Question

Is a cytoplasmic caclium ion influx sufficient to induce cell division in an unfertilizeg egg in sea urchins?

Answer 1

Sea urchin are a well established model system for studying fertilization and early development. When sperm come into contact with egg cytoplasmic calcium intiate exocytosis of cortical granules, causing the fertilization envelop to elevate around the egg. Cytoplamic calcium influx in unfertilized egg render ER membrane permeable to calcium ion via activation of phospholipase C. This signal transduction mechanism help in opening of calcium channel in Er membrane. Unfertilized sea urchin eggs are metabolically quiescent and arrested in interphase of the cell division cycle. Cell division cycle resume after fertilization. Yes, calcium influx help in induction of cell division in unfertlized egg when fertilization process already begun. Sea urchin egg also needed sperm centriole for the division otherwise development ceases before the first mitosis.