Compensatory endocytosis occurs after cortical granule exocytosis in mouse eggs

Abstract

Compensatory endocytosis (CE) is one of the primary mechanisms through whichcells maintain their surface area after exocytosis. Considering that in eggs massiveexocytosis of cortical granules (CG) takes place after fertilization, the aim of this was to evaluate the occurrence of CE following cortical exocytosis in mouseeggs. For this purpose, we developed a pulse‐chase assay to detect CG membraneinternalization. Results showed internalized labeling in SrCl2‐activated and fertilized eggs when chasing at 37°C, but not at a nonpermissive temperature (4°C). The use of kinase and calcineurin inhibitors led us to conclude that this internal labeling corresponded to CE. Further experiments showed that CE in mouse eggs isdependent on actin dynamics and dynamin activity, and could be associated with atransient exposure of phosphatidylserine. Finally, CE was impaired in A23187ionophore‐activated eggs, highlighting once again the mechanistic differencesbetween the activation methods. Altogether, these results demonstrate for the firsttime that egg activation triggers CE in mouse eggs after exocytosis of CG, probably as a plasma membrane homeostasis mechanism.