Oocyte Maturation

This chapter discusses oocyte maturation. The outstanding phenomenon associated with sexual reproduction in animals is that every cell of an individual derives from a single germ cell. Accordingly, it is thought that germ cells, in contrast to somatic cells, retain developmental totipotentiality throughout the life of the individual. Germ cells become as highly differentiated as somatic cells during ontogenesis. In female germ cells, this specialization begins during the very early stages of life. The cells enter meiosis at the fetal or larval stage. Before they begin to grow, meiosis proceeds to the terminal stage of the first meiotic prophase, the diplotene stage. Growing primary oocytes have an enormously enlarged nucleus called the “germinal vesicle (GV).” Characteristically, it contains lampbrush chromosomes which have been actively engaged in RNA synthesis. Toward the end of the growth period the loops of the lampbrush chromosomes regress after which the oocytes enter a stationary state that persists until ovulation.