Temporal Effect of Hydrocortisone Treatment on Conjunctival Papillae in the Chicken Eye

Abstract

Intramembranous ossification is still poorly understood. Chicken embryos (Gallus gallus) have served as excellent models for investigating bone development. Scleral ossicles are a series of 13–15 bones that overlap to constitute a single sclerotic ring of bone. They have no articulation with the skull and are positioned in the corneal‐scleral limbus of the eye. The scleral ossicles are ideal elements in which to investigate the developmental processes underlying intramembranous ossification, as they are easily accessible for embryonic manipulations. Each ossicle is induced by corresponding regions of thickened epithelia called conjunctival papillae. The cells below the papillae ultimately differentiate into osteoblasts and deposit bone matrix. Research in the past decade has examined various factors that affect ossicle development, such as bone morphogenetic protein (BMP) and hedgehog (HH) signalling pathways, hydrocortisone treatment, vasculature, and vascular endothelial‐derived growth factor (VEGF) expression. The objective of this research is to further elucidate the mechanism by which hydrocortisone affects the development of scleral papillae. Here we explore the precise timing of hydrocortisone injections that is sufficient to inhibit the formation of all scleral papillae. Our previous research showed that delivering hydrocortisone injections at HH29 and HH30 produced the most significant effects on scleral condensation morphology and number. By adjusting the injection time points by an hour in each experiment, we determined the ideal window when hydrocortisone injections are sufficient to completely disrupt all papillae in 100 % of the injected embryos. For example, delivering the injections 18 hours apart results in the prevention of 12/13 conjunctival papillae in 100% of the embryos (n=4). This result indicates signalling mechanisms responsible for inducing conjunctival papillae are likely active almost a full day prior to the first papilla becoming morphologically visible at HH29. This study has implications for future research towards elucidating the genetic mechanisms underlying conjunctival papillae development.Support or Funding InformationThis research was funded by the Natural Sciences and Engineering Research Council of Canada.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.