Observed Synostoses in an Avian and Murine Crania following in utero Thyroxine Exposure

Abstract

Hyperthyroidism is a condition that leads to increased concentration of thyroid hormones (THs), such as triiodothyronine (T₃) and thyroxine (T₄). An increase in these circulating THs, or thyrotoxicosis, in utero can lead to developmental conditions such as craniosynostosis. Craniosynostosis is the premature fusion of cranial sutures during development. This study focused on the development of sagittal and coronal sutures within crania of both juvenile mice and embryonic chickens following in utero thyroxine exposure. In previous studies, the murine model of induced thyrotoxicosis has shown a widening of the sagittal suture and a narrowing of the coronal suture. We hypothesized that we would see a similar morphology in the murine and avian crania following our model for induced thyrotoxicosis. For the (1) murine model, pregnant dams were given levothyroxine (synthetic thyroxine; 667 ng per day) or a vehicle dose (no treatment) daily to their drinking water. At 3 weeks post-natal, skulls from pups were then harvested. In the (2) avian model, 25 ng thyroxine or saline (control) was injected into the air cell of fertilized chicken eggs on days 11 and 15 post-fertilization. At 19 days post-fertilization, skulls from chicken embryos were then harvested. All crania were whole-mount stained with Alizarin red and Alcian blue, photographed, and measured from both treatment and control groups. This data was then analyzed in R-Studio using unpaired t-tests to determine significance. This morphological study supports our previous findings demonstrating that the coronal and sagittal sutures undergo differential development with increased thyroxine exposure.