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Crossing over is coupled to late meiotic prophase bivalent differentiation through asymmetric disassembly of the SC.

Nabeshima K, Villeneuve AM, Colaiácovo MP - J. Cell Biol. (2005)

Bottom Line: This and other manifestations of asymmetry along chromosomes are lost in synapsis-proficient crossover-defective mutants, which often retain SYP-1,2 along the full lengths of coiled diplotene axes.Moreover, a gamma-irradiation treatment that restores crossovers in the spo-11 mutant also restores asymmetry of SYP-1 localization.We propose that crossovers or crossover precursors serve as symmetry-breaking events that promote differentiation of subregions of the bivalent by triggering asymmetric disassembly of the SC.

View Article: PubMed Central - PubMed

Affiliation: Department of Developmental Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.

ABSTRACT
Homologous chromosome pairs (bivalents) undergo restructuring during meiotic prophase to convert a configuration that promotes crossover recombination into one that promotes bipolar spindle attachment and localized cohesion loss. We have imaged remodeling of meiotic chromosome structures after pachytene exit in Caenorhabditis elegans. Chromosome shortening during diplonema is accompanied by coiling of chromosome axes and highly asymmetric departure of synaptonemal complex (SC) central region proteins SYP-1 and SYP-2, which diminish over most of the length of each desynapsing bivalent while becoming concentrated on axis segments distal to the single emerging chiasma. This and other manifestations of asymmetry along chromosomes are lost in synapsis-proficient crossover-defective mutants, which often retain SYP-1,2 along the full lengths of coiled diplotene axes. Moreover, a gamma-irradiation treatment that restores crossovers in the spo-11 mutant also restores asymmetry of SYP-1 localization. We propose that crossovers or crossover precursors serve as symmetry-breaking events that promote differentiation of subregions of the bivalent by triggering asymmetric disassembly of the SC.

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Immunolocalization of axis and SC components during wild-type meiosis. (Top) Whole mount germ line oriented with the distal premeiotic region at the left and the region of the pachytene–diplotene transition at the right. Bar, 10 μm. (Bottom) Pachytene nuclei exhibiting essentially full colocalization of SC central region protein SYP-1 and axis protein REC-8 between parallel tracks of DAPI-stained chromatin. Bar, 5 μm.
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fig1: Immunolocalization of axis and SC components during wild-type meiosis. (Top) Whole mount germ line oriented with the distal premeiotic region at the left and the region of the pachytene–diplotene transition at the right. Bar, 10 μm. (Bottom) Pachytene nuclei exhibiting essentially full colocalization of SC central region protein SYP-1 and axis protein REC-8 between parallel tracks of DAPI-stained chromatin. Bar, 5 μm.

Mentions: At the pachytene stage of meiotic prophase, when SC is present along the full lengths of parallel-aligned homologue pairs, immunofluorescence (IF) signals corresponding to SC central region protein SYP-1 are flanked by parallel tracks of DAPI-stained chromatin and exhibit essentially complete colocalization with IF signals corresponding to chromosome axis components HIM-3 and cohesin REC-8 (Zetka et al., 1999; Pasierbek et al., 2001; MacQueen et al., 2002; Nabeshima et al., 2004; Fig. 1). However, upon exit from pachynema, axis and central region proteins exhibit highly discordant behavior.


Crossing over is coupled to late meiotic prophase bivalent differentiation through asymmetric disassembly of the SC.

Nabeshima K, Villeneuve AM, Colaiácovo MP - J. Cell Biol. (2005)

Immunolocalization of axis and SC components during wild-type meiosis. (Top) Whole mount germ line oriented with the distal premeiotic region at the left and the region of the pachytene–diplotene transition at the right. Bar, 10 μm. (Bottom) Pachytene nuclei exhibiting essentially full colocalization of SC central region protein SYP-1 and axis protein REC-8 between parallel tracks of DAPI-stained chromatin. Bar, 5 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2171829&req=5

fig1: Immunolocalization of axis and SC components during wild-type meiosis. (Top) Whole mount germ line oriented with the distal premeiotic region at the left and the region of the pachytene–diplotene transition at the right. Bar, 10 μm. (Bottom) Pachytene nuclei exhibiting essentially full colocalization of SC central region protein SYP-1 and axis protein REC-8 between parallel tracks of DAPI-stained chromatin. Bar, 5 μm.
Mentions: At the pachytene stage of meiotic prophase, when SC is present along the full lengths of parallel-aligned homologue pairs, immunofluorescence (IF) signals corresponding to SC central region protein SYP-1 are flanked by parallel tracks of DAPI-stained chromatin and exhibit essentially complete colocalization with IF signals corresponding to chromosome axis components HIM-3 and cohesin REC-8 (Zetka et al., 1999; Pasierbek et al., 2001; MacQueen et al., 2002; Nabeshima et al., 2004; Fig. 1). However, upon exit from pachynema, axis and central region proteins exhibit highly discordant behavior.

Bottom Line: This and other manifestations of asymmetry along chromosomes are lost in synapsis-proficient crossover-defective mutants, which often retain SYP-1,2 along the full lengths of coiled diplotene axes.Moreover, a gamma-irradiation treatment that restores crossovers in the spo-11 mutant also restores asymmetry of SYP-1 localization.We propose that crossovers or crossover precursors serve as symmetry-breaking events that promote differentiation of subregions of the bivalent by triggering asymmetric disassembly of the SC.

View Article: PubMed Central - PubMed

Affiliation: Department of Developmental Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.

ABSTRACT
Homologous chromosome pairs (bivalents) undergo restructuring during meiotic prophase to convert a configuration that promotes crossover recombination into one that promotes bipolar spindle attachment and localized cohesion loss. We have imaged remodeling of meiotic chromosome structures after pachytene exit in Caenorhabditis elegans. Chromosome shortening during diplonema is accompanied by coiling of chromosome axes and highly asymmetric departure of synaptonemal complex (SC) central region proteins SYP-1 and SYP-2, which diminish over most of the length of each desynapsing bivalent while becoming concentrated on axis segments distal to the single emerging chiasma. This and other manifestations of asymmetry along chromosomes are lost in synapsis-proficient crossover-defective mutants, which often retain SYP-1,2 along the full lengths of coiled diplotene axes. Moreover, a gamma-irradiation treatment that restores crossovers in the spo-11 mutant also restores asymmetry of SYP-1 localization. We propose that crossovers or crossover precursors serve as symmetry-breaking events that promote differentiation of subregions of the bivalent by triggering asymmetric disassembly of the SC.

Show MeSH