Clock gene Bmal1 in mice embryo is dispensable for early embryo development but critical for live birth

In adult animals, the significance of circadian clocks in the regulation of physiology is well established. However, the physiological roles of embryonic clock genes on early embryo development, implantation and perinatal survival are still unclear. In the present study, using genotyping, embryo culture and transfer, the early embryo development, implantation, and perinatal survival of Bmal1+/+, Bmal1+/- and Bmal1-/- embryo were studied. At cleavage stage, the genotype ratio of Bmal1+/+, Bmal1+/- and Bmal1-/- embryo was 1:1.97:0.95, respectively (p > 0.05). Morula or early blastocyst developmental ratio was 83.8 +/- 14.3, 87.1 +/- 9.2 and 88.7 +/- 1 4.5%, respectively (p > 0.05). After transferring of the three types of embryos to pseudopregnant wild-type mice, the implantation sites 4days later was 7.7 +/- 0.9, 7.2 +/- 1.2 and 7.5 +/- 0.5 (n=4, F = 0.265, p = 0.773). Mean litter size of the mice after transferring with the three types of embryos was 5.5, 6.0, and 3.0 (n = 3, F = 30.3, p = 0.001). The development of Bmal1 null embryos was not impaired in preimplantation and early implantation stages, but the litter size had a trend to decrease.