Rac1 GTPase acts downstream of αPS1βPS integrin to control collective migration and lumen size in the Drosophila salivary gland

Abstract

During collective migration of the Drosophila embryonic salivary gland, the distal gland cells mediate integrin-based contacts with surrounding tissues while proximal gland cells change shape and rearrange. Here, we show that αPS1βPS integrin controls salivary gland migration through Rac1 GTPase which downregulates E-cadherin in proximal and distal gland cells, and promotes extension of actin-rich basal membrane protrusions in the distal cells. In embryos mutant for multiple edematous wings(mew), which encodes the αPS1 subunit of the αPS1βPS integrin heterodimer, or rac1 and rac2 GTPases, salivary gland cells failed to migrate, to downregulate E-cadherin and to extend basal membrane protrusions. Selective inhibition of Rac1 in just the proximal or distal gland cells demonstrate that proximal gland cells play an active role in the collective migration of the whole gland and that continued migration of the distal cells depends on the proximal cells. Loss of rac1rac2 also affected gland lumen length and width whereas, loss of mew affected lumen length only. Activation of rac1 in mew mutant embryos significantly rescued the gland migration, lumen length and basal membrane protrusion defects and partially rescued the E-cadherin defects. Independent of mew, Rac regulates cell shape change and rearrangement in the proximal gland, which is important for migration and lumen width. Our studies shed novel insight into a Rac1-mediated link between integrin and cadherin adhesion proteins in vivo, control of lumen length and width and how activities of proximal and distal gland cells are coordinated to result in the collective migration of the entire salivary gland.

Ribbon regulates morphogenesis of the Drosophila embryonic salivary gland through transcriptional activation and repression

“…3D,E). Since SG shape is also dependent on how the cells are arranged around the lumen (Chung and Andrew, 2014; Pirraglia et al, 2013; Xu et al, 2011), we analyzed cell arrangement by examining the cross-sectional images obtained along the luminal axis (Fig. 3D, E).…”

Drosophila KASH-domain protein Klarsicht regulates microtubule stability and integrin receptor localization during collective cell migration

“…The salivary gland migration defect of klar mutant embryos resembled that of embryos with mutations in integrin subunits where distal gland cells turn posteriorly but proximal gland cells do not (Bradley et al, 2003; Pirraglia et al, 2013). For example, in embryos homozygous for mew M6 , a mutation in the αPS1 integrin subunit, 100% of salivary glands fail to complete posterior turning (see also Figure 1C).…”

“…Collective migration of the salivary gland is dependent on distinct activities at the distal and proximal ends that are coordinated temporally and spatially. Proximal gland cells change shape from columnar to cuboidal, rearrange and migrate in a manner dependent on Rho and Rac GTPases (Pirraglia et al, 2013; Xu et al, 2011; Xu et al, 2008). In contrast, the distal gland cells elongate and extend basal membrane protrusions by forming integrin mediated contacts with surrounding mesoderm-derived tissues (Bradley et al, 2003; Pirraglia et al, 2013).…”

“…Proximal gland cells change shape from columnar to cuboidal, rearrange and migrate in a manner dependent on Rho and Rac GTPases (Pirraglia et al, 2013; Xu et al, 2011; Xu et al, 2008). In contrast, the distal gland cells elongate and extend basal membrane protrusions by forming integrin mediated contacts with surrounding mesoderm-derived tissues (Bradley et al, 2003; Pirraglia et al, 2013). During salivary gland migration, two classes of integrin adhesion receptors become enriched at gland-mesoderm contact sites: αPS1βPS (expressed in the salivary gland) and αPS2βPS (expressed in the surrounding mesoderm) (Jattani et al, 2009).…”

“…This integrin accumulation is functionally important as the salivary gland fails to turn and migrate posteriorly in embryos mutant for integrin subunits, such as myospheroid (encoding the βPS subunit), multiple edamatous wings (encoding αPS1) or inflated (encoding αPS2) (Bradley et al, 2003). αPS1βPS integrin controls salivary gland migration by downregulating E-cadherin and promoting basal membrane protrusions through Rac1 in the distal gland cells (Pirraglia et al, 2013). …”