The Fibroblast Growth Factor 9 (Fgf9) Participates in Palatogenesis by Promoting Palatal Growth and Elevation

Abstract

Cleft palate, a common global congenital malformation, occurs due to disturbances in palatal growth, elevation, contact, and fusion during palatogenesis. The Fibroblast growth factor 9 (FGF9) mutation has been discovered in humans with cleft lip and palate. Fgf9 is expressed in both the epithelium and mesenchyme, with temporospatial diversity during palatogenesis. However, the specific role of Fgf9 in palatogenesis has not been extensively discussed. Herein, we used Ddx4-Cre mice to generate an Fgf9–/– mouse model (with an Fgf9 exon 2 deletion) that exhibited a craniofacial syndrome involving a cleft palate and deficient mandibular size with 100% penetrance. A smaller palatal shelf size, delayed palatal elevation, and contact failure were investigated to be the intrinsic causes for cleft palate. Hyaluronic acid accumulation in the extracellular matrix (ECM) sharply decreased, while the cell density correspondingly increased in Fgf9–/– mice. Additionally, significant decreases in cell proliferation were discovered in not only the palatal epithelium and mesenchyme but also among cells in Meckel’s cartilage and around the mandibular bone in Fgf9–/– mice. Serial sections of embryonic heads dissected at embryonic day 14.5 (E14.5) were subjected to craniofacial morphometric measurement. This highlighted the reduced oral volume owing to abnormal tongue size and descent, and insufficient mandibular size, which disturbed palatal elevation in Fgf9–/– mice. These results indicate that Fgf9 facilitates palatal growth and timely elevation by regulating cell proliferation and hyaluronic acid accumulation. Moreover, Fgf9 ensures that the palatal elevation process has adequate space by influencing tongue descent, tongue morphology, and mandibular growth.

Targeted deletion of Fgf9 in tendon disrupts mineralization of the developing enthesis

“…Surprisingly, despite the thinner mineral thickness at the adult supraspinatus and Achilles entheses, Fgf9 ScxCre mice had increased cellular density at the attachment site. Previously, increased mesenchymal cellularity has been linked to the delayed palatal growth in embryos with global deletion of Fgf9 30 . Thus, the increased cellularity in the mature enthesis we observed is likely due to delayed maturation in the Fgf9 ScxCre enthesis that is also evident by smaller area of active matrix mineralization in the young enthesis.…”

Targeted Deletion of Fgf9 in Tendon Disrupts Mineralization of the Developing Enthesis

“…Previously, increased mesenchymal cellularity has been linked to the delayed palatal growth in embryos with global deletion of Fgf9 . 33 Thus, the increased cellularity we observed is likely due to delayed maturation in the Fgf9 ScxCre enthesis. Additionally, the acellular metachromatic defect at the Achilles enthesis of Fgf9 ScxCre mice may indicate an altered extracellular matrix at the tendon-bone attachment, caused by changes in compressive loading of the tendon that results in increased proteoglycan formation.…”

FGF9 Promotes Expression of HAS2 in Palatal Elevation via the Wnt/β-Catenin/TCF7L2 Pathway

“…Assays for generating the transgenic Fgf9 +/ − mice have been described earlier [ 8 ]. Mice were raised in a specific pathogen-free (SPF) condition at Shanghai Ninth People’s Hospital in accredited animal facilities.…”

“…In addition, cleft palate has been noted in Fgf9 −/− mice with 40% penetrance by different knock-out gene sites [ 7 ]. In our pilot study, we generated a Fgf9 −/− mouse model with 100% penetrance of cleft palate, delayed palatal elevation, and decreased hyaluronic acid accumulation [ 8 ].…”

“…In mammals, HAS are encoded by Has1 – 3 that display diverse expression profiles in embryogenesis [ 19 ]. Our previous study has reported that the knockout of Fgf9 in mice could delay palatal elevation and suppress HA accumulation [ 8 ]. However, the underlying molecular mechanism has not been elaborated.…”