Cell surface and cytoskeletal elements: Cavitation in the mouse preimplantation embryo

Abstract Cavitation is the process whereby the mouse preimplantation embryo develops a fluid-filled blastocoele. Prior to the appearance of the blastocoele fluid, when the embryo is a morula consisting of 16–32 closely apposed cells, cytoplasmic droplets and mitochondria become cortically localized to apposed cell surfaces. This study focused on the restriction of cortical localization of droplets to apposed cell surfaces. Morulae were preincubated 30 min in colcemid, cytochalasin B, or in calcium-free medium and then immunolabeled for “mouse species” cell surface antigens. Indirect immunofluorescence indicated that the apparent density of antigens differed greatly between free and apposed cell surfaces. All three types of preincubations inhibited cavitation and the cortical localization of droplets and mitochondria while none of them affected antigen distribution, as detected by indirect immunofluorescence. Control experiments showed that the apparent difference in antigen density between free and apposed cell surfaces was not due to antigen capping or to inaccessibility of apposed cell surfaces to antibodies. These results are discussed in terms of cell surface-cytoskeletal interactions in the restriction of cortical localization of droplets and mitochondria to apposed cell surfaces as it relates to cavitation.