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The ATM signaling cascade promotes recombination-dependent pachytene arrest in mouse spermatocytes.

Pacheco S, Marcet-Ortega M, Lange J, Jasin M, Keeney S, Roig I - PLoS Genet. (2015)

Bottom Line: TRIP13-deficient spermatocytes also progress to an H1t-positive stage if ATM activity is attenuated by hypomorphic mutations in Mre11 or Nbs1 or by elimination of the ATM-effector kinase CHK2.Our work supports the conclusion that recombination defects trigger spermatocyte arrest via pathways than are genetically distinct from sex body failure-promoted apoptosis and confirm that the latter can function even when recombination-dependent arrest is inoperative.Implications of these findings for understanding the complex relationships between spermatocyte arrest and apoptosis are discussed.

View Article: PubMed Central - PubMed

Affiliation: Genome Integrity and Instability Group, Institut de Biotecnologia i Biomedicina, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, Spain; Cytology and Histology Unit, Department of Cell Biology, Physiology and Immunology, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, Spain.

ABSTRACT
Most mutations that compromise meiotic recombination or synapsis in mouse spermatocytes result in arrest and apoptosis at the pachytene stage of the first meiotic prophase. Two main mechanisms are thought to trigger arrest: one independent of the double-strand breaks (DSBs) that initiate meiotic recombination, and another activated by persistent recombination intermediates. Mechanisms underlying the recombination-dependent arrest response are not well understood, so we sought to identify factors involved by examining mutants deficient for TRIP13, a conserved AAA+ ATPase required for the completion of meiotic DSB repair. We find that spermatocytes with a hypomorphic Trip13 mutation (Trip13mod/mod) arrest with features characteristic of early pachynema in wild type, namely, fully synapsed chromosomes without incorporation of the histone variant H1t into chromatin. These cells then undergo apoptosis, possibly in response to the arrest or in response to a defect in sex body formation. However, TRIP13-deficient cells that additionally lack the DSB-responsive kinase ATM progress further, reaching an H1t-positive stage (i.e., similar to mid/late pachynema in wild type) despite the presence of unrepaired DSBs. TRIP13-deficient spermatocytes also progress to an H1t-positive stage if ATM activity is attenuated by hypomorphic mutations in Mre11 or Nbs1 or by elimination of the ATM-effector kinase CHK2. These mutant backgrounds nonetheless experience an apoptotic block to further spermatogenic progression, most likely caused by failure to form a sex body. DSB numbers are elevated in Mre11 and Nbs1 hypomorphs but not Chk2 mutants, thus delineating genetic requirements for the ATM-dependent negative feedback loop that regulates DSB numbers. The findings demonstrate for the first time that ATM-dependent signaling enforces the normal pachytene response to persistent recombination intermediates. Our work supports the conclusion that recombination defects trigger spermatocyte arrest via pathways than are genetically distinct from sex body failure-promoted apoptosis and confirm that the latter can function even when recombination-dependent arrest is inoperative. Implications of these findings for understanding the complex relationships between spermatocyte arrest and apoptosis are discussed.

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Functions of the ATM signaling pathway during mouse meiotic prophase.We propose that DSBs induced by SPO11 at the beginning of meiotic prophase are sensed by the MRE11 complex, which activates ATM. ATM inhibits further DSB formation via a feedback loop and promotes DSB repair. ATM activates CHK2, which controls cell cycle progression but is not involved in regulating DSB formation. Recombination progression leads to homologous chromosome synapsis and sex body formation. Besides participating in recombination, TRIP13 is also needed for effective sex body formation. Proper recombination and sex body formation are required to permit meiotic progression.
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pgen.1005017.g007: Functions of the ATM signaling pathway during mouse meiotic prophase.We propose that DSBs induced by SPO11 at the beginning of meiotic prophase are sensed by the MRE11 complex, which activates ATM. ATM inhibits further DSB formation via a feedback loop and promotes DSB repair. ATM activates CHK2, which controls cell cycle progression but is not involved in regulating DSB formation. Recombination progression leads to homologous chromosome synapsis and sex body formation. Besides participating in recombination, TRIP13 is also needed for effective sex body formation. Proper recombination and sex body formation are required to permit meiotic progression.

Mentions: The array of phenotypes in the mutants analyzed here suggests that ATM participates in different aspects of meiotic prophase (Fig. 7). Our results further demonstrate that, while meiotic progression depends on the MRE11 complex, ATM and CHK2, the regulation of SPO11 activity requires the MRE11 complex to activate ATM but is independent of CHK2. This finding may indicate that direct ATM phosphorylation targets exert control of DSB formation, as has been argued in yeast [49]. Interestingly, yeast Mek1 promotes inter-homolog bias in the repair of DSBs [50,51]. The fact that homologous chromosome synapsis is not altered in the absence of mouse CHK2 suggests that this protein is not involved in recombination partner choice in mammals, although we cannot exclude that compensation by related kinases (e.g., CHK1) could be responsible for the absence of an obvious phenotype in Chk2−/− spermatocytes.


The ATM signaling cascade promotes recombination-dependent pachytene arrest in mouse spermatocytes.

Pacheco S, Marcet-Ortega M, Lange J, Jasin M, Keeney S, Roig I - PLoS Genet. (2015)

Functions of the ATM signaling pathway during mouse meiotic prophase.We propose that DSBs induced by SPO11 at the beginning of meiotic prophase are sensed by the MRE11 complex, which activates ATM. ATM inhibits further DSB formation via a feedback loop and promotes DSB repair. ATM activates CHK2, which controls cell cycle progression but is not involved in regulating DSB formation. Recombination progression leads to homologous chromosome synapsis and sex body formation. Besides participating in recombination, TRIP13 is also needed for effective sex body formation. Proper recombination and sex body formation are required to permit meiotic progression.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4358828&req=5

pgen.1005017.g007: Functions of the ATM signaling pathway during mouse meiotic prophase.We propose that DSBs induced by SPO11 at the beginning of meiotic prophase are sensed by the MRE11 complex, which activates ATM. ATM inhibits further DSB formation via a feedback loop and promotes DSB repair. ATM activates CHK2, which controls cell cycle progression but is not involved in regulating DSB formation. Recombination progression leads to homologous chromosome synapsis and sex body formation. Besides participating in recombination, TRIP13 is also needed for effective sex body formation. Proper recombination and sex body formation are required to permit meiotic progression.
Mentions: The array of phenotypes in the mutants analyzed here suggests that ATM participates in different aspects of meiotic prophase (Fig. 7). Our results further demonstrate that, while meiotic progression depends on the MRE11 complex, ATM and CHK2, the regulation of SPO11 activity requires the MRE11 complex to activate ATM but is independent of CHK2. This finding may indicate that direct ATM phosphorylation targets exert control of DSB formation, as has been argued in yeast [49]. Interestingly, yeast Mek1 promotes inter-homolog bias in the repair of DSBs [50,51]. The fact that homologous chromosome synapsis is not altered in the absence of mouse CHK2 suggests that this protein is not involved in recombination partner choice in mammals, although we cannot exclude that compensation by related kinases (e.g., CHK1) could be responsible for the absence of an obvious phenotype in Chk2−/− spermatocytes.

Bottom Line: TRIP13-deficient spermatocytes also progress to an H1t-positive stage if ATM activity is attenuated by hypomorphic mutations in Mre11 or Nbs1 or by elimination of the ATM-effector kinase CHK2.Our work supports the conclusion that recombination defects trigger spermatocyte arrest via pathways than are genetically distinct from sex body failure-promoted apoptosis and confirm that the latter can function even when recombination-dependent arrest is inoperative.Implications of these findings for understanding the complex relationships between spermatocyte arrest and apoptosis are discussed.

View Article: PubMed Central - PubMed

Affiliation: Genome Integrity and Instability Group, Institut de Biotecnologia i Biomedicina, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, Spain; Cytology and Histology Unit, Department of Cell Biology, Physiology and Immunology, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, Spain.

ABSTRACT
Most mutations that compromise meiotic recombination or synapsis in mouse spermatocytes result in arrest and apoptosis at the pachytene stage of the first meiotic prophase. Two main mechanisms are thought to trigger arrest: one independent of the double-strand breaks (DSBs) that initiate meiotic recombination, and another activated by persistent recombination intermediates. Mechanisms underlying the recombination-dependent arrest response are not well understood, so we sought to identify factors involved by examining mutants deficient for TRIP13, a conserved AAA+ ATPase required for the completion of meiotic DSB repair. We find that spermatocytes with a hypomorphic Trip13 mutation (Trip13mod/mod) arrest with features characteristic of early pachynema in wild type, namely, fully synapsed chromosomes without incorporation of the histone variant H1t into chromatin. These cells then undergo apoptosis, possibly in response to the arrest or in response to a defect in sex body formation. However, TRIP13-deficient cells that additionally lack the DSB-responsive kinase ATM progress further, reaching an H1t-positive stage (i.e., similar to mid/late pachynema in wild type) despite the presence of unrepaired DSBs. TRIP13-deficient spermatocytes also progress to an H1t-positive stage if ATM activity is attenuated by hypomorphic mutations in Mre11 or Nbs1 or by elimination of the ATM-effector kinase CHK2. These mutant backgrounds nonetheless experience an apoptotic block to further spermatogenic progression, most likely caused by failure to form a sex body. DSB numbers are elevated in Mre11 and Nbs1 hypomorphs but not Chk2 mutants, thus delineating genetic requirements for the ATM-dependent negative feedback loop that regulates DSB numbers. The findings demonstrate for the first time that ATM-dependent signaling enforces the normal pachytene response to persistent recombination intermediates. Our work supports the conclusion that recombination defects trigger spermatocyte arrest via pathways than are genetically distinct from sex body failure-promoted apoptosis and confirm that the latter can function even when recombination-dependent arrest is inoperative. Implications of these findings for understanding the complex relationships between spermatocyte arrest and apoptosis are discussed.

Show MeSH
Related in: MedlinePlus