Development of Cleaving Mouse Embryos under Pressure

A chamber for applying mechanical pressure to developing mouse eggs is described.
Morphologically normal blastocysts developed from 4-cell eggs cultured under pressure initially near to the point of cell rupture. Four-cell, 8-cell eggs and late morulae, developing with the pressure regularly adjusted to this point, formed trophoblast-like cells internally and peripherally to the cell mass. These observations are consistent with the idea that cells will become trophoblast unless subjected to a specific intercellular environment. A glass plate closely apposed to the cells cannot substitute for this environment. Total enclosure by other cells seems necessary for inner cell mass differentiation.