280. Reproductive consequences of circadian dysfunction: fertility in the Bmal1 null mouse

Abstract

Circadian rhythms are generated by a suite of genes called clock genes that are expressed in the brain and also in many peripheral tissues. In the peripheral tissues, these genes assist in regulating the expression of many genes involved in cell growth, angiogenesis and development. Bmal1 is a critical gene involved in circadian rhythm generation. Here we report on the fertility and fecundity of Bmal1 knockout mice (Bmal1^–/–). Male Bmal1^–/– mice have impaired fertility compared to controls [(litters produced/number of animals) wild type (5/5), CBA controls (5/5), Bmal1^–/– (1/15)]. Fifty percent of male Bmal1^–/– mice had defective caudal sperm, showing sperm that was both non-motile and malformed. Seminal vesicle weight was significantly reduced in the Bmal1^–/– mice (50% reduction) in males at both 4 and 5.5 months old. Female Bmal1^–/– mice had irregular oestrus cycles and failed to maintain a pregnancy to term following natural mating [(litters produced/number of animals) wild type (5/5) CBA controls (5/5) Bmal1^–/– (0/5)]. When embryos were flushed from the uterus 4 days after natural mating, there was a reduced number of released oocytes and a reduced development to blastocysts in the Bmal1^–/– female mice. Following a standard PMSG/HCG super ovulation protocol, Bmal1^–/– mice showed both a reduction in ovulation rate as well as a slowed progression of embryos to blastocyst stage (Table 1, see PDF file).

These results suggest that disruption of a key clock gene has detrimental consequences on fertility in the mouse. Further, this reduction in fertility appears to be acting at multiple levels. Continued investigation into the importance of rhythm genes in reproductive function is required.