A high incidence of chromosome abnormalities in two-cell stage porcine IVP embryos

Abstract

In pigs, in vitro production is difficult with a high occurrence of polyspermy and low blastocyst formation rates. To test the hypothesis that this may, at least in part, be due to chromosomal errors, we employed whole genome amplification and comparative genomic hybridization, performing comprehensive chromosome analysis to assess both cells of the two-cell stage in vitro porcine embryos. We thus described the incidence, nature and origin of chromosome abnormalities, i.e. whether they derived from incorrect meiotic division during gametogenesis or aberrant mitotic division in the zygote. We observed that 19 out of 51 (37%) of two-cell stage early pig IVP embryos had a chromosome abnormality, mostly originating from an abnormal division in the zygote. Moreover, we frequently encountered multiple aneuploidies and segmental chromosome aberrations. These results indicate that the pig may be particularly sensitive to in vitro production, which may, in turn, be due to incorrect chromosome segregations during meiosis and early cleavage divisions. We thus accept our hypothesis that chromosome abnormality could explain poor IVP outcomes in pigs.

Aneuploidy Detection and mtDNA Quantification in Bovine Embryos with Different Cleavage Onset Using a Next-Generation Sequencing-Based Protocol

“…In our study, up to 48 samples were barcoded and sequenced in a massively parallel fashion. The final cost per sample was comparable with the metaphase-CGH technology employed in our previous study [Hornak et al, 2015]. The disadvantage of NGS technology is its inability to detect polyploidy.…”

“…In order to validate a new NGS-based protocol, we reanalysed the Whole Genome Amplification (WGA) product of the aneu-ploid porcine embryos examined by CGH in our recent study [Hornak et al, 2015]. In total, 22 chromosome abnormalities observed in 7 aneuploid embryos by CGH were reanalysed by NGS, and we observed full concordance for chromosome losses and gains between both methods (online suppl.…”

“…In pigs, the frequency of aneuploidy in preimplantation embryos varies from 14.3 to 37.3% based on screening of all chromosomes by comparative genomic hybridization (CGH) [Hornak et al, 2009[Hornak et al, , 2015. In cattle, studies mainly focused on polyploidy and mixoploidy, revealing that mixoploidy occurs in 25-90% of bovine embryos [Viuff et al, 1999;Jakobsen et al, 2006;Garcia-Herreros et al, 2010].…”

“…when embryonic biopsies are analysed during preimplantation genetic diagnosis [Fiorentino et al, 2014;Yang et al, 2015]. We subsequently performed a validation study of our NGS-based protocol by a comparison of metaphase-CGH and NGS results from the same WGA product of the previously analysed porcine blastomeres using metaphase-CGH [Hornak et al, 2015]. The metaphase-CGH and NGS charts are shown in online supplementary figure 1.…”

“…Current evidence suggests that the overall frequency of aneuploidy is higher in in vitro-produced (IVP) embryos compared to embryos generated in vivo across all farm animal species studied thus far [Viuff et al, 1999;Rambags et al, 2005;Coppola et al, 2007;Lechniak et al, 2007;Ulloa Ullo et al, 2008;Hornak et al, 2015]. This, in turn, indicates that suboptimal oocyte maturation media, maturation and embryo cultivation protocols, and/or media supplements may induce aneuploidy at this early stage of development [Demyda-Peyrás et al, 2013].…”