glo-3, a Novel Caenorhabditis elegans Gene, Is Required for Lysosome-Related Organelle Biogenesis

Abstract

Gut granules are specialized lysosome-related organelles that act as sites of fat storage in Caenorhabditis elegans intestinal cells. We identified mutations in a gene, glo-3, that functions in the formation of embryonic gut granules. Some glo-3(À) alleles displayed a complete loss of embryonic gut granules, while other glo-3(À) alleles had reduced numbers of gut granules. A subset of glo-3 alleles led to mislocalization of gut granule contents into the intestinal lumen, consistent with a defect in intracellular trafficking. glo-3(À) embryos lacking gut granules developed into adults containing gut granules, indicating that glo-3(1) function may be differentially required during development. We find that glo-3(1) acts in parallel with or downstream of the AP-3 complex and the PGP-2 ABC transporter in gut granule biogenesis. glo-3 encodes a predicted membrane-associated protein that lacks obvious sequence homologs outside of nematodes. glo-3 expression initiates in embryonic intestinal precursors and persists almost exclusively in intestinal cells through adulthood. GLO-3TGFP localizes to the gut granule membrane, suggesting it could play a direct role in the trafficking events at the gut granule. smg-1(À) suppression of glo-3(À) nonsense alleles indicates that the C-terminal half of GLO-3, predicted to be present in the cytoplasm, is not necessary for gut granule formation. Our studies identify GLO-3 as a novel player in the formation of lysosome-related organelles.

Statins inhibit protein lipidation and induce the unfolded protein response in the non-sterol producing nematode Caenorhabditis elegans

“…The discrepancy between the Nile red staining and the three other methods used to monitor lipid stores, i.e., CARS microscopy, Sudan black, and gas chromatography, point to some limitation of the Nile red staining method as an indicator of lipid store status in C. elegans. Indeed, others have shown that Nile red merely stains lysosome-related compartments in C. elegans (22,37), and our results also show that Nile red allows the visualization of only a subset of the lipid droplets. There are obviously a variety of gut granules types in the C. elegans intestine, of which only a subset is stained by Nile red, and staining of this subset by Nile red does not always correlate with lipid content.…”

Loss of the apical V-ATPase a-subunit VHA-6 prevents acidification of the intestinal lumen during a rhythmic behavior in C. elegans

“…Although VHA-6 certainly plays a role in facilitating proton pumping activity by the apical V-ATPase, we acknowledge that VHA-6 may also recruit cytosolic proteins to the membrane and that the lack of these proteins could have an indirect effect on nutrient absorption or fat metabolism. However, any activity of VHA-6 not related to proton pumping would be expected to occur at the apical membrane because of its restricted expression there, and we have shown that VHA-6 does not contribute to the acidification of terminally mature lysosomes, as the gut storage granules have been suggested to be (24,53,55). Nonetheless, the absence of intestinal Oil Red O staining suggests a loss of fat mass, perhaps downstream of a deficit in nutrient uptake.…”

“…In fact, the formation of acidic lysosomes has been shown to require V-ATPase activity in worms (48), and fat storage granules are specialized lysosome-related organelles (14,24,53,55). Given the lack of fat storage granules in the intestine of vha-6 mutants, we used LysoTracker Red to determine whether disruption of vha-6 expression altered staining of acidic organelles in RNAi-treated worms (Fig.…”

Lysosome-Related Organelles in Intestinal Cells Are a Zinc Storage Site in C. elegans

“…We analyzed three genes, pgp-2, glo-1 and glo-3, because well characterized loss-of-function mutations in these genes cause Glo phenotypes of different severities; wild-type animals contain hundreds of gut granules, whereas pgp-2(kx49) animals contain 10–100 gut granules, and glo-1(zu391) and glo-3(zu446) animals contain less than 10 gut granules (Hermann et al, 2005; Rabbitts et al, 2008; Schroeder et al, 2007). pgp-2 encodes an ABC transporter that localizes to the membrane of gut granules, glo-1 encodes a predicted Rab GTPase that localizes to gut granules, and glo-3 has not been molecularly identified.…”