Budding Yeast Has a Minimal Endomembrane System

Abstract

The endomembrane system consists of the secretory and endocytic pathways, which communicate by transport to and from the trans-Golgi network (TGN). In mammalian cells, the endocytic pathway includes early, late, and recycling endosomes. In budding yeast, different types of endosomes have been described, but the organization of the endocytic pathway has been unclear. We performed a spatial and temporal analysis of yeast endosomal markers and endocytic cargoes. Our results indicate that the yeast TGN also serves as an early and recycling endosome. In addition, as previously described, yeast contains a late or prevacuolar endosome (PVE). Endocytic cargoes localize to the TGN shortly after internalization, and manipulations that perturb export from the TGN can slow the passage of endocytic cargoes to the PVE. Yeast apparently lacks a distinct early endosome. Thus, yeast has a simple endocytic pathway that may reflect the ancestral organization of the endomembrane system. eTOC Blurb Although mammalian endocytic pathway has early, late, and recycling endosomes, the Saccharomyces cerevisiae system is unresolved. Day et al. show that yeast only has two endosome types: the trans-Golgi network, functioning as both early and recycling endosome, and the longlived prevacuolar endosome, possibly reflecting ancestral organization of the endomembrane system.

ESCRT‐dependent protein sorting is required for the viability of yeast clathrin‐mediated endocytosis mutants

“…To determine if increased recycling of endocytosed proteins is responsible for the elevated cargo concentration observed at cell surfaces in the absence of Vps4, we generated vps4 Δ rcy1 Δ double mutant strains expressing Ste3‐, Mep3‐ or Ptr2‐GFP. Rcy1 is involved in the recycling of endocytosed proteins, aiding in the return of cargo from endosomes to the PM 60 ; because recent reports suggest that yeast is devoid of early endosomes and that the functions of these organelles are instead carried out at the trans ‐Golgi network, this path may in fact be from Golgi to PM 10 …”

“…It is possible that these structures are enlarged early or recycling endosomes, or exaggerated versions of the prevacuolar organelles normally observed in class E mutants. However, if new thinking regarding the yeast endomembrane system is correct in that the trans ‐Golgi supports early and recycling endosome functions, 10 it is possible that they are, instead, expanded trans ‐Golgi networks, especially since prior studies have shown that Rcy1 acts with Drs2 at the Golgi to promote endocytic recycling 61‐63 …”

“…Some cargoes undergo endocytic recycling and are returned to the PM via delivery to recycling endosomes, 6‐9 while other proteins remain at the early endosome for delivery to the late endosome. Recent evidence suggests that, unlike other eukaryotic species, budding yeast lack early endosomes 10 . In place of these organelles, the trans ‐Golgi network may be the initial target of endocytosed material, which then either recycles proteins or transfers them to the yeast equivalent of the late endosome.…”

Papel de los adaptadores de clatrina GGA y Ent3, y de la SNARE Fsv1 en el tráfico entre la red trans del Golgi, el endosoma prevacuolar y la vacuola

“…En estos microorganismos la distinción entre TGN y endosomas tempranos ha resultado siempre complicada. En este sentido, un estudio reciente ha establecido que los endosomas tempranos se corresponden en realidad con diferentes estadios de maduración del TGN (Day et al, 2018 (Cowles et al, 1997;Frankel and Audhya, 2018;Stepp et al, 1997).…”

“…Abreviaturas: RE, retículo endoplásmico; TGN, red trans del Golgi; PM, membrana plasmática; y PVE, endosoma prevacuolar. Adaptado de Day et al, 2018. B: Parte superior: Representación de la estructura de un trisquelión.…”