Cellular Aspects of Oocyte Growth in Teleosts

Abstract

In teleosts, the transformation of oogonia into oocytes apparently occurs within the germinal regions of the luminal epithelium of the ovary. As observed to particular advantage in syngnathans, prefollicle cells surround each oocyte, which is arrested in meiotic prophase, and the entire oocyte-follicle cell complex buds off the germinal nest as a primordial follicle. Oocyte growth within the follicle is due, to some extent, to the accumulation of normal cytoplasmic components; however, the preponderant mechanisms that contribute to oocyte growth are the endogenous synthesis of cortical alveoli, the accumulation of hepatically derived yolk protein (vitellogenesis) and in some (particularly marine) teleosts, a pronounced water uptake, which occurs concomitant with the resumption of meiosis (oocyte maturation). Our current understanding of these events is discussed and a new perspective on oocyte staging is presented, which is based on data indicating that the cellular events of oocyte growth do not sequentially replace one another, but rather are initiated sequentially and remain active throughout oocyte development.