Abstract:

Objective To reveal the role of family with sequence similarity member 20-b (Fam20b) in the development of craniofacial organs originating from the first branchial arch mesenchyme. Methods Pax2-Cre;Fam20b^f/f mice were generated and analyzed for postnatal skeletal morphology by whole-mount Alcian blue-Alizarin red staining, for histological features by Masson’s trichrome staining, for cell proliferation/apoptosis in the first branchial arch using Ki67/TUNEL assays, and for frontal bone mineralization by Von-Kossa staining, for glycosaminoglycan chains (GAGs) distribution by Alcian blue staining. Results At embryonic day 10.5 (E10.5), extensive apoptosis in proximal mandibular mesenchyme of Pax2-Cre;Fam20b^f/f mice led to a Pierre Robin sequence-like phenotype (micrognathia, glossoptosis and cleft palate) with microcephaly, delayed anterior fontanelle closure and condylar hypoplasia. Furthermore, Pax2-Cre;Fam20b^f/f mice exhibited the impaired vertical growth and hypomineralization of the frontal bone, as well as the reduced GAGs deposition, premature chondrocyte differentiation and enhanced subperichondral ossification in condyle. Conclusion Conditional knockout of Fam20b in the first branchial mesenchyme induced excessive apoptosis in proximal mandibular mesenchyme which resulted in micrognathia. Additionally, impaired ossification and mineralization of the frontal bone, combined with reduced GAGs deposition and premature maturation in condylar cartilage, suggests the suppressed intramembranous ossification and the enhanced subperichondral ossification by the deficient GAG chain synthesis.

Key words: Fam20b, first branchial arch mesenchymal cells, craniofacial malformations, Pierre Robin sequence, apoptosis