Molecular Mechanisms Underlying Xenopus Somitogenesis

描述（由申请人提供）：躯体发育包括近轴中胚层向骨骼肌、轴向骨骼和成人真皮的分割和分化。虽然许多参与调节小体形成的周期性的基因已经被表征，但这一过程背后的细胞行为仍然知之甚少。本研究的目的是确定非洲爪蟾（Xenopus laevis）体形态发生的分子机制。我们的中心假设是分泌的细胞因子，基质衍生因子-1 (SDF-1)，通过激活特定的肌动蛋白调节分子RhoA， Rac1或Cdc42来调节非洲爪蟾的形态发生。对这一假设的具体支持是基于最近对斑马鱼的研究，这些研究表明，与somite旋转相关的细胞行为（Hollway等人，2007；Stellabote等人，2007）与我们实验室和其他人在非洲爪蟾（Afonin等人，2006）中记录的相似。此外，分泌的细胞因子，基质衍生因子-1 （SDF-1）被证明是斑马鱼体体旋转相关的细胞重排所必需的（Hollway等人，2007），这是重要的，因为它是第一个被证明调节体体旋转的信号分子。在非洲爪蟾中，SDF-1被证明在原肠胚形成期间的中胚层迁移中发挥作用（Fukui等，2006），并在胚胎早期发育的轴组织中表达（Braun等，2002）。因此，SDF-1在适当的时间和地点出现，在某些细胞的形态发生中发挥作用。

DESCRIPTION (provided by applicant): Somitogenesis consists of the segmentation and differentiation of the paraxial mesoderm into the skeletal muscle, axial skeleton and dermis of the adult. While many genes involved in regulating the periodic nature of somite formation have been characterized, the cell behaviors underlying this process remain poorly understood. The objective of this proposal is to determine the molecular mechanism underlying somite morphogenesis in the vertebrate Xenopus laevis. Our central hypothesis is that the secreted cytokine, stromal-derived factor-1 (SDF-1), regulates Xenopus somite morphogenesis by activating the specific actin regulatory molecules RhoA, Rac1, or Cdc42. Specific support for this hypothesis is based on recent studies in zebrafish that showed that the cell behaviors associated with somite rotation (Hollway et al., 2007; Stellabote et al., 2007) are similar to those documented by our lab and others in Xenopus (Afonin et al., 2006). Furthermore, the secreted cytokine, stromal-derived factor-1 (SDF-1), was shown to be required for the cell rearrangements associated with zebrafish somite rotation (Hollway et al., 2007), which is significant as it is the first signaling molecule shown to regulate somite rotation. In Xenopus, SDF-1 was shown to play a role in mesoderm migration during gastrulation (Fukui et al., 2006) and is expressed in axial tissues throughout early embryonic development (Braun et al., 2002). Thus, SDF-1 is present at the right time and place to play a role in somite morphogenesis. To test our central hypothesis, we will modulate SDF-1 signaling by using morpholinos to knockdown expression levels and in vivo mRNA injections to up-regulate protein levels of SDF-1 and its receptor, CXCR4, in the cell (aim 1). Previous studies have shown that SDF-1 signaling affects changes in cell behaviors by activating specific Rho GTPases (Tan et al., 2006). These actin regulatory molecules have been shown to play an important role in tissue remodeling and thus are likely downstream targets of the SDF-1 signaling pathway during somitogenesis. To test this hypothesis, we will determine whether SDF-1 signaling modulates the activity of specific Rho GTPases during Xenopus somitogenesis (aim 2). Another goal of this proposal is to introduce new molecular approaches that along with the existing expertise in imaging techniques will provide an excellent environment for training students, many of whom are underrepresented minorities (aim 3). Furthermore, we also developed a mentorship plan with three senior scientists (Drs. Amacher, Symes, and Weisblat) whose research expertise complements the objectives presented in this proposal and will increase the research productivity of our lab. Relevance to Public Health: The proposed research is expected to provide critical information on how vertebrate somites are formed. This information will help in developing tools for diagnosing or preventing vertebral disorders such as scoliosis and other congenital spinal cord deformities.