Lipid transfer and signaling at organelle contact sites: the tip of the iceberg

Abstract

Membrane contact sites (MCSs) are formed by the close apposition of membranes of two organelles. They are zones where signals and small molecules, such as lipids and calcium, are exchanged between intracellular compartments. The past few years have seen considerable progress in our understanding of how MCSs form and facilitate the exchange of lipids and signals. Here we summarize what has been learned about MCSs between the endoplamic reticulum (ER) and the plasma membrane, the ER and mitochondria, and the ER and endosomes or lysosomes. These findings suggest that we are just beginning to understand how MCSs form and function.

Figure 1. Location of membrane contact sites

A. Endoplasmic reticulum (ER) - plasma membrane (PM) B. ER - Mitochondria (Mito) C. ER - Late endosome (LE)/ multivesicular bodies (MVB) and ER - lysosome. In yeast there are contacts between the nucleus and vacuole. D. ER – Golgi complex. E. ER and chloroplast (chloro). F. ER – peroxisome (Pex) G. ER and lipid droplets (LD). H. Contact sites between the inner and outer membranes of mitochondria and chloroplasts. Similar contacts are also found in Gram negative bacteria (not shown).