Differential Expression of Signaling Molecules in Cranial Sutures Following Thyroxine Exposure

TYLER HILL, Dept of Biological Sciences, West Liberty University, West Liberty, WV, 26047, and HOLLY RACINE, Dept of Biological Sciences, West Liberty University, West Liberty, WV, 26047. Differential Expression of Signaling Molecules in Cranial Sutures Following Thyroxine Exposure. This study aimed to assess differential gene expression in crania following exposure to excess thyroid hormone (TH) during embryonic development. The coronal and sagittal sutures develop from mesodermal and neural crest-derived embryonic origins, respectively. These tissues utilize both the Wnt and BMP signaling pathways. The impact of excess TH on pathway regulation in cranial sutures is not understood. Using an avian model of induced thyrotoxicosis cranial suture tissues were collected from chicken embryos. Quantitative real-time PCR was used to quantify the expression of relevant genes. SMAD1 is the primary gene relating to the BMP pathway, while TWIST1 is linked to the Wnt signaling family. RUNX2 interacts with both pathways and is linked to the differentiation of early osteoblasts. The SOST gene encodes the protein Sclerostin which is produced by mature osteocytes. ELISA was used to quantify the levels of two proteins, osteocalcin which is primarily produced by osteoblasts, and CD34 which is a surface marker for osteoprogenitors. Following thyroxine exposure, qRT-PCR from coronal suture samples showed no change in SMAD1 (p=0.387), decreased TWIST (p<0.05), decreased RUNX2 (p<0.05), increased SOST (p<0.05). In the sagittal suture there was a decrease in SMAD1 (p<0.01), no change in TWIST (p=0.4816), increased RUNX2 (p<0.001), decreased SOST (p<0.01). Results of the ELISA showed no significant change in CD34 and an increase in osteocalcin when exposed to thyroxine in both suture types (p<0.05). These findings suggest that the coronal and sagittal sutures demonstrate significantly different levels of expression following thyroxine exposure in utero. This research was made possible by the NASA West Virginia Space Grant Consortium, Grant # 80NSSC20M0055.