DEVELOPMENTAL GENE EXPRESSION IN C ELEGANS

我们对在发育过程中调控细胞命运决定的转录因子感兴趣。我们的模型系统是秀丽隐杆线虫（一种非寄生蠕虫），由于其体积小，易于在实验室培养，解剖简单，增殖迅速和遗传学，被广泛用于发育研究。我们目前对几种转录因子（MyoD， E， Twist和Mef-2）感兴趣，这些转录因子在其他系统中被发现对肌肉形成很重要。通过与华盛顿卡内基研究所安迪·菲尔博士的团队合作，我们已经证明秀丽隐杆线虫的MyoD和Twist因子对包括肌肉在内的胚胎后中胚层细胞的形成和模式很重要。通过研究这些基因突变导致的表型，我们开始确定它们在调节秀丽隐杆线虫特定肌肉细胞亚群发育中的确切作用。突变体也为基因筛选提供了一个起点，以确定在调控层次结构中起作用的其他因素。我们工作的第二个方面集中在细胞分化和细胞周期之间的联系。通常，细胞必须退出细胞周期（停止增殖）才能分化。这通常涉及G1细胞周期蛋白（D和E）及其相关的细胞周期蛋白依赖性激酶（CDKs）的抑制。在其他生物和组织培养中的研究已经证明分化因子，如肌细胞中的MyoD，在对抗G1细胞周期因子的作用中起直接作用。使用正向和反向遗传方法，我们已经证明了cyclin D和CDK-4/6因子调节秀丽隐杆线虫细胞周期的G1期。令人惊讶的是，这些G1调节因子仅在胚胎后发育期间起作用，因此它们对胚胎发生期间的肌肉分化并不重要。相反，细胞周期蛋白E似乎是发育过程中所有细胞分裂所必需的，并且可能是MyoD等分化因子的共同目标。我们目前正在探索解决这些细胞周期调节因子和胚胎后发育过程中肌生成因子之间可能的相互作用的方法。我们认为，在正常发育的背景下，线虫提供了研究促进进入或退出细胞周期的信号平衡的机会。

We are interested in transcription factors that function in the regulation of cell fate determination during development. Our model system is the nematode C. elegans (a non-parasitic worm) that is widely used for developmental studies because of its small size, ease of culture in the laboratory, simple anatomy, rapid proliferation, and genetics. We are currently interested in several transcription factors (MyoD, E, Twist, and Mef-2) that have been identified in other systems as important for muscle formation. In collaboration with Dr. Andy Fire's group at the Carnegie Institution of Washington we have shown that the C. elegans MyoD and Twist factors are important for the formation and patterning of post-embryonic mesodermal cells including muscle. By studying the phenotypes that result from mutations in these genes we are beginning to define their exact roles in regulating the development of specific subsets of muscle cells in C. elegans. The mutants also provide a starting point for genetic screens to identify other factors operating in the regulatory hierarchy. A second aspect of our work focuses on the connection between cellular differentiation and the cell cycle. Usually, cells must exit the cell cycle (stop proliferating) in order to differentiate. This usually involves inhibition of the G1 cyclins (D and E) and their associated cyclin-dependent kinases (CDKs). Studies in other organisms and tissue culture have demonstrated a direct role for differentiation factors, such as MyoD in muscle cells, in antagonizing the action of G1 cell cycle factors. Using forward and reverse genetic approaches we have demonstrated that cyclin D and CDK-4/6 factors regulate the G1 phase of the cell cycle in C. elegans. Surprisingly, these G1 regulators only function during postembryonic development so they can not be important for muscle differentiation during embryogenesis. In contrast, cyclin E appears to be required for all cell division during development and is likely a common target of differentiation factors such as MyoD. We are currently exploring ways to address possible interactions between these cell cycle regulators and myogenic factors during post-embryonic development. We think the nematode offers the opportunity to study the balance of signals promoting either entry or withdrawal from the cell cycle in the context of normal development.