Analyse des molekularen Mechanismus der Cadherin-11- und GEF Trio-vermittelten Migration von Neuralleistenzellen in Xenopus

The neural crest is a highly motile and multipotent cell population that gives rise to a variety of different cell types during development. Their migration has been linked to cancer metastasis and provide a good model to study the mechanisms controlling cell migration. During Xenopus cranial neural crest (CNC) cell migration the cell-cell-adhesion molecule Cadherin-11 (Cad11) is upregulated. In addition, Cad11 localizes typically at cell-cell contacts but also in cell protrusions. Furthermore, Cad11 loss of function leads to CNC migration defects in whole embryos and the Cad11-depleted CNC cells show a blebbing phenotype in vitro. Interestingly the guanine nucleotide exchange factor (GEF) Trio, which interacts with Cad11, or constitutive active forms of the small GTPases RhoA and Rac1 can rescue cell protrusion formation and migration of CNC cells in Cad11-depleted embryos. In this study it has been confirmed, that Trio is expressed in CNC cells and that it is essential for their directional migration and protrusion formation. In addition, knockdown studies showed that Trio affects cell polarity and cytoskeleton dynamics likely through its ability to regulate the small Rho GTPases. Furthermore, the Trio GEF2-domain showed a dynamic localization in association with microtubules in CNC cells, which point to a micorubule-dependent function of the GEF2-domain. Moreover, this study reveal a novel role of the Wnt/PCP member Dishevelled (Dsh) in mediating CNC cell migration downstream of Cad11 and Trio. Both Trio GEF-domains interact with Dsh, whereas an interaction between Cad11 and Dsh was not detected. But reconstitution experiments revealed that Dsh, in particular its PDZ- and DEP-domain are necessary for Cad11 mediated migration and protrusion formation of CNC cells. In summary, the results indicate that the molecules have different functions during CNC cell migration dependent on their subcellular localization and that Trio mediates CNC cell migration via Dsh and by regulating the activity of the small Rho GTPases downstream of Cad11. Furthermore, beside the function of Trio during CNC cell migration, Trio seems to have additional roles during Xenopus development. Thereby Trio seems to have a conserved function in neural and muscle development.