G o ing for the Correct Orientation

Abstract

Development of the Drosophila sensory organ depends on the polarization and subsequent asymmetric division of sensory organ precursor cells (SOPs), which give rise to all of the cell types that make up the mature structure. Although SOPs can become polarized and divide asymmetrically in the absence of external signals, their ability to achieve the correct orientation depends on extracellular signals transduced through the Frizzled (Fz) receptor. Fz is known to signal through heterotrimeric guanosine triphosphate (GTP)-binding proteins containing G o -type α subunits in some Drosophila systems, leading Katanaev and Tomlinson to investigate its role in sensory organ development. Clonal cells containing mutant G o or overexpressing wild-type or activated G o showed phenotypic defects in both orientation and asymmetric division, as well as mislocalization of Numb, a phosphoprotein whose polarized distribution in SOPs is key to cell fate determination. G o itself was asymmetrically distributed in mitotic SOPs and both coprecipitated with Pins (Partner of Inscuteable, a protein that binds to Gα and is part of a complex necessary for asymmetric distribution of Numb) and interacted genetically with it. The phenotypic effects of overexpressing wild-type G o depended on the expression of Fz and were enhanced by Fz overexpression. G o thus appears to be involved both in the establishment of asymmetry and in determining its correct orientation, leading the authors to propose that it may act to integrate these two processes. V. L. Katanaev, A. Tomlinson, Dual roles for the trimeric G protein Go in asymmetric cell division in Drosophila . Proc. Natl. Acad. Sci. U.S.A. 103 , 6524-6529 (2006). [Abstract] [Full Text]