Increased spatiotemporal resolution reveals highly dynamic dense tubular matrices in the peripheral ER

TLDR

The endoplasmic reticulum is a large, membrane‑bound organelle essential for many cellular functions, and its peripheral components have traditionally been described as a mix of tubules and flat sheets. Using emerging super‑resolution imaging, the authors examined the morphology and dynamics of the peripheral ER, which interfaces with most other organelles. They found that the peripheral ER is almost entirely composed of densely packed tubules forming dynamic matrices, a structure previously mistaken for sheets and accounting for earlier reports of sheet proliferation upon overexpression of junction‑forming proteins.

Abstract

The endoplasmic reticulum (ER) is an expansive, membrane-enclosed organelle that plays crucial roles in numerous cellular functions. We used emerging superresolution imaging technologies to clarify the morphology and dynamics of the peripheral ER, which contacts and modulates most other intracellular organelles. Peripheral components of the ER have classically been described as comprising both tubules and flat sheets. We show that this system consists almost exclusively of tubules at varying densities, including structures that we term ER matrices. Conventional optical imaging technologies had led to misidentification of these structures as sheets because of the dense clustering of tubular junctions and a previously uncharacterized rapid form of ER motion. The existence of ER matrices explains previous confounding evidence that had indicated the occurrence of ER "sheet" proliferation after overexpression of tubular junction-forming proteins.