Protecting the heritable genome: DNA damage response mechanisms in spermatogonial stem cells.
Spermatogonial stem cells (SSCs) must maintain the integrity of their genome to prevent reproduction failure and limit the hereditary risk associated with transmission to the progeny. SSCs must therefore have robust response mechanisms to counteract the potentially deleterious effects of DNA damage, with DNA double-strand breaks (DSBs) representing the greatest threat to genomic integrity. Through in vivo analysis of the DNA damage response of SSCs within their physiological tissue context, we aimed to gain insights into the mechanisms by which SSCs preserve genome integrity. After whole-body irradiation of repair-proficient and repair-deficient (DNA-PK- and ATM-deficient) mice, the formation and rejoining of DSBs was analyzed in SSCs of testis compared with somatic cells of other tissues by enumerating γH2AX-, MDC1-, and 53BP1-foci. Caspase-3 and PARP-1 were used as markers for apoptotic cell death. Our results show that DNA damage response mechanisms in SSCs characterized by unique chromatin compositions are markedly different from those of somatic cells. In SSCs lacking compact heterochromatin, histone-associated signaling components of the DNA repair machinery are completely absent and radiation-induced DSBs are rejoined predominantly by DNA-PK-independent pathways, suggesting the existence of alternative repair mechanisms. As a complimentary mechanism characterized by low thresholds for ATM-dependent checkpoint activation, the differentiating progeny, but not the SSCs themselves, promote apoptosis in response to low levels of DNA damage. By evaluating SSCs within their stem cell niche, we show that DNA repair, cell-cycle checkpoints, and apoptosis function together to maintain the integrity of the heritable genome.
Department of Radiation Oncology, Saarland University, Saarland University, Homburg/Saar, Germany. claudia.ruebe@uks.eu
Claudia E
CE
Rübe
Sheng
S
Zhang
Nadine
N
Miebach
Andreas
A
Fricke
Christian
C
Rübe
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D017209:Apoptosis / Q000528:radiation effects; D064007:Ataxia Telangiectasia Mutated Proteins; D053148:Caspase 3 / Q000235:genetics / Q000502:physiology; D018797:Cell Cycle Proteins / Q000235:genetics; D002843:Chromatin / Q000235:genetics / Q000528:radiation effects; D053903:DNA Breaks, Double-Stranded; D004249:DNA Damage; D004260:DNA Repair; D051747:DNA-Activated Protein Kinase / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D018816:Genes, cdc; D016678:Genome; D042822:Genomic Instability; D006657:Histones / Q000235:genetics / Q000378:metabolism; D007150:Immunohistochemistry; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D016513:Mice, SCID; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases / Q000235:genetics / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000235:genetics; D013093:Spermatogonia / Q000502:physiology* / Q000528:radiation effects; D013234:Stem Cells / Q000502:physiology* / Q000528:radiation effects; D025521:Tumor Suppressor Proteins / Q000235:genetics; D014916:Whole-Body Irradiation
D048868:Adaptor Proteins, Signal Transducing; D064007:Ataxia Telangiectasia Mutated Proteins; D053148:Caspase 3; D018797:Cell Cycle Proteins; D002843:Chromatin; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins; D006657:Histones; D047908:Intracellular Signaling Peptides and Proteins; D009687:Nuclear Proteins; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; D017346:Protein Serine-Threonine Kinases; D025521:Tumor Suppressor Proteins; C508937:MDC1 protein, mouse; C499321:Parp1 protein, mouse; C576325:Atm protein, mouse; C497264:Prkdc protein, mouse; C475961:gamma-H2AX protein, mouse