The pre-implantation period is a critical time in embryo development. Following fertilisation, development proceeds according to a strict timetable as the embryo progresses through the oviduct. Any perturbation to this precisely timed process can be expected to result in poor embryo survival. The critical role of the circadian timing system in many other physiological systems has emerged over the last few years, but little is known about circadian rhythmicity in the oviduct. We have conducted the first comprehensive analysis of gene expression rhythmicity in the oviduct. We chose 2 critical periods; the 24 hours post fertilisation and the last 24 hours before embryo implantation into the uterus.
Oviducts were obtained from unstimulated C57Bl/6 mice (n = 6 per time point) at proestrus (2000h & 2400h) in the absence of males and at 0400h, 0800h, 1200h, 1600h, 2000h and 2400h in the presence of males. Oviducts were also collected at 4 hour intervals from 66 – 86 hours post insemination. Only oviducts with embryos at the appropriate developmental stages were used. RNA was extracted from the left oviduct of each mouse, pooled at each time point and analysed using Affymetrix Mouse Gene 1.0 ST Arrays. The data was fitted to a sine curve using CircWave software. Expression of genes of interest highlighted by the microarrays were subsequently confirmed by Real Time RT-PCR.
Analysis of the expression profiles indicated that more than 1000 genes were rhythmically expressed in the early pre-implantation period and 2400 genes were rhythmic in the late pre-implantation period. Thus up to 10% of the oviduct transcriptome is rhythmic. In addition we identified many genes that were highly induced around 0400h, several hours after insemination. The functions of the genes that were rhythmically expressed ranged from those involved in carbohydrate and lipid metabolism to those involved in tissue remodelling, solute transport and hormone synthesis pathways. The oviduct is clearly far more dynamic in its function than previous appreciated and further studies on the precise role of the rhythmic genes may lead to a better understanding of the needs of embryos during their development.