Imaginal disk 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 enzyme's 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. Little is known, however, 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 viability and fertility. We also showed that Idgfs play roles in epithelial morphogenesis, maintaining proper epithelial architecture and cell shape, regulating E-cadherin and cortical Actin, and remarkably, 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.

CO2 exposure drives a rapid pH response in live adult Drosophila

“…Thus, the dorsal appendages provide a readout for proper tube formation ( Fig 1D” and 1D”‘ ). The defects in Idgf-null dorsal appendages peaked at 8–10 hours after the CO 2 pulse and returned to the basal level by 27 hours [ 3 ]. The wild-type flies developed normally despite the loss of cortical actin apparent at 30 minutes post CO 2 exposure.…”

“…We previously tested how different CO 2 exposure regimes affected dorsal appendage development, including a single 1-minute pulse of 100% CO 2 , which increased defects in Idgf-null eggs but not in control eggs; a 1-minute pulse of 100% CO 2 every 12 hours for 3.5 days, which increased defects in Idgf-null eggs but not in control eggs; and continuous 20% CO 2 for up to eight days, which produced no increase in defects in either genotype [ 3 ]. Note that CO 2 makes up about 0.04% of the ambient atmosphere [ 24 ].…”

“…CO 2 anesthesia, however, can have adverse effects: it impairs fertility, suppresses the immune system, and it can negatively impact climbing and flight behavior for hours or days [ 1 , 2 ]. We demonstrated that CO 2 exposure enhances specific morphogenetic defects in flies with null mutations in Imaginal disc growth factor s ( Idgf s), a family of six genes that encode Drosophila chitinase-like proteins with orthologs in humans [ 3 ]. In addition, CO 2 exposure induces a loss of cortical actin during oogenesis and embryonic development in both wild-type and Idgf-null flies [ 3 ].…”

“…We demonstrated that CO 2 exposure enhances specific morphogenetic defects in flies with null mutations in Imaginal disc growth factor s ( Idgf s), a family of six genes that encode Drosophila chitinase-like proteins with orthologs in humans [ 3 ]. In addition, CO 2 exposure induces a loss of cortical actin during oogenesis and embryonic development in both wild-type and Idgf-null flies [ 3 ]. Wild-type flies proceed to develop normally, but Idgf-null flies do not, suggesting a possible role for Idgf s in protecting against adverse effects of CO 2 .…”

Molecular identification and functional analysis of chitinase genes reveal their importance in the metamorphosis of Sarcophaga peregrina (Diptera: Sarcophagidae)

“…Notably, the down-regulation of Cht10 results in severe phenotypes, including wing differentiation failure, ecdysis disturbance, growth inhibition, pupariation failure, and death ( Dong et al 2020 , Qu et al 2021 ). Meanwhile, it was reported that IDGFs were essential for Drosophila fertility ( Sustar et al 2023 ). Despite extensive studies on chitinase function in numerous insects, its role in the flesh fly remains unexplored.…”