A fundamental question in development is how cells are specified. Elucidating mechanisms of cell-type specification is essential to the understanding and eventually treating human diseases, such as cancer, where this process is altered. One mechanism that specifies cell type is Asymmetric Cell Division, where a cell divides to produce two daughter cells that adopt distinct fates. Both asymmetrically distributed molecules and cell signaling appear to polarize dividing cells, but a connection between these two mechanisms has been lacking. A physical interaction between HAM-l, an asymmetrically distributed molecule, and DSH-2, a conserved Wnt signaling component, provides a link between asymmetric molecules and signaling. The overall goal of the proposed research is to define the roles of DSH-2 and HAM-1 in asymmetric cell division. The proposal has four specific aims. 1. To explore the interaction between DSH-2 and HAM-1. Immunoprecipitation experiments will be conducted to confirm a DSH-2/HAM-1 complex. Molecular genetic experiments will probe whether the interaction between the proteins is necessary for their function in asymmetric divisions and whether one protein is necessary for the others distribution. 2. To test whether the asymmetric distributions of DSH-2 and HAM-1 are necessary for their roles in asymmetric cell division. The localization domains of both proteins will be defined, and mislocalization experiments will test whether asymmetric distribution of two proteins is important to specify daughter cell fate. 3. To determine which proteins act upstream of DSH-2 and HAM-1 to control their asymmetric distribution. Using genetic and immunocytochemical approaches, Wnts and Frizzled receptors will be tested for roles in the distribution of DSH-2 and HAM-1. These molecules will then be misexpressed to test whether asymmetric signaling regulates DSH-2 and HAM-1 distribution. 4. To determine how DSH-2 and HAM-1 signal to control asymmetric cell division. Using reverse genetic approaches, candidate genes will be tested for roles in asymmetric divisions that require DSH-2 and HAM-1. In addition, genes identified in genetic screens will be tested for a role the HAM-1 /DSH-2 pathway. Genes that act in the pathway will be characterized molecularly.
