CONTROL OF CHROMOSOME CONDENSATION IN THE SEA-URCHIN EGG

Ammonia-activated sea urchin eggs are capable of inducing premature chromosome condensation (PCC) in fertilizing sperm nuclei introduced during the period of maternal pronuclear chromosome condensation. Activated nucleated and enucleated egg halves (merogons) are also capable of inducing PCC during this period. However, the lifetime of the PCC-inducing activity in the enucleated merogons is 5-10 times shorter than in corresponding nucleated merogons, whether they are prepared by density gradient centrifugation or manual bisection. Transcription of maternal nuclear or cytoplasmic genomes or of the sperm nuclear genomes is not required for the induction of PCC. PCC induction becomes independent of protein synthesis in late S or early G2 of the activated egg cycle. These results suggest that the only genetic contribution required to initiate the first chromosome condensation is the translation of stored maternal mRNA prior to G2. However, some maternal pronuclear component, possibly the chromosomes themselves, is responsible for stabilizing the chromosome condensing environment. © 1979.