UC San Diego

Pre-implantation development depends on several processes, including the deposition of maternal factors into the oocyte during oogenesis, the expression of maternal mRNAs, and the degradation of maternal mRNA in tandem with zygotic genome activation during the maternal-to-zygotic transition (MZT). These processes ultimately determine whether an embryo implants into the uterine lining, which is necessary for pregnancy. It is known that mice with whole body knockouts of Bmal1 (hereafter referred to as Bmal1-/- mice) are infertile. Previous studies have indicated that this infertility deficit occurs in pre-implantation development. Furthermore, other studies found the presence of Bmal1 mRNAs in mouse pre-implantation development. With this, I hypothesized that the maternal expression of Bmal1 is necessary for pre-implantation development. To investigate this hypothesis, I performed immunostaining on embryos from the MZT, and whole ovary sections from wildtype (WT) mice to characterize the expression of BMAL1. I also quantified the number of metaphase II oocytes obtained from WT and Bmal1-/- mice, to look for deficits in pre-implantation development. I found a higher percentage of abnormal oocytes from Bmal1-/- mothers. Fluorescent imaging of these embryos reveals fluorescence of BMAL1 in the cytoplasm and nucleus of embryos throughout the MZT. Immunostaining of whole ovary sections revealed the presence of both BMAL1 and CLOCK protein within developing oocytes and the surrounding ovarian tissue. Now that BMAL1 expression has been characterized, further investigation can begin on the molecular roles of BMAL1 in mouse pre-implantation development.