Functional analysis of the atypical DSL protein DLL3

Notch信号通路是介导相邻细胞之间直接通讯的进化保守机制。Notch信号在线虫、昆虫和脊椎动物等多种生物体的多种发育过程中起着重要的调控作用。最近在脊椎动物胚胎中的研究已经证明Notch信号在体节形成和图案化中的重要作用。Notch信号传导的中断在体节发生过程中导致严重的缺陷：边界不对齐和不规则，体节极性被废除或扰乱，并且节边界不被维持。Notch的5个配体中的2个，Delta1（Dll1）和Delta3（Dll3）在小鼠的体节发生中具有重要功能。然而，尽管Dll 1和Dll 3在有丝分裂前中胚层中的表达有很大的重叠，但Dll 1（Dll 1lacZ）和Dll 3（Dll 3pu）的无效等位基因对有丝分裂前中胚层中的图案化过程的影响不同，这表明Dll 1和Dll 3在体节形成过程中具有不同的非冗余功能。在这项研究中，我们提出的假设，即Dll1和Dll3有非冗余的功能，特别是在体节发生，和Dll1和Dll3的具体功能所带来的不同的生化特性。这将通过用Dll 3的编码序列替换Dll 1和分析携带该基因替换的小鼠以及Dll 1和Dll 3与Notch受体在体外相互作用的生物化学表征来实现。这些实验将进一步阐明Notch配体Dll 1和Dll 3的功能和生化特性，并有助于了解它们在近轴中胚层中的功能和哺乳动物中中胚层分割的基本分子机制。

The Notch signaling pathway is an evolutionary conserved mechanism mediating the direct communication between adjacent cells. Notch signaling is pivotal for the regulation of multiple developmental processes in diverse organisms such as nematodes, insects and vertrebrates. Recent studies in vertebrate embryos have demonstrated an essential role for Notch signaling in somite formation and patterning. Disruption of Notch signaling causes severe defects during somitogenesis: boundaries are misaligned and irregular, somite polarity is abolished or perturbed, and segment borders are not maintained. Two of the five ligands for Notch in mouse, Delta1 (Dll1) and Delta3 (Dll3), have essential functions during somitogenesis. However, despite the largely overlapping expression of Dll1 and Dll3 in the presomitic mesoderm, null alleles of both Dll1 (Dll1lacZ) and Dll3 (Dll3pu) affect patterning processes in the presomitic mesoderm differently, suggesting that Dll1 and Dll3 have distinct, non-redundant functions during somite formation. In this study we propose to test the hypothesis that Dll1 and Dll3 have non-redundant functions especially during somitogenesis, and that the specific functions of Dll1 and Dll3 are brought about by different biochemical properties. This will be achieved by replacing Dll1 with the coding sequence of Dll3 and analysis of mice carrying this gene replacement, and biochemical characterization of the interaction of Dll1 and Dll3 with Notch receptors in vitro. These experiments should further elucidate the functions and biochemical properties of the Notch ligands Dll1 and Dll3 and help to understand their functions in the paraxial mesoderm and the basic molecular mechanisms underlying mesoderm segmentation in mammals.