Mitochondria-ER contact sites expand during mitosis.

Overview

Mitochondria-ER contact sites (MERCS) are involved in energy homeostasis, redox and Ca²⁺ signaling, and inflammation. MERCS are heavily studied; however, little is known about their regulation during mitosis. Here, we show that MERCS expand during mitosis in three cell types using various approaches, including transmission electron microscopy, serial EM coupled to 3D reconstruction, and a split GFP MERCS marker. We further show enhanced Ca²⁺ transfer between the ER and mitochondria using either direct Ca²⁺ measurements or by quantifying the activity of Ca²⁺-dependent mitochondrial dehydrogenases. Collectively, our results support a lengthening of MERCS in mitosis that is associated with improved Ca²⁺ coupling between the two organelles. This augmented Ca²⁺ coupling could be important to support the increased energy needs of the cell during mitosis.