Pattern of Segregation of Mitochondria into Muscle Lineage Cells during Embryogenesis of the Ascidian Halocynthia roretzi

Abstract

Unequal partition of preexisting egg cytoplasmic components is one of possible cues to produce various types of cell in development. Segregation during ascidian embryogenesis of mitochondria into muscle lineage cells is a well‐known example of cytoplasmic localization and segregation. In this study, using a monoclonal antibody specific to mitochondria, we re‐examined changes in the distribution of mitochondria during oogenesis and embryogenesis of the ascidian, Halocynthia roretzi . The quantification method of the relative amount of the mitochondria‐specific antigen revealed differences in the amount of mitochondria contained in four blastomere‐pairs of an 8‐cell embryo; the primary muscle lineage B4.1‐pair contained about 40% of the total amount of mitochondria, while the secondary lineage b4.2‐ and A4.1‐pairs contained about 23% and 20% respectively, and non‐muscle lineage a 4.2‐pair about 17%. In addition, it was shown that the total amount of mitochondria‐specific antigen in the embryo remained constant throughout H. roretzi embryonic development. These results suggest that preferential segregation of preexisting mitochondria causes the characteristic distribution pattern of mitochondria within the embryo.