Ratio of inner cell mass and trophoblastic cells in blastocysts derived from porcine 4- and 8-cell embryos and isolated blastomeres cultured in vitro in the presence or absence of protein and human leukemia inhibitory factor

In this study we investigated effects of developmental stage at onset of individual in vitro culture on the progress of development in intact embryos and individual blastomeres derived from 4-cell and 8-cell porcine embryos (referred to as 1/4 and 1/8, respectively), the necessity of serum or BSA supplementation in culture media for embryos and blastomeres (in contrast to development in a defined medium), and the role of two concentrations of human leukemia inhibitory factor (hLIF) on development of blastomeres and embryos. More (p < 0.05) 1/4 blastomeres developed to the blastocyst stage than did 1/8 blastomeres. In the serum-supplemented medium, the percentage of inner cell mass (ICM)/total cells in 8-cell- and 1/8-derived blastocysts was higher (p < 0.05) than that in 4-cell- and 1/4-derived embryos. Development to blastocysts was similar in BSA-supplemented and defined medium as compared ttl that in serum-enriched medium in intact 4-cell and 8-cell embryos, and 1/4 blastomeres. More (p < 0.05) 1/8 blastomeres developed to the blastocyst stage in serum-supplemented medium than in defined medium. The high hLIF concentration (1000 IU/ml) decreased (p < 0.05) blastocyst development in 1/4 blastomeres in defined medium, but fewer blastocysts (p > 0.05) lacked an ICM (blastocyst-like vesicles) than in defined medium without hLIF. It is concluded that 1) porcine intact embryos and isolated blastomeres can be cultured individually in defined medium up to the blastocyst stage from the 4-cell stage onwards; 2) more 1/4 isolated blastomeres develop to blastocysts with more total cells but with a lower ratio of ICM to total cells than blastocysts derived from 1/8 blastomeres; 3) the effects of hLIF are dependent an proteins present in the culture medium and on the embryonic stage; and 4) in defined medium, high concentrations of hLIF are inhibitory to blastocyst formation, but fewer blastocyst-like vesicles are formed. The defined culture system employed in this study allows examination of the effects of growth factors or cytokines in porcine early embryonic development.