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Proc Natl Acad Sci U S A. 2017 Jun 13;114(24):E4734-E4743. doi: 10.1073/pnas.1702312114. Epub 2017 May 30.

Superresolution microscopy reveals the three-dimensional organization of meiotic chromosome axes in intact Caenorhabditis elegans tissue.

Köhler S1,2, Wojcik M3,4, Xu K5,4,6, Dernburg AF7,2,4,8.

Author information

1
Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3220.
2
Howard Hughes Medical Institute, Chevy Chase, MD 20815.
3
Department of Chemistry, University of California, Berkeley, CA 94720-3220.
4
California Institute for Quantitative Biosciences, Berkeley, CA 94720.
5
Department of Chemistry, University of California, Berkeley, CA 94720-3220; afdernburg@berkeley.edu xuk@berkeley.edu.
6
Division of Molecular Biophysics and Integrated Bioimaging, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.
7
Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3220; afdernburg@berkeley.edu xuk@berkeley.edu.
8
Division of Biological Systems and Engineering, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.

Abstract

When cells enter meiosis, their chromosomes reorganize as linear arrays of chromatin loops anchored to a central axis. Meiotic chromosome axes form a platform for the assembly of the synaptonemal complex (SC) and play central roles in other meiotic processes, including homologous pairing, recombination, and chromosome segregation. However, little is known about the 3D organization of components within the axes, which include cohesin complexes and additional meiosis-specific proteins. Here, we investigate the molecular organization of meiotic chromosome axes in Caenorhabditis elegans through STORM (stochastic optical reconstruction microscopy) and PALM (photo-activated localization microscopy) superresolution imaging of intact germ-line tissue. By tagging one axis protein (HIM-3) with a photoconvertible fluorescent protein, we established a spatial reference for other components, which were localized using antibodies against epitope tags inserted by CRISPR/Cas9 genome editing. Using 3D averaging, we determined the position of all known components within synapsed chromosome axes to high spatial precision in three dimensions. We find that meiosis-specific HORMA domain proteins span a gap between cohesin complexes and the central region of the SC, consistent with their essential roles in SC assembly. Our data further suggest that the two different meiotic cohesin complexes are distinctly arranged within the axes: Although cohesin complexes containing the kleisin REC-8 protrude above and below the plane defined by the SC, complexes containing COH-3 or -4 kleisins form a central core, which may physically separate sister chromatids. This organization may help to explain the role of the chromosome axes in promoting interhomolog repair of meiotic double-strand breaks by inhibiting intersister repair.

KEYWORDS:

C. elegans; chromosome axis; cohesin; meiosis; superresolution microscopy

PMID:
28559338
PMCID:
PMC5474826
DOI:
10.1073/pnas.1702312114
[Indexed for MEDLINE]
Free PMC Article

Conflict of interest statement

The authors declare no conflict of interest.

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