EFFECTS OF BREFELDIN-A AND MONENSIN ON ORGANELLE DISTRIBUTION AND MORPHOLOGY IN THE PREIMPLANTATION MOUSE EMBRYO

The intracellular trafficking of integral membrane and secreted protei ns is likely to be a key element involved in the morphogenesis and dif ferentiation of the early mammalian embryo. In this study, we used tra nsmission electron microscopy (TEM) to analyse the effects of brefeldi n-A (BFA) and monensin, well known inhibitors of vesicular protein tra fficking in somatic cells, on the structure of preimplantation mouse e mbryos. Both BFA and monensin distinctively altered the morphology of Golgi compartments in the blastomeres of treated morulae. BFA-treated morulae lacked recognizable Golgi complexes but possessed heterogeneou s organelle clusters consisting of an abundance of smooth tubular and vesicular membrane compartments in addition to mitochondria, endosomes and lysosomes. Treatment of morulae with monensin was associated with swelling of Golgi compartments in addition to altering the morphology of mitochondria, lysosomes and the plasma membrane. BFA, and to a les ser extent monensin, inhibited cytokinesis as evidenced by the detecti on of binucleate blastomeres. In addition, BFA induced morulae to deco mpact. These latter effects have not been reported previously for thes e agents in mammalian somatic cell lines or other vertebrate or invert ebrate embryos. These results provide the first demonstration of the s tructural effects of BFA and monensin on cells of the early mammalian embryo, some of which are consistent with the known actions of these a gents on components of the vesicular protein trafficking system in mam malian somatic cells. This information serves as a foundation for the further use of these agents in studies of vesicular protein traffickin g as an agent of preimplantation morphogenesis.