Ku70 and non-homologous end joining protect testicular cells from DNA damage

Abstract

SummarySpermatogenesis is a complex process that generates haploid germ cells or spores and implements meiosis, a succession of two special cell divisions that are required for homologous chromosome segregation. During prophase to the first meiotic division, homologous recombination (HR) repairs Spo11-dependent DNA double-strand breaks (DSBs) in the presence of telomere movements to allow for chromosome pairing and segregation at the meiosis I division. In contrast to HR, non-homologous end joining (NHEJ), the major DSB repair mechanism during the G1 cell cycle phase, is downregulated during early meiotic prophase. At somatic mammalian telomeres, the NHEJ factor Ku70/80 inhibits HR, as does the Rap1 component of the shelterin complex. Here, we investigated the role of Ku70 and Rap1 in meiotic telomere redistribution and genome protection in spermatogenesis by studying single and double knockout mice. Ku70 2/2 mice display reduced testis size and compromised spermatogenesis, whereas meiotic telomere dynamics and chromosomal bouquet formation occurred normally in Ku70 2/2 and Ku70 2/2Rap1 D/D knockout spermatocytes. Elevated mid-preleptotene frequencies were associated with significantly increased DNA damage in Ku-deficient B spermatogonia, and in differentiated Sertoli cells. Significantly elevated levels of cH2AX foci in Ku70 2/2 diplotene spermatocytes suggest compromised progression of DNA repair at a subset of DSBs. This might explain the elevated meiotic metaphase apoptosis that is present in Ku70-deficient stage XII testis tubules, indicating spindle assembly checkpoint activation. In summary, our data indicate that Ku70 is important for repairing DSBs in somatic cells and in late spermatocytes of the testis, thereby assuring the fidelity of spermatogenesis.

The Meiotic Checkpoint Network: Step-by-Step through Meiotic Prophase

“…Alternatively, S. cerevisiae can adapt to the damage by inactivating the MCN, and attempt meiosis Hochwagen et al 2005;Iacovella et al 2010). In contrast, meiocytes in metazoans are frequently culled by checkpoint-dependent induction of the apoptotic cell death program (Gartner et al 2000;Bhalla and Dernburg 2005;Di Giacomo et al 2005), a process that also functions as a screening mechanism against germ cell precursors with chromosomal abnormalities (Ahmed et al 2013;Stevens et al 2013;Titen et al 2014). As in the mitotic DNA damage response, the decision to enter the apoptotic program in response to repair defects requires CHK2-dependent ac- tivation of the p53 family of proteins, and is generally restricted to specific stages in meiotic prophase (Derry et al 2001;Barchi et al 2005;Suh et al 2006;Rutkowski et al 2011;BolcunFilas et al 2014;Kim and Suh 2014).…”

Chromatin Organization and Remodeling of Interstitial Telomeric Sites During Meiosis in the Mongolian Gerbil (Meriones unguiculatus)

“…Interestingly, the mechanisms of DNA repair acting at these later stages would be preferentially nonhomologous pathways, mainly nonhomologous end joining (NHEJ) (Ahmed et al 2010). Furthermore, some telomere-associated proteins like Ku-70 have been reported to be important for the proper repair of DNA by the NHEJ pathway (Ahmed et al 2013). Thus, the presence of RAP1 and TRF1 during late pachytene and diplotene could be attributed to a role in the regulation and/or protection of ITSs once these DNA repair mechanisms are triggered.…”

Low-dose radiation-induced risk in spermatogenesis

“…As shown in Figure 2, at the onset of first meiotic prophase, chromosomes have Spo11-dependent DSBs that are repaired by homologous recombination (HR) to promote crossing over and ensure homolog separation during the meiosis I division (Bannister and Schimenti 2004;Ahmed et al 2013). In contrast to HR, non-homologous end joining (NHEJ), the major DSB repair mechanism during the G1 cell cycle phase (Mao et al 2008), is downregulated during early meiotic prophase (Ahmed et al 2013).…”

“…In contrast to HR, non-homologous end joining (NHEJ), the major DSB repair mechanism during the G1 cell cycle phase (Mao et al 2008), is downregulated during early meiotic prophase (Ahmed et al 2013). The classical DNA-PKcs dependent NHEJ pathway involving the DNA-PKcs which is recruited by the Ku70 and Ku80 proteins to the site of damage and subsequently, both end-positioned Ku and DNAPKcs mediate the recruitment of the XRCC4/DNA ligase IV complex (Gonz alez-Mar ın et al 2012).…”

“…NHEJ contributes to the repair of replication-dependent and radiation-induced DNA damage in somatic testis cells. This may also be required for the repair of persistent Spo11-dependent and radiation-induced DSBs in late spermatocytes (Ahmed et al 2013). However, studies using DNA-PKcs deficient round spermatids from SCID mice have shown almost identical DSB repair kinetics to those of DNA-PKcs proficient spermatids.…”