James R. LaFountain

Cell Biology: Mechanism of Chromosome Segregation

Professor

Ph.D 1970 University at Albany
Postdoctoral work 1971 Swiss Federal Institute of Technology, Zurich
Assistant Professor 1972;
Associate Professor 1977;
Professor 1986 University at Buffalo

Address Information

James R. LaFountain
Department of Biological Sciences
657 Cooke Hall
State University of New York at Buffalo
Buffalo, NY 14260

(716) 645-4965

To send e-mail: jrl@buffalo.edu

RESEARCH SUMMARY

Meiosis results in the haploidization of an organism's genome through the segregation of chromosomes during two nuclear divisions. Research over the past several years has involved studying events of the meiotic divisions in spermatocytes from the crane-fly, Nephrotoma suturalis.

Crane-fly spermatocytes offer a model system for addressing questions about chromosome orientation and the forces that are exerted on or by chromosomes during their movement within the meiotic spindle. Studies are aimed at understanding both kinetochore-based and kinetochore-independent forces. Evidence for forces acting independent of kinetochores has been obtained from analysis of acentric chromosome fragments that were severed from chromosomes with a laser microbeam. Forces characterized to date include both pole-directed and away-from-the-pole forces that may be participating in the movement and positioning of chromosomes in the spindle.

From the analysis of acentric fragments, it is apparent that the spermatocyte spindle is a highly dynamic system, and the many microtubules comprising it appear to be turning over through coordinated addition of subunits at their plus ends and removal of subunits from their minus ends (microtubule flux).

Recent discoveries include direct observation of microtubule flux within spindle microtubules of living spermatocytes and induction of chromosome malorientations that give rise to nondisjunction. Work in progress is aimed at resolving the mechanism(s) underlying flux and malorientation.


Micrographs of a crane-fly spermatocyte viewed with a differential interference contrast microscopy
(a) and with polarized light microscopy (b and c) illustrating the birefringent spindle fibers that extend from kinetochores to the spindle poles at metaphase.

PUBLICATIONS

  • LaFountain, J.R., Jr., and Oldenbourg, R. 2004.
    Maloriented bivalents have metaphase positions at the spindle equator with more kinetochore microtubules to one pole than to the other.
    Molecular Biology of the Cell 15:5346-5355.
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  • LaFountain, J.R., Jr., Cohan, C.S., Siegel, A.J. and LaFountain, D.J. 2004.
    Direct visualization of microtubule flux during metaphase and anaphase in crane-fly spermatocytes.
    Molecular Biology of the Cell 15:5724-5732.
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  • LaFountain, J.R., Jr., Cole, R.W., and Rieder, C.L. (2002)
    Partner telomeres during anaphase in crane-fly spermatocytes are connected by an elastic tether that exerts a backward force and resists poleward motion.
    Journal of Cell Science 115:1541-1549
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  • LaFountain, J.R., Jr., Cole, R.W., and Rieder, C.L. (2002)
    Polar ejection forces are operative in crane-fly spermatocytes, but their action is limited to the spindle periphery.
    Cell Motility and the Cytoskeleton 51:16-26
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  • LaFountain, J.R., Jr., Oldenbourgh, R., Cole, R.W., and Rieder, C.L. (2001)
    Microtubule flux mediates poleward motion of acentric chromosome fragments during meiosis in insect spermatocytes.
    Molecular Biology of the Cell 12:4054-4065
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  • J.R. LaFountain, Jr., A.J. Siegel, and G.K. Richards (1999)
    Chromosome movement during meiotic prophase in crane-fly spermatocytes. IV. Actin and the effects of cytochalasin D
    Cell Motility and the Cytoskeleton 43:199-212
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  • J.R. LaFountain Jr., R. Hard, and A.J. Siegel (1998)
    Visualization of kinetochores and analysis of their refractility in crane-fly spermatocytes after aldehyde fixation
    Cell Motility and the Cytoskeleton 40:147-159
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