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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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spd-3(me85) mutants display reduced mobility of SUN-1 aggregates.Left-hand side column: examples of the displacement tracks of all SUN-1::GFP aggregates within a nucleus over a period of 15 minutes. spd-3(me85) and sun-1(jf18) mutants show obvious reductions in both the area explored by SUN-1::GFP aggregates and in the overlap of different tracks. Middle column: each arc represents the distance traveled by a SUN-1::GFP aggregate inside a nucleus, with larger angles indicating larger distance traveled. Arcs corresponding to all SUN-1 aggregates from 5 nuclei are shown per genotype, arcs are severely reduced in spd-3(me85) mutants, although not as much as in sun-1(jf18) mutants. Right-hand column: Each line represents the distribution of the projected speeds of all SUN-1 aggregates inside a nucleus over a period of 15 minutes. spd-3(me85) and sun-1(jf18) mutants show a strong reduction in the percentage of SUN-1 aggregates moving at high speeds.
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pgen-1003497-g006: spd-3(me85) mutants display reduced mobility of SUN-1 aggregates.Left-hand side column: examples of the displacement tracks of all SUN-1::GFP aggregates within a nucleus over a period of 15 minutes. spd-3(me85) and sun-1(jf18) mutants show obvious reductions in both the area explored by SUN-1::GFP aggregates and in the overlap of different tracks. Middle column: each arc represents the distance traveled by a SUN-1::GFP aggregate inside a nucleus, with larger angles indicating larger distance traveled. Arcs corresponding to all SUN-1 aggregates from 5 nuclei are shown per genotype, arcs are severely reduced in spd-3(me85) mutants, although not as much as in sun-1(jf18) mutants. Right-hand column: Each line represents the distribution of the projected speeds of all SUN-1 aggregates inside a nucleus over a period of 15 minutes. spd-3(me85) and sun-1(jf18) mutants show a strong reduction in the percentage of SUN-1 aggregates moving at high speeds.

Mentions: Using the plotting tools developed in [22], we tracked the movement of individual SUN-1 aggregates and calculated the projected speed and the area explored by the aggregates in spd-3(me85), sun-1(jf18) and wild-type controls. Tracking in wild-type nuclei showed extensive overlap of individual SUN-1 tracks, while the displacement tracks in spd-3(me85) mutants showed little overlap, with most tracks covering a small area around a fixed position. Similar displacement tracks were observed in sun-1(jf18) mutants (Figure 6). Quantification of the area covered by SUN-1 aggregates in spd-3(me85) mutants showed an average arc of 39° (maximum 103°, minimum 11°), a substantial reduction compared to wild-type controls (average arc 90°, maximum 164°, minimum 21°). Interestingly, the area covered by SUN-1 aggregates in sun-1(jf18) mutants (average arc 26°, maximum 50°, minimum 11°) was reduced compared to spd-3(me85) mutants. Finally, the analysis of the distribution of projected speeds demonstrated a clear reduction in the speed of SUN-1 aggregates in spd-3(me85) mutants, with just 40% of aggregates moving at speeds above 40 nm/s, compared to 65% in wild-type controls (Figure 6). Furthermore, aggregates moving at high speed (160 nm/s and higher) represented 10% in wild-type nuclei, but only 0.82% in spd-3(me85) mutants, and 0.29% in sun-1(jf18) mutants. The decrease in high-speed moving aggregates suggests a defect in motor-driven motion, since dynein-dependent movement of SUN-1/ZYG-12 aggregates is characterized by an average speed of 190 nm/s [23]. This quantitative analysis demonstrates that movement of SUN-1 aggregates is reduced in spd-3(me85) mutants, although not as much as in sun-1(jf18) mutants, which are completely deficient in homolog pairing [44].


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)

spd-3(me85) mutants display reduced mobility of SUN-1 aggregates.Left-hand side column: examples of the displacement tracks of all SUN-1::GFP aggregates within a nucleus over a period of 15 minutes. spd-3(me85) and sun-1(jf18) mutants show obvious reductions in both the area explored by SUN-1::GFP aggregates and in the overlap of different tracks. Middle column: each arc represents the distance traveled by a SUN-1::GFP aggregate inside a nucleus, with larger angles indicating larger distance traveled. Arcs corresponding to all SUN-1 aggregates from 5 nuclei are shown per genotype, arcs are severely reduced in spd-3(me85) mutants, although not as much as in sun-1(jf18) mutants. Right-hand column: Each line represents the distribution of the projected speeds of all SUN-1 aggregates inside a nucleus over a period of 15 minutes. spd-3(me85) and sun-1(jf18) mutants show a strong reduction in the percentage of SUN-1 aggregates moving at high speeds.
© Copyright Policy
Related In: Results  -  Collection

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

pgen-1003497-g006: spd-3(me85) mutants display reduced mobility of SUN-1 aggregates.Left-hand side column: examples of the displacement tracks of all SUN-1::GFP aggregates within a nucleus over a period of 15 minutes. spd-3(me85) and sun-1(jf18) mutants show obvious reductions in both the area explored by SUN-1::GFP aggregates and in the overlap of different tracks. Middle column: each arc represents the distance traveled by a SUN-1::GFP aggregate inside a nucleus, with larger angles indicating larger distance traveled. Arcs corresponding to all SUN-1 aggregates from 5 nuclei are shown per genotype, arcs are severely reduced in spd-3(me85) mutants, although not as much as in sun-1(jf18) mutants. Right-hand column: Each line represents the distribution of the projected speeds of all SUN-1 aggregates inside a nucleus over a period of 15 minutes. spd-3(me85) and sun-1(jf18) mutants show a strong reduction in the percentage of SUN-1 aggregates moving at high speeds.
Mentions: Using the plotting tools developed in [22], we tracked the movement of individual SUN-1 aggregates and calculated the projected speed and the area explored by the aggregates in spd-3(me85), sun-1(jf18) and wild-type controls. Tracking in wild-type nuclei showed extensive overlap of individual SUN-1 tracks, while the displacement tracks in spd-3(me85) mutants showed little overlap, with most tracks covering a small area around a fixed position. Similar displacement tracks were observed in sun-1(jf18) mutants (Figure 6). Quantification of the area covered by SUN-1 aggregates in spd-3(me85) mutants showed an average arc of 39° (maximum 103°, minimum 11°), a substantial reduction compared to wild-type controls (average arc 90°, maximum 164°, minimum 21°). Interestingly, the area covered by SUN-1 aggregates in sun-1(jf18) mutants (average arc 26°, maximum 50°, minimum 11°) was reduced compared to spd-3(me85) mutants. Finally, the analysis of the distribution of projected speeds demonstrated a clear reduction in the speed of SUN-1 aggregates in spd-3(me85) mutants, with just 40% of aggregates moving at speeds above 40 nm/s, compared to 65% in wild-type controls (Figure 6). Furthermore, aggregates moving at high speed (160 nm/s and higher) represented 10% in wild-type nuclei, but only 0.82% in spd-3(me85) mutants, and 0.29% in sun-1(jf18) mutants. The decrease in high-speed moving aggregates suggests a defect in motor-driven motion, since dynein-dependent movement of SUN-1/ZYG-12 aggregates is characterized by an average speed of 190 nm/s [23]. This quantitative analysis demonstrates that movement of SUN-1 aggregates is reduced in spd-3(me85) mutants, although not as much as in sun-1(jf18) mutants, which are completely deficient in homolog pairing [44].

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