Genetic regulation of developmental clocks

为什么人类的妊娠期是9个月，而老鼠的妊娠期是3周？创造更大的体重需要更多的时间，这是有道理的，但发育事件的时间如何与物种特有的生长差异协调在很大程度上是未知的。值得注意的是，多能干细胞（PSCs）的体外分化率再现了物种特异性的体内发育时间。因此，许多使用灵长类PSCs的分化方案可能需要几个月甚至几年才能完成，这反映了较长的妊娠期。另一方面，小鼠psc在体外完成相同的事件只需几天或几周，反映了三周的妊娠期。这些观察结果表明，即使没有来自完整胚胎和胚胎外成分的正常发育线索，细胞中也存在内在的发育定时/时钟机制。因此，使用体外分化范式进行比较分析将有助于理解和描述调节发育时间的基本机制。我的研究计划的长期目标是确定调节发育时间的机制，了解发育时钟，并确定可以改变时钟节奏的因素。我们最近利用psc衍生的中胚层祖细胞建立了体外分割时钟模型，再现了物种特异性基因在体内的振荡周期。因此，我们的首要假设是，物种特异性遗传因素在调节发育时间方面起着核心作用。配备我们新颖的体外发育时钟系统，这项发现资助申请的具体目的是：1)确定NOTCH信号通路中调节分割时钟同步和周期性的可调节因子；2)确定外来或内在因素是否可以调节物种特有的时钟周期；3)确定分段时钟与HOX时钟之间的链路。这些目标的完成不仅将阐明在椎骨发育过程中控制发育时钟的分子机制，而且还将为理解细胞和组织如何合作制定基本的身体计划提供路线图。对发育时间的基本理解可能最终导致加速体外分化持续时间的方法，并将其与体内妊娠长度脱钩。值得注意的是，由于发育时间、体型、代谢率和寿命都是相互关联的，了解胚胎发生过程中控制时间的因素可能会为控制组织再生和衰老过程提供新的见解。

Why do humans have a nine-month gestation period and mice have a three-week gestation period? It makes sense that more time is required to create a larger body mass, but how the timing of developmental events coordinates with species-specific differences in growth is largely unknown. Remarkably, the in vitro differentiation rate of pluripotent stem cells (PSCs) recapitulates species-specific developmental timing in vivo. Thus, many differentiation protocols using primate PSCs may require several months or sometimes years to complete, reflecting a longer gestation period. On the other hand, murine PSCs complete the same events in vitro in just days or weeks, reflecting a three-week gestation period. These observations suggest that even without normal developmental cues from intact embryonic and extraembryonic components, an intrinsic development timing/clock mechanism exists in cells. Therefore, a comparative analysis using an in vitro differentiation paradigm will help understand and characterize the fundamental mechanisms regulating developmental timing. The long-term goal of my research program is to determine the mechanisms regulating developmental timing, understand developmental clocks, and identify the factors that can modify the clock tempo. We recently established in vitro segmentation clock models using PSC-derived mesoderm progenitors, recapitulating species-specific gene oscillatory periodicity in vivo. Thus, our overarching hypothesis is that species-specific genetic factors play a central role in regulating developmental timing. Equipped with our novel in vitro developmental clock systems, this Discovery Grant application specifically aims to: 1) determine the tunable factors in the NOTCH signaling pathway that regulate the synchronization and periodicity of the segmentation clock; 2) determine if extrinsic or intrinsic factors could regulate species-specific clock periodicity; and 3) identify the links between the segmentation clock and HOX clock. The completion of these aims will not only shed light on the molecular mechanisms controlling a developmental clock during vertebrae development, but also provide a road map to understand how cells and tissues cooperate to make essential body plans. A basic understanding of developmental timing may ultimately lead to methods to accelerate the duration of in vitro differentiation and decouple it from in vivo gestation length. Notably, because developmental timing, body size, metabolic rate, and life span are all interconnected, understanding what controls timing during embryogenesis may offer new insights into what controls tissue regeneration and the aging processes.