Development of egg fragments of the ascidian Ciona savignyi: the cytoplasmic factors responsible for muscle differentiation are separated into a specific fragment.
The eggs of ascidians contain cytoplasmic determinants responsible for differentiation of larval muscle cells. However, the molecular nature and mode of action of muscle determinants are unknown at present. To establish an appropriate experimental system for studying muscle determinants, we have devised a method for separating the determinants into specific egg fragments. The treatment of unfertilized eggs of Ciona savignyi with cytochalasin B followed by centrifugation yielded (1) a large, nucleated red fragment, (2) a small, enucleated black fragment, (3) a small, enucleated clear fragment, and (4) a small, enucleated brown fragment. When inseminated, only red fragments cleaved and developed into so-called "permanent blastulae," in which the differentiation of epidermal cells was evident. However, when red fragments were fused with black fragments and the fusion products were inseminated, the fusion products showed a remarkable ability to express muscle-specific markers. In addition, the ability of black fragments to promote the expression of muscle-specific markers was evident when the fragments were fused with presumptive-epidermis blastomeres. In contrast, clear and brown fragments showed limited ability to promote muscle differentiation. These results suggest that the muscle determinants are present in unfertilized eggs and that the determinants are concentrated into black fragments and depleted from red fragments. These two fragments may serve as an appropriate experimental system to determine the molecular nature of muscle determinants in ascidian eggs.
Marikawa
Y
Y
Department of Zoology, Faculty of Science, Kyoto University, Japan.
Yoshida
S
S
Satoh
N
N
D000818:Animals; D001685:Biological Factors / Q000502:physiology; D001757:Blastomeres; D002454:Cell Differentiation / Q000502:physiology; D002458:Cell Fractionation; D003593:Cytoplasm / Q000502:physiology*; D009132:Muscles / Q000196:embryology*; D010063:Ovum / Q000166:cytology*; D014561:Urochordata
D001685:Biological Factors