A comparison of the fine structure of late mouse blastocysts developed <i>in vivo</i> and <i>in vitro</i>

Abstract

Abstract The utrastructure of the in vivo developed late preimplantation mouse blastocyst has been compared with the fine structure of mouse blastocysts developed in vitro for 72 and 92 hours from the late two‐cell stage, as well as those grown in vitro for 26 hours from the late morula or early blastocyst stage. Very little difference was observed between the in vivo developed blastocysts and those cultured 26 hours in vitro . The differences between 72 and 92 hour‐embryos and the in vivo grown ones were significant. The in vivo specimen and those grown 26 hours in vitro had differentiated a layer of endoderm cells while the ones cultured in vitro from the two‐cell stage did not. Nuclear and cytoplasmic structures in the in vivo developed blastocysts are well‐differentiated while those of the embryos grown in vitro from the two‐cell stage were less advanced. Possible reasons for the apparently less differentiated stage of blastocysts developed in vitro from the two‐cell stage are discussed.