The structure of the mitochondrial cloud of Xenopus laevis oocytes

The ultrastructure of the mitochondrial cloud (Balbiani body) of the pre-vitellogenic oocytes of Xenopus laevis has been examined using transmission and stereoscan electron microscopy. Examination of conventional thin sections confirm previous observations which suggest that the cloud consists essentially of many thousands mitochondria and numerous small vesicles; larger clouds, in oocytes greater than 200 mum in diameter, contain relatively more vesicles. Using a standard electron microscope at 100 kV very long and coursing arrays of mitochondrial profiles can be detected. The presence of very long mitochondrial elements has been confirmed using a high voltage microscope operating at 500-1000 kV. Stereoscan preparations, isolated from pre-vitellogenic oocytes, lend some support to the view that the mitochondrial cloud amy consist of a mass of long filamentous mitochondria and the possibility that there are large continuous regions of mitochondrial material cannot be ruled out.