Observations on the mitochondrial distribution in normal, rotated and cold-treated 2-cell stage embryos of Xenopus...

The distribution of mitochondrial profiles at the level of the frontal plane dividing dorsal and ventral halves of the Xenopus 2-cell stage embryo was studied. It was found that the mitochondria are distributed asymmetrically in the two embryo sides which appear non-equivalent in terms of mitochondrial density. Egg rotation experiments indicated that the observed asymmetry is coupled with sidedness and essential to it. Cold shock of the eggs resulted in a disturbed mitochondrial distribution, suggesting involvement of cytoskeletal elements. In cold-treated eggs, the most impressive changes were in the animal and vegetal areas where a 3-4-fold inversion of mitochondrial density was found. The results are discussed taking into consideration the involvement of cytoskeleton in cytoplasmic rearrangements in various cell types and the effect that cleavage has on the segregation of cytoplasmic contents in the embryos of many species.