Biopolymers and cell. 1997; 13 (2): 161 - 167

Factors affecting readiness of mouse blastocysts for implantation

I. N. Vagyna, S. V. Evsikov, A. P. Solomko

Mechanisms of cell number regulation in mouse blastocysts have been investigated using embryo transfers into the oviducts of pseudopregnant Day 0 females. It was shown that the retarded after in vitro culture embryos are overtaking in their cell number the in vivo developed embryos during the period of implantation delay. Studies on cell numbers of blastocysts developed from one blastomere of 2-cell embryo, and experimentally produced tetraploids, demonsrate that blastocysts are entering the pre-implantation diapause during the 8-th cell cycle. This process does not depend upon absolute cell number or number of cell divisions. Blastocysts, which developed from the half-embryos with doubled cytoplasm content, had on average 70.5±2.4 cells. This observation proves that blastocyst entering to the diapause depend upon reaching of definite nucleo-cytoptasmic ratio. It seems that the readiness of blastocysts for implantation depends on two factors, number of cell cycles and nucleo-cytoplasmic ratio.