The integrity of
polarized epithelia is critical for development and human health. Many questions remain concerning the full complement and the function of the proteins that regulate cell polarity. Here we report that the Drosophila FERM proteins Yurt (Yrt) and Coracle (Cora) and the
membrane proteins Neurexin IV (Nrx-IV) and Na(+),K(+)-
ATPase are a new group of functionally cooperating
epithelial polarity proteins. This 'Yrt/Cora group' promotes
basolateral membrane stability and shows negative regulatory interactions with the apical determinant Crumbs (Crb).
Genetic analyses indicate that Nrx-IV and Na(+),K(+)-
ATPase act together with Cora in one pathway, whereas Yrt acts in a second redundant pathway. Moreover, we show that the Yrt/Cora group is essential for
epithelial polarity during
organogenesis but not when
epithelial polarity is first established or during terminal differentiation. This property of Yrt/Cora group proteins explains the recovery of polarity in
embryos lacking the function of the Lethal giant larvae (Lgl) group of
basolateral polarity proteins. We also find that the mammalian Yrt
orthologue EPB41L5 (also known as YMO1 and Limulus) is required for lateral membrane formation, indicating a conserved function of Yrt proteins in
epithelial polarity.
