Mechanisms of cell number regulation in the peri-implantation mouse blastocyst

Abstract

Low viability of manipulated or in vitro cultured embryos is caused primarily by the reduced cell number in the implanting blastocysts. In order to investigate the effect of implantation delay on embryo viability and cell number, mouse blastocysts were transferred into oviducts of day 0 pseudopregnant females. This type of transfer improved embryo survival rates, indicating that embryos retarded by in vitro culture restored their viability during 3 days of delayed implantation. Our results showed that even in the cases when the initial cell count was as low as 28.2 0.7 cells per blastocyst (vs. 60.5 f 1.4 cells in the control blastocysts, developed in vivo), implantation delay increased this number to 107.2 2 3.5 cells (control blastocysts had at this stage on average 111.0 3.7 cells). Half-blastocysts, developed from the single blastomeres of the 2-cell embryos or from experimentally produced tetraploids, had around 50 cells after 3 days of implantation delay. This indicates that the start of blastocyst dormancy is triggered during the eighth cell cycle and independent of the absolute cell number or the number of cytokineses. Implantation-delayed blastocysts, developed from the half-embryos with the doubled volume of cytoplasm, had on average 70.5 * 2.4 cells, suggesting that embryo fall into quiescence is also dependent upon the attainment of a definite nucleo-cytoplasmic ratio. We conclude that blastocyst readiness for implantation is determined by two factors: number of cell cycles and nucleo-cytoplasmic ratio.

Effect of Stem Cell Activation, Culture Media of Manipulated Embryos, and Site of Embryo Transfer in the Production of F0 Embryonic Stem Cell Mice1

“…Moreover, asynchronously transferred blastocysts into oviduct of a 0.5-dpc female, or synchronously transferred into the uterus of a 2.5-dpc female, resulted in differences in weight of fetuses recovered 13 days after the embryo transfer, indicating that blastocysts transferred into the oviduct implant later than embryos transferred into the uterus. In agreement with previous work [28], we have found that the implantation delay increases blastocyst cell number and allows them to develop beyond the hatching blastocyst stage. However, these embryos went into diapause in the hatched blastocyst stage.…”

Improved Development of ICR Mouse 2-Cell Embryos by the Addition of Amino Acids to a Serum-, Phosphate- and Glucose-Free Medium.

“…Furthermore, the ICM cell to TE cell ratio was somewhat lower than that obtained from other studies using different mouse strains [6,7]. This may be due to the strain specificity or the loss of some ICM cells during the labeling of the blastocyst.…”

“…In addition, we employed a continuous culture system for establishing a high embryo per volume ratio, but the accumulation of embryotoxic substances in culture system may be possible. For example, accumulating ammonia of a final product of amino acid metabolism may be responsible for lowing the ratio of ICM cells to trophectodermal cells [6,12]. An alternative strategy such as the employment of a sequential culture system and the use of culture medium containing the detoxicants for embryotoxin may further promote the growth of blastocysts.…”

Characterization and potential function of a novel pre‐implantation embryo‐specific RING finger protein: TRIML1

“…So the decreased cell number of blastocyst may result from the retarded cell division in the stage. The fewer number of cells means delayed and poor development (Evsikov et al, 1996;Goossens et al, 2006). It is well known that a critical threshold number of cells in blastocysts is required for normal postimplantation development.…”