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

Abstract

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.