Chromosome Structure

Higher-order chromosome structure is known to play a critical role in modulating gene transcription and in facilitating chromosomal segregation. In collaboration with dr. John Sedat’s laboratory, our goals are to determine the three-dimensional structure of diploid chromosomes as a function of condensation state using high resolution electron microscope tomography. EM Tomography, uniquely, provides the ability to study the internal organization of supramolecular assemblies in three dimensions. We are pursuing the examination of higher-order chromatin structure from minimally-perturbed tissue culture cells and are trying to determine the structure of the ~130nm fiber seen in both telophase and in interphase. In parallel, we are using a Xenopus in-vitro chromosome condensation system developed by Dr. Tim Mitchison (Harvard) to provide well defined chromosome samples in different condensation states. Furthermore, the in vitro system will allow the direct coupling of structural and biochemical data through the use of immunolabeling and depletion studies.

Relevant Publications

Peter König, Michael B. Braunfeld, John W. Sedat and David A. Agard, "The three-dimensional structure of in vitro reconstituted Xenopus laevis chromosomes by EM tomography, " Chromosoma 2007 Mar (pdf).

Marshall, W.F., Marko, J.F., Agard, D.A., Sedat, J.W. (2001) Chromosome elasticity and mitotic polar ejection force measured in living Drosophila embryos by four-dimensional microscopy-based motion analysis. Curr Biol. 2001 Apr 17;11(8):569-78 (html or pdf).

Fung, J.C., Marshall, W.F., Dernburg, A., Agard, D.A., Sedat, J.W. (1998). Homologous Chromosome Pairing in Drosophila Melanogaster Proceeds through Multiple Independent Initiations. J. Cell Biol. 141:5-20 (pdf).

Marshall, W.F., Straight, A., Marko, J.F., Swedlow, J.R., Dernburg, A.F., Murray, A.W., Belmont, A.S., Agard, D.A., and Sedat, J.W. (1997). Interphase chromosomes undergoes large-scale diffusional motion in living cells. Current Biology. 7:930-939. (pdf).

Bass, H.W., Marshall, W.F., Sedat, J.W., Agard, D.A., and Cande, W.Z. (1997). Telomeres cluster de novo before the initiation of synapsis; a 3-dimensional spatial analysis of telomere positions before and during meiotic prophase. J. Cell. Biol. 137: 5-18 (pdf).

Marshall, W.F., Dernburg, A.F., Harmon, B., Agard, D.A., and Sedat, J.W. (1996). Specific interactions of chromatin with the nuclear envelope: Positional determination within the nucleus in D. melanogaster. Mol. Biol. Cell 7: 825-842. (pdf).

Dernburg, A.F., Broman, K.W., Fung, J.C., Marshall, W.F., Philips, J., Agard, D.A., and Sedat, J.W. (1996). Perturbation of nuclear architecture by long-distance chromosome interactions. Cell 85: 745-759 (pdf).

Paddy, M.R., Saumweber, H., Agard, D.A., and Sedat, J.W. (1996). Time-resolved, in vivo studies of mitotic spindle formation and nuclear lamina breakdown in Drosophila early embryos. J. Cell Science 109: 591-607 (pdf).

Urata, Y., Parmelee, S.J., Agard, D.A., and Sedat, J.W. (1995). A three-dimensional structural dissection of Drosophila polytene chromosomes. J. Cell. Biol. 131: 279-295. (pdf).

Marshall, W.F., Agard, D.A., and Sedat, J.W. (1995). Quantitative analysis of chromosome motion in Drosophila melanogaster. proc. SPIE 2412: 33042.

Horowitz, R.A., Agard, D.A., Sedat, J.W., and Woodcock, C.L. (1994). The three-dimensional architecture of chromatin in situ: electron tomography of reveals fibers composed of a continuously zig-zag nucleosomal ribbon. J. Cell Biol. 125: 1-10. (pdf).

Dawe, R.K., Sedat, J.W., Agard, D.A., and Cande, W.Z. (1994). Meiotic chromosome pairing in maize is associated with a novel chromatin organization. Cell 76: 901-912. (pdf).

Hiraoka, Yasushi; Dernburg, Abby F.; Parmelee, Susan J.; Rykowski, Mary C.; Agard, David A.; Sedat, John W. The onset of homologous chromosome pairing during Drosophila melanogaster embryogenesis. Journal of Cell Biology (1993), 120(3), 591-600.(pdf).

Swedlow, J.R., Agard, D.A., and Sedat, J.W. (1993). Chromosome structure inside the nucleus. Curr. Opinion Cell Biol. 5: 412-416. (pdf).

Paddy, M.R., Belmont, A.S., Saumweber, H., Agard, D.A., and Sedat, J.W. (1990). Interphase nuclear envelope lamins form a discontinuous network that interacts with only a fraction of the chromatin in the nuclear periphery. Cell 62: 89-106 (pdf).

Hiraoka, Y., Agard, D.A., and Sedat, J.W. (1990). Temporal and spatial coordination of chromosome movement, spindle formation and nuclear envelope breakdown during prometaphase in Drosophila melanogaster embryos. J. Cell Biol., 111: 2815-2828. (pdf).

Hiraoka, Y., Rykowski, M.C., Lefstin, J.A., Agard, D.A., and Sedat, J.W. (1990). Three-dimensional organization of chromosomes studied by in situ hybridization and optical sectioning microscopy. SPIE Bioimaging & Two-dimens. Spectroscopy 1205: 11-19. (pdf).

Hiraoka, Y., Minden, J.S., Agard, D.A., and Sedat, J.W. (1989). Focal points for chromosome condensation and decondensation on the nuclear envelope revealed by three-dimensional in vivo microscopy. Nature 342: 392-296. (pdf).

Belmont, A., Braunfeld, M.B., Sedat, J.W., and Agard, D.A. (1989). Large-scale chromatin structural domains within mitotic and interphase chromosomes in vivo and in vitro. Chromosoma, 98:129-143. (pdf).

Rykowksi, M.C., Parmalee, S.J., Agard, D.A., and Sedat, J.W. (1988). Precise determination of the molecular limits of a polytene chromosome band: regulatory sequences for the Notch gene are in the interband. Cell 54: 461-472.(pdf).

Agard, D.A., Hiraoka, Y., Shaw, P., and Sedat, J.W. (1988). Three-dimensional light microscopy of diploid Drosophila chromosomes. Cell Motility & Cytoskeleton 10: 18-27.(pdf).

Belmont, A., Sedat, J.W., and Agard, D.A. (1987). A 3-D approach to mitotic chromosome structure: evidence for a hierarchical organization. J. Cell Biol. 105: 77-92 (pdf).

Gruenbaum, Y., Hochstrasser, M., Mathog, D., Saumweber, H., Agard, D.A., and Sedat, J.W. (1984). Spatial organisation of the drosophila nucleus: a three-dimensional cytogenetic study. J. Cell Science Suppl. 1: 223-234. (pdf).

Agard, D.A. and Sedat, J.W. (1983). Three-dimensional architecture of a polytene nucleus. Nature 302: 676-681.(pdf).