Spatial Patterning of Scleral Papillae in the Embryonic Chicken Eye

Abstract

The anterior portion of the eye in birds is supported by a ring of bony elements within the sclera, constituting the scleral ossicles. These intramembranous bones are induced by a series of transient papillae in the overlying conjunctival epithelium during embryonic development. A well‐defined spatiotemporal pattern of formation is followed, resulting in a complete circle of 13–16 evenly‐spaced papillae per eye in the chicken embryo. The regular distribution and variable number of papillae in this system give it a strong similarity to other reaction‐diffusion models of patterning, such as feather and carapace formation, in which short‐range activation is coupled with long‐range inhibition. Therefore, the objective of this study is to investigate whether scleral papillae are formed through a reaction‐diffusion mechanism in the embryonic chicken eye. To carry out this study, chicken embryos at Hamburger and Hamilton stages 28–34 (5.5–8 days post fertilization) were collected, corresponding to the induction and formation of a complete set of scleral papillae. Quantitative morphometrical analyses were performed on dissected eyes, confirming that while eye size increases throughout development, the spacing between the papillae does not. Computer modelling using the Meinhardt‐Gierer equation indicates that scleral papillae development likely follows the typical Turing mechanism of reaction‐diffusion pattern formation. Quantitative PCR on discrete papillary and interpapillary regions will enable us to study the interactions of known signalling molecules including Hedgehog (Hh), Bone Morphogenic Proteins (BMPs), Fibroblast Growth Factors (FGFs) and Wingless (Wnt). The results of this study provide considerable insight into the spacing pattern of scleral papillae. A reaction‐diffusion mechanism explains the ability of scleral papillae to maintain their even distribution regardless of differences in numbers among species or between left and right eyes in the same individual. Identifying the signalling pathways implicated in scleral papillae spacing would further enhance our understanding of not only the position, but also the size and shape of the scleral ossicles as compensation for gaps in the sclerotic ring is known to occur.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.