Transition from a meiotic to a somatic-like DNA damage response during the pachytene stage in mouse meiosis
Transition from a meiotic to a somatic-like DNA damage response during the pachytene stage in mouse meiosis
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DOI：
10.1371/journal.pgen.1007439
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发表时间：
2019-01-01
期刊：
影响因子：
4.5
通讯作者：
Page, Jesus
中科院分区：
文献类型：
--
作者：
Enguita-Marruedo, Andrea;Martin-Ruiz, Marta;Page, Jesus
同源重组（HR）是减数分裂过程中DNA修复的主要机制，是染色体分离和遗传多样性增加的基础。然而，非同源末端连接（NHEJ）机制也可以在减数分裂过程中发挥作用，主要是在第一次减数分裂前期的后期阶段响应外源诱导的DNA损伤。为了更好地理解这两种修复途径之间的关系，我们研究了γ射线照射后雄性小鼠减数分裂期间对DNA损伤的反应。我们在治疗后立即清楚地发现了两种类型的反应。从细线期到粗线期早期，外源性损伤触发了H2AX在整个细胞核中的大量存在，这与HR组分（DMC 1和RAD 51）介导的DNA修复相关。这一早期途径随着DMC 1和RAD 51的顺序去除而结束，并且在粗线期中期不再是可诱导的。然而，从粗线期中期到双线期，H2AX表现为大的离散灶。这种晚期修复模式最初由NHEJ介导，涉及组成性存在的Ku70和XRCC 4，以及照射后不久出现在损伤部位的53 BP 1。然而，照射后24小时，涉及RAD 51但不涉及DMC 1的HR途径主要取代NHEJ。此外，我们观察到二价体之间联会复合体桥的发生，最有可能代表可能涉及DMC 1，RAD 51或53 BP 1的染色体易位事件。我们的研究结果加强了这样一种观点，即在减数分裂开始时默认作用的早期减数分裂修复途径从粗线期中期开始被类似体细胞的修复模式所取代。这种转变对于解决早期减数分裂机制无法修复的DNA损伤（内源性或外源性）可能很重要，例如性染色体中缺乏同源染色体进行修复。这种转变代表了另一层的功能变化，发生在减数分裂细胞在粗线期中期，除了表观遗传重编程，转录的重新激活，基因表达谱的变化和收购的能力进行到matriase.Author摘要DNA修复是至关重要的体细胞和减数分裂细胞。在减数分裂期间，内源性地引入数百个DNA双链断裂（DSB）。为了修复这种损伤，减数分裂细胞使用同源重组（HR）途径的特殊版本，该途径使用特定的减数分裂重组酶（例如DMC 1）来促进与同源染色体而不是姐妹染色单体的修复。这个过程对于确保减数分裂期间的染色体分离很重要，并且作为副作用，增加了后代的遗传多样性。然而，在特定情况下，减数分裂细胞可以使用其他DNA修复机制，如非同源末端连接（NHEJ），这是容易出错的。我们研究了小鼠精母细胞对伽马辐射引起的DNA损伤增加的反应，伽马辐射通常用于癌症治疗。我们发现，在第一次减数分裂前期的早期阶段，辐射产生的过量DSB是通过精母细胞中的减数分裂HR重组途径处理的。然而，从粗线期中期开始，这种反应是不可诱导的。从这一点开始，精母细胞依赖于一种与体细胞有许多共同特征的反应。在这种反应中，NHEJ途径首先用于修复DNA损伤，但随后被不使用DMC 1的HR机制取代。相反，它只依赖于RAD 51，它已知在体细胞和减数分裂细胞中起作用，与DMC 1相反，它对姐妹染色单体有偏好。这种从减数分裂到体细胞样反应的转变伴随着对DNA损伤的表观遗传反应的显著变化，加强了在粗线期中期减数分裂细胞中发生功能转变的想法。
Homologous recombination (HR) is the principal mechanism of DNA repair acting during meiosis and is fundamental for the segregation of chromosomes and the increase of genetic diversity. Nevertheless, non-homologous end joining (NHEJ) mechanisms can also act during meiosis, mainly in response to exogenously-induced DNA damage in late stages of first meiotic prophase. In order to better understand the relationship between these two repair pathways, we studied the response to DNA damage during male mouse meiosis after gamma radiation. We clearly discerned two types of responses immediately after treatment. From leptotene to early pachytene, exogenous damage triggered the massive presence of H2AX throughout the nucleus, which was associated with DNA repair mediated by HR components (DMC1 and RAD51). This early pathway finished with the sequential removal of DMC1 and RAD51 and was no longer inducible at mid pachytene. However, from mid-pachytene to diplotene, H2AX appeared as large discrete foci. This late repair pattern was mediated initially by NHEJ, involving Ku70 and XRCC4, which were constitutively present, and 53BP1, which appeared at sites of damage soon after irradiation. Nevertheless, 24 hours after irradiation, a HR pathway involving RAD51 but not DMC1 mostly replaced NHEJ. Additionally, we observed the occurrence of synaptonemal complex bridges between bivalents, most likely representing chromosome translocation events that may involve DMC1, RAD51 or 53BP1. Our results reinforce the idea that the early meiotic repair pathway that acts by default at the beginning of meiosis is replaced from mid-pachytene onwards by a somatic-like repair pattern. This shift might be important to resolve DNA damage (either endogenous or exogenous) that could not be repaired by the early meiotic mechanisms, for instance those in the sex chromosomes, which lack a homologous chromosome to repair with. This transition represents another layer of functional changes that occur in meiotic cells during mid pachytene, in addition to epigenetic reprograming, reactivation of transcription, changes in the gene expression profile and acquisition of competence to proceed to metaphase.Author summary DNA repair is critical for both somatic and meiotic cells. During meiosis, hundreds of DNA double strand breaks (DSBs) are introduced endogenously. To repair this damage, meiotic cells use a specialized version of the homologous recombination (HR) pathway that uses specific meiotic recombinases, such as DMC1, to promote repair with the homologous chromosome instead of the sister chromatid. This process is important to ensure chromosome segregation during meiosis and, as a side consequence, increases the genetic diversity of offspring. Nevertheless, under specific circumstances, meiotic cells can use other DNA repair mechanisms such as non-homologous end joining (NHEJ), which is error-prone. We investigated the response of mouse spermatocytes to increased DNA damage caused by gamma radiation, which is commonly used in cancer therapy. We found that the excess of DSBs produced by irradiation is processed by the meiotic HR recombination pathway in spermatocytes at the early stages of first meiotic prophase. However, this response is not inducible from the mid-pachytene stage onwards. From this point on, spermatocytes rely on a response that shares many features with that of somatic cells. In this response, the NHEJ pathway is first used to repair DNA damage but is subsequently replaced by a HR mechanism that does not use DMC1. Instead, it relies only on RAD51, which is known to function in both somatic and meiosis cells and, contrary to DMC1, has a preference for the sister chromatid. This switch from a meiotic to a somatic-like response is accompanied by a conspicuous change in the epigenetic response to DNA damage, reinforcing the idea that a functional transition occurs in meiotic cells during the mid-pachytene stage.