Toward understanding the development of scleral ossicles in the chicken, Gallus gallus

Area of Science:

• Developmental biology
• Vertebrate anatomy
• Molecular genetics

Background:

• Scleral ossicles are dermal bones found in the eyes of numerous vertebrate species.
• The developmental processes and inductive factors governing scleral ossicle formation remain largely uncharacterized.

Purpose of the Study:

• To investigate the cellular dynamics during and after the induction of scleral ossicles.
• To identify the specific molecular factors responsible for inducing scleral ossicle development.
• To elucidate the role of sonic hedgehog (SHH) signaling in this process.

Main Methods:

• Analysis of cellular dynamics including cell death and proliferation.
• Gene expression analysis using real-time reverse transcriptase polymerase chain reaction (RT-PCR).
• Localization of gene expression via in situ hybridization.
• Pharmacological inhibition of Hedgehog signaling using cyclopamine.

Main Results:

• Cell death and proliferation play minor roles in initial mesenchymal condensation but are involved in inducing epithelium development.
• Significant upregulation of sonic hedgehog (SHH) gene expression was detected.
• SHH expression was localized exclusively to conjunctival (scleral) papillae, not the mesenchyme.
• Inhibition of Hedgehog signaling with cyclopamine supported SHH's role in induction.
• A consistent nonfluctuating asymmetry in the number of ossicles per eye was observed.

Conclusions:

• Sonic hedgehog (SHH) signaling is a critical factor in the induction of vertebrate scleral ossicles.
• The study clarifies cellular dynamics and identifies key molecular players in scleral ossicle development.
• Findings offer significant insights into the development of neural crest-derived dermal bones in the vertebrate eye.