MOUSE HALF EMBRYOS - VIABILITY AND ALLOCATION OF CELLS IN THE BLASTOCYST

We have investigated the developmental capacity of mouse embryos in wh ich one blastomere was destroyed by lysis at the 2-cell stage. The all ocation of cells to the trophectoderm and inner cell mass (ICM) was do cumented by differential cell counts on single embryos after 2 days un der different culture conditions. Viability and further developmental potential were tested by embryo transfer to foster mothers. The condit ions used were: (1) in vitro culture in modified BMOC-2 medium, (2) in vivo oviduct transfer to immature (prepuberal) females, and (3) in vi vo oviduct transfer to pseudopregnant females. Half embryos almost alw ays fared less well for all parameters of development than control emb ryos developing under the same conditions. Lower total cell numbers in half embryos were accounted for by decreases in both ICM and trophect oderm with a disproportionate decrease in ICM in smaller embryos. In b oth half and control embryos, the growth conditions affected the rate of morphological development, the total cell number, and embryo viabil ity. Unlike the effect of halving embryos, the growth condition effect s on total cell number can be accounted for primarily by differences i n ICM cell number, with trophectoderm cell number remaining constant. These results provide new information on the ability of the mouse embr yo to differentially regulate ICM and trophectoderm cell number under different conditions, and confirm our previous work showing the advant age of short-term development in vivo over short-term in vitro culture (Papaioannou and Ebert [1986] J. Reprod. Fertil. 76:605-608). They al so clearly document that lower total cell number and a lower proportio n of ICM is correlated with compromised development. (C) 1995 Wiley-Li ss, Inc.