Loss of focal adhesions in glia disrupts both glial and photoreceptor axon migration in the Drosophila visual system

Abstract

Many aspects of glial development are regulated by extracellular signals, including those from the extracellular matrix (ECM). Signals from the ECM are received by cell surface receptors, including the integrin family. Previously, we have shown that Drosophila integrins form adhesion complexes with Integrin-linked kinase and talin in the peripheral nerve glia and have conserved roles in glial sheath formation. However, integrin function in other aspects of glial development is unclear. The Drosophila eye imaginal disc (ED) and optic stalk (OS) complex is an excellent model with which to study glial migration, differentiation and glia-neuron interactions. We studied the roles of the integrin complexes in these glial developmental processes during OS/eye development. The common beta subunit βPS and two alpha subunits, αPS2 and αPS3, are located in puncta at both glia-glia and glia-ECM interfaces. Depletion of βPS integrin and talin by RNAi impaired the migration and distribution of glia within the OS resulting in morphological defects. Reduction of integrin or talin in the glia also disrupted photoreceptor axon outgrowth leading to axon stalling in the OS and ED. The neuronal defects were correlated with a disruption of the carpet glia tube paired with invasion of glia into the core of the OS and the formation of a glial cap. Our results suggest that integrin-mediated extracellular signals are important for multiple aspects of glial development and non-autonomously affect axonal migration during Drosophila eye development.

Drosophila glia: Few cell types and many conserved functions

“…Wrapping glial morphogenesis depends on Integrin and Laminin signaling (Petley-Ragan et al, 2016;Xie & Auld, 2011;Xie, Gilbert, Petley-Ragan, & Auld, 2014) and requires enzymes controlling sphingolipid biosynthesis (Ghosh et al, 2013). In line with that, a role for the glycosphingolipid synthesis in peripheral glial development was shown in mutants of the glycosyltransferase egghead (Dahlgaard et al, 2012).…”

Drosophila PS2 and PS3 integrins play distinct roles in retinal photoreceptors–glia interactions

“…Most crosses were raised at 25 C under standard conditions. Exceptions were the ones using the tub-Gal80 ts (McGuire et al, 2003) that were raised at 18 C for approximately 72 h and then moved to 25 C. The following stocks (described in FlyBase, unless stated otherwise) were used: If-GFP (DGRC #115467; Xie et al, 2014), repo-Gal4 (pan-glia; Xiong et al, 1994), moody-Gal4 (subperineurial glia; Bainton et al, 2005), Mz97-Gal4, UAS Stinger (wrapping glia; Hummel et al, 2002), UAS-dicer-2 (Dietzl et al, 2007), UAS-lacZ, UAS-CD8GFP (Lee and Luo, 1999), UAS-CD4tdTOM (Han et al, 2011), UAS-aPS2 RNAi (JF02695, previously validated Liu et al, 2013), UAS-bPS RNAi (VDRC KK100518; and GD15002, previously validated (Nishimura et al, 2014;Xie and Auld, 2011) and TRIP JF02819), UAS-aPS3 RNAi (JF02696; and VDRC KK106326, both previously validated by Vanderploeg et al, 2012), UAS-talin RNAi (HMS00799 and HMS00856), UAS-RpL7a RNAi (VDRC GD10934), UAS-eIF-4a RNAi (VDRC GD14111), UAS-Ef1c RNAi (VDRC GD7427), UAS-aPS3 EY10270 , UAS-Egfr ktop (Queenan et al, 1997), and repo4.3-Gal4 (Lee and Jones, 2005). For bPS, aPS3, and Talin the lines used were KK100518, JF02696, and HMS00799, respectively, except where otherwise stated.…”

“…To study aPS3 expression ( Fig. 1G-J) we used a validated anti-aPS3 antibody (Wada et al, 2007;Xie and Auld, 2011;Xie et al, 2014; and Supp. Info.…”

Raw regulates glial population of the eye imaginal disc

“…The lack of glial spreading suggests a role for Raw in SPG, while the reduced number of glia populating the eye imaginal disc suggests that Raw may have a specific role in the PG or WG. Therefore, to explore the requirement for Raw in specific glial subtypes, glial subtype-specific Gal4 drivers were utilized to knockdown raw in the comparing pan-glial knockdown to glial subtype-specific knockdown (Xie et al, 2014). The lack of a glial reduction phenotype suggests that…”

“…Finally, cell adhesion proteins also function as critical regulators of neuron-glia interactions in the developing eye. Specifically, integrins are required in multiple glial layers for glial migration, organization of glia and neurons in the eye disc and optic stalk, and for axonal projections through the optic stalk to the brain (Tavares et al, 2015;Xie, Gilbert, Petley-Ragan, & Auld, 2014).…”