title: Ultrastructural features of the cytoplasm of respective kinds of cell lineages of cleavage-arrested ascidian embryo.
abstract: We observed the ultrastructural features of the cytoplasm in the cell lineages of the cleavage-arrested embryos of the ascidian, Halocynthia roretzi, and compared them with those of the cytoplasm in the corresponding cell lineages of the normal embryos or in the corresponding tissues of the normal larva, in order to examine the presence or the degree of the cellular differentiation without the cleavage. The cleavage of the embryos was arrested by the cytochalasin B at the 16-cell and the embryos were cultured in sea water containing cytochalasin B until the developmental time equivalent to the hatching of the control larva. As a result, the cytoplasmic components in the cleavage-arrested 16-cell embryos resembled those observed in the corresponding tissues of the normal larvae, especially in the b5.3 and b5.4 blastomers (epidermal lineage cells) and in the B5.1 blastomeres (which give rise to the endodermal, mesenchymal and muscle cells) but they were less uniformly organized and their polarity or orientation was very random and irregular, compared with those in the normal larvae. These results demonstrated that the morphological differentiation similar to the larval tissue differentiation could proceed even in the cleavage-arrested embryos to a certain extent.
authors.forename: Y
authors.initials: Y
authors.lastname: Nishimura
authors.forename: K
authors.initials: K
authors.lastname: Wake
mesh_terms: D000110:Acetylcholinesterase / Q000032:analysis; D000818:Animals; D001757:Blastomeres / Q000648:ultrastructure; D003593:Cytoplasm / Q000648:ultrastructure*; D005314:Embryonic and Fetal Development; D004707:Endoderm / Q000648:ultrastructure; D004817:Epidermis / Q000196:embryology; D006651:Histocytochemistry; D007814:Larva / Q000648:ultrastructure; D009132:Muscles / Q000196:embryology; D009420:Nervous System / Q000196:embryology; D009940:Organoids / Q000648:ultrastructure; D014561:Urochordata / Q000196:embryology*
chemical_list: D000110:Acetylcholinesterase