Ultrastructure of oogenesis in the brushtail possum

Marsupial ova are slightly larger on average than those of eutherians. They have often been described as "yolky", although the nature and roles of the ir contents in later development are poorly understood. In the ova of all m arsupial species studied, large quantities of electron-lucent Vesicles are present. This study describes the ultrastructure of oogenesis in the brusht ail possum, Trichosurus vulpecula. Oocytes of primordial follicles contain a variety of organelles of unknown function, some of which have been descri bed previously in bandicoots. Large electron-lucent Vesicles begin to accum ulate after the transition from primordial follicle to primary follicle and are derived at least partly from the Golgi and endoplasmic reticulum. Othe r inclusions that are absent in some other marsupial species are present in growing possum oocytes in smaller quantities, including yolklike lipid bod ies and electron-dense granular bodies. (C) 2001 Wiley-Liss, Inc.