Imaginal disc growth factors are Drosophila Chitinase-like Proteins with roles in morphogenesis and CO2 response

Abstract

Chitinase-like proteins (CLPs) are members of the family 18 glycosyl hydrolases, which include chitinases and the enzymatically inactive CLPs. A mutation in the enzymes catalytic site, conserved in vertebrates and invertebrates, allowed CLPs to evolve independently with functions that do not require chitinase activity. CLPs normally function during inflammatory responses, wound healing, and host defense, but when they persist at excessive levels at sites of chronic inflammation and in tissue-remodeling disorders, they correlate positively with disease progression and poor prognosis. However, little is known about their physiological function. Drosophila melanogaster has six CLPS, termed Imaginal disc growth factors (Idgfs), encoded by Idgf1, Idgf2, Idgf3, Idgf4, Idgf5, and Idgf6. In this study we developed tools to facilitate characterization of the physiological roles of the Idgfs by deleting each of the Idgf genes using the CRISPR/Cas9 system and assessing loss-of-function phenotypes. Using null lines, we showed that loss-of-function for all six Idgf proteins significantly lowers fertility and viability and compromises germ cell migration. We also showed that Idgfs play roles in epithelial morphogenesis, maintaining proper epithelial architecture and cell shape, regulating E-cadherin and cortical Actin, and protecting these tissues against CO2 exposure. Defining the normal molecular mechanisms of CLPS is key to understanding how deviations tip the balance from a physiological to a pathological state.