How the Endoplasmic Reticulum Gets Into Shape

How is the characteristic shape of a membrane-bound organelle achieved? We have addressed the mechanism by which the morphology of the endoplasmic reticulum (ER) is generated. ER tubules are shaped by two families of integral membrane proteins, the reticulons and DP1/Yop1p, which are necessary and sufficient for tubule formation. These proteins may use hydrophobic insertion and scaffolding mechanisms to shape lipid bilayers into tubules. The interconnection of ER tubules in mammalian cells requires the atlastins, membrane-bound GTPases of the dynamin family, which probably promote homotypic fusion of the tubules. A similar GTPase in yeast, Sey1p, may have an analogous function. Our recent results suggest that the reticulons and DP1/Yop1p are also a major determinant of peripheral ER sheets, which can be further stabilized by sheet-promoting proteins.