Heterotrimeric G Proteins Regulate a Noncanonical Function of Septate Junction Proteins to Maintain Cardiac Integrity in Drosophila

The gene networks regulating heart morphology and cardiac integrity are largely unknown. We previously reported a role for the heterotrimeric G protein γ subunit 1 (Gγ1) in mediating cardial-pericardial cell adhesion in Drosophila. Here we show G-oα47A and Gβ13F cooperate with Gγ1 to maintain cardiac integrity. Cardial-pericardial cell adhesion also relies on the septate junction (SJ) proteins Neurexin-IV (Nrx-IV), Sinuous, Coracle, and Nervana2, which together function in a common pathway with Gγ1. Furthermore, Gγ1 signaling is required for proper SJ protein localization, and loss of at least one SJ protein, Nrx-IV, induces cardiac lumen collapse. These results are surprising because the embryonic heart lacks SJs and suggest that SJ proteins perform noncanonical functions to maintain cardiac integrity in Drosophila. Our findings unveil the components of a previously unrecognized network of genes that couple G protein signaling with structural constituents of the heart.