The Study of Downstream Components in the Frizzled Signalizing Pathway in Planar Cell Polarity

This dissertation reports on molecular and genetic studies of downstream components in the frizzled signaling pathway in controlling planar cell polarity (PCP) (also known as tissue polarity). The frizzled signaling pathway plays a key role in establishing and regulating planar cell polarity in Drosophila melanogaster. In chapter 2, I describe my studies on a recently molecularly cloned gene, multiple-wing-hairs (mwh). mwh encodes an 836 residue protein, which contains a GTPase-binding domain (GBD) and a formin homology 3 (FH3) domain. I found that the subcellular localization of Mwh was dynamic and unique. It localized at the proximal side of wing cells prior to hair initiation, in the hair during hair growth and to the base of the hair at later stages in hair morphogenesis. Only the early proximal accumulation, but not the later sites of Mwh accumulation were dependent on the function of the fz pathway. Mwh and Inturned physically interacted; this suggests that Mwh is recruited to the proximal side of wing cells by the upstream Inturned protein. I also showed that Mwh physically and genetically interacted with Rho1. I found that the expression of a dominant negative or constitutively active Rho1 protein altered the accumulation of Mwh consistent with Rho1 functioning upstream of and regulating Mwh. Other results indicate that Rho1 has functions in wing hair morphogenesis that are independent of mwh. Inturned (in), fuzzy (fy) and fritz (frtz) are PCP effector genes, that function downstream of frizzled and upstream of mwh. In chapter 3, I study the genetic and molecular interactions among these three components. I found and II further investigated the physical interactions between In and Fy and In and Fritz. I determined that the N-terminus of Frtz, which contains a coiled-coiled domain and WD40 repeats, and the C-terminus of Inturned were required for direct protein-protein interactions. Co-immunoprecipitation experiments indicated that In, Fy and Frtz can be pull down together in transgenic flies. These genes also interacted genetically. These results suggest that in, fy and frtz function together downstream in the frizzled signaling pathway. III Contents General Abstract I Contents …………………………………………………………………….. III List of Figures and Tables ………………………………………………….

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