6533b821fe1ef96bd127c053

RESEARCH PRODUCT

MITOCHONDRIOGENESIS IN MATURING SEA URCHIN OOCYTES: A COMPUTERIZED RECONSTRUCTION ANALYSIS

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Abstract The dynamics of chondriome changes in oogenesis of the sea urchinParacentrotus lividuswere studied by electron microscopy. An oocyte-enriched fraction obtained by gonad mechanical dissociation without protease treatment was used. The shape, size and arrangement of mitochondria (Mt) in cells were quantitatively analysed on the basis of data from reconstruction experiments, with serial sections performed using a specific computer program. At all stages of oogenesis, the chondriome was shown to consist of rod-shaped Mt of various lengths and also of small amounts of globular Mt about 0.3 μm in diameter. Chondriome transformation during oogenesis is shown to involve the following processes: (1) a 64-fold increase in number of Mt, with the ratio of cytoplasm to Mt volume quite constant in the course of oogenesis; (2) an increase in length of Mt to a maximum of 1.54 μm in medium oocytes and successive considerable mitochondrial division; (3) changes in Mt ultrastructure; and (4) a clustering of Mt. In a mature egg, the modal value of Mt length was reduced and, unlike the oocytes, was more homogeneous, and the Mt were completely clustered.