Role of Dachs localization and ATPase activity in Fat signaling. Abhijit A Ambegaonkar, Cordelia Rauskolb, Kenneth Irvine. Waksman Institute of Microbiology, Rutgers, the State University of New Jersey, Piscataway, NJ.

   Dachs, a myosin family protein, is a downstream effector of Fat signaling pathway that regulates planar cell polarity (PCP) in Drosophila. Dachs also interacts with Zyxin, a LIM domain protein which is a component of Hippo signaling pathway that regulates growth. Both Dachs and Zyxin are localized in the sub-apical region of the cell. However, Dachs is polarized towards the distal side of the cell membrane whereas Zyxin is present around the entire circumference of the cell. Earlier studies have identified a correlation between Dachs localization and Fat signaling. To confirm the importance of Dachs membrane localization and distinguish it from other potential influences of Fat, we targeted Dachs to the membrane independent of Fat activity by fusing Dachs to Zyxin. When expressed under UAS control, the Zyxin-Dachs fusion protein was observed to localize around the entire circumference of the cell. Zyxin-Dachs overexpression resulted in strong overgrowth and upregulation of Hippo pathway target genes. Moreover, wing hair polarity and cell division orientation was randomized, indicating that PCP is disrupted. These results confirm that Dachs localization is sufficient for both PCP and Hippo signaling. We have also tested Zyxin-Dachs fusion protein with mutation in Dachs ATPase site (Zyxin-Dachs^R424E), which would abolish its motor activity. Expression of Zyxin-Dachs^R424E resulted in overgrowth, but PCP was not affected. These results suggest that Dachs myosin motor activity is required for its effect on PCP but not for Hippo signaling.