HOMOLOGY BETWEEN MITOCHONDRIOGENESIS IN THE AVIAN AND AMPHIBIAN OOCYTE

Cytochrome oxidase cytochemistry was used to unequivocally identify th e spread of mitochondria during oogenesis in the adult Japanese quail. This enabled us to compare their distribution with the distribution i n the Xenopus laevis oocyte (Tourte ef al. 1984). In the quail the par anuclear mitochondrial cloud initially disperses homogeneously but aft erwards segregates into 2 populations: (i) a population localized in t he basophilic cortical layer (surrounding the vegetal pole); and (ii) clusters of mitochondria distributed geometrically around the germinal vesicle in the animal pole. The mitochondria in these clusters have a high cytochrome oxidase activity, which reflects their functionality. This perinuclear crown of mitochondrial clusters actively replicates mtDNA in both animal species and builds up most of the stock of the mi tochondria in the full-grown oocyte. Our study suggests that the perin uclear group of mitochondria will segregate in the somatic cells of th e future embryo, whilst the original subcortical group will become loc alized in the primordial germ cells.