Detecting new allies: Modifier screen identifies a genetic interaction betweenImaginal disc growth factor 3and a Rho-kinase substrate during dorsal appendage tube formation inDrosophila

Abstract

Biological tube formation underlies organ development, and when disrupted, can cause severe birth defects. To investigate the genetic basis of tubulogenesis, we study the formation of Drosophila melanogaster eggshell structures, called dorsal appendages, which are produced by epithelial tubes. Previously we found that precise levels of Drosophila Chitinase-like proteins (CLPs), encoded by the Imaginal disc growth factor (Idgf) gene family, are needed to regulate dorsal-appendage tube closure and tube migration. To identify factors that act in the Idgf pathway, we developed a genetic modifier screen based on the finding that overexpressing Idgf3 causes dorsal appendage defects with ~50% frequency. Using a library of partially overlapping heterozygous deficiencies, we scanned chromosome 3L and found regions that enhanced or suppressed the Idgf3-overexpression phenotype. Using smaller deletions, RNAi, and mutant alleles, we further mapped five regions and refined the interactions to 58 candidate genes. Importantly, mutant alleles identified combover (cmb), a substrate of Rho-kinase (Rok) and a component of the Planar Cell Polarity (PCP) pathway, as an Idgf3-interacting gene: loss of function enhanced while gain of function suppressed the dorsal appendage defects. Since PCP drives cell intercalation in other systems, we asked if cmb/+ affected cell intercalation in our model, but we found no evidence of its involvement in this step. Instead, we found that loss of cmb dominantly enhanced tube defects associated with Idgf3 overexpression by expanding the apical area of dorsal appendage cells. Apical surface area determines tube volume and shape; in this way, Idgf3 and cmb regulate tube morphology. ! 6!

Imaginal disc growth factors areDrosophilaChitinase-like Proteins with roles in morphogenesis and CO2response

“…A common thread among the various phenotypes produced by loss of all Idgfs is the disruption of E-cadherin and Actin, an outcome that could interfere with cell migration, segmentation, and tissue morphogenesis. Consistent with this hypothesis, we recently identified eukaryotic translation initiation factor 3 subunit e (eIF3e) as a strong enhancer of Idgf3 overexpression (E spinoza and B erg 2020). eIF3e is part of a complex that regulates the redox enzyme, Mical, which functions to disassemble Actin filaments and inhibit Actin polymerization (G rintsevich et al .…”

“…We previously observed disruption of DA morphogenesis using Idgf1 and Idgf3 overexpression (E spinoza and B erg 2020; Z immerman et al . 2017) and Idgf RNAi for each single mutant (Z immerman et al .…”

“…2017). Both over- and under-expression in egg chamber cells disrupt epithelial tube morphogenesis (E spinoza and B erg 2020; Z immerman et al . 2017).…”

“…In the ovary, Idgfs are expressed in dynamic patterns specific to the different cell types of the egg chamber (ZIMMERMAN et al 2017). Both over-and under-expression in egg chamber cells disrupt epithelial tube morphogenesis (ESPINOZA AND BERG 2020;ZIMMERMAN et al 2017). Thus, Idgfs function in diverse processes in different tissues.…”