Endoplasmic reticulum contact sites regulate the dynamics of membraneless organelles

ER regulates stress granule fission A hallmark of eukaryotic cells is the ability to compartmentalize essential reactions into membrane-bound and membraneless organelles. Membrane-bound organelles form networks through transport vesicles and interorganellar contact sites. The endoplasmic reticulum (ER) has emerged as a network hub and forms physical connections with nearly every membrane-bound organelle. Lee et al. now identify another class of ER contact sites that appear to help regulate the biogenesis and fission of membraneless ribonucleoprotein (RNP) granules (see the Perspective by Kornmann and Weis). Live-cell fluorescence microscopy of human cells revealed that ER tubule dynamics are spatially and temporally coupled to the fission site of two types of RNP granules, processing bodies (P-bodies) and stress granules. Science , this issue p. eaay7108 ; see also p. 507