Transcriptome analysis reveals that fertilization with cryopreserved sperm downregulates genes relevant for early embryo development in the horse

PLoS One. 2019 Jun 25;14(6):e0213420. doi: 10.1371/journal.pone.0213420. eCollection 2019.

Abstract

Artificial insemination with cryopreserved spermatozoa is a major assisted reproductive technology in many species. In horses, as in humans, insemination with cryopreserved sperm is associated with lower pregnancy rates than those for fresh sperm, however, direct effects of sperm cryopreservation on the development of resulting embryos are largely unexplored. The aim of this study was to investigate differences in gene expression between embryos resulting from fertilization with fresh or cryopreserved sperm. Embryos were obtained at 8, 10 or 12 days after ovulation from mares inseminated post-ovulation on successive cycles with either fresh sperm or frozen-thawed sperm from the same stallion, providing matched embryo pairs at each day. RNA was isolated from two matched pairs (4 embryos) for each day, and cDNA libraries were built and sequenced. Significant differences in transcripts per kilobase million (TPM) were determined using (i) genes for which the expression difference between treatments was higher than 99% of that in the random case (P < 0.01), and (ii) genes for which the fold change was ≥ 2, to avoid expression bias in selection of the candidate genes. Molecular pathways were explored using the DAVID webserver, followed by network analyses using STRING, with a threshold of 0.700 for positive interactions. The transcriptional profile of embryos obtained with frozen-thawed sperm differed significantly from that for embryos derived from fresh sperm on all days, showing significant down-regulation of genes involved in biological pathways related to oxidative phosphorylation, DNA binding, DNA replication, and immune response. Many genes with reduced expression were orthologs of genes known to be embryonic lethal in mice. This study, for the first time, provides evidence of altered transcription in embryos resulting from fertilization with cryopreserved spermatozoa in any species. As sperm cryopreservation is commonly used in many species, including human, the effect of this intervention on expression of developmentally important genes in resulting embryos warrants attention.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cryopreservation / veterinary
  • Down-Regulation
  • Embryo, Mammalian
  • Embryonic Development / genetics*
  • Female
  • Gene Expression Profiling*
  • Horses
  • Insemination, Artificial / methods*
  • Insemination, Artificial / veterinary
  • Male
  • Semen Preservation / adverse effects
  • Semen Preservation / veterinary*

Grants and funding

FJP received financial support for this study from the Ministerio de Economía y Competitividad-FEDER, Madrid, Spain, grant AGL2017-83149-R. FJP also received support from the Junta de Extremadura-FEDER (IB16030 and GR18008). HRM received support from the Swedish Research councils VR, (Grant 521-2011-6553) and FORMAS (Grant 2017-00946), Stockholm. JMOR holds a Predoctoral grant from the Valhondo Calaaf Foundation, Cáceres, Spain. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.