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

Homologues undergo dramatic structural reorganization during prophase of meiosis I. This diagram depicts the progression of a pair of homologues through prophase I. Homologue pairing and alignment initiate in leptotene–zygotene (not depicted). In pachytene, SC (yellow line) stabilizes homologue synapsis (red and green lines). A single crossover typically divides each homologue pair into long and short segments. SC disassembly in diplotene results first in desynapsis of the long segment of each homologue pair and then of the short segment (Nabeshima, K., M. Colaiácovo, and A. Villeneuve, personal communication). Recombinant homologues are reorganized around the crossover site and condensed to form highly compacted, cruciform bivalents. The short segment becomes the short arm of the diakinesis bivalent, where cohesin-mediated linkages maintain the association of homologues. Importantly, HCP-6 and MIX-1 (blue dots) become enriched on chromosomes after pachytene exit, and our evidence indicates that both proteins are required for the reorganization of homologues and formation of discrete, compacted diakinesis bivalents.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2172564&req=5

fig4: Homologues undergo dramatic structural reorganization during prophase of meiosis I. This diagram depicts the progression of a pair of homologues through prophase I. Homologue pairing and alignment initiate in leptotene–zygotene (not depicted). In pachytene, SC (yellow line) stabilizes homologue synapsis (red and green lines). A single crossover typically divides each homologue pair into long and short segments. SC disassembly in diplotene results first in desynapsis of the long segment of each homologue pair and then of the short segment (Nabeshima, K., M. Colaiácovo, and A. Villeneuve, personal communication). Recombinant homologues are reorganized around the crossover site and condensed to form highly compacted, cruciform bivalents. The short segment becomes the short arm of the diakinesis bivalent, where cohesin-mediated linkages maintain the association of homologues. Importantly, HCP-6 and MIX-1 (blue dots) become enriched on chromosomes after pachytene exit, and our evidence indicates that both proteins are required for the reorganization of homologues and formation of discrete, compacted diakinesis bivalents.

Mentions: In the C. elegans germline, meiotic nuclei are arranged in a temporal-spatial order, revealing the dramatic morphological changes that occur during meiosis I prophase. The premeiotic germline, which lies at the distal end of the gonad, contains mitotically proliferating nuclei and nuclei in premeiotic S-phase. Pairing and alignment of homologues initiate downstream in the gonad, in the “transition zone,” the equivalent of leptotene–zygotene. In pachytene, homologues are fully synapsed (Fig. 4), are distinct from one another, and appear in DAPI-stained nuclei as discrete, parallel tracks separated by a narrow gap occupied by the synaptonemal complex (SC). A single crossover forms during pachytene between each pair of homologues. The SC disassembles as nuclei exit pachytene and enter diplotene, but desynapsed homologues remain tethered by sister chromatid cohesion flanking the crossover (Fig. 4). Cellularized oocytes pause in diakinesis of prophase I with condensed homologue pairs until fertilization, the event that triggers meiosis I and II (McCarter et al., 1999).


Condensin restructures chromosomes in preparation for meiotic divisions.

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

Homologues undergo dramatic structural reorganization during prophase of meiosis I. This diagram depicts the progression of a pair of homologues through prophase I. Homologue pairing and alignment initiate in leptotene–zygotene (not depicted). In pachytene, SC (yellow line) stabilizes homologue synapsis (red and green lines). A single crossover typically divides each homologue pair into long and short segments. SC disassembly in diplotene results first in desynapsis of the long segment of each homologue pair and then of the short segment (Nabeshima, K., M. Colaiácovo, and A. Villeneuve, personal communication). Recombinant homologues are reorganized around the crossover site and condensed to form highly compacted, cruciform bivalents. The short segment becomes the short arm of the diakinesis bivalent, where cohesin-mediated linkages maintain the association of homologues. Importantly, HCP-6 and MIX-1 (blue dots) become enriched on chromosomes after pachytene exit, and our evidence indicates that both proteins are required for the reorganization of homologues and formation of discrete, compacted diakinesis bivalents.
© Copyright Policy
Related In: Results  -  Collection

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

fig4: Homologues undergo dramatic structural reorganization during prophase of meiosis I. This diagram depicts the progression of a pair of homologues through prophase I. Homologue pairing and alignment initiate in leptotene–zygotene (not depicted). In pachytene, SC (yellow line) stabilizes homologue synapsis (red and green lines). A single crossover typically divides each homologue pair into long and short segments. SC disassembly in diplotene results first in desynapsis of the long segment of each homologue pair and then of the short segment (Nabeshima, K., M. Colaiácovo, and A. Villeneuve, personal communication). Recombinant homologues are reorganized around the crossover site and condensed to form highly compacted, cruciform bivalents. The short segment becomes the short arm of the diakinesis bivalent, where cohesin-mediated linkages maintain the association of homologues. Importantly, HCP-6 and MIX-1 (blue dots) become enriched on chromosomes after pachytene exit, and our evidence indicates that both proteins are required for the reorganization of homologues and formation of discrete, compacted diakinesis bivalents.
Mentions: In the C. elegans germline, meiotic nuclei are arranged in a temporal-spatial order, revealing the dramatic morphological changes that occur during meiosis I prophase. The premeiotic germline, which lies at the distal end of the gonad, contains mitotically proliferating nuclei and nuclei in premeiotic S-phase. Pairing and alignment of homologues initiate downstream in the gonad, in the “transition zone,” the equivalent of leptotene–zygotene. In pachytene, homologues are fully synapsed (Fig. 4), are distinct from one another, and appear in DAPI-stained nuclei as discrete, parallel tracks separated by a narrow gap occupied by the synaptonemal complex (SC). A single crossover forms during pachytene between each pair of homologues. The SC disassembles as nuclei exit pachytene and enter diplotene, but desynapsed homologues remain tethered by sister chromatid cohesion flanking the crossover (Fig. 4). Cellularized oocytes pause in diakinesis of prophase I with condensed homologue pairs until fertilization, the event that triggers meiosis I and II (McCarter et al., 1999).

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