Ciliopathic micrognathia is caused by aberrant skeletal differentiation and remodeling

Abstract

Ciliopathies represent a growing class of diseases caused by defects in microtubule-based organelles called primary cilia. Approximately 30% of ciliopathies can be characterized by craniofacial phenotypes such as craniosynostosis, cleft lip/palate and micrognathia. Patients with ciliopathic micrognathia experience a particular set of difficulties including impaired feeding and breathing and have extremely limited treatment options. To understand the cellular and molecular basis for ciliopathic micrognathia, we utilized the talpid2 (ta2), a bona fide avian model for the human ciliopathy Oral-Facial-Digital syndrome subtype 14 (OFD14). Histological analyses revealed that the onset of ciliopathic micrognathia in ta2 embryos occurred at the earliest stages of mandibular development. Neural crest-derived skeletal progenitor cells were particularly sensitive to a ciliopathic insult, undergoing unchecked passage through the cell cycle and subsequent increased proliferation. Furthermore, whereas neural crest-derived skeletal differentiation was initiated, osteoblast maturation failed to progress to completion. Additional molecular analyses revealed that an imbalance in the ratio of bone deposition and resorption also contributed to ciliopathic micrognathia in ta2 embryos. Thus, our results suggest that ciliopathic micrognathia is a consequence of multiple, aberrant cellular processes necessary for skeletal development, and provide potential avenues for future therapeutic treatments.