297. Reproduction in the arrhythmic Bmal1 knockout mouse

Abstract

There is strong epidemiological evidence indicating that disruption of the endogenous circadian rhythms can cause a range of health problems ranging from metabolic and cardiovascular disorders to reproductive failure. Circadian rhythmicity is generated by a suite of genes called ‘clock genes’ that are cyclically expressed in the brain and peripheral tissues. The CLOCK and BMAL1 transcription factors regulate the expression of many genes involved in cell growth, angiogenesis and development. The Bmal1 knockout mouse provides an interesting model to analyse the impact of arrhythmicity on reproductive physiology. Female Bmal1–/– mice show a delay in the onset of puberty (WT = 32.7 d, KO = 38.6 d, n = 8–16). Female Bmal1–/– mice reproductive tissues are significantly smaller than in WT mice (Ovaries –40%, Oviduct –25%, Uterus –60%, n = 10). Female Bmal1–/– mice have essentially normal estrus cycles (cycle length WT = 4.2 d, KO = 4.8 d, n = 8) and are able to ovulate and mate but are unable to establish viable pregnancies. They are as responsive to a standard superovulation protocol as their wild type littermates (ovulated oocytes WT = 23.8, KO=22.8, n = 7–10), suggesting the ovaries are developmentally competent. These results suggest disruption of circadian rhythmicity in the mouse affects fertility at multiple sites. Further investigation into the importance of rhythmicity, particularly post ovulation and post fertilisation is required.