Marking Time and Making Space: Chronology and Topography in the Early Mouse Embryo

Abstract

Publisher Summary This chapter discusses the way in which the preimplantation mouse embryo solves the problem of integrating space and time. The preimplantation stage spans 4.5 days of apparently autonomous existence such as development can proceed in vitro in simple defined media. At the end of this period the embryo develops into a blastocyst consisting of a fluid-filled cyst of trophectodermal epithelium that invades the uterine epithelium and contributes to the placenta, and an inner cell mass (ICM) that contributes to the embryo proper. The embryo has only a limited time in which to reach this stage and, if pregnancy is to continue, must coordinate its development with the short period during which the maternal uterus is sensitized for implantation. Mammalian embryos encounter an additional developmental dimension, in that space and time have to be integrated not only within the embryo itself but also in relation to the reproductive cycle of the mother. The detailed examination of the chronology and topography of early cleavage in the mouse embryo highlights the features of mouse development that contribute to the progressive acquisition of a stable developmental axis.