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

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Abstract
The 8-cell stage embryos of the ascidian H. roretzi, which had been prevented from undergoing further divisions by continuous treatment with cytochalasin B, could develop histospecific muscle acetylcholinesterase [AChE] in 2 blastomeres (B4.1 and .**GRAPHIC**. cells). If the cytoplasm of a B4.1 or .**GRAPHIC**. cell was transplanted by microinjection into either an A4.1 or .**GRAPHIC**. cell of recipient embryos and the transplanted embryos were permanently cleavage-arrested with cytochalasin B, a few eventually developed AChE in 3 blastomeres instead of in just the 2 blastomeres found in cleavage-arrested control embryos. Judging from the relative positions of the blastomeres, the 3rd AChE-producing cells appeared to be the A41 or .**GRAPHIC**. cells injected with the cytoplasm of B4.1 or .**GRAPHIC**. Although the success rate was considerably low, this result might indicate the presence in the cytoplasm of a determinant for muscle-specific enzyme development.