DEVELOPMENT OF TAIL MUSCLE ACETYLCHOLINESTERASE IN ASCIDIAN EMBRYOS LACKING MITOCHONDRIAL LOCALIZATION AND SEGREGATION

Abstract

The ascidian Molgula arenata produces a larva in which development of the tail has been suppressed. The embryo nevertheless developed part of the histospecific tail muscle acetylcholinesterase; the presumptive myoblasts have obviously acquired the muscle differentiation program. When cleavage-stage embryos were prevented from undergoing further division by treatment with cytochalasin B, acetylcholinesterase eventually developed in blastomeres of the muscle lineage. These embryos apparently segregate a cytoplasmic determinant concerned with acetylcholinesterase development into cells of the muscle lineage. In this species there was no localization and segregation of mitochondrial succinic dehydrogenase and cytochrome oxidase in the muscle lineage, as found in embryos of 2 ascidians, Ciona intestinalis and M. occidentalis. Neither is the causal determinant of histospecific acetylcholinesterase expression a differential localization of mitochondria, nor is segregation of the muscle determinants linked directly to mitochondrial segregation.