The hedgehog co-receptors cdon and boc function redundantly to regulate zebrafish craniofacial development.

BACKGROUND: Craniofacial development is a complex developmental process that involves formation of the skeleton, muscle, and tendons. Defects in craniofacial development result in common hereditary disorders. Among genetic factors regulating craniofacial development, dysregulated hedgehog signaling is associated with craniofacial skeletal defects such as orofacial clefting and holoprosencephaly. Here, we characterize craniofacial phenotypes associated with two hedgehog signaling co-receptors, cdon and boc, in zebrafish. Genetic pedigree analyses have previously linked both cdon and boc to microform holoprosencephaly, and mutations of Cdon and Boc in mouse result in craniofacial phenotypes. However, a detailed analysis of craniofacial phenotypes associated with cdon and boc in zebrafish has not been completed.

RESULTS: Our studies show that cdon and boc act redundantly to promote craniofacial cartilage, tendon, and muscle development in zebrafish. Using RNA-seq and HCR in situ hybridization, we show that mutations of cdon and boc result in misregulation of chondrogenesis gene expression including Indian hedgehog ligand, tendon-associated thrombospondin genes, and FOX transcription factors.

CONCLUSIONS: Our data are consistent with a model whereby cdon and boc together modify hedgehog activity in the head and establish a foundation for using zebrafish to further understand the role of cdon and boc in craniofacial hereditary disorders such as holoprosencephaly.