Targeted disruption of BMAL1 in the peripheral reproductive axis results in infertility in female mice

The product of the Bmal1 locus is an essential component of the circadian clock that plays important roles in various aspects of reproductive biology,and when disrupted results in infertility. In an effort to establish the identity of the tissue specific clock that is responsible for this infertility, we used the steroidogenic factor-1 (Sf1) promoter to drive Cre-mediated recombination and genetically delete Bmal1 within cells of the reproductive axis. We show that Bmal1 within the reproductive axis of females is essential for normal fertility through its role in maintaining implantation, but is not required for normal estrous cycling. At the root of this biology appears to be a defect in the ovaries, including regulation of ovarian lipid biosynthetic or metabolic processes and their roles in maintaining progesterone synthesis. This conclusion is based upon three observations. First, that deletion of Bmal1 within the reproductive axis reduces/leads to affected transcripts in steroidogenic pathways for the LH receptor and lowers progesterone levels. Second, that progesterone supplementation of these conditional mutants rescues implantation. Third, transplantation of wild type ovaries into Bmal1 reproductive axis mutants rescues fertility. Our study demonstrates the significance of ovarian Bmal1 as an overriding influence in experimental models of infertility. A time series was performed in time-mated C57Bl/6J mice to identify oscillating transcripts. During the peak and trough of the majority of transcripts (ZT0 and ZT12) samples from Bmal1fx/fx Sf1Cre mice and control litermates as well and global Bmal1 nulls were also analyzed. The tissue types (ovary, pituitary) are not comparable.Bmal1基因座（Bmal1 locus）的编码产物是生物钟（circadian clock）的核心组成部分，在生殖生物学的诸多方面发挥关键调控作用，其功能紊乱可导致不育。为明确介导该不育表型的组织特异性生物钟的身份，我们借助类固醇生成因子1（steroidogenic factor-1, Sf1）启动子驱动Cre重组酶介导的基因重组，在生殖轴细胞中特异性敲除Bmal1基因。研究结果显示，雌性小鼠生殖轴内的Bmal1可通过维持胚胎着床过程保障正常生育能力，但对正常动情周期并无必需作用。该生殖生物学现象的核心缺陷源于卵巢功能异常，包括卵巢脂质生物合成与代谢过程的调控紊乱，以及其在维持孕酮合成中的作用失衡。本结论基于三项观测结果：其一，生殖轴内Bmal1的敲除会影响黄体生成素（Luteinizing Hormone, LH）受体相关类固醇生成通路的转录本表达，并降低孕酮水平；其二，向该条件性基因敲除突变小鼠补充孕酮可恢复其胚胎着床能力；其三，将野生型卵巢移植至Bmal1生殖轴敲除小鼠体内可挽救其不育表型。本研究证实，在不育症实验模型中，卵巢Bmal1作为核心调控因子发挥决定性作用。我们对定时交配的C57Bl/6J小鼠开展时序采样，以鉴定周期性振荡表达的转录本。在多数转录本的表达峰值与谷值阶段（即授时时间0点与12点，Zeitgeber Time, ZT0和ZT12），我们同时采集了Bmal1fx/fx Sf1Cre小鼠、同窝对照小鼠以及全身性Bmal1基因敲除小鼠的样本并进行分析。卵巢与垂体两种组织的样本不具备可比性。