Mammals have a circadian rhythm that is synchronized by a master clock located in the hypothalamic suprachiasmatic nucleus (SCN). The SCN regulates additional clocks located in peripheral tissues, including some involved in endocrine or reproductive functions. Studies in humans and mice report that molecular clocks also exist in the placenta. However, little is known about the presence of “Clock genes,” namely Circadian Locomotor Output Cycles Kaput (CLOCK), Brain and Muscle Arnt-Like 1 (BMAL1), Period 1 (PER1), Period 2 (PER2), Cryptochrome 1 (CRY1), and Cryptochrome 2 (CRY2), in equine placenta. Pregnancy length in mares varies and shows fluctuations in hormone concentrations throughout pregnancy. We postulate that similar to humans and mice, Clock genes are present in the horse placentas. Our goal was to determine if relative levels of clock genes were different between placentas associated with males and female fetuses or correlated with gestational length. We used polymerase chain reaction and immunofluorescence to study the presence of CLOCK, BMAL1, PER1, PER2, CRY1, and CRY2 in full-term mare placentas. Clock genes were present in all placentas, with significant lower levels of CRY2 and CLOCK in placentas that were associated with male fetuses. There was no association between relative levels of Clock genes and gestational length. These data provide the stage for future studies aimed at uncovering a function for Clock genes in the horse placenta.

中文翻译：

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马足月胎盘中存在Clock基因。

哺乳动物的昼夜节律与位于下丘脑上眼睑上核（SCN）的主时钟同步。SCN调节位于周围组织中的其他时钟，包括一些涉及内分泌或生殖功能的时钟。对人类和小鼠的研究表明，胎盘中也存在分子钟。然而，人们对“时钟基因”的存在知之甚少，即昼夜运动输出周期Kaput（CLOCK），脑和肌肉类似神经1（BMAL1），时期1（PER1），时期2（PER2），隐色染料1（CRY1）和Cryptochrome 2（CRY2），放在马胎盘中。母马的怀孕时间长短不一，并显示整个怀孕期间激素浓度的波动。我们推测与人类和小鼠相似，Clock基因存在于马胎盘中。我们的目标是确定与男性和女性胎儿相关的胎盘之间或与妊娠长度相关的时钟基因的相对水平是否不同。我们使用聚合酶链反应和免疫荧光来研究CLOCK，BMAL1，PER1，PER2，CRY1和CRY2的存在在足月母马胎盘中。所有胎盘中都存在时钟基因，与男性胎儿相关的胎盘中CRY2和CLOCK的水平明显较低。Clock基因的相对水平与妊娠长度之间没有关联。这些数据为将来的研究提供了舞台，旨在揭示马胎盘中Clock基因的功能。