Developmental and Genomic Aspects of Thyroid Hormones During Early Embryo Development in Cattle
In vitro embryo production (IVP) has been successfully used for infertility treatment, farm animal breeding and preservation of endangered species. Embryo culture media and its composition play an important role in the developmental competency of in vitro produced embryos. To optimize IVP it is important to understand the physiology of the in vivo embryo medium. Previously, we confirmed the presence of thyroid hormones (THs) in the bovine reproductive tract and their beneficial effect on embryo quality in vitro. The aim of this study was to further investigate the developmental effect and mechanisms behind THs function in bovine early embryos by supplementing IVP media with 50ng/ml T3 and T4. In vitro embryo culture (IVC) media fortification with THs significantly improved blastocyst and hatching rates, which was observed in both fast and slow cleaving embryos. THs treatment significantly skewed male/female ratio toward femaleness (43% vs. 57%). Only %60 of supplemented THs was bioavailable in the IVC media. Gene microarray and blastocyst genes expression profile analysis showed that THs supplementation altered mRNA expression profile in blastocysts. 1,234 genes were expressed differentially in the treated embryos and these differences were statistically significant (>1.5 fold at p < 0.05); these findings were confirmed by qPCR. TH-related genes, including THs receptor (TRs) mRNA and deiodinases (DIOs), were expressed in the gene array data of both treated and control groups. TR mRNA was expressed in all stages of early embryo development (EED) and the expression was not inducible by THs. This finding was consistent in both gene array and qPCR. Suppression of embryo gene transcription by α-amanitin resulted in a significantly higher level of TR mRNA from 2-cell to 16-cell treated and control embryos. TR protein was expressed in both treated and control blastocysts but, differentially located and distributed in response to THs in the blastocysts. This study highlights the importance of THs in EED and therefore the need to include these factors in culture media. Furthermore, this study has better characterized THs effects and identified possible regulatory roles of these hormones in EED. Further investigation into embryo competency and pregnancy outcome can provide more details.