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Characteristic distribution density of organelles in the cytoplasm of respective kinds of cell lineages of ascidian embryos.

Authors
Type
Published Article
Journal
The Bulletin of Tokyo Medical and Dental University
Publication Date
Volume
33
Issue
2
Pages
49–69
Identifiers
PMID: 3471362
Source
Medline
License
Unknown

Abstract

In the early embryos of the ascidian (Halocynthia roretzi), regional cytoplasmic differences arise just after fertilization. We successively studied the characteristic features of the cytoplasm of those regions in the embryonic cells during the entire ontogenic process from the unfertilized egg to the tadpole larva. The embryos and larvae were fixed in a mixture of osmium and glutaraldehyde, and the distribution of the organelles in the entire cytoplasm was observed with light and electron microscopy. According to the analysis of the distribution density of the organelles which occupied a given area of the cytoplasm on the section, we introduced the "organelle region" in the cytoplasm and further calculated the approximate area ratios of the "organelle regions" in the cytoplasm of each cell lineage. As a result, it was demonstrated that the characteristic distribution mode was already present in the cytoplasm of the cell lineages of the 8-cell-stage embryos. The features of the cytoplasm in each embryonic cell lineage, moreover, reflected those of the corresponding larval tissue. Our results not only demonstrate that the structural tissue specificity is expressed at an extremely early stage during the ascidian embryogenesis but also suggest that the corresponding functional differentiation among the cell lineages occurs early.

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