Signaling by the Engulfment Receptor Draper: A Screen in Drosophila melanogaster Implicates Cytoskeletal Regulators, Jun N-Terminal Kinase, and Yorkie

Abstract

Draper, the Drosophila melanogaster homolog of the Ced-1 protein of Caenorhabditis elegans, is a cell-surface receptor required for the recognition and engulfment of apoptotic cells, glial clearance of axon fragments and dendritic pruning, and salivary gland autophagy. To further elucidate mechanisms of Draper signaling, we screened chromosomal deficiencies to identify loci that dominantly modify the phenotype of overexpression of Draper isoform II (suppressed differentiation of the posterior crossvein in the wing). We found evidence for 43 genetic modifiers of Draper II. Twenty-four of the 37 suppressor loci and 3 of the 6 enhancer loci were identified. An additional 5 suppressors and 2 enhancers were identified among mutations in functionally related genes. These studies reveal positive contributions to Drpr signaling for the Jun N-terminal Kinase pathway, supported by genetic interactions with hemipterous, basket, jun, and puckered, and for cytoskeleton regulation as indicated by genetic interactions with rac1, rac2, RhoA, myoblast city, Wiskcott-Aldrich syndrome protein, and the formin CG32138, and for yorkie and expanded. These findings indicate that Jun N-terminal Kinase activation and cytoskeletal remodeling collaborate in Draper signaling. Relationships between Draper signaling and Decapentaplegic signaling, insulin signaling, Salvador/Warts/Hippo signaling, apical-basal cell polarity, and cellular responses to mechanical forces are also discussed.

Scrambled Eggs: Apoptotic Cell Clearance by Non-Professional Phagocytes in the Drosophila Ovary

“…Activation of hep promotes Draper expression, suggesting JNK is required for draper induction during engulfment. Consistent with findings in the ovary, studies in the Drosophila embryonic central nervous system, adult brain, and wing epithelium have shown a requirement for the JNK pathway downstream of Draper ( 27 , 100 , 101 ). Studies in the embryonic central nervous system show that while expression levels of Draper and the bridging molecule Six-microns-under remain the same in glia that have active JNK signaling, hep CA gain of function in draper loss-of-function mutants restores defects in apoptotic clearance ( 101 ).…”

“…In macrophages, JNK is also required for the induction of draper in response to corpses ( 103 ). Surprisingly, overexpression of Draper II, the inhibitory isoform of Draper, results in increased JNK pathway activity in the wing ( 100 ). Taken together, these studies in Drosophila indicate that Draper and JNK regulate each other in multiple cellular contexts.…”

A novel Drosophila injury model reveals severed axons are cleared through a Draper/MMP-1 signaling cascade

“…We sought to develop an in vivo injury model that would elicit a broader glial response in order to identify differentially expressed genes using a large-scale transcriptional profiling screen. Recent studies revealed that peripheral sensory neurons in the wing undergo a classic Wallerian degeneration program and are cleared by glia in a Draper-dependent manner after axotomy ( Fang et al, 2012 ; Fullard and Baker, 2015 ), suggesting that glial cells throughout the adult fly nervous system use common pathways to sense and respond to degenerating axons. Thus, we turned to the ventral nerve cord (VNC) of the fly with the goal of establishing a more robust in vivo nerve injury assay to query changes in glial gene expression.…”

Critical genomic regulation mediated by Enhancer of Polycomb

“…Early studies of E(Pc) in Drosophila illustrated its critical role in chromatin regulation and we learned that E(Pc) is also involved in genomic imprint maintenance in Drosophila , likely through its role in heterochromatin maintenance (Joanis and Lloyd 2002). E(Pc) has been further highlighted for its important interactions (Table 2) with various genes and proteins involved in apoptosis and chromatin regulation, such as with ISWI (Imitation SWI), His1 (Histone H1), and Polycomb group genes (Ali and Bender 2004; Arancio et al 2010; Fullard and Baker 2015; Kavi et al 2015). As in yeast, E(Pc) is important in the cell cycle in Drosophila , where is it required during development for mitotic exit during the transition to a post-mitotic state (Flegel et al 2016).…”