Studies on the Cytoplasmic Determinant for Muscle Cell Differentiation in Ascidian Embryos: An Attempt at Transplantation of the Myoplasm

Abstract

The 8-cell stage embryos of the ascidian Halocynthia roretzi which had been prevented from undergoing further divisions by continuous treatment with cytochalasin B could develop histospecific muscle acetylcholinesterase in two blastomeres (B4.1 and B4.1 cells). If the cytoplasm of a B4.1 or B4.1 cell was transplanted by microinjection into either an A4.1 or A4.1 cell of recipient embryos and the transplanted embryos were permanently cleavage-arrested with cytochalasin B, a few eventually developed AChE in three blastomeres instead of in just the two blastomeres found in cleavage-arrested control embryos. Judging from the relative positions of the blastomeres, the third AChE-producing cells appeared to be the A4.1 or A4.1 cells injected with the cytoplasm of B4.1 or B4.1. Although the success rate was considerably low, this result might indicate the presence in the cytoplasm of a determinant for the muscle-specific enzyme development.