Regulation of Somitic Cell Migration by Paraxis

Arizona State University, Scottsdale AZ

Investigators

Abstract

0131726 Rawls In vertebrates, the metameric pattern of the axial skeleton and peripheral nerves is dependent on the establishment of the anterior/posterior (A/P) polarity of somites during early embryogenesis. Individual vertebrae are derived from the anterior and posterior halves of the sclerotome compartment of adjacent somites. The proper segmentation of these axial structures is critical to the viability of the animal. Therefore, determining the molecular basis of A/P polarity is of fundamental importance. Preliminary studies in Dr. Rawl's laboratory, tracing cell migration in the presomitic mesoderm of mouse embryos indicates the presence of active sorting of cells into anterior- and posterior-specific domains. Similar cell sorting mechanisms have been shown to regulate compartmental boundaries between segments of the vertebrate hindbrain. The first aim of this proposal is to perform a detailed analysis of cell sorting in the presomitic mesoderm and epithelial somite. Cell migration will be examined using a novel in vivo assay developed in the laboratory for tracing the movement of cells in the somites of mouse embryos. This technique also will allow for the comparison of cell migration in wild type embryos to that of existing genetic mutations that are deficient in A/P polarity. Preliminary studies indicate that the cell sorting activity is compromised in embryos deficient for paraxis, a bHLH transcription factor required for proper epithelialization of the somite. Migration and sorting are dependent on the cell adhesion properties of the cells. Therefore, the loss of somite epithelialization and increased cell migration associated with the paraxis mutant are both consistent with a reduction in the cell adhesiveness of the presomitic cells. The cell adhesion properties of the mutant cells will be examined using in vitro aggregation assays and gene expression studies. The specificity of the cell migration activity will also be assessed by examining cell movement in Dll1 and Lunatic Fringe embryos. In these mutants A/P polarity is disrupted but epithelialization occurs normally, Collectively these experiments will provide valuable insight into a mechanism for regulating spatial identity during somitogenesis. Examination of targeted null mutations will be used to identify the genes that regulate this process. Because segmentation and compartmental boundaries are a common strategy for patterning during development, the information gained from these experiments can potentially be used to understand other systems.