The role of the plasma membrane and pericortical cytoplasm in early mammalian development

Abstract

In a clinical context, each stage of mammalian oogenesis is usually considered in terms of nuclear and cytoplasmic processes that convey meiotic, fertilization and developmental competence to a preovulatory and ovulated oocyte, respectively. While the progression of changes in chromsomal configurations define specific stages of the meiotic cell cycle, which in the human can be decades long, cytoplasmic changes that lead to fertilization and developmental competence for the ovulated oocyte tend to be poorly understood. Yet, fertilization and early developmental failures are often attributed to largely undefined or putative defects in cytoplasmic development during oogenesis in general, and preovulatory maturation in particular. Failures of sperm penetration in meiotically mature oocytes, or the inability of a penetrated oocyte to support the resumption of meiosis or the normal evolution of pronuclei, are usually viewed as consequences of a global rather than focal cytoplasmic defect(s). It is likely that most clinical embryologists consider the human ooplasm to be spatially unstructured with respect to physiological, biochemical and regulatory functions. Here, the notion that the mammalian oocyte may be functionally structured is discussed in the context of critical regulatory and physiological processes that current findings indicate may be differentially localized to the plasma membrane, subplasmalemmal and pericortical cytoplasm. Confirmation that spatial localization or compartmentalization of regulatory and developmental functions and activities exists in the in the mature human oocyte may have important clinical implications if a greater understanding of the fundamental cell biology of the human oocyte results in information that can identify new causes of infertility, or explain failures in treatments such as IVF.