Temperature-Independent Period Immediately After Fertilization in Sea Urchin Eggs

The experiments described here explore the regulation of the duration of cleavage cycles in sea urchin eggs. We measured the timing of early cleavages in individual fertilized eggs under various temperature conditions and applied methods of statistical analysis to the data obtained. At least for the first three cleavages, the temperature dependence of the cleavage intervals was nearly equal. In addition, we identified a temperature-independent period at the beginning of the first cleavage cycle. This period occurs immediately after fertilization and lasts for several minutes. Our results suggest that this interval of temperature independence is related to the process of egg activation.