Double Strand Break DNA Repair occurs via Non-Homologous End-Joining in Mouse MII Oocytes

Abstract

The unique biology of the oocyte means that accepted paradigms for DNA repair and protection are not of direct relevance to the female gamete. Instead, preservation of the integrity of the maternal genome depends on endogenous protein stores and/or mRNA transcripts accumulated during oogenesis. The aim of this study was to determine whether mature (MII) oocytes have the capacity to detect DNA damage and subsequently mount effective repair. For this purpose, DNA double strand breaks (DSB) were elicited using the topoisomerase II inhibitor, etoposide (ETP). ETP challenge led to a rapid and significant increase in DSB (P = 0.0002) and the consequential incidence of metaphase plate abnormalities (P = 0.0031). Despite this, ETP-treated MII oocytes retained their ability to participate in in vitro fertilisation, though displayed reduced developmental competence beyond the 2-cell stage (P = 0.02). To account for these findings, we analysed the efficacy of DSB resolution, revealing a significant reduction in DSB lesions 4 h post-ETP treatment. Notably, this response was completely abrogated by pharmacological inhibition of key elements (DNA-PKcs and DNA ligase IV) of the canonical non-homologous end joining DNA repair pathway, thus providing the first evidence implicating this reparative cascade in the protection of the maternal genome.

Single and Double Strand Sperm DNA Damage: Different Reproductive Effects on Male Fertility

“…This may be crucial at the zygote, because it may give a chance to correctly repair both free ends of the double-strand break. There is a consensus point that oocyte quality may play a role in this DNA repair, since different studies proved that early embryos are able to repair DNA damage [ 79 , 80 , 81 , 82 , 83 , 84 ]. In this sense, in patients with DSB, the most significant delay observed in the embryo kinetics was just after fertilization, indicating that DNA repair machinery may be active in this stage [ 69 ].…”

DNA Damage and Repair in Human Reproductive Cells

“…These transcripts and proteins play a role during fertilization to address changes in chromatin remodeling and maintain chromatin integrity and are also used in the zygote until the embryo genome becomes active and it can transcribe its own DNA repair genes [141]. Recently Martin et al [144] provided the first evidence that the MII oocyte has the potential to DNA repair via NHEJ in mice. However, a RNA-seq analysis suggested that there may be species differences in the ability of GV (germinal vesical stage) and MII oocytes to undertake DNA repair [145].…”

Crosstalk between PTEN/PI3K/Akt Signalling and DNA Damage in the Oocyte: Implications for Primordial Follicle Activation, Oocyte Quality and Ageing

“…DNA DSBs can be repaired by two main mechanisms: non-homologous end-joining (NHEJ) [49], and homologous recombination (HR) [20,50]. NHEJ is error-prone since it mediates the direct re-ligation of the two ends of broken DNA and is not based on a complementary DNA template.…”

“…Given that primordial follicles are arrested at G2/M and accurate repair is a prerequisite to conserve genetic information [63], HR appears to be the pathway of choice for oocytes within primordial (immature) follicles [10,48,58,59]. While NHEJ can occur in the late stage of oocyte development [49,60,64].…”