The Joint Annual Scientific Meetings of the Endocrine Society of Australia and the Society for Reproductive Biology 2018

 DNA repair and protection in the female germline (#107)

Jacinta H Martin 1 , Elizabeth G Bromfield 1 , Tessa Lord 2 , John Aitken 1 , Brett Nixon 1
  1. Priority Research Centre in Reproductive Science (PRC), University of Newcastle, Callaghan, Newcastle, NSW, Australia
  2. School of Molecular Biosciences, Centre for Reproductive Biology, College of Veterinary Medicine, Washington State University, Pullman, WA,, USA

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. To improve our understanding of these systems, the aim of this research project was to determine whether mature oocytes are able to utilize these resources to detect, respond and subsequently mount protective and/or reparative strategies to mitigate the impact of genotoxic insult. For this purpose, DNA double strand breaks (DSB) were elicited using etoposide (ETP); which led to a rapid increase in DSB (P = 0.0002). Utilizing this model, we documented 2 distinct responses, namely: (i) the MII oocyte engaged a reparative cascade known as the non-homologous end joining (NHEJ) DNA repair pathway and (ii) oocytes experience a developmental change in their vulnerability to ETP, with fertilisation leading to a rapid increase in the expression of permeability glycoprotein (PGP) which acts as a drug transporter to minimize the intracellular accumulation of ETP. In support of these responses, we were able to document a significant reduction in DSB lesions 4h post-ETP treatment. Notably, this repair was completely abrogated by pharmacological inhibition of key elements of the canonical NHEJ pathway (i.e. DNA-PKcs and DNA ligase IV), thus providing the first evidence implicating this reparative cascade in the protection of the maternal genome. Similarly, we were able to utilize dye exclusion assays, in the presence of a selective PGP pharmacological inhibitor (PSC833) to confirm this multidrug efflux transporter does provide a first line of defence to protect the zygote against genotoxic agents capable of inducing DSB DNA damage. Our collective data therefore encourages a reappraisal of the paradigm the oocyte/embryo is largely refractory to DSB DNA repair and protection.