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Chromosome movements promoted by the mitochondrial protein SPD-3 are required for homology search during Caenorhabditis elegans meiosis.

Labrador L, Barroso C, Lightfoot J, Müller-Reichert T, Flibotte S, Taylor J, Moerman DG, Villeneuve AM, Martinez-Perez E - PLoS Genet. (2013)

Bottom Line: Preventing SC assembly in spd-3 mutants does not improve homolog pairing, demonstrating that SPD-3 is required for homology search at the start of meiosis.However, quantitative analysis of SUN-1 aggregate movement in spd-3 mutants demonstrates a clear reduction in mobility, although this defect is not as severe as that seen in sun-1(jf18) mutants, which also show a stronger pairing defect, suggesting a correlation between chromosome-end mobility and the efficiency of pairing.Our work reveals how chromosome mobility impacts the different early meiotic events that promote homolog pairing and suggests that efficient homology search at the onset of meiosis is largely dependent on motor-driven chromosome movement.

View Article: PubMed Central - PubMed

Affiliation: MRC Clinical Sciences Centre, Imperial College Faculty of Medicine, London, United Kingdom.

ABSTRACT
Pairing of homologous chromosomes during early meiosis is essential to prevent the formation of aneuploid gametes. Chromosome pairing includes a step of homology search followed by the stabilization of homolog interactions by the synaptonemal complex (SC). These events coincide with dramatic changes in nuclear organization and rapid chromosome movements that depend on cytoskeletal motors and are mediated by SUN-domain proteins on the nuclear envelope, but how chromosome mobility contributes to the pairing process remains poorly understood. We show that defects in the mitochondria-localizing protein SPD-3 cause a defect in homolog pairing without impairing nuclear reorganization or SC assembly, which results in promiscuous installation of the SC between non-homologous chromosomes. Preventing SC assembly in spd-3 mutants does not improve homolog pairing, demonstrating that SPD-3 is required for homology search at the start of meiosis. Pairing center regions localize to SUN-1 aggregates at meiosis onset in spd-3 mutants; and pairing-promoting proteins, including cytoskeletal motors and polo-like kinase 2, are normally recruited to the nuclear envelope. However, quantitative analysis of SUN-1 aggregate movement in spd-3 mutants demonstrates a clear reduction in mobility, although this defect is not as severe as that seen in sun-1(jf18) mutants, which also show a stronger pairing defect, suggesting a correlation between chromosome-end mobility and the efficiency of pairing. SUN-1 aggregate movement is also impaired following inhibition of mitochondrial respiration or dynein knockdown, suggesting that mitochondrial function is required for motor-driven SUN-1 movement. The reduced chromosome-end mobility of spd-3 mutants impairs coupling of SC assembly to homology recognition and causes a delay in meiotic progression mediated by HORMA-domain protein HTP-1. Our work reveals how chromosome mobility impacts the different early meiotic events that promote homolog pairing and suggests that efficient homology search at the onset of meiosis is largely dependent on motor-driven chromosome movement.

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Localization of PC proteins to the NE in spd-3(me85) mutants.(A–B) Projections of transition zone nuclei from wild type and spd-3(me85) mutant worms expressing SUN-1::GFP and stained with anti-HIM-8 and anti-ZIM-3 antibodies and counterstained with DAPI. HIM-8 and ZIM-3 signals are associated with SUN-1 aggregates in both wild type and spd-3(me85) mutant, which display elevated numbers of SUN-1 aggregates. Videos S1 and S2 show three-dimensional reconstructions of nuclei from panel A. Scale bar = 5 µm in both panels. (C) Quantification of SUN-1 aggregates. Y axis indicates the percentage of nuclei with a given number of SUN-1 foci (aggregates smaller that 1.1 µm in diameter) or patches (aggregates larger than 1.1 µm in diameter), the X axis indicates regions along the germ line as indicated in the diagram. Note the big increase in SUN-1 foci in spd-3(me85) mutant and their persistence until mid/late pachytene.
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pgen-1003497-g004: Localization of PC proteins to the NE in spd-3(me85) mutants.(A–B) Projections of transition zone nuclei from wild type and spd-3(me85) mutant worms expressing SUN-1::GFP and stained with anti-HIM-8 and anti-ZIM-3 antibodies and counterstained with DAPI. HIM-8 and ZIM-3 signals are associated with SUN-1 aggregates in both wild type and spd-3(me85) mutant, which display elevated numbers of SUN-1 aggregates. Videos S1 and S2 show three-dimensional reconstructions of nuclei from panel A. Scale bar = 5 µm in both panels. (C) Quantification of SUN-1 aggregates. Y axis indicates the percentage of nuclei with a given number of SUN-1 foci (aggregates smaller that 1.1 µm in diameter) or patches (aggregates larger than 1.1 µm in diameter), the X axis indicates regions along the germ line as indicated in the diagram. Note the big increase in SUN-1 foci in spd-3(me85) mutant and their persistence until mid/late pachytene.

Mentions: Pairing at the onset of meiosis requires tethering of the chromosomal end carrying the PC to the inner NE, where PCs are seen localizing to aggregates formed by the SUN-1 protein [11], [39], [44]. To investigate if PC localization to SUN-1 aggregates on the NE was disrupted in spd-3(me85) mutants, we introduced a transgene expressing a functional SUN-1::GFP fusion protein [39] into the spd-3(me85) mutant background, and these germ lines were stained with anti-GFP (to visualize SUN-1) and anti-HIM-8 or anti-ZIM-3 antibodies to visualize PC regions. Transition zone nuclei from wild-type germ lines typically displayed between 2 and 4 large SUN-1 aggregates that colocalized with the PC-binding proteins. In spd-3(me85) mutants, both HIM-8 and ZIM-3 were always found associated with SUN-1 aggregates, showing that localization of PC regions to SUN-1 aggregates is not disrupted and suggesting normal tethering of PCs to the NE (Figure 4A and Videos S1, S2). However, transition zone nuclei of spd-3(me85) mutants displayed a clear increase in the overall number of SUN-1 aggregates and most aggregates were much smaller in size than those seen in wild-type controls. Small and round SUN-1 aggregates (foci) have been proposed to represent the attachment to the NE of a single chromosomal end, while larger SUN-1 aggregates (patches) are thought to include several chromosomal ends [39]. Quantification of SUN-1 aggregates during meiotic prophase revealed a strong increase of SUN-1 foci in spd-3(me85) mutant germ lines, where in zone three 50% of the nuclei displayed between 6 and 10 SUN-1 foci, while no nuclei with 6 or more foci were found in wild-type controls (Figure 4C). The extensive presence of SUN-1 foci in spd-3(me85) mutants suggests that many PC regions are attached to the NE in isolation, failing to be included in larger aggregates where PC regions from several chromosomes come together. Furthermore, SUN-1 aggregates persisted in substantial numbers until zone 5 of spd-3(me85) mutant germ lines, demonstrating a delay in the dissolution of SUN-1 aggregates.


Chromosome movements promoted by the mitochondrial protein SPD-3 are required for homology search during Caenorhabditis elegans meiosis.

Labrador L, Barroso C, Lightfoot J, Müller-Reichert T, Flibotte S, Taylor J, Moerman DG, Villeneuve AM, Martinez-Perez E - PLoS Genet. (2013)

Localization of PC proteins to the NE in spd-3(me85) mutants.(A–B) Projections of transition zone nuclei from wild type and spd-3(me85) mutant worms expressing SUN-1::GFP and stained with anti-HIM-8 and anti-ZIM-3 antibodies and counterstained with DAPI. HIM-8 and ZIM-3 signals are associated with SUN-1 aggregates in both wild type and spd-3(me85) mutant, which display elevated numbers of SUN-1 aggregates. Videos S1 and S2 show three-dimensional reconstructions of nuclei from panel A. Scale bar = 5 µm in both panels. (C) Quantification of SUN-1 aggregates. Y axis indicates the percentage of nuclei with a given number of SUN-1 foci (aggregates smaller that 1.1 µm in diameter) or patches (aggregates larger than 1.1 µm in diameter), the X axis indicates regions along the germ line as indicated in the diagram. Note the big increase in SUN-1 foci in spd-3(me85) mutant and their persistence until mid/late pachytene.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3649994&req=5

pgen-1003497-g004: Localization of PC proteins to the NE in spd-3(me85) mutants.(A–B) Projections of transition zone nuclei from wild type and spd-3(me85) mutant worms expressing SUN-1::GFP and stained with anti-HIM-8 and anti-ZIM-3 antibodies and counterstained with DAPI. HIM-8 and ZIM-3 signals are associated with SUN-1 aggregates in both wild type and spd-3(me85) mutant, which display elevated numbers of SUN-1 aggregates. Videos S1 and S2 show three-dimensional reconstructions of nuclei from panel A. Scale bar = 5 µm in both panels. (C) Quantification of SUN-1 aggregates. Y axis indicates the percentage of nuclei with a given number of SUN-1 foci (aggregates smaller that 1.1 µm in diameter) or patches (aggregates larger than 1.1 µm in diameter), the X axis indicates regions along the germ line as indicated in the diagram. Note the big increase in SUN-1 foci in spd-3(me85) mutant and their persistence until mid/late pachytene.
Mentions: Pairing at the onset of meiosis requires tethering of the chromosomal end carrying the PC to the inner NE, where PCs are seen localizing to aggregates formed by the SUN-1 protein [11], [39], [44]. To investigate if PC localization to SUN-1 aggregates on the NE was disrupted in spd-3(me85) mutants, we introduced a transgene expressing a functional SUN-1::GFP fusion protein [39] into the spd-3(me85) mutant background, and these germ lines were stained with anti-GFP (to visualize SUN-1) and anti-HIM-8 or anti-ZIM-3 antibodies to visualize PC regions. Transition zone nuclei from wild-type germ lines typically displayed between 2 and 4 large SUN-1 aggregates that colocalized with the PC-binding proteins. In spd-3(me85) mutants, both HIM-8 and ZIM-3 were always found associated with SUN-1 aggregates, showing that localization of PC regions to SUN-1 aggregates is not disrupted and suggesting normal tethering of PCs to the NE (Figure 4A and Videos S1, S2). However, transition zone nuclei of spd-3(me85) mutants displayed a clear increase in the overall number of SUN-1 aggregates and most aggregates were much smaller in size than those seen in wild-type controls. Small and round SUN-1 aggregates (foci) have been proposed to represent the attachment to the NE of a single chromosomal end, while larger SUN-1 aggregates (patches) are thought to include several chromosomal ends [39]. Quantification of SUN-1 aggregates during meiotic prophase revealed a strong increase of SUN-1 foci in spd-3(me85) mutant germ lines, where in zone three 50% of the nuclei displayed between 6 and 10 SUN-1 foci, while no nuclei with 6 or more foci were found in wild-type controls (Figure 4C). The extensive presence of SUN-1 foci in spd-3(me85) mutants suggests that many PC regions are attached to the NE in isolation, failing to be included in larger aggregates where PC regions from several chromosomes come together. Furthermore, SUN-1 aggregates persisted in substantial numbers until zone 5 of spd-3(me85) mutant germ lines, demonstrating a delay in the dissolution of SUN-1 aggregates.

Bottom Line: Preventing SC assembly in spd-3 mutants does not improve homolog pairing, demonstrating that SPD-3 is required for homology search at the start of meiosis.However, quantitative analysis of SUN-1 aggregate movement in spd-3 mutants demonstrates a clear reduction in mobility, although this defect is not as severe as that seen in sun-1(jf18) mutants, which also show a stronger pairing defect, suggesting a correlation between chromosome-end mobility and the efficiency of pairing.Our work reveals how chromosome mobility impacts the different early meiotic events that promote homolog pairing and suggests that efficient homology search at the onset of meiosis is largely dependent on motor-driven chromosome movement.

View Article: PubMed Central - PubMed

Affiliation: MRC Clinical Sciences Centre, Imperial College Faculty of Medicine, London, United Kingdom.

ABSTRACT
Pairing of homologous chromosomes during early meiosis is essential to prevent the formation of aneuploid gametes. Chromosome pairing includes a step of homology search followed by the stabilization of homolog interactions by the synaptonemal complex (SC). These events coincide with dramatic changes in nuclear organization and rapid chromosome movements that depend on cytoskeletal motors and are mediated by SUN-domain proteins on the nuclear envelope, but how chromosome mobility contributes to the pairing process remains poorly understood. We show that defects in the mitochondria-localizing protein SPD-3 cause a defect in homolog pairing without impairing nuclear reorganization or SC assembly, which results in promiscuous installation of the SC between non-homologous chromosomes. Preventing SC assembly in spd-3 mutants does not improve homolog pairing, demonstrating that SPD-3 is required for homology search at the start of meiosis. Pairing center regions localize to SUN-1 aggregates at meiosis onset in spd-3 mutants; and pairing-promoting proteins, including cytoskeletal motors and polo-like kinase 2, are normally recruited to the nuclear envelope. However, quantitative analysis of SUN-1 aggregate movement in spd-3 mutants demonstrates a clear reduction in mobility, although this defect is not as severe as that seen in sun-1(jf18) mutants, which also show a stronger pairing defect, suggesting a correlation between chromosome-end mobility and the efficiency of pairing. SUN-1 aggregate movement is also impaired following inhibition of mitochondrial respiration or dynein knockdown, suggesting that mitochondrial function is required for motor-driven SUN-1 movement. The reduced chromosome-end mobility of spd-3 mutants impairs coupling of SC assembly to homology recognition and causes a delay in meiotic progression mediated by HORMA-domain protein HTP-1. Our work reveals how chromosome mobility impacts the different early meiotic events that promote homolog pairing and suggests that efficient homology search at the onset of meiosis is largely dependent on motor-driven chromosome movement.

Show MeSH
Related in: MedlinePlus