RhoL controls invasion and Rap1 localization during immune cell transmigration in Drosophila

Abstract

Human immune cells penetrate an endothelial barrier during their beneficial pursuit of infection and their destructive infiltration in autoimmune diseases. This transmigration requires Rap1 GTPase to activate Integrin affinity1. We define a new model system for this process by demonstrating with live imaging and genetics that during embryonic development, Drosophila melanogaster immune cells penetrate an epithelial, DE-Cadherin-based tissue barrier. A mutant in RhoL, a GTPase homolog that is specifically expressed in hemocytes, blocks this invasive step but not other aspects of guided migration. RhoL mediates Integrin adhesion caused by Drosophila Rap1 over-expression and moves Rap1 away from a cytoplasmic concentration to the leading edge during invasive migration. These findings indicate that a programmed migratory step during Drosophila development bears striking molecular similarities to vertebrate immune cell transmigration during inflammation and identify RhoL as a new regulator of invasion, adhesion and Rap1 localization. Our work establishes the utility of Drosophila for identifying novel components of immune cell transmigration and for understanding the in vivo interplay of immune cells with the barriers they penetrate.

Isoform-specific differences between Rap1A and Rap1B GTPases in the formation of endothelial cell junctions

“…In epithelial cells, GFP-Rap1 was found at sites of cell-cell contact, colocalizing with E-cadherin, however, which isoform of Rap1 used was not disclosed in this paper. 70 Recently, GFP-Rap1 (isoform not specified) was found to be recruited to the leading edge during migration of Drosophila immune cells undergoing developmental migration 71 and in endothelial cells during wound healing, 39 indicating there may be a dynamic regulation of localization during certain cellular events. Here we explored whether the Rap1 isoforms localize to different subcellular regions, which might account for their functional specificity.…”

Emergence of embryonic pattern through contact inhibition of locomotion

“…Drosophila haemocytes are highly migratory cells that are readily amenable to analysis of their developmental movements in vivo (Wood et al, 2006;Stramer et al, 2008;Siekhaus et al, 2010;Stramer et al, 2010). They are initially derived at stage 10-11 of Drosophila development and subsequently disperse evenly throughout the embryo, taking stereotypical migratory routes.…”

Drosophilacellular immunity: a story of migration and adhesion

“…A recent study demonstrated that, in Drosophila embryonic plasmatocytes, RhoL interferes with Rap1 GTPase-induced integrin adhesion, by inhibiting the localisation of Rap1 to the leading edge. Inhibition of integrinbased adhesion is necessary to regulate the cadherin interactions that allow plasmatocytes to transmigrate from the head region, through the epithelium, to the posterior of the embryo (Siekhaus et al, 2010). The molecular events underlying this transmigration are very similar to those in the migration of vertebrate immune cells during inflammation (Basoni et al, 2005; Ebisuno et al, 2009;M'Rabet et al, 1998).…”

“…As a mutation in Ras85D is known to affect larval haemocyte behaviour and cell morphology, Ras85D might be required for 1375 Drosophila cellular immunity (Bakal et al, 2007;Rogers et al, 2003;Zettervall et al, 2004). It has been demonstrated that RhoL is not necessary for Pvr-induced plasmatocyte migration along the VNC (Paladi and Tepass, 2004;Siekhaus et al, 2010). Taken together, however, the above results suggest that Drosophila Pvr activates Ras and Rac GTPases (Rap1, Ras85D, Rac1 and Rac2) to ensure appropriate cellular migration in response to developmental signals, in a manner similar to that with the mammalian PDGF receptor.…”