Impact of vitrification cryopreservation on the transcriptomic profile of metaphase II mouse oocytes

BACKGROUND: Vitrification freezing has been shown to reduce mammalian oocyte developmental competence, and this has been strongly associated with abnormal mRNA expression in oocytes thawed by vitrification freezing. However the effect of vitrification freezing on the transcriptional machinery of oocytes examined by RNA sequencing has rarely been reported. OBJECTIVE: To study differentially expressed genes in mouse oocytes as a result of vitrification freezing. MATERIALS & METHODS: Differential gene expression was determined using DEseq2 (p-value <0.05, minimum multiplicity set at 1.5), and the transcriptomes of mouse stage MII oocytes from the Fresh and Vitrification groups were analyzed by employing the Smart-seq technique. The differentially expressed mRNAs were retrieved according to the Gene Ontology (GO) and KEGG databases, and finally, a real-time fluorescence quantitative PCR was used to characterize the reliability of the transcriptome data. RESULTS: Among them, 545 genes were detected to be up-regulated and 274 genes were up-regulated. Ten genes related to oxidative phosphorylation were screened to be downregulated, and 44 genes were down-regulated with genes related to the HIF-signaling pathway, ribosomes and apoptosis.GO enrichment analysis showed that these genes were mainly concentrated in the cytoplasm, organelle membranes, mitochondrial membranes, and the Golgi apparatus. The four randomly selected candidate genes’ mRNA expression levels were consistent with the results of RNAseq. CONCLUSION: Our results suggest that vitrification freezing affects mouse M II stage oocytes mainly through down-regulation of transcription, which leads to a decrease in the developmental capacity of vitrified oocytes. Our findings will help to identify ways to improve the vitrification efficiency of oocytes.