Early development in the mouse: would it be affected by microgravity?

Gravity has been identified as a morphogenetic signal in Amphibian and bird embryonic development so it is plausible that it might be such in mammals as well. Since early mammalian development shows some apparently significant differences to these other groups, a brief summary of mouse embryogenesis will be given identifying events in which polarity is an important feature and consequently, in which gravity may be a causative factor. These include compaction and polarization during cleavage, establishment of the radial axis, the embryonic-abembryonic axis, the dorso-ventral axis, and the anterior-posterior axis, implantation, and the later rotation of the embryo. The experimental data on these morphogenetic steps will be discussed and an assessment of the possible involvement of gravity will be made.