The ABC Transporter Eato Promotes Cell Clearance in the Drosophila melanogaster Ovary

Abstract

The clearance of dead cells is a fundamental process in the maintenance of tissue homeostasis. Genetic studies in Drosophila melanogaster, Caenorhabditis elegans, and mammals have identified two evolutionarily conserved signaling pathways that act redundantly to regulate this engulfment process: the ced-1/-6/-7 and ced-2/-5/-12 pathways. Of these engulfment genes, only the ced-7/ABCA1 ortholog remains to be identified in D. melanogaster. Homology searches have revealed a family of putative ced-7/ABCA1 homologs encoding ATP-binding cassette (ABC) transporters in D. melanogaster. To determine which of these genes functions similarly to ced-7/ABCA1, we analyzed mutants for engulfment phenotypes in oogenesis, during which nurse cells (NCs) in each egg chamber undergo programmed cell death (PCD) and are removed by neighboring phagocytic follicle cells (FCs). Our genetic analyses indicate that one of the ABC transporter genes, which we have named Eato (Engulfment ABC Transporter in the ovary), is required for NC clearance in the ovary and acts in the same pathways as drpr, the ced-1 ortholog, and in parallel to Ced-12 in the FCs. Additionally, we show that Eato acts in the FCs to promote accumulation of the transmembrane receptor Drpr, and promote membrane extensions around the NCs for their clearance. Since ABCA class transporters, such as CED-7 and ABCA1, are known to be involved in lipid trafficking, we propose that Eato acts to transport membrane material to the growing phagocytic cup for cell corpse clearance. Our work presented here identifies Eato as the ced-7/ABCA1 ortholog in D. melanogaster, and demonstrates a role for Eato in Drpr accumulation and phagocytic membrane extensions during NC clearance in the ovary.

Lysosomal Machinery Drives Extracellular Acidification to Direct Non-apoptotic Cell Death

“…Phagoptosis is defined as a type of cell death that requires phagocytosis machinery (Brown and Neher, 2012). We have previously demonstrated that NC death requires phagocytic machinery, such as Draper and Ced-12 (Santoso et al, 2018; Timmons et al, 2016). In the present study, we identified lysosome-associated genes required by the SFCs that non-autonomously control the elimination of NCs.…”

“…At the end of oogenesis, the NCs dump their cytoplasmic contents into the oocyte, become surrounded by a subset of FCs called stretch follicle cells (SFCs) (Duhart et al, 2017), and are eliminated without the requirement of apoptosis or autophagy genes (Peterson and McCall, 2013). We have previously found that the SFCs require phagocytic machinery to eliminate the NCs, demonstrating that the NCs die by phagoptosis (Santoso et al, 2018; Timmons et al, 2016, 2017); however, our understanding of how NC elimination is carried out remained limited.…”

Transmission of Cricket paralysis virus via exosome-like vesicles during infection of Drosophila cells

“…From our proteomic analysis, the only protein to be enriched outside of viral proteins in the cell pellet was CG31731-RC, also recently termed Eato 42 . This protein is homologous to the C. elegans CED-7 and mammalian ABCA1 proteins and has recently been shown to be important for the cellular engulfment pathway in Drosophila ovaries 42 .…”

“…From our proteomic analysis, the only protein to be enriched outside of viral proteins in the cell pellet was CG31731-RC, also recently termed Eato 42 . This protein is homologous to the C. elegans CED-7 and mammalian ABCA1 proteins and has recently been shown to be important for the cellular engulfment pathway in Drosophila ovaries 42 . In mouse hemocytes and thymocytes, ABCA1 has a role in presentation of phosphatidylserine after apoptotic stimuli, and thus may act in dying cells to promote phagocytic engulfment 43 .…”

I Spy in the Developing Fly a Multitude of Ways to Die

“…Disruption of engulfment genes ( draper , Ced-12 , Eato , α-PS3 , βPS , or the JNK pathway) in stretch follicle cells blocks multiple cell death events including nurse cell acidification, DNA fragmentation and clearance [118,120,121]. Blocking the ABCA transporter Eato (Engulfment ABC transporter in the ovary) in stretch follicle cells additionally prevents some of the follicle cells from completely surrounding the nurse cells [121]. However, knockdown of draper or ced-12 does not block stretch follicle cells from completely surrounding the nurse cells, but does block nurse cell acidification [118].…”