Temporal and spatial profiles of alkaline phosphatase activity during embryogenesis of amphioxus Branchiostoma belcheri tsingtaunese

Temporal and spatial profiles of alkaline phosphatase (ALP) activity during the development of amphioxus have not been fully documented and thus the p resent study investigated this activity spectrophotometrically, electrophor etically and histochemically. The following results were observed: (1) spec trophotometrically, ALP activity increased markedly at the late gastrula st age and reached a plateau at 15 hr postfertilization; (2) the electrophoret ic pattern of ALP isozymes changed dramatically during development; (3) ALP activity was initially localized in the posterior wall of the primitive gu t and the anterior 5 to 6 somites at about the 15 hr larva stage, and then in the notochord and all the somites at about the 18 hr larva stage; (4) in I-day larvae, ALP activity decreased in the posterior wall of the primitiv e gut and in the anterior 5 to 6 somites which had ALP activity at 15 hr, b ut it appeared in the newly formed somites, especially in the myosepta, the crevices cut in between adjoining somites; (5) in 2-day larvae, ALP activi ty was no longer visible in somites but became highly evident in most of th e notochord except for its rostral region; and (6) when the lateral plate m esoderm pushed down ventrally on either side of the intestine and conjoined beneath the intestine, ALP activity was also detected in the conjoining la teral plate mesoderm. Apparently, two types of ALP exist in amphioxus larva e, the transient endodermal ALP and the constant mesodermal ALP, and the sp atial and temporal correlation of ALP activity with the developing mesoderm , including the notochord, suggests that it plays a role in the differentia tion of mesodermal structures during the development of amphioxus.