Abstract: Brain and muscle arnt-like 1 (Bmal1) as one of the core genes of the clock geneis mainly expressed in the female reproductive system. The circadian rhythm of Bmal1 expression is involved in estrous cycle, ovulation, implantation, and the maintenance of pregnancy. The changed expression of Bmal1 is related to spontaneous abortion, possibly by a variety of mechanisms. Down-regulation of Bmal1 expression can decrease the expressions of matrix metalloproteinase 2/9 through SP1-DNMT1/DAB2IP pathway, which followed by the inhibition of trophoblast migration and invasion. The deletion of Bmal1 gene interferes with the transcription and translation of steroid synthesis-related genes in ovarian granulosa cells, which affects the secretion of pregnancy-related hormones and promotes the apoptosis of granulosa cells through PI3K/Akt/mTOR signaling pathway. The decreased expression of Bmal1 gene can cause the increased reactive oxygen species in ovary and fallopian tube, which can reduce oocyte fertilization, early embryo development and implantation potential, and eventually lead to embryo loss. In this article, the influence of Bmal1 on early spontaneous abortion was reviewed.

Key words: Biological clocks, Circadian rhythm, Bmal1, Gene expression, Abortion, spontaneous, Embryonic development, Embryo implantation