Subcellular structure of prenatal human ovary: mitochondrial distribution during meiotic prophase.

The dynamics of mitochondrial population during the first meiotic prophase in the fetal human ovary was studied in sequential stages of development, from week 13 to week 23 of intrauterine life; the study was performed by means of electron microscopy. Two mitochondrial translocations were observed: first, from a random cytoplasmic distribution during leptotene, the mitochondria translocate toward a perinuclear location during zygotene. Second, from this perinuclear position they migrate toward a pole of the cell where they contribute during diplotene to form the Balbiani's vitelline body. Coincident with these mitochondrial redistributions, changes in mitochondrial cristae morphology were observed. From a tubular profile during early leptotene, they turn parallel with a more electron dense matrix during zygotene and pachytene, and finally arciform in diplotene. Since meiosis is a process that probably requires high levels of energy, these dynamic changes in mitochondrial population and the close association between mitochondria and nuclear membrane may be related with energy producing reaction that may be necessary for insuring the completion of the first meiotic prophase.