Expression of DIO2 in the porcine ovary and the granulosa cells of humans

The two main functions of the ovary are production of gametes and steroidogenesis. Ovarian follicles are the functional component of the ovary and respond to hormonal changes in the body during reproductive cycles. As follicles develop, the somatic cells of the ovary differentiate into granulosa cells and theca cells. Following a luteinizing hormone surge these cells further differentiate into small and large luteal cells and steroidogenesis increases. The rate-limiting step in steroidogenesis is the transfer of cholesterol to the inner mitochondrial membrane, a process that is facilitated by steroidogenic acute regulatory protein (StAR). Recently, our lab has shown that StAR mRNA is modulated by transcription factors GATA4 and GATA6. These GATA factors have been shown to regulate gene expression in the ovary. Using Stealth RNAi coupled with cDNA microarray analysis using Affymetrix Porcine Genome Arrays, our lab sought to identify genes altered by reduction of GATA4, GATA6, or their coreduction. From this initial work, we identified several genes regulated by these factors and analyzed them using real-time PCR. We found the gene DIO2 was regulated and chose to conduct further studies. Although, DIO2 is well characterized in the heart and other tissues it has not been characterized in the ovary. The DIO2 enzyme is primarily responsible for converting the less active form the thyroid hormone, thyroxine (T4), to the more active from of the thyroid hormone, triiodothyronine (T3). Real-time PCR showed reducing the transcription factors GATA4 and GATA6, with and without cyclic AMP stimulation, enhances DIO2 mRNA expression. Immunohistochemistry showed DIO2 is present in all developmental stages of healthy follicles in the porcine ovary. Real-time PCR showed DIO2 mRNA levels change in various porcine tissue as follicles development progresses. Finally, we determined there was no difference in DIO2 mRNA expression in IVF patients with polycystic ovarian syndrome and control IVF patients. In conclusion, we have found DIO2 is present in follicles and its mRNA is regulated by GATA4 and GATA6.