Developmental capacity of mechanically bisected mouse morulae and blastocysts

Abstract

Mouse embryos were mechanically bisected at the morula, early blastocyst or expanded blastocyst stages of development and cultured in vitro to the expanded blastocyst stage. Their capacity for postimplantation development was assessed after transfer to pseudopregnant foster mice. Embryos bisected at blastocyst stages had a higher survival rate in vitro than those bisected at the morula stage. Half-embryos had approximately half the number of cells at the blastocyst stage as control embryos, but the proportion of cells in the inner cell mass (ICM) was unaltered. The implantation rate of blastocysts derived from bisected embryos was only slightly lower than that of control embryos, but bisected embryos had a significantly reduced capacity to form fetuses. Histological analyses showed that failure to form a fetus is due to the absence of egg cylinder development, which correlates with the reduced number of cells in the ICM of bisected embryos. Postimplantation viability of half-embryos was significantly higher when blastocysts were transferred to Day-3 rather than Day-4 pseudopregnant recipients, presumably because of an increase in cell number in vivo prior to implantation.

Production of mouse by inter-strain inner cell mass replacement

“…Reduction in ICM and trophoblast cells may affect implantation and development (Chan et al, 2000;Modlinski et al, 2002). Failure to form a fetus may be due to the absence of egg cylinder development, which is correlated with the reduced number of the ICM cells (Wang et al, 1990). Failure to form a fetus may be due to the absence of egg cylinder development, which is correlated with the reduced number of the ICM cells (Wang et al, 1990).…”

Multiplying embryos: experimental monozygotic polyembryony in mammals and its uses

“…This was ascribed to the diminution of cell numbers in the ICM due to the bisection procedure. Consequently, the embryos failed in the egg-cylinder formation (Wang et al, 1990).…”

“…In sheep, it was also shown to be beneficial to twin embryo development if the embryos were transferred to recipients that had more than one ovulation during the estrus of transfer (Szell and Hudson, 1991). Monozygotic twin blastocysts generated by bisection of mouse embryos in the blastocyst stage revealed that it is not only important to have synchrony in estruses, but also to provide extra time for the embryo to propagate its cells in an in vivo environment before implanting to the uterus (Wang et al, 1990).…”

Factors controlling embryo viability

“…Finally, assuming the trophectoderm is sufficient, adequate function of the inner cell mass is also essential to provide the body of the embryo. A critical mass of functional cells will be required to form a viable fetus (mice: Wang et al, 1990); failure to form the critical mass of cells may result in early pregnancy loss or an anembryonic pregnancy. The development of a blood circulation within the fetus relies upon mesoderm formation and this is key for survival of the early post-implantation mouse embryo (Copp, 1995).…”