Biology subjects

Mak, H. Y.

Publications and source records attributed to Mak, H. Y..

6 recordsLinked to original sources

bioRxiv2024

A distant TANGO1 family member promotes vitellogenin export from the ER in C. elegans

Vitellogenin belongs to the Large Lipid Transfer Protein superfamily and is thought to share a common ancestor with human Apolipoprotein B (ApoB) for systemic lipid transport1-5. Vitellogenin forms part of yolk granules (also known as yolk organelles), as maternal contribution of nutrients that support the embryonic development of oviparous animals6,7. In Caenorhabditis elegans, vitellogenin proteins (VIT-1 to VIT-6) are synthesized in the hermaphrodite intestine, secreted into the pseudocoelom and internalized by oocytes8-13. Although a general route for inter-tissue vitellogenin transport has been described, the full mechanism that underlies its intracellular trafficking within the intestine remains obscure9,12,13. In humans, transport and Golgi organization protein 1 (TANGO1) and TANGO1-like (TALI) proteins generate super-sized membrane carriers to accommodate bulky ApoB-containing lipoprotein particles for their export from ER exit sites14-17. Transport facilitated by TANGO1 family of proteins is considered as an alternative, COPII-independent ER exit pathway18-24. Thus far, TANGO1 orthologs have been discovered in most metazoans, except nematodes24,25. Here, we report the C. elegans protein R148.3 (now Transport and Golgi organization 1-like or TNGL-1) as a mediator of vitellogenin export from the ER. TNGL-1 depletion triggers VIT-2 accumulation in the intestinal ER lumen. TNGL-1 requires its C-terminal unstructured domain for its localization to ER exit sites. Like TANGO1, it utilizes a luminal globular domain for cargo engagement. Our findings support TNGL-1 as a distant TANGO1 family member.

cell biology↗

bioRxiv2022

A flexible network of lipid droplet associated proteins support embryonic integrity of C. elegans

In addition to coordinating the storage and mobilization of neutral fat, lipid droplets (LDs) are conserved organelles that can accommodate additional cargos in order to support animal development. However, it is unclear if each type of cargo is matched with a specific subset of LDs. Is the identity of each subset rigidly maintained? Here, we report that SEIP-1/seipin defines a subset of oocyte LDs that are required for proper eggshell formation in C. elegans. Using a photoconvertible fluorescent protein-based imaging assay, we found that SEIP-1 positive LDs were selectively depleted after fertilization, coincident of the formation of a lipid-rich permeability barrier of the eggshell. Loss of SEIP-1 function caused impenetrant embryonic arrest, which could be suppressed by depleting a LD-structural protein PLIN-1/perilipin. The embryonic development of seip-1; plin-1 mutant in turn depended on another LD-associated protein, RAB-18/Rab18. Our results are consistent with the hypothesis that SEIP-1 dependent and independent mechanisms act redundantly to ensure the packaging and export of lipid-rich permeability barrier constituents via LDs. The identity of these LDs, as defined by their associated proteins, exhibits unexpected plasticity that ultimately ensures the survival of embryos ex utero.

cell biology↗

bioRxiv2021

The endoplasmic reticulum-resident protein TMEM-120/TMEM120A promotes fat storage in C. elegans and mammalian cells

The synthesis of triacylglycerol (TAG) is essential for the storage of excess fatty acids, which can subsequently be used for energy or cell growth. A series of enzymes act in the endoplasmic reticulum (ER) to synthesize TAG, prior to its transfer to lipid droplets (LDs), which are conserved organelles for fat storage. Here, we report that the deficiency of TMEM-120/TMEM120A, a protein with 6-transmembrane helices, retards TAG synthesis and LD expansion in C. elegans. A missense mutation near the predicted coenzyme A binding site of TMEM-120 confers strong loss of function phenotypes. GFP fusion proteins of TMEM-120, expressed at the endogenous level in live worms, were observed throughout the ER network. Using Stimulated Raman Scattering, we discovered a specific requirement of TMEM-120 in the storage of exogenous fatty acids in LDs. Knockdown of TMEM120A impedes adipogenesis of pre-adipocytes in vitro, while its over-expression is sufficient to promote LD expansion. Pharmacological studies indicate that TMEM120A most likely acts upstream of diacylglycerol O-acyltransferase 1 (DGAT1). Our results suggest that TMEM-120/TMEM120A plays a conserved role in increasing the efficiency of TAG synthesis.

cell biology↗

bioRxiv2020

Nuclear receptor NHR-49 promotes peroxisome proliferation to compensate for aldehyde dehydrogenase deficiency in C. elegans

The intracellular level of fatty aldehydes is tightly regulated to minimize the formation of toxic aldehyde adducts of cellular components. Accordingly, deficiency of a fatty aldehyde dehydrogenase FALDH causes the neurologic disorder Sjogren-Larsson syndrome (SLS) in humans. However, cellular responses to unresolved, elevated fatty aldehyde levels are poorly understood. Based on lipidomic and imaging analysis, we report that the loss of endoplasmic reticulum-, mitochondria- and peroxisomes-associated ALH-4, the C. elegans FALDH ortholog, increases fatty aldehyde levels and reduces fat storage. ALH-4 deficiency in the intestine, cell-nonautonomously induces NHR-49/NHR-79-dependent hypodermal peroxisome proliferation. This is accompanied by the upregulation of catalases and fatty acid catabolic enzymes, as indicated by RNA sequencing. Such a response is required to counteract ALH-4 deficiency since alh-4; nhr-49 double mutant animals are not viable. Our work reveals unexpected inter-tissue communication of fatty aldehyde levels, and suggests pharmacological modulation of peroxisome proliferation as a therapeutic strategy for SLS.

cell biology↗

bioRxiv2020

Dietary S. maltophilia promotes fat storage by enhancing lipogenesis and ER-LD contacts in C. elegans

Dietary and symbiotic bacteria can exert powerful influence on metazoan lipid metabolism. Here, we demonstrate that feeding Caenorhabditis elegans (C. elegans) with the opportunistic pathogenic bacteria Stenotrophomonas maltophilia (S. maltophilia) retards growth and promotes excessive fat storage. Gene expression analysis reveals that dietary S. maltophilia induces a lipogenic transcriptional response that includes the SREBP ortholog SBP-1, and fatty acid desaturases FAT-6 and FAT-7. Live imaging and ultrastructural analysis suggest that excess fat is stored in greatly expanded lipid droplets (LDs), as a result of enhanced endoplasmic reticulum-LD interaction. We also report that loss of function mutations in cyp-35B1 or dpy-9 in C. elegans confers resistance to S. maltophilia. Our work delineates a new model for understanding microbial regulation of metazoan physiology.

cell biology↗

bioRxiv2018

Dietary fatty acids promote lipid droplet diversity through seipin enrichment in an ER subdomain

Exogenous metabolites from microbial and dietary origins have profound effects on host metabolism. Here, we report that a sub-population of lipid droplets (LDs), which are conserved organelles for fat storage, is defined by metabolites-driven targeting of the C. elegans seipin ortholog, SEIP-1. Loss of SEIP-1 function reduced the size of a subset of LDs while over-expression of SEIP-1 had the opposite effect. Ultrastructural analysis revealed SEIP-1 enrichment in an endoplasmic reticulum (ER) subdomain, which co-purified with LDs. Analyses of C. elegans and bacterial genetic mutants indicated a requirement of polyunsaturated fatty acids (PUFAs) and microbial cyclopropane fatty acids (CFAs) for SEIP-1 enrichment, as confirmed by dietary supplementation experiments. In mammalian cells, heterologous expression of SEIP-1 promoted lipid droplet expansion from ER subdomains in a conserved manner. Our results suggest that microbial and polyunsaturated fatty acids serve unexpected roles in regulating cellular fat storage by enforcing LD diversity.

cell biology↗