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Condensin II resolves chromosomal associations to enable anaphase I segregation in Drosophila male meiosis.

Hartl TA, Sweeney SJ, Knepler PJ, Bosco G - PLoS Genet. (2008)

Bottom Line: These persistent chromosome associations likely consist of DNA entanglements, but may be more specific as anaphase I bridging was rescued by mutations in the homolog conjunction factor teflon.We propose that the consequence of condensin II mutations is a failure to resolve heterologous and homologous associations mediated by entangled DNA and/or homolog conjunction factors.Furthermore, persistence of homologous and heterologous interchromosomal associations lead to anaphase I chromatin bridging and the generation of aneuploid gametes.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona, United States of America.

ABSTRACT
Several meiotic processes ensure faithful chromosome segregation to create haploid gametes. Errors to any one of these processes can lead to zygotic aneuploidy with the potential for developmental abnormalities. During prophase I of Drosophila male meiosis, each bivalent condenses and becomes sequestered into discrete chromosome territories. Here, we demonstrate that two predicted condensin II subunits, Cap-H2 and Cap-D3, are required to promote territory formation. In mutants of either subunit, territory formation fails and chromatin is dispersed throughout the nucleus. Anaphase I is also abnormal in Cap-H2 mutants as chromatin bridges are found between segregating heterologous and homologous chromosomes. Aneuploid sperm may be generated from these defects as they occur at an elevated frequency and are genotypically consistent with anaphase I segregation defects. We propose that condensin II-mediated prophase I territory formation prevents and/or resolves heterologous chromosomal associations to alleviate their potential interference in anaphase I segregation. Furthermore, condensin II-catalyzed prophase I chromosome condensation may be necessary to resolve associations between paired homologous chromosomes of each bivalent. These persistent chromosome associations likely consist of DNA entanglements, but may be more specific as anaphase I bridging was rescued by mutations in the homolog conjunction factor teflon. We propose that the consequence of condensin II mutations is a failure to resolve heterologous and homologous associations mediated by entangled DNA and/or homolog conjunction factors. Furthermore, persistence of homologous and heterologous interchromosomal associations lead to anaphase I chromatin bridging and the generation of aneuploid gametes.

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Male sterile Cap-H2 mutants have irregular territory formation throughout prophase I.Three wild-type early prophase I (S2) primary spermatocyte nuclei stained with DAPI. Chromatin clustering is likely an early indicator of chromosome territory formation. Scale bar indicates 5 µm and serves all panels. (B) Mid wild-type prophase I (S4) nucleus where territory formation becomes more clear as indicated by three DAPI staining regions. (C) Late prophase I (S6) wild-type nucleus where the three DAPI staining chromosome territories are prominent. (D) Two prophase I (S2) nuclei from Cap-H2Z3-0019/Cap-H2TH1 mutants displaying abnormal chromatin organization that likely represents failure in the early stages of chromosome territory formation. This phenotype is 100% penetrant as it was observed in all S2 nuclei (n = 100). (E) Mid Prophase I (S4) nucleus from a Cap-H2Z3-0019/Cap-H2TH1 male where chromosome territory formation fails and instead chromatin appears throughout the nucleus. All S4 nuclei observed were similarly defective (n = 100). (F) Late prophase I (S6) nucleus from a Cap-H2Z3-0019/Cap-H2TH1 male where no discrete chromosome territories can be observed. All S6 nuclei observed had a similar abnormal morphology (n = 100). (G) Three early prophase I (S2) nuclei from a Cap-D3EY00456 male where chromosome morphology is abnormal and likely represents failure in the early stages of territory formation. All S2 nuclei observed were similarly defective (n = 100). (H) Mid prophase I (S4) nucleus from a Cap-D3EY00456 male where chromosome territory formation fails and instead chromatin appears throughout the nucleus. All S4 nuclei observed carried a similarly abnormal chromosome organization (n = 100). (I) Late prophase I (S6) nucleus from a Cap-D3EY00456 mutant male where discrete territory formation is absent. All S6 nuclei were similarly defective (n = 100).
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pgen-1000228-g002: Male sterile Cap-H2 mutants have irregular territory formation throughout prophase I.Three wild-type early prophase I (S2) primary spermatocyte nuclei stained with DAPI. Chromatin clustering is likely an early indicator of chromosome territory formation. Scale bar indicates 5 µm and serves all panels. (B) Mid wild-type prophase I (S4) nucleus where territory formation becomes more clear as indicated by three DAPI staining regions. (C) Late prophase I (S6) wild-type nucleus where the three DAPI staining chromosome territories are prominent. (D) Two prophase I (S2) nuclei from Cap-H2Z3-0019/Cap-H2TH1 mutants displaying abnormal chromatin organization that likely represents failure in the early stages of chromosome territory formation. This phenotype is 100% penetrant as it was observed in all S2 nuclei (n = 100). (E) Mid Prophase I (S4) nucleus from a Cap-H2Z3-0019/Cap-H2TH1 male where chromosome territory formation fails and instead chromatin appears throughout the nucleus. All S4 nuclei observed were similarly defective (n = 100). (F) Late prophase I (S6) nucleus from a Cap-H2Z3-0019/Cap-H2TH1 male where no discrete chromosome territories can be observed. All S6 nuclei observed had a similar abnormal morphology (n = 100). (G) Three early prophase I (S2) nuclei from a Cap-D3EY00456 male where chromosome morphology is abnormal and likely represents failure in the early stages of territory formation. All S2 nuclei observed were similarly defective (n = 100). (H) Mid prophase I (S4) nucleus from a Cap-D3EY00456 male where chromosome territory formation fails and instead chromatin appears throughout the nucleus. All S4 nuclei observed carried a similarly abnormal chromosome organization (n = 100). (I) Late prophase I (S6) nucleus from a Cap-D3EY00456 mutant male where discrete territory formation is absent. All S6 nuclei were similarly defective (n = 100).

Mentions: In prophase I stage S2 (Figure 2A), nuclei appear to commence the formation of chromosome territories. By mid-prophase I stage S4, territory formation is more evident (Figure 2B) and in late prophase I, stage S6 nuclei exhibit three discrete chromosome territories seemingly associated with the nuclear envelope (Figure 2C) [35]. Each of the three chromosome territories corresponds to the 2nd, 3rd, and sex chromosomal bivalents and are thought to have important chromosome organizational roles for meiosis I [33]–[36]. In male sterile mutants of the genotype Cap-H2Z3-0019/Cap-H2TH1, chromosome organizational steps throughout prophase I are defective, as normal territory formation is never observed in 100% of S2, S4, and S6 stages (n = 100 nuclei of each stage). Instead, chromatin is seemingly dispersed within the nucleus (Figures 2D–2F). Male sterile Cap-D3EY00456 mutants mimic these defects (Figure 2G–2I), suggesting that Cap-D3 and Cap-H2 function together within a condensin II complex to facilitate territory formation. No prophase I defects were observed in Cap-H2Z3-0019/Cap-H2Z3-5163 males, although subtle morphological changes may be difficult to detect.


Condensin II resolves chromosomal associations to enable anaphase I segregation in Drosophila male meiosis.

Hartl TA, Sweeney SJ, Knepler PJ, Bosco G - PLoS Genet. (2008)

Male sterile Cap-H2 mutants have irregular territory formation throughout prophase I.Three wild-type early prophase I (S2) primary spermatocyte nuclei stained with DAPI. Chromatin clustering is likely an early indicator of chromosome territory formation. Scale bar indicates 5 µm and serves all panels. (B) Mid wild-type prophase I (S4) nucleus where territory formation becomes more clear as indicated by three DAPI staining regions. (C) Late prophase I (S6) wild-type nucleus where the three DAPI staining chromosome territories are prominent. (D) Two prophase I (S2) nuclei from Cap-H2Z3-0019/Cap-H2TH1 mutants displaying abnormal chromatin organization that likely represents failure in the early stages of chromosome territory formation. This phenotype is 100% penetrant as it was observed in all S2 nuclei (n = 100). (E) Mid Prophase I (S4) nucleus from a Cap-H2Z3-0019/Cap-H2TH1 male where chromosome territory formation fails and instead chromatin appears throughout the nucleus. All S4 nuclei observed were similarly defective (n = 100). (F) Late prophase I (S6) nucleus from a Cap-H2Z3-0019/Cap-H2TH1 male where no discrete chromosome territories can be observed. All S6 nuclei observed had a similar abnormal morphology (n = 100). (G) Three early prophase I (S2) nuclei from a Cap-D3EY00456 male where chromosome morphology is abnormal and likely represents failure in the early stages of territory formation. All S2 nuclei observed were similarly defective (n = 100). (H) Mid prophase I (S4) nucleus from a Cap-D3EY00456 male where chromosome territory formation fails and instead chromatin appears throughout the nucleus. All S4 nuclei observed carried a similarly abnormal chromosome organization (n = 100). (I) Late prophase I (S6) nucleus from a Cap-D3EY00456 mutant male where discrete territory formation is absent. All S6 nuclei were similarly defective (n = 100).
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Related In: Results  -  Collection

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pgen-1000228-g002: Male sterile Cap-H2 mutants have irregular territory formation throughout prophase I.Three wild-type early prophase I (S2) primary spermatocyte nuclei stained with DAPI. Chromatin clustering is likely an early indicator of chromosome territory formation. Scale bar indicates 5 µm and serves all panels. (B) Mid wild-type prophase I (S4) nucleus where territory formation becomes more clear as indicated by three DAPI staining regions. (C) Late prophase I (S6) wild-type nucleus where the three DAPI staining chromosome territories are prominent. (D) Two prophase I (S2) nuclei from Cap-H2Z3-0019/Cap-H2TH1 mutants displaying abnormal chromatin organization that likely represents failure in the early stages of chromosome territory formation. This phenotype is 100% penetrant as it was observed in all S2 nuclei (n = 100). (E) Mid Prophase I (S4) nucleus from a Cap-H2Z3-0019/Cap-H2TH1 male where chromosome territory formation fails and instead chromatin appears throughout the nucleus. All S4 nuclei observed were similarly defective (n = 100). (F) Late prophase I (S6) nucleus from a Cap-H2Z3-0019/Cap-H2TH1 male where no discrete chromosome territories can be observed. All S6 nuclei observed had a similar abnormal morphology (n = 100). (G) Three early prophase I (S2) nuclei from a Cap-D3EY00456 male where chromosome morphology is abnormal and likely represents failure in the early stages of territory formation. All S2 nuclei observed were similarly defective (n = 100). (H) Mid prophase I (S4) nucleus from a Cap-D3EY00456 male where chromosome territory formation fails and instead chromatin appears throughout the nucleus. All S4 nuclei observed carried a similarly abnormal chromosome organization (n = 100). (I) Late prophase I (S6) nucleus from a Cap-D3EY00456 mutant male where discrete territory formation is absent. All S6 nuclei were similarly defective (n = 100).
Mentions: In prophase I stage S2 (Figure 2A), nuclei appear to commence the formation of chromosome territories. By mid-prophase I stage S4, territory formation is more evident (Figure 2B) and in late prophase I, stage S6 nuclei exhibit three discrete chromosome territories seemingly associated with the nuclear envelope (Figure 2C) [35]. Each of the three chromosome territories corresponds to the 2nd, 3rd, and sex chromosomal bivalents and are thought to have important chromosome organizational roles for meiosis I [33]–[36]. In male sterile mutants of the genotype Cap-H2Z3-0019/Cap-H2TH1, chromosome organizational steps throughout prophase I are defective, as normal territory formation is never observed in 100% of S2, S4, and S6 stages (n = 100 nuclei of each stage). Instead, chromatin is seemingly dispersed within the nucleus (Figures 2D–2F). Male sterile Cap-D3EY00456 mutants mimic these defects (Figure 2G–2I), suggesting that Cap-D3 and Cap-H2 function together within a condensin II complex to facilitate territory formation. No prophase I defects were observed in Cap-H2Z3-0019/Cap-H2Z3-5163 males, although subtle morphological changes may be difficult to detect.

Bottom Line: These persistent chromosome associations likely consist of DNA entanglements, but may be more specific as anaphase I bridging was rescued by mutations in the homolog conjunction factor teflon.We propose that the consequence of condensin II mutations is a failure to resolve heterologous and homologous associations mediated by entangled DNA and/or homolog conjunction factors.Furthermore, persistence of homologous and heterologous interchromosomal associations lead to anaphase I chromatin bridging and the generation of aneuploid gametes.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona, United States of America.

ABSTRACT
Several meiotic processes ensure faithful chromosome segregation to create haploid gametes. Errors to any one of these processes can lead to zygotic aneuploidy with the potential for developmental abnormalities. During prophase I of Drosophila male meiosis, each bivalent condenses and becomes sequestered into discrete chromosome territories. Here, we demonstrate that two predicted condensin II subunits, Cap-H2 and Cap-D3, are required to promote territory formation. In mutants of either subunit, territory formation fails and chromatin is dispersed throughout the nucleus. Anaphase I is also abnormal in Cap-H2 mutants as chromatin bridges are found between segregating heterologous and homologous chromosomes. Aneuploid sperm may be generated from these defects as they occur at an elevated frequency and are genotypically consistent with anaphase I segregation defects. We propose that condensin II-mediated prophase I territory formation prevents and/or resolves heterologous chromosomal associations to alleviate their potential interference in anaphase I segregation. Furthermore, condensin II-catalyzed prophase I chromosome condensation may be necessary to resolve associations between paired homologous chromosomes of each bivalent. These persistent chromosome associations likely consist of DNA entanglements, but may be more specific as anaphase I bridging was rescued by mutations in the homolog conjunction factor teflon. We propose that the consequence of condensin II mutations is a failure to resolve heterologous and homologous associations mediated by entangled DNA and/or homolog conjunction factors. Furthermore, persistence of homologous and heterologous interchromosomal associations lead to anaphase I chromatin bridging and the generation of aneuploid gametes.

Show MeSH
Related in: MedlinePlus