Abstract
ABSTRACTDifferentiation of germline stem cells (GSCs) in the Drosophila ovary is induced by somatic escort cells (ECs), which extend membrane protrusions encapsulating the germline cells (GCs). Germline encapsulation requires activated epidermal growth factor receptor (Egfr) signaling within the ECs, following secretion of its ligands from the GCs. We show that the conserved family of irre cell recognition module (IRM) proteins is essential for GC encapsulation by ECs, with a requirement for roughest (rst) and kin of irre (kirre) in the germline and for sticks and stones (sns) and hibris (hbs) in ECs. In the absence of IRM components in their respective cell types, EC extensions are reduced concomitantly with a decrease in Egfr signaling in these cells. Reintroducing either activated Egfr in the ECs, or overexpressing its ligand Spitz (Spi) from the germline, rescued the requirement for IRM proteins in both cell types. These experiments introduce novel essential components, the IRM proteins, into the process of inductive interactions between GCs and ECs, and imply that IRM-mediated activity is required upstream of the Egfr signaling.
Highlights
Stem cell function depends on proper input from their environment
Kirre and Rst are required within germline cells for their encapsulation by escort cells (ECs) In order to identify novel components required for germline encapsulation by ECs, an RNAi-based screen with candidate genes coding for putative membrane or ECM proteins was performed
Whereas sns-RNAi caused decreased ECs extensions in 61% of the germaria (n=40), its co-expression with epidermal growth factor receptor (Egfr)-CA decreased the reduction of EC extension to 38% of the germaria (n=42, P
Summary
Anchoring of the germline stem cells (GSCs) to the maintenance niche is essential for them to preserve a stem cell state (Song and Xie, 2002; Xie and Spradling, 2000), and the encapsulation of the differentiating germline cells (GCs) by escort cells (ECs) is a prerequisite for their differentiation (Kirilly et al, 2011; Maimon et al, 2014; Su et al, 2018). Continuous egg production depends on GSCs, which are housed at the anterior tip of each ovariole, in the germarium (Kirilly and Xie, 2007; Xie and Spradling, 2000). The cap cells of the maintenance niche and the GSCs express the DE-cadherin shotgun, which mediates their attachment to each other, and lack of DE-cadherin results in stem
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