Mitochondria and endosomes undergo fission and fusion to, respectively, maintain their integrity and properly sort signalling receptors in the cell.

Additionally, ER Ca 2+ release may regulate protein complexes at ER MCS. Organelles can sequester Ca 2+ released from the ER, which can regulate processes in these organelles. ER MCS may also transfer lipids between membranes.ĮR–organelle MCSs are sites of dynamic Ca 2+ crosstalk. Lipid-synthesis proteins on the ER can modify lipids on the membrane of another organelle or on protein complexes. Recently identified factors have been shown to regulate organelle trafficking through MCS formation.ĮR–organelle MCSs regulate the lipid environment of the organelle membrane apposed to the ER. Live-cell fluorescence microscopy reveals that ER-organelle MCSs can remain stable while both organelles traffic through the cell on the cytoskeleton. Ribosomes are excluded from the ER membrane at MCSs, and the distance between the ER and other membranes is close enough to suggest that the two organelles are tethered together by other proteins located on apposing membranes. The function of MCSs between the ER and mitochondria and endosomes are summarized in this Review.Įlectron microscopy studies reveal that although MCSs are less than 30 nm apart, the membranes do not fuse and each organelle maintains its identity. The endoplasmic reticulum (ER) forms tight membrane contact sites (MCSs) with several organelles in animal cells and yeast.

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