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J R McIntosh

Other affiliations: Harvard University
Bio: J R McIntosh is an academic researcher from University of Colorado Boulder. The author has contributed to research in topics: Microtubule & Dynein. The author has an hindex of 38, co-authored 51 publications receiving 11375 citations. Previous affiliations of J R McIntosh include Harvard University.


Papers
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Journal ArticleDOI
TL;DR: IMOD is useful for studying and modeling data from tomographic, serial section, and optical section reconstructions and allows image data to be visualized by several different methods.

4,830 citations

Journal ArticleDOI
TL;DR: The fibrous, fluorescence patterns that developed in the microinjected cells were almost indistinguishable from the pattern of microtubules seen in the same cells by indirect immunofluorescence, and mean half times of redistribution were 18-fold shorter in mitotic cells than they were in interphase cells.
Abstract: Bovine neurotubulin has been labeled with dichlorotriazinyl-aminofluorescein (DTAF-tubulin) and microinjected into cultured mammalian cells strains PTK1 and BSC. The fibrous, fluorescence patterns that developed in the microinjected cells were almost indistinguishable from the pattern of microtubules seen in the same cells by indirect immunofluorescence. DTAF-tubulin participated in the formation of all visible, microtubule-related structures at all cell cycle stages for at least 48 h after injection. Treatments of injected cells with Nocodazole or Taxol showed that DTAF-tubulin closely mimicked the behavior of endogenous tubulin. The rate at which microtubules incorporated DTAF-tubulin depended on the cell-cycle stage of the injected cell. Mitotic microtubules became fluorescent within seconds while interphase microtubules required minutes. Studies using fluorescence redistribution after photobleaching confirmed this apparent difference in tubulin dynamics between mitotic and interphase cells. The temporal patterns of redistribution included a rapid phase (approximately 3 s) that we attribute to diffusion of free DTAF-tubulin and a second, slower phase that seems to represent the exchange of bleached DTAF-tubulin in microtubules with free, unbleached DTAF-tubulin. Mean half times of redistribution were 18-fold shorter in mitotic cells than they were in interphase cells.

496 citations

Journal ArticleDOI
17 May 1990-Nature
TL;DR: It is shown that during mitosis, cytoplasmic dynein antigens concentrate near the kinetochores, centrosomes and spindle fibres of HeLa and PtK1 cells, whereas at interphase they are distributed throughout the cy toplasm.
Abstract: Recent evidence suggests that the force for poleward movement of chromosomes during mitosis is generated at or close to the kinetochores. Chromosome movement depends on motion relative to microtubules, but the identities of the motors remain uncertain. One candidate for a mitotic motor is dynein, a large multimeric enzyme which can move along microtubules toward their slow growing end. Dyneins were originally found in axonemes of cilia and flagella where they power microtubule sliding. Recently, cytoplasmic dyneins have also been found, and specific antibodies have been raised against them. The cellular localization of dynein has previously been studied with several antibodies raised against flagellar dynein, but the relevance of these data to the distribution of cytoplasmic dynein is not known. Antibodies raised against cytoplasmic dyneins have shown localization of dynein antigens to the mitotic spindles in Caenorhabditis elegans embryos (Lye et al., personal communication) and punctate cytoplasmic structures in Dictyostelium amoebae. Using antibodies that recognize subunits of cytoplasmic dyneins, we show here that during mitosis, cytoplasmic dynein antigens concentrate near the kinetochores, centrosomes and spindle fibres of HeLa and PtK1 cells, whereas at interphase they are distributed throughout the cytoplasm. This is consistent with the hypothesis that cytoplasmic dynein is a mitotic motor.

489 citations

Journal ArticleDOI
TL;DR: The three dimensional organization of microtubules in mitotic spindles of the yeast Saccharomyces cerevisiae has been determined by computer- aided reconstruction from electron micrographs of serially cross- sectioned spindes, and interpretation of these reconstructed spindle offers some insights into the mechanisms of mitosis in this yeast.
Abstract: The three dimensional organization of microtubules in mitotic spindles of the yeast Saccharomyces cerevisiae has been determined by computer-aided reconstruction from electron micrographs of serially cross-sectioned spindles. Fifteen spindles ranging in length from 0.6-9.4 microns have been analyzed. Ordered microtubule packing is absent in spindles up to 0.8 micron, but the total number of microtubules is sufficient to allow one microtubule per kinetochore with a few additional microtubules that may form an interpolar spindle. An obvious bundle of about eight interpolar microtubules was found in spindles 1.3-1.6 microns long, and we suggest that the approximately 32 remaining microtubules act as kinetochore fibers. The relative lengths of the microtubules in these spindles suggest that they may be in an early stage of anaphase, even though these spindles are all situated in the mother cell, not in the isthmus between mother and bud. None of the reconstructed spindles exhibited the uniform populations of kinetochore microtubules characteristic of metaphase. Long spindles (2.7-9.4 microns), presumably in anaphase B, contained short remnants of a few presumed kinetochore microtubules clustered near the poles and a few long microtubules extending from each pole toward the spindle midplane, where they interdigitated with their counterparts from the other pole. Interpretation of these reconstructed spindles offers some insights into the mechanisms of mitosis in this yeast.

476 citations

Journal ArticleDOI
01 Nov 1969-Nature
TL;DR: Chromosome motion during mitosis can be explained by combining the facts available about the equilibrium between the mitotic spindle and its subunits with the postulate that the recently described cross-bridges between spindle microtubules are capable of sliding adjacent tubules over one another.
Abstract: Chromosome motion during mitosis can be explained by combining the facts available about the equilibrium between the mitotic spindle and its subunits with the postulate that the recently described cross-bridges between spindle microtubules are capable of sliding adjacent tubules over one another.

379 citations


Cited by
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Journal ArticleDOI
TL;DR: IMOD is useful for studying and modeling data from tomographic, serial section, and optical section reconstructions and allows image data to be visualized by several different methods.

4,830 citations

Journal ArticleDOI
TL;DR: Highly dynamic mitotic-spindle microtubules are among the most successful targets for anticancer therapy, and it is now known that at lower concentrations, microtubule-targeted drugs can suppress micro Tubule dynamics without changingmicrotubule mass; this action leads to mitotic block and apoptosis.
Abstract: Highly dynamic mitotic-spindle microtubules are among the most successful targets for anticancer therapy. Microtubule-targeted drugs, including paclitaxel and Vinca alkaloids, were previously considered to work primarily by increasing or decreasing the cellular microtubule mass. Although these effects might have a role in their chemotherapeutic actions, we now know that at lower concentrations, microtubule-targeted drugs can suppress microtubule dynamics without changing microtubule mass; this action leads to mitotic block and apoptosis. In addition to the expanding array of chemically diverse antimitotic agents, some microtubule-targeted drugs can act as vascular-targeting agents, rapidly depolymerizing microtubules of newly formed vasculature to shut down the blood supply to tumours.

4,007 citations

Journal ArticleDOI
TL;DR: A new method was developed to acquire images automatically at a series of specimen tilts, as required for tomographic reconstruction, using changes in specimen position at previous tilt angles to predict the position at the current tilt angle.

3,995 citations

Journal ArticleDOI
TL;DR: EMAN2 has been under development for the last two years, with a completely refactored image processing library, and a wide range of features to make it much more flexible and extensible than EMAN1.

2,852 citations

Journal ArticleDOI
TL;DR: This review describes progress toward understanding the mechanism of dynamic instability of pure tubulin and discusses the function and regulation of microtubule dynamic instability in living cells.
Abstract: The polymerization dynamics of microtubules are central to their biological functions. Polymerization dynamics allow microtubules to adopt spatial arrangements that can change rapidly in response to cellular needs and, in some cases, to perform mechanical work. Microtubules utilize the energy of GTP hydrolysis to fuel a unique polymerization mechanism termed dynamic instability. In this review, we first describe progress toward understanding the mechanism of dynamic instability of pure tubulin and then discuss the function and regulation of microtubule dynamic instability in living cells.

2,484 citations