The apical scaffold big bang binds to spectrins and regulates the growth of Drosophila melanogaster wing discs

During development, cell numbers are tightly regulated, ensuring that tissues and organs reach their correct size and shape. Recent evidence has highlighted the intricate connections between the cytoskeleton and the regulation of the key growth control Hippo pathway. Looking for apical scaffolds regulating tissue growth, we describe that Drosophila melanogaster big bang (Bbg), a poorly characterized multi-PDZ scaffold, controls epithelial tissue growth without affecting epithelial polarity and architecture. bbg-mutant tissues are smaller, with fewer cells that are less apically constricted than normal. We show that Bbg binds to and colocalizes tightly with the β-heavy–Spectrin/Kst subunit at the apical cortex and promotes Yki activity, F-actin enrichment, and the phosphorylation of the myosin II regulatory light chain Spaghetti squash. We propose a model in which the spectrin cytoskeleton recruits Bbg to the cortex, where Bbg promotes actomyosin contractility to regulate epithelial tissue growth.