Cisternal Organization of the Endoplasmic Reticulum during Mitosis

TLDR

The endoplasmic reticulum is a continuous membrane network of cisternae and tubules that extends throughout the cytosol and is reorganized during mitosis as the nuclear envelope partitions its contents into the ER. The study aims to determine whether the ER undergoes a major architectural transformation during cell division. Live‑cell 3‑D imaging and high‑resolution electron tomography reveal that from prometaphase to telophase most ER adopts extended cisternae with few tubules, whereas interphase ER retains a reticular network of cisternae linked to tubules.

Abstract

The endoplasmic reticulum (ER) of animal cells is a single, dynamic, and continuous membrane network of interconnected cisternae and tubules spread out throughout the cytosol in direct contact with the nuclear envelope. During mitosis, the nuclear envelope undergoes a major rearrangement, as it rapidly partitions its membrane-bound contents into the ER. It is therefore of great interest to determine whether any major transformation in the architecture of the ER also occurs during cell division. We present structural evidence, from rapid, live-cell, three-dimensional imaging with confirmation from high-resolution electron microscopy tomography of samples preserved by high-pressure freezing and freeze substitution, unambiguously showing that from prometaphase to telophase of mammalian cells, most of the ER is organized as extended cisternae, with a very small fraction remaining organized as tubules. In contrast, during interphase, the ER displays the familiar reticular network of convolved cisternae linked to tubules.