Differential morphometric analysis of the anterior fontanelle in an embryonic avian model of induced-thyrotoxicosis.

Abstract

Craniosynostosis (CS) is the premature fusion of the cranial sutures during embryonic development, and this results in intracranial pressure and skull deformities. Thyrotoxicosis, specifically maternal hyperthyroidism, has been linked to the development of CS. Our lab is currently validating an avian model of thyroxine-induced CS to study the mechanism involved in thyroxine-enhanced cranial ossification. We hypothesized that thyroxine exposure will alter skull morphology. Two groups of fertilized chicken eggs were injected with saline or 25 ng T₄ into the air cell on embryonic days (E) 11 and 15. A set of skulls from each group were collected on E17-19 (n = 17-21/day). They were fixed in formalin and processed using Alizarin Red whole-mount staining, imaged (superior view), and quantified to determine thyroxine-induced alteration in skull morphology. Geometric morphometric analysis using MorphoJ was performed to identify shape variation between treatment groups of the fibrous space between ossifying regions of the anterior fontanelle. These preliminary results demonstrated a significant variation in the shape of the fibrous gap between developing sutures on embryonic days 17, 18, and 19 (p<0.05). Using the same methodology, an additional set of skulls on E19 were collected from each group and processed using both Alizarin red and Alcian blue whole-mount staining to better delineate the ossifying region of bone. Analysis is currently in progress. In conclusion, these findings support that our model is successful in promoting the fusing of the cranial bones with thyroxine exposure in our avian model through altered skull morphology visualized in the anterior fontanelle.