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Mouse pachytene checkpoint 2 (trip13) is required for completing meiotic recombination but not synapsis.

Li XC, Li X, Schimenti JC - PLoS Genet. (2007)

Bottom Line: The chromosomes of mutant spermatocytes synapse fully, yet retain several markers of recombination intermediates, including RAD51, BLM, and RPA.These chromosomes also exhibited the chiasmata markers MLH1 and MLH3, and okadaic acid treatment of mutant spermatocytes caused progression to metaphase I with bivalent chromosomes.Our data indicate that TRIP13 is required after strand invasion for completing a subset of recombination events, but possibly not those destined to be crossovers.

View Article: PubMed Central - PubMed

Affiliation: Cornell University, College of Veterinary Medicine, Department of Biomedical Sciences, Ithaca, New York, United States of America.

ABSTRACT
In mammalian meiosis, homologous chromosome synapsis is coupled with recombination. As in most eukaryotes, mammalian meiocytes have checkpoints that monitor the fidelity of these processes. We report that the mouse ortholog (Trip13) of pachytene checkpoint 2 (PCH2), an essential component of the synapsis checkpoint in Saccharomyces cerevisiae and Caenorhabditis elegans, is required for completion of meiosis in both sexes. TRIP13-deficient mice exhibit spermatocyte death in pachynema and loss of oocytes around birth. The chromosomes of mutant spermatocytes synapse fully, yet retain several markers of recombination intermediates, including RAD51, BLM, and RPA. These chromosomes also exhibited the chiasmata markers MLH1 and MLH3, and okadaic acid treatment of mutant spermatocytes caused progression to metaphase I with bivalent chromosomes. Double mutant analysis demonstrated that the recombination and synapsis genes Spo11, Mei1, Rec8, and Dmc1 are all epistatic to Trip13, suggesting that TRIP13 does not have meiotic checkpoint function in mice. Our data indicate that TRIP13 is required after strand invasion for completing a subset of recombination events, but possibly not those destined to be crossovers. To our knowledge, this is the first model to separate recombination defects from asynapsis in mammalian meiosis, and provides the first evidence that unrepaired DNA damage alone can trigger the pachytene checkpoint response in mice.

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Immunocytological Analysis of Trip13 Compound MutantsSurface-spread chromosomes were immunolabeled with the indicated antibodies and fluorophores. Genotypes are indicated, as are those panels in which dual staining patterns are merged. Note that (H) and (I) are at lower magnification to show multiple nuclei.
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pgen-0030130-g005: Immunocytological Analysis of Trip13 Compound MutantsSurface-spread chromosomes were immunolabeled with the indicated antibodies and fluorophores. Genotypes are indicated, as are those panels in which dual staining patterns are merged. Note that (H) and (I) are at lower magnification to show multiple nuclei.

Mentions: To determine if TRIP13 deficiency prevents apoptosis triggered by asynapsis as in C. elegans, we analyzed mice that were doubly mutant for Spo11 and Trip13. SPO11 is a transesterase that is essential for the creation of genetically programmed DSB during leptonema of many organisms, including mice [18]. In C. elegans, spo-11 mutant gametes have extensive asynapsis, which triggers PCH-2 dependent apoptosis in pachynema [2]. In mice, Spo11−/− spermatocytes are severely defective in homologous chromosome synapsis [34,35], and arrest with chromosomes in a state characteristic of the zygotene/pachytene transition (Figure 3H). Spermatocytes in Trip13Gt/Gt Spo11−/− testes progressed maximally to that point before undergoing death (Figs 3I), well before the spindle checkpoint that eliminates achiasmate spermatocytes [36]. There was no evidence of metaphase I spermatocytes or postmeiotic spermatids in these testes, unlike those seen in Trip13 single mutants (Figure 3G). In contrast to the complete synapsis in Trip13Gt/Gt pachytene spermatocytes (Figure 5A), in which SPO11 is available in leptonema to initiate (via DSB induction, Figure S2A and S2B) a recombination-driven homolog search, chromosome synapsis in doubly mutant spermatocytes was highly disrupted as in Spo11 single mutants (Figure 5B and 5C). Identical studies were performed with mice deficient for Mei1, a vertebrate-specific gene also required for DSB formation and chromosome synapsis [37], with similar results (Figure 3J and 3K; immunocytology not shown).


Mouse pachytene checkpoint 2 (trip13) is required for completing meiotic recombination but not synapsis.

Li XC, Li X, Schimenti JC - PLoS Genet. (2007)

Immunocytological Analysis of Trip13 Compound MutantsSurface-spread chromosomes were immunolabeled with the indicated antibodies and fluorophores. Genotypes are indicated, as are those panels in which dual staining patterns are merged. Note that (H) and (I) are at lower magnification to show multiple nuclei.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1941754&req=5

pgen-0030130-g005: Immunocytological Analysis of Trip13 Compound MutantsSurface-spread chromosomes were immunolabeled with the indicated antibodies and fluorophores. Genotypes are indicated, as are those panels in which dual staining patterns are merged. Note that (H) and (I) are at lower magnification to show multiple nuclei.
Mentions: To determine if TRIP13 deficiency prevents apoptosis triggered by asynapsis as in C. elegans, we analyzed mice that were doubly mutant for Spo11 and Trip13. SPO11 is a transesterase that is essential for the creation of genetically programmed DSB during leptonema of many organisms, including mice [18]. In C. elegans, spo-11 mutant gametes have extensive asynapsis, which triggers PCH-2 dependent apoptosis in pachynema [2]. In mice, Spo11−/− spermatocytes are severely defective in homologous chromosome synapsis [34,35], and arrest with chromosomes in a state characteristic of the zygotene/pachytene transition (Figure 3H). Spermatocytes in Trip13Gt/Gt Spo11−/− testes progressed maximally to that point before undergoing death (Figs 3I), well before the spindle checkpoint that eliminates achiasmate spermatocytes [36]. There was no evidence of metaphase I spermatocytes or postmeiotic spermatids in these testes, unlike those seen in Trip13 single mutants (Figure 3G). In contrast to the complete synapsis in Trip13Gt/Gt pachytene spermatocytes (Figure 5A), in which SPO11 is available in leptonema to initiate (via DSB induction, Figure S2A and S2B) a recombination-driven homolog search, chromosome synapsis in doubly mutant spermatocytes was highly disrupted as in Spo11 single mutants (Figure 5B and 5C). Identical studies were performed with mice deficient for Mei1, a vertebrate-specific gene also required for DSB formation and chromosome synapsis [37], with similar results (Figure 3J and 3K; immunocytology not shown).

Bottom Line: The chromosomes of mutant spermatocytes synapse fully, yet retain several markers of recombination intermediates, including RAD51, BLM, and RPA.These chromosomes also exhibited the chiasmata markers MLH1 and MLH3, and okadaic acid treatment of mutant spermatocytes caused progression to metaphase I with bivalent chromosomes.Our data indicate that TRIP13 is required after strand invasion for completing a subset of recombination events, but possibly not those destined to be crossovers.

View Article: PubMed Central - PubMed

Affiliation: Cornell University, College of Veterinary Medicine, Department of Biomedical Sciences, Ithaca, New York, United States of America.

ABSTRACT
In mammalian meiosis, homologous chromosome synapsis is coupled with recombination. As in most eukaryotes, mammalian meiocytes have checkpoints that monitor the fidelity of these processes. We report that the mouse ortholog (Trip13) of pachytene checkpoint 2 (PCH2), an essential component of the synapsis checkpoint in Saccharomyces cerevisiae and Caenorhabditis elegans, is required for completion of meiosis in both sexes. TRIP13-deficient mice exhibit spermatocyte death in pachynema and loss of oocytes around birth. The chromosomes of mutant spermatocytes synapse fully, yet retain several markers of recombination intermediates, including RAD51, BLM, and RPA. These chromosomes also exhibited the chiasmata markers MLH1 and MLH3, and okadaic acid treatment of mutant spermatocytes caused progression to metaphase I with bivalent chromosomes. Double mutant analysis demonstrated that the recombination and synapsis genes Spo11, Mei1, Rec8, and Dmc1 are all epistatic to Trip13, suggesting that TRIP13 does not have meiotic checkpoint function in mice. Our data indicate that TRIP13 is required after strand invasion for completing a subset of recombination events, but possibly not those destined to be crossovers. To our knowledge, this is the first model to separate recombination defects from asynapsis in mammalian meiosis, and provides the first evidence that unrepaired DNA damage alone can trigger the pachytene checkpoint response in mice.

Show MeSH
Related in: MedlinePlus