Limits...
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.

Show MeSH

Related in: MedlinePlus

HCP-6 and MIX-1 first associate with meiotic chromosomes at diplotene–diakinesis. In confocal images of wild-type transition zone (A) and pachytene (B) nuclei, HCP-6 appeared nucleoplasmic but excluded from DNA (arrowheads indicate regions devoid of HCP-6 staining). (C) HCP-6 and MIX-1 accumulate in four quadrants on wild-type diakinesis bivalents. CENP-A was also present in four foci per bivalent, but these foci were broader than the HCP-6 and MIX-1 foci. The four HCP-6 foci (fourth row, arrowheads) were bisected by SMC-1 staining, indicating that each quadrant represents one sister chromatid. (D) After partial depletion of REC-8, two HCP-6 foci (arrowheads) were present on each univalent, correlating with the presence of two sister chromatids per univalent. (E) MIX-1 was undetectable on bivalents in mix-1(b285, RNAi) mutants, but HCP-6 still accumulated on chromosomes. In contrast, MIX-1 required HCP-6 for its association with meiotic chromosomes. MIX-1 was undetectable on bivalents in animal mutants for the partial loss-of-function allele hcp-6(mr17), which also disrupted HCP-6 loading. Association of MIX-1 with the dosage compensation complex does not require HCP-6: MIX-1 antibodies stained X chromosomes in gut nuclei of hcp-6(mr17) and hcp-6(mr17, RNAi) mutants (not depicted). Both MIX-1 and HCP-6 loaded on meiotic chromosomes in CENP-A depleted worms, and CENP-A localized on chromosomes in mix-1(b285, RNAi) and hcp-6(mr17, RNAi) oocytes. Bars, 2 μm.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2172564&req=5

fig5: HCP-6 and MIX-1 first associate with meiotic chromosomes at diplotene–diakinesis. In confocal images of wild-type transition zone (A) and pachytene (B) nuclei, HCP-6 appeared nucleoplasmic but excluded from DNA (arrowheads indicate regions devoid of HCP-6 staining). (C) HCP-6 and MIX-1 accumulate in four quadrants on wild-type diakinesis bivalents. CENP-A was also present in four foci per bivalent, but these foci were broader than the HCP-6 and MIX-1 foci. The four HCP-6 foci (fourth row, arrowheads) were bisected by SMC-1 staining, indicating that each quadrant represents one sister chromatid. (D) After partial depletion of REC-8, two HCP-6 foci (arrowheads) were present on each univalent, correlating with the presence of two sister chromatids per univalent. (E) MIX-1 was undetectable on bivalents in mix-1(b285, RNAi) mutants, but HCP-6 still accumulated on chromosomes. In contrast, MIX-1 required HCP-6 for its association with meiotic chromosomes. MIX-1 was undetectable on bivalents in animal mutants for the partial loss-of-function allele hcp-6(mr17), which also disrupted HCP-6 loading. Association of MIX-1 with the dosage compensation complex does not require HCP-6: MIX-1 antibodies stained X chromosomes in gut nuclei of hcp-6(mr17) and hcp-6(mr17, RNAi) mutants (not depicted). Both MIX-1 and HCP-6 loaded on meiotic chromosomes in CENP-A depleted worms, and CENP-A localized on chromosomes in mix-1(b285, RNAi) and hcp-6(mr17, RNAi) oocytes. Bars, 2 μm.

Mentions: HCP-6 and MIX-1 colocalize with the centromeric histone variant CENP-A on the poleward faces of metaphase chromosomes during mitotic divisions in embryos and in the germline (Fig. 1 E and Fig. 2 A; Hagstrom et al., 2002; Stear and Roth, 2002). This pattern of localization and the biochemistry above indicate that HCP-6 and MIX-1 form a complex that associates with centromeres of mitotic chromosomes. To further define the roles for condensin in mitosis, we identified conditions that severely reduce HCP-6 function. The hcp-6(mr17) allele has a missense mutation (Stear and Roth, 2002) that results in temperature-sensitive embryonic lethality (Table S1, available at http://www.jcb.org/cgi/content/full/jcb.200408061/DC1); however, HCP-6 protein levels are not reduced (Fig. 1 C, lanes 1 and 2). Therefore, we treated hcp-6(mr17) mutants with hcp-6 RNA interference (RNAi) to deplete HCP-6 to levels undetectable by Western blot analysis (Fig. 1 C, lane 3) and immunostaining (Fig. 2 A, Fig. 5 E). Any residual protein would be compromised by the hcp-6(mr17) mutation. MIX-1 function was similarly reduced by mix-1 RNAi in worms homozygous for the maternal-effect embryonic lethal allele mix-1(b285) (Fig. 2 A, Fig. 5 E).


Condensin restructures chromosomes in preparation for meiotic divisions.

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

HCP-6 and MIX-1 first associate with meiotic chromosomes at diplotene–diakinesis. In confocal images of wild-type transition zone (A) and pachytene (B) nuclei, HCP-6 appeared nucleoplasmic but excluded from DNA (arrowheads indicate regions devoid of HCP-6 staining). (C) HCP-6 and MIX-1 accumulate in four quadrants on wild-type diakinesis bivalents. CENP-A was also present in four foci per bivalent, but these foci were broader than the HCP-6 and MIX-1 foci. The four HCP-6 foci (fourth row, arrowheads) were bisected by SMC-1 staining, indicating that each quadrant represents one sister chromatid. (D) After partial depletion of REC-8, two HCP-6 foci (arrowheads) were present on each univalent, correlating with the presence of two sister chromatids per univalent. (E) MIX-1 was undetectable on bivalents in mix-1(b285, RNAi) mutants, but HCP-6 still accumulated on chromosomes. In contrast, MIX-1 required HCP-6 for its association with meiotic chromosomes. MIX-1 was undetectable on bivalents in animal mutants for the partial loss-of-function allele hcp-6(mr17), which also disrupted HCP-6 loading. Association of MIX-1 with the dosage compensation complex does not require HCP-6: MIX-1 antibodies stained X chromosomes in gut nuclei of hcp-6(mr17) and hcp-6(mr17, RNAi) mutants (not depicted). Both MIX-1 and HCP-6 loaded on meiotic chromosomes in CENP-A depleted worms, and CENP-A localized on chromosomes in mix-1(b285, RNAi) and hcp-6(mr17, RNAi) oocytes. Bars, 2 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172564&req=5

fig5: HCP-6 and MIX-1 first associate with meiotic chromosomes at diplotene–diakinesis. In confocal images of wild-type transition zone (A) and pachytene (B) nuclei, HCP-6 appeared nucleoplasmic but excluded from DNA (arrowheads indicate regions devoid of HCP-6 staining). (C) HCP-6 and MIX-1 accumulate in four quadrants on wild-type diakinesis bivalents. CENP-A was also present in four foci per bivalent, but these foci were broader than the HCP-6 and MIX-1 foci. The four HCP-6 foci (fourth row, arrowheads) were bisected by SMC-1 staining, indicating that each quadrant represents one sister chromatid. (D) After partial depletion of REC-8, two HCP-6 foci (arrowheads) were present on each univalent, correlating with the presence of two sister chromatids per univalent. (E) MIX-1 was undetectable on bivalents in mix-1(b285, RNAi) mutants, but HCP-6 still accumulated on chromosomes. In contrast, MIX-1 required HCP-6 for its association with meiotic chromosomes. MIX-1 was undetectable on bivalents in animal mutants for the partial loss-of-function allele hcp-6(mr17), which also disrupted HCP-6 loading. Association of MIX-1 with the dosage compensation complex does not require HCP-6: MIX-1 antibodies stained X chromosomes in gut nuclei of hcp-6(mr17) and hcp-6(mr17, RNAi) mutants (not depicted). Both MIX-1 and HCP-6 loaded on meiotic chromosomes in CENP-A depleted worms, and CENP-A localized on chromosomes in mix-1(b285, RNAi) and hcp-6(mr17, RNAi) oocytes. Bars, 2 μm.
Mentions: HCP-6 and MIX-1 colocalize with the centromeric histone variant CENP-A on the poleward faces of metaphase chromosomes during mitotic divisions in embryos and in the germline (Fig. 1 E and Fig. 2 A; Hagstrom et al., 2002; Stear and Roth, 2002). This pattern of localization and the biochemistry above indicate that HCP-6 and MIX-1 form a complex that associates with centromeres of mitotic chromosomes. To further define the roles for condensin in mitosis, we identified conditions that severely reduce HCP-6 function. The hcp-6(mr17) allele has a missense mutation (Stear and Roth, 2002) that results in temperature-sensitive embryonic lethality (Table S1, available at http://www.jcb.org/cgi/content/full/jcb.200408061/DC1); however, HCP-6 protein levels are not reduced (Fig. 1 C, lanes 1 and 2). Therefore, we treated hcp-6(mr17) mutants with hcp-6 RNA interference (RNAi) to deplete HCP-6 to levels undetectable by Western blot analysis (Fig. 1 C, lane 3) and immunostaining (Fig. 2 A, Fig. 5 E). Any residual protein would be compromised by the hcp-6(mr17) mutation. MIX-1 function was similarly reduced by mix-1 RNAi in worms homozygous for the maternal-effect embryonic lethal allele mix-1(b285) (Fig. 2 A, Fig. 5 E).

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