fertilization. Histochemical localization of enzyme activity at the light microscope level showed the increased activity associates initially with a limited number of large macromeres and is progressively restricted to the cells forming the tip of the growing archenteron. Electron microscopy shows the activity is restricted to the luminal and lateral plasma membrane of these cells.