Abstract
Cell polarity genes provide positional cues for elongating photoreceptors during photoreceptor morphogenesis. Coordinated interactions between cytoskeleton and cell polarity proteins are involved in many polarized cellular processes. It has recently been found that stable microtubules in Drosophila photoreceptors, a non-ciliary rhabdomeric eye, were linked to photoreceptor cell polarity. Interactions between microtubules and actin are a basic phenomenon that underlies many fundamental cell biological processes in which dynamic cellular polarity need to be established and maintained. Since Spectraplakin, an actin-microtubule cross-linker, is able to bind microtubule and actin cytoskeletons, the role of Spectraplakin was analyzed in the regulations of photoreceptor cell polarity. The Spectraplakin in developing pupal photoreceptors specifically localizes at rhabdomere terminal web, a sub-rhabdomeric fibrous actin meshwork, which was recently proposed to be involved in a secretory trafficking. Photoreceptors lacking the Spectraplakin showed dramatic misplacements of apical membrane domains, adherens junctions, and the stable microtubules. This role of Spectraplakin in photoreceptor cell polarity was further supported by gain-of-function studies. Spectraplakin overexpression in photoreceptors caused an apical-basal cell polarity defect. These data suggest that Spectraplakin, an actin-microtubule cross-linker, at rhabdomere terminal web is essential in photoreceptor cell polarity.