The RBG-1–RBG-2 complex modulates autophagy activity by regulating lysosomal biogenesis and function in C. elegans

Abstract

Vici syndrome is a severe and progressive multisystem disease caused by mutations in the EPG5 gene. In patient tissues and animal models, loss of EPG5 function is associated with defective autophagy caused by accumulation of non-degradative autolysosomes, but very little is known about the mechanism underlying this cellular phenotype. Here, we demonstrate that loss of function of the RBG-1-RBG-2 complex ameliorates the autophagy defect in C. elegans epg-5 mutants. The suppression effect is independent of the complex's activity as a RAB-3 GAP and a RAB-18 GEF. Loss of rbg-1 activity promotes lysosomal biogenesis and function, and also suppresses the accumulation of non-functional autolysosomes in epg-5 mutants. The mobility of late endosome-and lysosomeassociated RAB-7 is reduced in epg-5 mutants, and this defect is rescued by simultaneous loss of function of rbg-1. Expression of the GDP-bound form of RAB-7 also promotes lysosomal biogenesis and suppresses the autophagy defect in epg-5 mutants. Our study reveals that the RBG-1-RBG-2 complex acts by modulating the dynamics of membrane-associated RAB-7 to regulate lysosomal biogenesis, and provides insights into the pathogenesis of Vici syndrome.

The ER-Localized Transmembrane Protein TMEM39A/SUSR2 Regulates Autophagy by Controlling the Trafficking of the PtdIns(4)P Phosphatase SAC1

“…We also monitored the transport of the lysosome-localized DNaseII NUC-1 in C. elegans by examining the expression of a NUC-1::sfGFP::mCherry tandem reporter driven by the heat shock promoter (Wang et al, 2019). Heat shock induces the synthesis of NUC-1::sfGFP::mCherry, which is transported into the extracellular region and then endocytosed and delivered to lysosomes (Wang et al, 2019). The GFP signal is quenched in lysosomes whereas the Cherry signal is stable.…”

Spaceflight affects neuronal morphology and alters transcellular degradation of neuronal debris in adult Caenorhabditis elegans

“…The unexpected distribution of fluorescence that we observed in spaceflight P mec-4 mCherry1 animals appears comprised of two main components ( Figure 6A): small fluorescent particles resembling the Starry Night phenotype and large rounded fluorescent structures (''spaceflight vesicles'' or ''sVesicles'') that we have not previously found in this C. elegans strain under standard culture conditions (even in much older adults) (Arnold et al, 2020;. These large rounded structures have the appearance of the enlarged hypodermal lysosomes that can be found in C. elegans mutants defective in lysosomal function and assembly (Li et al, 2016;Liu et al, 2018;Wang et al, 2019).…”

“…In the case of C. elegans, touch receptor neurons are fully surrounded by hypodermal tissue, and therefore, the hypodermis assumes an analogous function to mammalian glia regarding the clearance of neuronal waste. Even though we were unable to definitively identify the hypodermal structures in which mCherry fluorescence accumulates in response to spaceflight, it is striking that the large rounded fluorescent structures (sVesicles) resemble enlarged hypodermal lysosomes found in animals defective in lysosomal function and assembly (Li et al, 2016;Liu et al, 2018;Wang et al, 2019). Moreover, the small fluorescent particles (Starry Night) have been previously described as neuron-derived mCherry that becomes dispersed in the hypodermal lysosomal network (Arnold et al, 2020;.…”

Spaceflight Affects Neuronal Morphology and Alters Transcellular Degradation of Neuronal Debris in AdultCaenorhabditis elegans

“…In the case of C. elegans , touch receptor neurons are fully surrounded by hypodermal tissue and therefore, hypodermis assumes an analogous function to mammalian glia regarding the clearance of neuronal waste. Even though we were unable to definitively identify the hypodermal structures in which mCherry fluorescence accumulates in response to spaceflight, it is striking that the large rounded fluorescent structures (sVesicles) resemble enlarged hypodermal lysosomes found in animals defective in lysosomal function and assembly [33–35]. Moreover, the small fluorescent particles (Starry Night) have been previously described as neuron-derived mCherry that becomes dispersed in the hypodermal lysosomal network [18, 19].…”

“…6A). These large rounded structures have the appearance of the enlarged hypodermal lysosomes that can be found in C. elegans mutants defective in lysosomal function and assembly [33][34][35].…”