Overexpression of signal transducers and activators of transcription in embryos derived from vitrified oocytes negatively affect E-cadherin expression and embryo development.

Vitrification apart from all drawbacks on oocyte ultra-structure can affect the oocyte mRNA content. Among those evaluated transcripts, no data is available regarding the effect of vitrification on signal transducer and activator of transcription (STAT3) expression in oocytes and the resulting preimplantation embryos. Considering the bidirectional relationship between E-cadherin (CDH1) and STAT3 and the adverse effect of cryopreservation on adherent junctions, we aimed to ascertain to what extent STAT3 and CDH1 genes expression is affected by vitrification in oocytes and the resulting embryos. The ovine vitrified-warmed and fresh GV oocytes were separately subjected to in vitro maturation and fertilization and cultured up to the blastocyst stage. The relative abundance of STAT3 and CDH1 transcripts were analysed by RT-PCR in both classes of fresh and vitrified GV and MII oocytes and the resulting embryos at 2-7 cells, 8-16 cells, morula, and blastocyst stages. Vitrified oocytes showed lower cleavage (37.8% vs. 95.9%, P<0.001) and blastocyst (8.1% vs. 52.7%, P<0.001) rates compared to control. The relative mRNA abundance of both genes was increased after oocyte maturation indicating their expression was started earlier than expected time proposed for embryonic genomic activation. In embryos derived from both fresh and vitrified oocytes, the maximum concentrations of STAT3 and CDH1 transcripts were observed at 2-7 cells and morula stages, respectively. Moreover, in contrast to CDH1 the relative expression of STAT3 in vitrified derived embryos was higher than embryos derived from fresh oocytes. The overexpression of STAT3 in embryos derived from vitrified oocytes might be the reason for the lower CDH1 expression and in turn the lower developmental competence of the resulting embryos.