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Condensin restructures chromosomes in preparation for meiotic divisions.

Chan RC, Severson AF, Meyer BJ - J. Cell Biol. (2004)

Bottom Line: We showed that condensin, the protein complex needed for mitotic chromosome compaction, restructures chromosomes during meiosis in Caenorhabditis elegans.Condensin helps resolve cohesin-independent linkages between sister chromatids and alleviates recombination-independent linkages between homologues.The safeguarding of chromosome resolution by condensin permits chromosome segregation and is crucial for the formation of discrete, individualized bivalent chromosomes.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA.

ABSTRACT
The production of haploid gametes from diploid germ cells requires two rounds of meiotic chromosome segregation after one round of replication. Accurate meiotic chromosome segregation involves the remodeling of each pair of homologous chromosomes around the site of crossover into a highly condensed and ordered structure. We showed that condensin, the protein complex needed for mitotic chromosome compaction, restructures chromosomes during meiosis in Caenorhabditis elegans. In particular, condensin promotes both meiotic chromosome condensation after crossover recombination and the remodeling of sister chromatids. Condensin helps resolve cohesin-independent linkages between sister chromatids and alleviates recombination-independent linkages between homologues. The safeguarding of chromosome resolution by condensin permits chromosome segregation and is crucial for the formation of discrete, individualized bivalent chromosomes.

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HCP-6 mediates chromosome compaction and resolution at diplotene–diakinesis. (A) Confocal images of DAPI staining and 5S rDNA FISH revealed normal DNA morphology and homologue association in pachytene of hcp-6 mutants. Moreover, staining of cohesin subunit SMC-1 and SC central element SYP-1 were indistinguishable in wild-type and hcp-6 mutant pachytene nuclei. (B) Residual SYP-1 staining in late pachytene and diplotene nuclei was similar in wild-type and hcp-6(mr17, RNAi) animals (left column, arrowhead), suggesting normal SC disassembly in hcp-6 mutants. However, wild-type chromosomes compacted rapidly in diplotene but hcp-6 mutant chromosomes were decondensed (right column, magnified images of nuclei marked with arrowheads in left column). (C) Diplotene chromosomes decondensed in hcp-6(mr17, RNAi) and hcp-6(mr17) mutants. (D) Resolution of diakinesis bivalents failed in hcp-6(mr17, RNAi) animals. Six compact bivalents were resolved by late diakinesis in hcp-6(mr17) mutants, as in wild type (see Fig. 8 E). (E) 5S rDNA FISH indicated that homologue realignment of chromosome V (arrowhead) was achieved by diakinesis in hcp-6(mr17) mutants. Bars, 5 μm.
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fig6: HCP-6 mediates chromosome compaction and resolution at diplotene–diakinesis. (A) Confocal images of DAPI staining and 5S rDNA FISH revealed normal DNA morphology and homologue association in pachytene of hcp-6 mutants. Moreover, staining of cohesin subunit SMC-1 and SC central element SYP-1 were indistinguishable in wild-type and hcp-6 mutant pachytene nuclei. (B) Residual SYP-1 staining in late pachytene and diplotene nuclei was similar in wild-type and hcp-6(mr17, RNAi) animals (left column, arrowhead), suggesting normal SC disassembly in hcp-6 mutants. However, wild-type chromosomes compacted rapidly in diplotene but hcp-6 mutant chromosomes were decondensed (right column, magnified images of nuclei marked with arrowheads in left column). (C) Diplotene chromosomes decondensed in hcp-6(mr17, RNAi) and hcp-6(mr17) mutants. (D) Resolution of diakinesis bivalents failed in hcp-6(mr17, RNAi) animals. Six compact bivalents were resolved by late diakinesis in hcp-6(mr17) mutants, as in wild type (see Fig. 8 E). (E) 5S rDNA FISH indicated that homologue realignment of chromosome V (arrowhead) was achieved by diakinesis in hcp-6(mr17) mutants. Bars, 5 μm.

Mentions: Pachytene chromosome organization appeared normal in hcp-6 mutants (Fig. 6 A), consistent with the association of HCP-6 with chromosomes after pachytene exit. 5S rDNA FISH indicated that synapsis was unaffected by hcp-6 inactivation. Moreover, SC central element SYP-1 and cohesin subunits SMC-1 and SMC-3 localized between homologues, as in wild type (Fig. 6 A, Fig. 7 A). In hcp-6(mr17) and hcp-6(mr17, RNAi) animals, homologue pairs appeared normally compacted and had no obvious attachments to other homologue pairs in late pachytene nuclei (Fig. 6 A; unpublished data). Finally, linkages between homologues were resolved because rec-8(RNAi) caused similar levels of asynapsis in late pachytene nuclei of hcp-6(mr17) animals grown at 15 and 25°C (Fig. 8 A). Both the timing of condensin localization and the phenotypes of condensin mutants suggest that factors other than HCP-6 mediate the condensation, individualization, and resolution of chromosomes accompanying entry into pachytene. However, we cannot exclude the possibility that residual condensin function is sufficient for these processes.


Condensin restructures chromosomes in preparation for meiotic divisions.

Chan RC, Severson AF, Meyer BJ - J. Cell Biol. (2004)

HCP-6 mediates chromosome compaction and resolution at diplotene–diakinesis. (A) Confocal images of DAPI staining and 5S rDNA FISH revealed normal DNA morphology and homologue association in pachytene of hcp-6 mutants. Moreover, staining of cohesin subunit SMC-1 and SC central element SYP-1 were indistinguishable in wild-type and hcp-6 mutant pachytene nuclei. (B) Residual SYP-1 staining in late pachytene and diplotene nuclei was similar in wild-type and hcp-6(mr17, RNAi) animals (left column, arrowhead), suggesting normal SC disassembly in hcp-6 mutants. However, wild-type chromosomes compacted rapidly in diplotene but hcp-6 mutant chromosomes were decondensed (right column, magnified images of nuclei marked with arrowheads in left column). (C) Diplotene chromosomes decondensed in hcp-6(mr17, RNAi) and hcp-6(mr17) mutants. (D) Resolution of diakinesis bivalents failed in hcp-6(mr17, RNAi) animals. Six compact bivalents were resolved by late diakinesis in hcp-6(mr17) mutants, as in wild type (see Fig. 8 E). (E) 5S rDNA FISH indicated that homologue realignment of chromosome V (arrowhead) was achieved by diakinesis in hcp-6(mr17) mutants. Bars, 5 μm.
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fig6: HCP-6 mediates chromosome compaction and resolution at diplotene–diakinesis. (A) Confocal images of DAPI staining and 5S rDNA FISH revealed normal DNA morphology and homologue association in pachytene of hcp-6 mutants. Moreover, staining of cohesin subunit SMC-1 and SC central element SYP-1 were indistinguishable in wild-type and hcp-6 mutant pachytene nuclei. (B) Residual SYP-1 staining in late pachytene and diplotene nuclei was similar in wild-type and hcp-6(mr17, RNAi) animals (left column, arrowhead), suggesting normal SC disassembly in hcp-6 mutants. However, wild-type chromosomes compacted rapidly in diplotene but hcp-6 mutant chromosomes were decondensed (right column, magnified images of nuclei marked with arrowheads in left column). (C) Diplotene chromosomes decondensed in hcp-6(mr17, RNAi) and hcp-6(mr17) mutants. (D) Resolution of diakinesis bivalents failed in hcp-6(mr17, RNAi) animals. Six compact bivalents were resolved by late diakinesis in hcp-6(mr17) mutants, as in wild type (see Fig. 8 E). (E) 5S rDNA FISH indicated that homologue realignment of chromosome V (arrowhead) was achieved by diakinesis in hcp-6(mr17) mutants. Bars, 5 μm.
Mentions: Pachytene chromosome organization appeared normal in hcp-6 mutants (Fig. 6 A), consistent with the association of HCP-6 with chromosomes after pachytene exit. 5S rDNA FISH indicated that synapsis was unaffected by hcp-6 inactivation. Moreover, SC central element SYP-1 and cohesin subunits SMC-1 and SMC-3 localized between homologues, as in wild type (Fig. 6 A, Fig. 7 A). In hcp-6(mr17) and hcp-6(mr17, RNAi) animals, homologue pairs appeared normally compacted and had no obvious attachments to other homologue pairs in late pachytene nuclei (Fig. 6 A; unpublished data). Finally, linkages between homologues were resolved because rec-8(RNAi) caused similar levels of asynapsis in late pachytene nuclei of hcp-6(mr17) animals grown at 15 and 25°C (Fig. 8 A). Both the timing of condensin localization and the phenotypes of condensin mutants suggest that factors other than HCP-6 mediate the condensation, individualization, and resolution of chromosomes accompanying entry into pachytene. However, we cannot exclude the possibility that residual condensin function is sufficient for these processes.

Bottom Line: We showed that condensin, the protein complex needed for mitotic chromosome compaction, restructures chromosomes during meiosis in Caenorhabditis elegans.Condensin helps resolve cohesin-independent linkages between sister chromatids and alleviates recombination-independent linkages between homologues.The safeguarding of chromosome resolution by condensin permits chromosome segregation and is crucial for the formation of discrete, individualized bivalent chromosomes.

View Article: PubMed Central - PubMed

Affiliation: Howard Hughes Medical Institute, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA.

ABSTRACT
The production of haploid gametes from diploid germ cells requires two rounds of meiotic chromosome segregation after one round of replication. Accurate meiotic chromosome segregation involves the remodeling of each pair of homologous chromosomes around the site of crossover into a highly condensed and ordered structure. We showed that condensin, the protein complex needed for mitotic chromosome compaction, restructures chromosomes during meiosis in Caenorhabditis elegans. In particular, condensin promotes both meiotic chromosome condensation after crossover recombination and the remodeling of sister chromatids. Condensin helps resolve cohesin-independent linkages between sister chromatids and alleviates recombination-independent linkages between homologues. The safeguarding of chromosome resolution by condensin permits chromosome segregation and is crucial for the formation of discrete, individualized bivalent chromosomes.

Show MeSH
Related in: MedlinePlus