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Abstract: The endoplasmic reticulum (ER) is involved in many critical processes, including protein and lipid synthesis and calcium storage. Morphologically, the ER can be divided into two subdomains: a network of interconnected tubules and interspersed sheets. Until recently, how these different compartments form in a continuous membrane system was unclear. Several classes of integral membrane proteins have been identified in the ER; the reticulons and DP1/Yop1p play roles in the generation of ER tubules, and possibly in stabilizing ER sheets, atlastins and Sey1p are dynamin-like GTPases that facilitate tubular network formation by mediating ER membrane fusion, and Climp63, p180, and kinectin are enriched in ER sheets and influence their formation. In this review, we summarize recent advances in our understanding of how these proteins participate in ER shaping. We also discuss possible mechanisms for regulating ER morphology via the cytoskeleton. Lessons learned about sculpting the ER membrane may be applicable to other organelles. [Copyright &y& Elsevier]

Summary In eukaryotic cells, organelles and the cytoskeleton undergo highly dynamic yet organized interactions capable of orchestrating complex cellular functions. Visualizing these interactions requires noninvasive, long-duration imaging of the intracellular environment at high spatiotemporal resolution and low background. To achieve these normally opposing goals, we developed grazing incidence structured illumination microscopy (GI-SIM) that is capable of imaging dynamic events near the basal cell cortex at 97-nm resolution and 266 frames/s over thousands of time points. We employed multi-color GI-SIM to characterize the fast dynamic interactions of diverse organelles and the cytoskeleton, shedding new light on the complex behaviors of these structures. Precise measurements of microtubule growth or shrinkage events helped distinguish among models of microtubule dynamic instability. Analysis of endoplasmic reticulum (ER) interactions with other organelles or microtubules uncovered new ER remodeling mechanisms, such as hitchhiking of the ER on motile organelles. Finally, ER-mitochondria contact sites were found to promote both mitochondrial fission and fusion. Graphical Abstract Highlights • Super-resolution live-cell imaging up to 266 fps at 97-nm resolution • Hitchhiking interactions among organelles remodel ER and mitochondrial networks • ER-mitochondrion contacts promote coalescence of mitochondrial membranes • Collision of late endosomes or lysosomes carried along microtubules split ER tubules A new approach for visualizing dynamic processes within cells offers insight into membrane-membrane contact interactions and microtubule function. [ABSTRACT FROM AUTHOR]