title: Spatial organization of the Ran pathway by microtubules in mitosis.
abstract: Concentration gradients of soluble proteins are believed to be responsible for control of morphogenesis of subcellular systems, but the mechanisms that generate the spatial organization of these subcellular gradients remain poorly understood. Here, we use a newly developed multipoint fluorescence fluctuation spectroscopy technique to study the ras-related nuclear protein (Ran) pathway, which forms soluble gradients around chromosomes in mitosis and is thought to spatially regulate microtubule behaviors during spindle assembly. We found that the distribution of components of the Ran pathway that influence microtubule behaviors is determined by their interactions with microtubules, resulting in microtubule nucleators being localized by the microtubules whose formation they stimulate. Modeling and perturbation experiments show that this feedback makes the length of the spindle insensitive to the length scale of the Ran gradient, allows the spindle to assemble outside the peak of the Ran gradient, and explains the scaling of the spindle with cell size. Such feedback between soluble signaling pathways and the mechanics of the cytoskeleton may be a general feature of subcellular organization.
authors.affiliation: John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138; Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138; Faculty of Arts and Sciences Center for Systems Biology, Harvard University, Cambridge, MA 02138 doogieoh@fas.harvard.edu dneedle@seas.harvard.edu.
authors.forename: Doogie
authors.initials: D
authors.lastname: Oh
authors.affiliation: John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138;
authors.forename: Che-Hang
authors.initials: CH
authors.lastname: Yu
authors.affiliation: John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138; Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138; Faculty of Arts and Sciences Center for Systems Biology, Harvard University, Cambridge, MA 02138 doogieoh@fas.harvard.edu dneedle@seas.harvard.edu.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Needleman
mesh_terms: D000465:Algorithms; D045744:Cell Line, Tumor; D025461:Feedback, Physiological; D006801:Humans; D018613:Microscopy, Confocal; D008870:Microtubules / Q000378:metabolism*; D008938:Mitosis; D011485:Protein Binding; D034622:RNA Interference; D015398:Signal Transduction; D008941:Spindle Apparatus / Q000378:metabolism; D020931:ran GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: C120587:RAN protein, human; D020931:ran GTP-Binding Protein
keywords: RanGTP gradient; feedback loop; microtubule nucleation; spatial organization; spindle size