The roles of the cadherins Fat and Dachsous in planar polarity specification in Drosophila.

Planar polarity is generated through the activity of two groups of proteins, the "core" system and the Fat (Ft)/Dachsous (Ds) system. Although both are conserved from insects to mammals, vertebrate studies into planar polarity have primarily focussed on core planar polarity proteins and have only recently branched into the study of the Ft/Ds system. In Drosophila, however, years of detailed analysis have started to elucidate some of the mechanisms by which Ft/Ds signalling might set up polarity across a tissue, and how this may impact upon core protein-mediated planar polarity. In this review, we discuss the major findings, models, and controversies that have emerged from Drosophila research into the Ft/Ds system, and indicate some areas for further investigation.