IRM adhesion complexes in Drosophila melanogaster

The IRM (Irre cell recognition module) proteins are four immunoglobulin- superfamily adhesion receptors that bind each other in trans between neighbouring cells. Kin of irre (Kirre, also called Dumbfounded) and Roughest (Rst) form one pair of paralogs, and Sticks and stones (Sns) and Hibris (Hbs) the other; each Kirre/Rst protein can bind each Sns/Hbs protein. In the embryonic mesoderm, Kirre and Rst on founder cells bind Sns and Hbs on fusion-competent myoblasts to attract them and initiate myoblast fusion. The same heterophilic pairs pattern the interommatidial cells of the eye and, in nephrocytes, Sns and Kirre form the slit diaphragm.

Each pair is formed in trans between a Kirre/Rst protein on one cell and an Sns/Hbs protein on the neighbouring cell, so each gene appears in two of the four pairs. Downstream fusion machinery (for example the WAVE and WASp Arp2/3 activators and their adaptors) is context and not part of this module. The contribution of each pair differs between tissues; in myoblast fusion Kirre and Rst act redundantly in founder cells, and Sns has the major role in fusion-competent myoblasts. Sns and Hbs are given cell adhesion mediator activity (GO:0098631), which both carry in GOA by IPI; Kirre and Rst carry only cell adhesion molecule binding terms and are left without an annoton function. FlyBase groups realized by this module: IRM-CAM (FBgg0001980). Subgroups folded into it: HK-CAM, RS-CAM, HR-CAM, SK-CAM. Participants were generated from the FlyBase gene-group membership and mapped to UniProtKB by projects/FLYBASE_GENE_GROUPS/generate_modules.py from module_specs/dmel_irm_myoblast_adhesion.yaml. Member genes with a gene review in this repository: hbs, kirre, rst, sns.