Sperm chromatin integrity and DNA methylation in Norwegian Red bulls of contrasting fertility.

Birgitte Narud,Jane M Morrell,Else‐Berit Stenseth,Abdolrahman Khezri,Frøydis Deinboll Myromslien,Philippe Collas,Teklu Tewoldebrhan Zeremichael,Anders Johannisson,Bjørg Heringstad,Elisabeth Kommisrud

doi:10.1002/mrd.23461

Abstract

In this study, the complexity of chromatin integrity was investigated in frozen-thawed semen samples from 37 sires with contrasting fertility, expressed as 56-day non-return rates (NR56). Protamine deficiency, thiols, and disulfide bonds were assessed and compared with previously published data for DNA fragmentation index (DFI) and high DNA stainability (HDS). In addition, in vitro embryo development and sperm DNA methylation were assessed using semen samples from 16 of these bulls. The percentages of DFI and HDS were negatively associated with NR56 and cleavage rate and positively associated with sperm protamine deficiency (p < 0.05). Significant differences in cleavage and blastocyst rates were observed between bulls of high and low NR56. However, once fertilization occurred, further development into blastocysts was not associated with NR56. The differential methylation analysis showed that spermatozoa from bulls of low NR56 were hypermethylated compared to bulls of high NR56. Pathway analysis showed that genes annotated to differentially methylated cytosines could participate in different biological pathways and have important biological roles related to bull fertility. In conclusion, sperm cells from Norwegian Red bulls of inferior fertility have less compact chromatin structure, higher levels of DNA damage, and are hypermethylated compared with bulls of superior fertility.

Highlights

1.1 General background Fertility is a necessity for evolution, development and, above all, food production for an increasing world population expected to reach 8.6 billion people in 2030 (UN, 2017)
In the current thesis work, we demonstrated that the combination of different flow cytometry methods and computer-assisted sperm analysis (CASA) enabled assessments of multiple sperm characteristics and were valuable tools for the assessment of sperm quality in relation to age differences and bull fertility potential
We further demonstrated that the conventional sperm quality parameters only explain part of the variation observed in bull fertility, and that underlying factors affecting fertility might be explained by the assessment of metabolites in semen and sperm DNA methylation

Summary

Introduction

1.1 General background Fertility is a necessity for evolution, development and, above all, food production for an increasing world population expected to reach 8.6 billion people in 2030 (UN, 2017) In foodproducing species such as cattle, reproductive success is critical for production efficiency. The sperm cell has a unique chromatin structure where most of the histones are replaced by smaller proteins, called protamines, during spermatogenesis (Champroux, Cocquet, Henry-Berger, Drevet, & Kocer, 2018). This histone to protamine transition facilitates tight packaging of DNA in the sperm nucleus. Fertilization of an oocyte by a sperm cell with damaged DNA may affect embryo development negatively and contribute to diseases in future generations, as the oocyte only has the ability to correct a certain degree of DNA damage (Johnson et al, 2011; Ménézo, Dale, & Cohen, 2010)

Methods

Results

Discussion

Conclusion