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First published online August 17, 2004
doi: 10.1242/10.1242/jcs.01363

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A bouquet of chromosomes

Department of Molecular and Cell Biology, University of California Berkeley, 345 LSA 3200, Berkeley, CA 94720-3200, USA

View larger version (61K): [in a new window]   Fig. 1. Chromatin rearrangement and bouquet formation in meiotic prophase of maize. Images of each nucleus were acquired using a DeltaVision Microscopy system (Applied Precision) followed by computational deconvolution (Golubovskaya et al., 2002). This results in a 3D data stack. Shown here are 2D projections from whole or partial 3D data stacks. We encourage you to view the movies of rotating 3D images of these same nuclei in the supplemental material (http://jcs.biologists.org/supplemental/). Chromatin (stained with DAPI) is shown in red; telomeres (FITC) are shown in green; centromeres (Cy3 or Cy5) are shown in blue in A, B and G; and the single 5SrRNA (Cy3 or Cy5) locus is shown in blue in C, D, E, F and H. (A) Leptotene. Telomeres and centromeres are distributed throughout the nuclear volume. Chromosomes can be seen as thin threads almost like beads on a string, and heterochromatin knobs appear spherical. (B) Late leptotene. Telomeres are attached to the inner surface of the nuclear envelope (NE). Centromeres are distributed throughout the nuclear volume. Chromosomes are still completely unsynapsed but appear more condensed. (C) Early zygotene. Telomeres are gathered in a narrow patch on the NE, but are not yet completely clustered. Chromatin is more condensed, and some regions are beginning to synapse. This can be seen more easily in the supplemental material as thicker and apparently paired regions of the chromosomes. Some knobs are round, and some are elongated. The two 5SrRNA foci, seen here as blue dots, one on each homolog, are obviously not paired. (D,E) Classic zygotene. Telomeres are clustered in the bouquet. These cells are very typical of the maize bouquet. Chromatin structure has not changed from earlier zygotene, except that more chromosome regions are paired. This is readily apparent in the supplemental material. The 5SrRNA foci are still not paired, but we imagine that they are in the process of pairing in E (compare distances between two foci in C, D and E). (F) Pachytene. All chromosomes are completely paired and synapsed. This can be seen as a doubled chromatin width (compare E and F), and there is only one 5SrRNA focus. All telomeres are still on the NE, but they are beginning to disperse from the bouquet. (G,H) Late pachytene. All chromosomes are still completely paired and synapsed, but telomeres are being released from the NE. Centromeres (G) are dispersed throughout the nucleus, and the 5SrRNA foci is paired (H). The chromatin appears thinner in G owing to a different fixation.

View larger version (210K): [in a new window]   Fig. 2. Transmission electron microscopy (TEM) of telomere attachments in the wild-type mouse spermatocyte I nucleus. This TEM shows electron-dense lateral elements (LE) and the central element (CE) of the synatonemal complex (SC) terminate with a conical thickening (arrowheads) at the inner nuclear envelope (NE). An electron-dense plate connects the wide end of the LE thickening with the inner NE (indented arrow). Bar, 0.2 µm. Reproduced from Molecular Biology of the Cell (Liebe et al., 2004), with permission from The American Society for Cell Biology.

View larger version (19K): [in a new window]   Fig. 3. The telomere bouquet in Schizosaccharomyces pombe: the horsetail stage. Heterochromatic centromeres and telomeres are visualized with swi6-GFP (bright dots), which also lightly stains the entire nucleus. Here, the nucleus is elongated, as it is whipped about the cell in a swishing horsetail-like movement. To see this movement, please view our supplemental movies (http://jcs.biologists.org/supplemental/). Telomeres are clustered at one point in the nucleus, on the left, which is adjacent to the spindle pole body (SPB) attached to cytoplasmic microtubules (not visible here). Two centromeric dots can be seen in the interior of the nucleus. The third centromere is out of the plane of focus. Image courtesy of Ye Jin, UC Berkeley.