Abstract
Mouse embryos sequentially developed in vitro were classified by stages according to several established in vivo criteria. At least three heat-sensitive macromolecules from embryonic sera were found to be successively required for mouse embryos to continuously develop from stage 6 to stage 15 in vitro. Fetal calf serum (FCS) was found to be required for in vitro development only from stage 6 to stage 11, and human placental cord serum (HCS) was found essential from stage 11 to stage 15. The factors have been tentatively designated as embryo growth and differentiation factors (EGDF). FCS was separated by molecular sieving into at least two fractions: a large fraction (EGDF-1) and a smaller fraction (EGDF-2). EGDF-1 is required for embryos to develop from stage 7 to stage 8, EGDF-2 is required from stage 8 to stage 11. EGDF-3, the factor in human cord serum, was found to be indispensable for mouse embryonic development from stage 11 to stage 15. Since blastocysts (stage 6) were able to develop to stage 15 in the medium containing HCS as the sole source of macromolecules [Hsu, Y-C., et al. (1974). J. Embryol. Exp. Morphol. 31, 235–245], it is apparent that HCS also contains EGDF-1 and EGDF-2. Embryonic development was significantly retarded in decreasing concentrations of the three EGDFs.
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