Tokyo Metropolitan Institute of Medical Sciences, Tokyo, Japan.
Department of Biological Sciences, School of Science, University of Tokyo, Tokyo, Japan.
Commun Biol. 2024 Feb 28;7(1):243. doi: 10.1038/s42003-024-05894-3.
Animals have internal clocks that generate biological rhythms. In mammals, clock genes such as Period form the circadian clock to generate approximately 24-h biological rhythms. In C. elegans, the clock gene homologs constitute the "developmental clock", which has an 8-h period during larval development to determine the timing of molting. Thus, the ancestral circadian clock has been believed to evolve into the oscillator with a shorter period in C. elegans. However, circadian rhythms have also been observed in adult C. elegans, albeit relatively weak. This prompts the question: if the clock gene homologs drive the developmental rhythm with 8-h period, which genes generate the circadian rhythms in C. elegans? In this study, we discovered that nhr-23, a homolog of the mammalian circadian clock gene Ror, is essential for circadian transcriptional rhythms in adult C. elegans. Interestingly, nhr-23 was also known to be essential for the molting clock. The bilaterian ancestral circadian clock genes might have evolved to function over multiple periods depending on developmental contexts rather than a single 8-h period in C. elegans.
动物有内部时钟，产生生物节律。在哺乳动物中，周期等时钟基因构成生物钟，产生大约 24 小时的生物节律。在秀丽隐杆线虫中，时钟基因同源物构成“发育时钟”，在幼虫发育期间具有 8 小时的周期，以确定蜕皮的时间。因此，人们认为祖先的生物钟已经进化为具有较短周期的振荡器。然而，在成年秀丽隐杆线虫中也观察到了昼夜节律，尽管相对较弱。这就提出了一个问题：如果时钟基因同源物驱动具有 8 小时周期的发育节律，那么哪些基因在秀丽隐杆线虫中产生昼夜节律？在这项研究中，我们发现 nhr-23，一种哺乳动物生物钟基因 Ror 的同源物，是成年秀丽隐杆线虫中昼夜转录节律所必需的。有趣的是，nhr-23 也被认为是蜕皮时钟所必需的。两侧对称动物祖先的生物钟基因可能已经进化为根据发育背景而不是在秀丽隐杆线虫中具有单一的 8 小时周期来发挥多种功能。
