The Drosophila Planar Polarity Proteins Inturned and Multiple Wing Hairs Interact Physically and Function Together

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ABSTRACT

The conserved frizzled (fz) pathway regulates planar cell polarity in both vertebrate and invertebrate animals. This pathway has been most intensively studied in the wing of Drosophila, where the proteins encoded by pathway genes all accumulate asymmetrically. Upstream members of the pathway accumulate on the proximal, distal, or both cell edges in the vicinity of the adherens junction. More downstream components including Inturned and Multiple Wing Hairs accumulate on the proximal side of wing cells prior to hair initiation. The Mwh protein differs from other members of the pathway in also accumulating in growing hairs. Here we show that the two Mwh accumulation patterns are under different genetic control with the early proximal accumulation being regulated by the fz pathway and the latter hair accumulation being largely independent of the pathway. We also establish recruitment by proximally localized Inturned to be a putative mechanism for the localization of Mwh to the proximal side of wing cells. Genetically inturned (in) acts upstream of mwh (mwh) and is required for the proximal localization of Mwh. We show that Mwh can bind to and co-immunoprecipitate with Inturned. We also show that these two proteins can function in close juxtaposition in vivo. An In::Mwh fusion protein provided complete rescue activity for both in and mwh mutations. The fusion protein localized to the proximal side of wing cells prior to hair formation and in growing hairs as expected if protein localization is a key for the function of these proteins.

THE frizzled (fz) signaling pathway regulates tissue planar cell polarity (PCP) in the epidermis of both vertebrate and invertebrate animals (Lawrence et al. 2007; Montcouquiol 2007; Wang and Nathans 2007; Zallen 2007). PCP is dramatic in the cuticle of insects such as Drosophila, which is decorated with arrays of hairs and sensory bristles.

The genetic basis for tissue polarity has been most extensively studied in the fly wing (Wong and Adler 1993). The Planar Polarity (PCP) genes of the fz pathway (also known as the core PCP genes), the planar polarity effector (PPE) genes and the multiple wing hairs (mwh) gene encode key components that regulate planar polarity in the wing. fz, disheveled (dsh), prickle/spiny leg (pk/sple), Van Gogh (Vang) (aka strabismus), starry night (stan) (aka flamingo) and diego (dgo) are members of the PCP group (Vinson and Adler 1987;Wong and Adler 1993; Taylor et al. 1998; Wolff and Rubin 1998; Chae et al. 1999; Gubb et al. 1999; Usui et al. 1999). A distinctive feature of these genes is that their protein products accumulate asymmetrically on the distal (Fz, Dsh, and Dgo) (Axelrod 2001; Feiguin et al. 2001; Shimada et al. 2001; Strutt 2001), proximal (Vang, Pk)(Tree et al. 2002; Bastock et al. 2003), or both distal and proximal (Stan) (Usui et al. 1999) sides of wing cells. These genes/proteins act as a functional group and are corequirements for the asymmetric accumulation of the others.

The PPE includes inturned (in), fuzzy (fy), and fritz (frtz) (Park et al. 1996; Collier and Gubb 1997; Collier et al. 2005). These genes are thought to function downstream of the PCP genes and the proteins encoded by these genes also accumulate asymmetrically in wing cells (Adler et al. 2004; Strutt and Warrington 2008). As is the case for the PCP genes, the PPE genes/ proteins also appear to be a functional group and to be corequirements for the asymmetric accumulation of the others. Several observations support the hypothesis that the PPE genes are essential downstream effectors of the PCP genes. The earliest appreciation of this came from careful observations of the mutant phenotypes. A common feature of mutations in all of these genes is that they do not result in a randomization of hair polarity, but rather in a similar complicated and abnormal stereotypic pattern (Gubb and Garcia-Bellido 1982; Adler et al. 2000). That the abnormal patterns were so similar suggested that these genes all functioned in the same process (Wong and Adler 1993). …