Extra-uterine development of mouse blastocysts cultured in vitro from early cleavage stages.

Many experiments indicate that oviducal mouse eggs are unable to form embryonic tissues following transplantation to extra-uterine sites; they give rise only to trophoblast and extra-embryonic membranes (Fawcett, Wislocki & Waldo, 1947; Fawcett, 1950; Chester-Jones, 1951; Whitten, 1958; Kirby, 1962; Billington, 1965). Possible rare exceptions exist in the reports by Runner (1947) and Stevens (1967). In contrast, about a quarter of uterine blastocysts form morphologically normal embryos when similarly transplanted (Kirby, 1963; Billington, 1965). The conditions under which the mouse eggs reach the blastocyst stage may also have developmental consequences. Eggs cultured in vitro to the blastocyst stage (Whitten, 1956) or tube-locked blastocysts (Kirby, 1962) did not develop embryonic tissue in extra-uterine sites, but were capable of complete development following transfer to a receptive uterus. These findings suggest that mouse eggs must be subjected to the uterine environment if they are to ' realize totipotency' in an extra-uterine site (Kirby., 1962, 1965). We have re-investigated this conclusion by culturing oviducal eggs in vitro to the blastocyst stage and then transferring them to the testis or kidney.