Expression of UAS-mys-RNAi or UAS-mew-RNAi in the wing causes severe wing blister (data not shown), a hallmark of defective integrin signaling ( Brower, 2003). We knocked-down mys and mew in da neurons with Gal421-7 ( Song et al., 2007) and examined the spatial relationship Selumetinib of class IV da dendrites and the ECM in third instar larvae. The ddaC dendrites at the dorsal midline are usually attached to the ECM, with only 1.75% of dendritic length enclosed in the epidermis ( Figure 3J). In RNAi control neurons with only UAS-Dicer-2 (UAS-Dcr-2)

expression ( Dietzl et al., 2007), the enclosed dendritic length is increased to 5.69% ( Figure 3F). In contrast, with mys or mew knockdown, the enclosed dendritic length is MDV3100 cost increased to 24.33% or 28.32%, respectively ( Figures 3G, 3H, 3I, and Movie S2), suggesting that defective positioning of dendrites is the underlying cause of the increased noncontacting dendritic crossings. Integrins function by forming heterodimers of α and β subunits. If integrin α subunit Mew and β subunit Mys regulate dendrite positioning by forming a functional dimer, mutant alleles of mew and mys may genetically interact with each other. Indeed, in transheterozygotes of mys1 and mewM6, the percentage of enclosed dendrites is increased to 22.62%, compared to 4.09% in mys1/+ and 4.18% in mewM6/+ ( Figures 3K–3N). Collectively, these data show that integrin genes mew and mys are important for attaching the class IV da

dendrites to the ECM and thus for nonoverlapping coverage of dendritic fields. Since removal of mys and mew from class IV da neurons causes detachment of dendrites from the ECM, we tested if supplying more integrins in the dendrites promotes attachment to the ECM, by expressing UAS-mys and UAS-mew, individually or in combination, in class IV da neurons. Overexpression of Mys, but not Mew, in class IV da neurons causes significant dendritic reduction ( Figures S1A and S1B). Expressing Mys and Mew simultaneously largely rescues the dendritic reduction associated with Mys overexpression ( Figure S1C). Because Mys and Mew function as heterodimers and the balance of their dosages is likely important, we

further analyzed the animals in which both Mys and Mew are overexpressed in class IV da neurons. At the ventral Suplatast tosilate midline, the percentage of enclosed dendrites of vdaB is 8.43% ( Figures 4A and 4C) in the wild-type control. In contrast, Mys and Mew coexpression in vdaB completely eliminated the dendrite enclosure and associated noncontacting dendritic crossing ( Figures 4B and 4C), suggesting that Mys and Mew mediate the attachment of dendrites to the ECM. Since studies of loss or gain of integrin function implicate Mys and Mew activity in dendrites, including terminal branches, we asked whether Mys and Mew are localized on class IV da dendrites. Unfortunately, the high levels of epidermal expression of Mys and Mew at the basal surface (Figures S1D–S1E″) render it difficult to distinguish Mys and Mew on dendrites.