Reassessment of the role of plasma membrane domains in the regulation of vesicular traffic in yeast

Abstract

SummaryThe Saccharomyces cerevisiae plasma membrane has been proposed to contain two stably distributed domains. One of these domains, known as MCC (membrane compartment of Can1) or eisosomes, consists of furrow-like membrane invaginations and associated proteins. The other domain, called MCP (membrane compartment of Pma1), consists of the rest of the membrane area surrounding the MCC patches. The role of this plasma membrane domain organization in endocytosis is under debate. Here we show by live-cell imaging that vesicular traffic is restricted to the MCP and the distribution of endocytic and exocytic sites within the MCP is independent of the MCC patch positions. Photobleaching experiments indicated that Can1 and Tat2, two MCC-enriched permeases, exchange quickly between the two domains. Total internal reflection fluorescence and epi-fluorescence microscopy showed that the enrichment of Can1 at the MCC persisted after addition of its substrate, whereas the enrichment of Tat2 disappeared within 90 seconds. The rates of stimulated endocytosis of Can1 as well as Tat2 were similar in both wild-type cells and pil1D cells, which lack the MCC. Thus, our data suggest that the enrichment of certain plasma membrane proteins in the MCC does not regulate the rate of their endocytosis.

Phosphoinositide-bis-phosphate is required for Saccharomyces cerevisiae invasive growth

“…Using the GFP-PH Plcd -PH Plcd -GFP reporter we observed enrichment of PtdIns(4,5)P 2 throughout the plasma membrane of small buds with 2-3-fold the concentration of PtdIns(4,5)P 2 in the bud compared to the back of the mother cells. Previous studies have shown using the inositolpolyphosphate 5-phosphatase synaptojanin Sjl2p and the ANTH domain from Sla2p to visualize PtdIns(4,5)P 2 that this phospholipid is localized to endocytosis sites which are concentrated in small buds (Sun et al, 2007;Brach et al, 2011). The loss of PtdIns(4,5)P 2 polarity in the mss4-f12 cells is consistent with the suggestion that membrane traffic via endocytosis and exocytosis is important for invasive growth.…”

Microcompartments within the yeast plasma membrane

“…The lipid composition of the plasma membrane is apparently also monitored by the MCC transmembrane protein Nce102, which signals the two Pkh kinases (Fr ö hlich et al, 2009 ). As expected, the deletion of PIL1 leads to a loss of the MCC compartments, with a homogenous distribution of the respective membrane proteins within the plasma membrane and the accumulation in one or a few clusters of the ' eisosome remnants ' , which are only detectable in the later stages of cell growth (Brach et al , 2011 ). Surprisingly, the loss of the closely related Lsp1 function does not cause a disassembly of the eisosomes and the MCC microcompartment, indicating subtle functional differences.…”

“…Consistent with this observation, the position of the eisosomes in Ashbya gossypii , a filamentous fungus closely related to S. cerevisiae , did not coincide with the bulk of the endocytic traffic at the hyphal tip, but they rather accumulated in the subapical tip regions (Seger et al , 2011 ). In vivo photobleaching experiments in S. cerevisiae suggest that the organization of the MCC compartments within the yeast plasma membrane has no influence on the intracellular vesicle trafficking, also opposing a function in endocytosis (Brach et al , 2011 ). In fact, both endocytosis and exocytosis were found to be restricted to the MCP microcompartment, independent of the position of the neighboring MCC patches.…”

Endocytic Accessory Factors and Regulation of Clathrin-Mediated Endocytosis

“…At a smaller spatial scale the endocytic events in yeast appear random, except that they are excluded from plasma membrane regions that are in contact with cortical endoplasmic reticulum (Stradalova et al 2012) and from eisosomes, stable microdomains of the fungal plasma membrane (Brach et al 2011). The exclusion of endocytosis from these regions is most likely attributable to steric hindrance inhibiting bud nucleation.…”