Cooperation of the ER-shaping proteins atlastin, lunapark, and reticulons to generate a tubular membrane network.
In higher eukaryotes, the endoplasmic reticulum (ER) contains a network of membrane tubules, which transitions into sheets during mitosis. Network formation involves curvature-stabilizing proteins, including the reticulons (Rtns), as well as the membrane-fusing GTPase atlastin (ATL) and the lunapark protein (Lnp). Here, we have analyzed how these proteins cooperate. ATL is needed to not only form, but also maintain, the ER network. Maintenance requires a balance between ATL and Rtn, as too little ATL activity or too high Rtn4a concentrations cause ER fragmentation. Lnp only affects the abundance of three-way junctions and tubules. We suggest a model in which ATL-mediated fusion counteracts the instability of free tubule ends. ATL tethers and fuses tubules stabilized by the Rtns, and transiently sits in newly formed three-way junctions. Lnp subsequently moves into the junctional sheets and forms oligomers. Lnp is inactivated by mitotic phosphorylation, which contributes to the tubule-to-sheet conversion of the ER.
Howard Hughes Medical Institute, Harvard Medical School, Boston, United States.|Department of Cell Biology, Harvard Medical School, Boston, United States.
Songyu
S
Wang
Howard Hughes Medical Institute, Harvard Medical School, Boston, United States.|Department of Cell Biology, Harvard Medical School, Boston, United States.
Hanna
H
Tukachinsky
Howard Hughes Medical Institute, Harvard Medical School, Boston, United States.|Department of Cell Biology, Harvard Medical School, Boston, United States.
Fabian B
FB
Romano
Howard Hughes Medical Institute, Harvard Medical School, Boston, United States.|Department of Cell Biology, Harvard Medical School, Boston, United States.
Tom A
0000-0001-9911-4216
TA
Rapoport
D004721:Endoplasmic Reticulum / Q000378:metabolism*; D056890:Eukaryota; D008565:Membrane Proteins / Q000378:metabolism*; D001678:Organelle Biogenesis
D008565:Membrane Proteins
cell biology; endoplasmic reticulum; human; membrane structure; organelle morphology; xenopus