Digital Image Analysis Studies of Folliculogenesis and Oogenesis in Mammals

Abstract

Successful embryonic development has long been recognized to begin with the orderly sequence of events that occur during the intraovarian differentiation of the oocyte—the process of oogenesis. Simplistically, oogenesis can be viewed as a series of differentiative events that bestow on the oocyte important developmental capabilities, such as a) the ability to resume and complete meiosis, b) the ability to establish a block to polyspermy, and c) the ability to metabolically sustain cleavage activity of the preim- plantation embryo. Each of these capabilities are acquired during the various stages of oogenesis and involve structural and biochemical modifications in specific organellar components of the oocyte. For example, the embryo utilizes maternally inherited mRNAs and the machinery for protein synthesis derived from periods of heightened transcriptional activity during the growth phase of oogenesis [1, 2]. Similarly, the ability to first resume meiosis at the time of ovulation and then complete the second reductive division at fertilization is referred to as the expression of meiotic competence. Not only must this capability involve modifications in cell-cycle signalling mechanisms during the course of oogeneis, but it must directly rely on the regulatibn of chromatin organization and cytoplasmic components involved in the formation and function of the meiotic spindle. The central question that emerges from this discussion is, how are these properties acquired during oogenesis? The interplay of somatic ovarian cells with the oocyte, particularly those cells comprising the ovarian follicle, underlies the acquisition of specific oocyte capabilities that are required for the expression of embryonic potential. Therefore, just as embryogenesis finds its origins in oogenesis, this chapter will focus on how oogenesis is functionally integrated with the process of folliculogenesis.