The loss of these activities can explain the mwh mutant phenotype. We identified a fragment of Mwh with in vivo rescue activity and that bound and bundled F-actin filaments and inhibited actin polymerization in in vitro actin assays. As development proceeded additional hairs continued to form, further increasing hair number. Extra actin bundles/hairs are formed and do not completely fuse, in contrast to wild type. In mwh mutants hair initiation is not limited to a small region at the distal edge of pupal wing cells as in wild type, resulting in multiple hairs with aberrant polarity. The downstream PCP gene multiple wing hairs (mwh) plays a key role in this process and acts to antagonize the actin cytoskeleton. Using in vivo imaging we found that, early in hair growth, cells have multiple actin bundles and hairs that subsequently fuse into a single growing hair.
This pathway has been extensively studied in the Drosophila wing, where it is manifested by an array of distally pointing cuticular hairs. The evolutionarily conserved frizzled/starry night (fz/stan) pathway regulates planar cell polarity (PCP) in vertebrates and invertebrates.
