Histological studies on the onset of meiosis and changes in mitochondria in germ cells in fetal and infant rabbit ovaries
1990
Sasabe, M. (Hiroshima Univ., Fukuyama (Japan). Faculty of Applied Biological Science) | Maeda, T. | Terada, T. | Tsutsumi, Y.
To estimate changes in cell activities of germ cells around the onset of meiosis, numbers of mitochondria in ovarian germ cells of rabbit fetuses and week-old does were counted histologically with Altmann-Kull stain and the ultrastructure of those mitochondria was observed. The mean number of mitochondria per germ cell in each stage of mitotic and/or meiotic stages was not dependent on stage of development. The distribution of germ cells by the number of mitochondria was roughly uniform in each stage of oogonia and oocytes. The mean number of mitochondria per oogonium in mitotic and resting stage and per oocyte indicated approximately 40, 32, and 23, respectively. With the transmitting electron microscope, the mitochondria in the oogonia in high mitotic activity were ultrastructually pleomorphic, suggesting cylindrical shape of the mitochondria. Such mitochondria usually contained many cristae traversing partially or completely the organella. On the other hand, most mitochondria in the germ cells transforming into oocytes showed a small circular shape, suggesting spherical mitochondria. Such mitochondria never contained many cristae, and the cristae traversed more incompletely through the matrix in comparison with those of mitochondria of the oogonia with high mitotic activities. In general, the number of mitochondria in germ cells decreases and their function is declining during the progress of cell division, from oogonia in mitotic stage via resting stage to meiotic prophase I. It is suggested that the decline of activities of division and of the function of the oocytes may be caused by the changes in the mitochondria
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