Surface characteristics of oocytes from juvenile mice as observed in the scanning electron microscope

The in vivo and in vitro development of the zona pellucida as well as the vitelline membrane surface of oocytes isolated from juvenile mice aged between 8 and 30 days p.p. were investigated by scanning electron microscopy. In vivo a consistent development of the zona pellucida surface can be observed, namely the formation of a fibrous network like structure interspersed with numerous pores. After enzymatic removal of the zona pellucida the surface of the vitelline membrane was studied. In "normal" oocytes with intact germinal vesicles, microvilli were distributed over the entire oocyte surface in all age groups investigated. After resumption of meiosis in vitro a characteristic differentiation on the vitelline membrane occurs. A glabrous polar region appears in primary oocytes and a glabrous polar body in secondary oocytes. The same differentiation in surface organization could be observed in the in vivo precociously matured oocytes.