Mitochondrial DNA Deficiency and Supplementation in Sus scrofa Oocytes Influence Transcriptome Profiles in Oocytes and Blastocysts

Abstract

Mitochondrial DNA (mtDNA) deficiency correlates with poor oocyte quality and fertilisation failure. However, the supplementation of mtDNA deficient oocytes with extra copies of mtDNA improves fertilisation rates and embryo development. The molecular mechanisms associated with oocyte developmental incompetence, and the effects of mtDNA supplementation on embryo development are largely unknown. We investigated the association between the developmental competence of Sus scrofa oocytes, assessed with Brilliant Cresyl Blue, and transcriptome profiles. We also analysed the effects of mtDNA supplementation on the developmental transition from the oocyte to the blastocyst by longitudinal transcriptome analysis. mtDNA deficient oocytes revealed downregulation of genes associated with RNA metabolism and oxidative phosphorylation, including 56 small nucleolar RNA genes and 13 mtDNA protein coding genes. We also identified the downregulation of a large subset of genes for meiotic and mitotic cell cycle process, suggesting that developmental competence affects the completion of meiosis II and first embryonic cell division. The supplementation of oocytes with mtDNA in combination with fertilisation improves the maintenance of the expression of several key developmental genes and the patterns of parental allele-specific imprinting gene expression in blastocysts. These results suggest associations between mtDNA deficiency and meiotic cell cycle and the developmental effects of mtDNA supplementation on Sus scrofa blastocysts.

Mitochondrial DNA Supplementation of Oocytes Has Downstream Effects on the Transcriptional Profiles of Sus scrofa Adult Tissues with High mtDNA Copy Number

“…Since we did not find differences in imprinted gene expression pattern between autologous and heterologous mtDNA supplementation, this is not associated with heterologous transfer, but primarily as a result of adding extra copies of mtDNA which likely results from the changes to the genomic balance imposed by extra copies of mtDNA being introduced into the oocyte at the time of fertilisation. We have shown that mtDNA supplementation improved parental allele-specific imprinted gene expression patterns in blastocysts compared to non-supplemented blastocysts [35]; however, it may not be sufficient to recover levels similar to naturally conceived pigs.…”

“…We have previously shown that allele-specific imprinted gene expression patterns were different between blastocysts generated with and without mtDNA supplementation [35]. We also demonstrated that single nucleotide polymorphism (SNP) frequency, calculated by SNP number divided by transcript length (kb), can be used as an indicator of mono-allelic or bi-allelic expression of genes at low and high frequency, respectively.…”

“…Imprinted genes and neighbouring genes at the locus were analysed for the level of bi-allelic expression by SNP identification in the transcripts, as described [35]. Sus scrofa imprinted genes (https://www.geneimprint.com/site/genes-by-species.Sus+scrofa accessed on 16 April 2023) with sufficient read depth were selected for analysis.…”