Nonhuman Primate Oocyte Biology: Environmental Influences on Development

Proper oocyte maturation involves the remodeling of the nucleus from a diploid germinal vesicle (GV) configuration to the mature haploid metaphase II (MII) stage. At the same time the egg must already possess or create and store sufficient cytoplasmic constituents to carry the zygote through early embryonic development following activation by sperm. The functional distinction between nuclear (morphological) and cytoplasmic (developmental) oocyte maturation has been clearly revealed by application of in vitro fertilization (IVF) to in vitro-matured (IVM) oocytes. In spite of apparently normal nuclear maturation—that is, attainment of MII and extrusion of the first polar body (PB1)—IVM oocytes may have developmental defects (1–4). Some of these deficiencies include defects in blocks to polyspermy, inability to decondense sperm nuclei, underdevelopment of metaphase spindles, and inability of zygotes to progress beyond early cleavage stages.