Fertilization triggers several events in oocytes, including resumption of the cell cycle and, in many organisms, exocytosis of cortical granules, the contents of which modify the extracellular covering of the zygote. Bembenek and co-workers now identify cortical granules in C. elegans for the first time and show that their exocytosis after fertilization is regulated by several cell-cycle components, most notably separase, which is required for chromosome segregation during anaphase (see ). The exocytosis of cortical granules in fertilized C. elegans oocytes, the researchers report, leads to the formation of an impermeable three-layered eggshell. Using RNAi knockdown, they show that separase is required for granule exocytosis and chromosome segregation. Then, using immunofluorescence and live-cell imaging, they show that, after fertilization, separase moves from filamentous structures into cortical granules. These, they report, are exocytosed during anaphase I. Together, these results lead the researchers to propose that separase helps to coordinate the cell cycle with the other events that occur during egg activation.
