CONTROL OF CHROMOSOME BEHAVIOR DURING PROGESTERONE INDUCED MATURATION OF AMPHIBIAN OOCYTES

Fully grown oocytes isolated from Rana pipiens ovaries undergo maturation when they are exposed to progesterone. The cytoplasm of these oocytes develops the activity to induce metaphase chromosome condensation in foreign nuclei exposed to it. This chromosome condensation activity (CCA) persists until eggs are fertilized and resume meiosis. However, the present study shows that CCA develops and persists in blastomeres arrested by injection with unfertilized egg cytoplasmic extracts. The stability of metaphase chromosomes induced by CCA in eggs is dependent on substances from germinal vesicles (GV). Chromosomes in enucleated oocytes i.e. oocytes from which GVs had been removed prior to progesterone treatment, disintegrate soon after condensed to the metaphase state, and the ability of the oocytes to sustain metaphase chromosomes can be restored by introduction of GV extracts. Autoradiographic studies reveal that GV proteins as well as cytoplasmic proteins synthesized during the course of maturation are preferentially bound to metaphase chromosomes. It is suggested that cytoplasmic proteins synthesized in maturing oocytes may be responsible for CCA, while proteins discharged from GVs may be required for protection of metaphase chromosomes from cytoplasmic attack on DNA. © 1979.