Caenorhabditis elegans Myotubularin MTM-1 Negatively Regulates the Engulfment of Apoptotic Cells

Abstract

During programmed cell death, apoptotic cells are recognized and rapidly engulfed by phagocytes. Although a number of genes have been identified that promote cell corpse engulfment, it is not well understood how phagocytosis of apoptotic cells is negatively regulated. Here we have identified Caenorhabditis elegans myotubularin MTM-1 as a negative regulator of cell corpse engulfment. Myotubularins (MTMs) constitute a large, highly conserved family of lipid phosphatases. MTM gene mutations are associated with various human diseases, but the cellular functions of MTM proteins are not clearly defined. We found that inactivation of MTM-1 caused significant reduction in cell corpses in strong loss-of-function mutants of ced-1, ced-6, ced-7, and ced-2, but not in animals deficient in the ced-5, ced-12, or ced-10 genes. In contrast, overexpression of MTM-1 resulted in accumulation of cell corpses. This effect is dependent on the lipid phosphatase activity of MTM-1. We show that loss of mtm-1 function accelerates the clearance of cell corpses by promoting their internalization. Importantly, the reduction of cell corpses caused by mtm-1 RNAi not only requires the activities of CED-5, CED-12, and CED-10, but also needs the functions of the phosphatidylinositol 3-kinases (PI3Ks) VPS-34 and PIKI-1. We found that MTM-1 localizes to the plasma membrane in several known engulfing cell types and may modulate the level of phosphatidylinositol 3-phosphate (PtdIns(3)P) in vivo. We propose that MTM-1 negatively regulates cell corpse engulfment through the CED-5/CED-12/CED-10 module by dephosphorylating PtdIns(3)P on the plasma membrane.

Coordination of Recombination with Meiotic Progression in the Caenorhabditis elegans Germline by KIN-18, a TAO Kinase That Regulates the Timing of MPK-1 Signaling

“…N2 worms were utilized as the wild-type background. The following mutations and chromosome rearrangements were used (Ohmachi et al 2002;Zou et al 2009;Yokoo et al 2012;Spiga et al 2013): LGI-hT2[bli-4(e937) qIs48], ksr-2(dx27), glp-4(bn2) and LGIII-kin-18(ok395). The following transgenic lines were used: meIs8(GFP::COSA-1) and smIs34 [ced-1p::ced-1::GFP+rol-6(su1006)].…”

“…Germ-cell corpses were scored in adult hermaphrodites 18-20 hr post-L4 (Kelly et al 2000;Zou et al 2009). Statistical comparisons between genotypes were performed using the two-tailed Mann-Whitney test (95% C.I.).…”

“…Therefore, we asked whether kin-18 mutants also display ectopic apoptosis. We used both CED-1:: GFP and acridine orange staining as markers for apoptosis (Kelly et al 2000;Zou et al 2009). In wild-type gonads, apoptosis occurred only in late pachytene nuclei, prior to the bend region ( Figure 5, A9, C, and D).…”

Control of developmental networks by Rac/Rho small GTPases: How cytoskeletal changes during embryogenesis are orchestrated

“…For example, MTM‐1 causes X‐linked myotubular myopathy, a severe congenital muscular disorder. In C. elegans , MTM‐1 acts through the ced‐5/‐12/‐10 pathway and hence its inactivation causes significant reduction in cell corpses in strong loss‐of‐function mutants of ced‐1 , ced‐6 , ced‐7 , and ced‐2 , but not in ced‐5 , ced‐12 , or ced‐10 null mutant worms 75.In parallel to ABL‐1 and MTM‐1 a third negative regulator is acting: SRGP‐1 (Slit/Robo GTPase activating protein 1), a GAP for CED‐10/Rac. The GAP domain of SRGP‐1 binds active‐CED‐10 in vitro.…”

“…For example, MTM‐1 causes X‐linked myotubular myopathy, a severe congenital muscular disorder. In C. elegans , MTM‐1 acts through the ced‐5/‐12/‐10 pathway and hence its inactivation causes significant reduction in cell corpses in strong loss‐of‐function mutants of ced‐1 , ced‐6 , ced‐7 , and ced‐2 , but not in ced‐5 , ced‐12 , or ced‐10 null mutant worms 75.…”