Meeting Abstract
The daily and yearly rotations of the Earth have provided a constantly changing environment that has driven the evolution of biological rhythms. The ability to adapt to future predictable climatic conditions is an ancient adaptation; therefore, it should not be surprising to observe biological rhythms at genomic, physiological, and behavioral levels across taxa. In this presentation, the conjecture that DNA methylation is an evolutionary ancient and essential component for the genomic regulation of biological rhythms will be outlined. The studies used male or female Siberian hamsters (Phodopus sungorus) to investigate the role of photoperiod, oestrous and hormonal regulation of DNA methylation and de novo DNA methyltransferase (Dnmt3a/b) expression in the hypothalamus and peripheral reproductive tissues (i.e. testis, uterus). Hypothalamic DNA methylation and Dnmt3a/b are elevated in long day (LD) summer-like breeding conditions. Short days (SD) and melatonin were sufficient to reduce hypothalamic DNA methylation and Dnmt3a/b expression. In females, hypothalamic Dnmt3a expression increased during the transition from proestrous to oestrous states. A single bolus injection of diethylstilbestrol (DES) and progesterone (E2P4) was sufficient to increase Dnmt3a cell numbers and Dnmt3b immunoreactive intensity in the suprachiasmatic nucleus (SCN). Upregulating DNA methylation in vitro reduced expression of vasoactive intestinal polypeptide, Vip, and the circadian clock gene, Bmal1. Conversely, SD increased global DNA methylation and dnmt3a expression in the testes and uterine tissue. Ovariectomy increased Dnmt3a/b uterine expression that was rapidly reduced after a single injection of E2P4. Altogether, the data reveal a dynamic and oscillatory role of DNA methylation for timing biological rhythms in reproduction.
