Development of acetylchilinesterase during embryogenesis of the ascidian Ciona intestinalis.

We have characterized the embryonic muscle cell cholinesterase of the solitary ascidian, Ciona intestinalis (L.). The effects of selective enzyme inhibitors and the inhibition of enzyme activity at high concentrations of substrate suggest that the muscle cell enzyme is an acetylcholinesterase (E.C. 3.1.1.7). After gastrulation and before hatching, acetylcholinesterase activity increased 35- to 40-fold; after hatching (18 hours postfertilization) this activity continued to increase, leveling off at about 36 hours of development. Histochemical observations showed that before hatching acetylcholinesterase was located principally in the muscle cells of the tail and, after hatching, it began to develop in cells of the adult musculature and brain. Inhibition of protein syntnesis by puromycin and of RNA synthesis by actinomycin D, suggest that both protein and RNA synthesis were required for the increase in acetylcholinesterase activity observed in unhatched embryos. Although the continued increase in enzyme activity duirng embryonic development was sensitive to puromycin at all times tested, the actinomycin D sensitivity of this increase was restricted to a discrete time that was completed by about 11 hours of development.