In vitro development of core cells of the inner cell mass of the mouse blastocyst: effects of conditioned medium.

Blastocysts submitted to two rounds of immunosurgery give rise to cores of presumptive ectoderm cells, many of which do not survive for more than 48 hours when cultured individually. Precoating of the culture plates with conditioned medium (CM) from PYS-2 cells increases the incidence with which cores regenerate an outer layer. This procedure also improves the survival frequency of the cores, but only for a limited period of time. The small number of cores which survive for two weeks or more, either in uncoated or CM-coated plates, give rise to any array of cell types, including giant cells resembling trophoblast.