They found that in addition to being required for the formation of three-way junctions, atlastins are also necessary to maintain such junctions. performed CRISPR/Cas9 gene knock outs and stable gene transfections in mammalian cells and also investigated egg extracts from the frog Xenopus, which can form an endoplasmic reticulum network in vitro that is strikingly similar to that seen in intact cells. Now, in eLife, Tom Rapoport and co-workers at Harvard Medical School – including Songyu Wang, Hanna Tukachinsky and Fabian Romano – report on how three key proteins work together to shape and maintain the endoplasmic reticulum ( Wang et al., 2016). Proteins involved in shaping the endoplasmic reticulum have mostly been studied individually, even though they are known to interact with one another. Increasingly, studies have revealed dynamic changes in the shape of the endoplasmic reticulum in processes such as cell division and during electrical activity in neurons ( Goyal and Blackstone, 2013 Phillips and Voeltz, 2016). Several other proteins help the endoplasmic reticulum to maintain contact with the cell membrane, other cell compartments and the cytoskeleton. Atlastin proteins mediate the tethering and fusion of tubules to one other to form three-way junctions ( Hu et al., 2009 Orso et al., 2009), which appear to be stabilized by a membrane protein called lunapark ( Shemesh et al., 2014 Chen et al., 2015). Membrane proteins of the reticulon and REEP families can generate curves in membranes and act to maintain the tubules ( Voeltz et al., 2006). In many cases, these proteins are evolutionarily conserved across eukaryotes, from yeast to mammalian cells. Over the past decade, several proteins that shape the endoplasmic reticulum have been identified. Image credit: Goyle and Blackstone (public domain). From the rough endoplasmic reticulum, the tubules of the smooth endoplasmic reticulum (blue) form a network that extends across the cell and is interspersed with sheet-like structures (peripheral sheets).

The nuclear envelope is also connected to the stacked sheets (cisternae) of the rough endoplasmic reticulum, which is specialized for protein production. At the center of the cell, the nuclear envelope contains pores that control what molecules enter and exit the nucleus.

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