Midface and upper airway dysgenesis in FGFR2-craniosynostosis involves multiple tissue-specific and cell cycle effects

Abstract

Midface dysgenesis is a feature of more than 200 genetic conditions in which upper airway anomalies frequently cause respiratory distress, but its etiology is poorly understood. Mouse models of Apert and Crouzon craniosynostosis syndromes exhibit midface dysgenesis similar to the human conditions. They carry activating mutations of , which is expressed in multiple craniofacial tissues during development. Magnetic resonance microscopy of three mouse models of Apert and Crouzon syndromes revealed decreased nasal passage volume in all models at birth. Histological analysis suggested overgrowth of the nasal cartilage in the two Apert syndrome mouse models. We used tissue-specific gene expression and transcriptome analysis to further dissect the structural, cellular and molecular alterations underlying midface and upper airway dysgenesis in Apert mutants. Cartilage thickened progressively during embryogenesis because of increased chondrocyte proliferation in the presence of Oral epithelium expression of mutant which resulted in a distinctive nasal septal fusion defect, and premature facial suture fusion contributed to the overall dysmorphology. Midface dysgenesis in -related craniosynostosis is a complex phenotype arising from the combined effects of aberrant signaling in multiple craniofacial tissues.

Mandibular dysmorphology due to abnormal embryonic osteogenesis in FGFR2-related craniosynostosis mice

“…We observed dramatically increased size and cell number in MC of Fgfr2 +/S252W embryos, with increased proliferation of chondrocytes detected as early as E12.5. Previous studies have shown that Fgfr2 +/S252W mutant mice have increased cartilage of the basicranium (posterior to the hypophyseal cartilage) and thickened nasal cartilage owing to increased chondrocyte proliferation (Wang et al, 2005; Holmes et al, 2018). These results suggest a common mechanism of increased proliferation by the FGFR2 S252W mutation in these cranial cartilages, whether derived from cranial neural crest cells or mesoderm.…”

“…LCM was performed as previously described in detail (Holmes et al, 2018). The heads of female Fgfr2 +/+ littermates ( n =3) and female Apert Fgfr2 +/S252W ( n =3) embryos at E16.5 were embedded in OCT without fixation and rapidly frozen.…”

“…RNA was isolated using an Arcturus Picopure RNA Isolation Kit (Thermo Fisher Scientific). Library preparation with NuGEN Ovation RNA-seq System v2 (NuGEN Technologies) and Nextera XT Library Prep kit (Illumina) was performed by the Gene Expression Core Facility at the Cincinnati Children's Hospital Medical Center as described (Holmes et al, 2018). Library sequencing was performed on an Illumina HiSeq 2500 instrument using standard protocols for paired-end 100 bp sequencing by the Genetic Resources Core Facility at the Johns Hopkins School of Medicine.…”

“…We have previously reported statistical differences in craniofacial bone morphology, brain morphology, soft tissue and negative space (nasopharynx, inner ear) volumes, and morphological integration of brain and skull in mouse models for Apert and Crouzon/Pfeiffer syndromes relative to their respective littermates that do not carry the mutation and show no phenotypic effects (Aldridge et al, 2010; Holmes et al, 2018; Martínez-Abadías et al, 2013; Motch Perrine et al, 2014, 2017). However, investigations of the mandible have not been included in any of these studies.…”

Identifying the Misshapen Head: Craniosynostosis and Related Disorders

“…[16][17][18][19][20][21] Various mouse models expressing FGFR pathogenic variants have been developed and demonstrate phenotypes analogous to the human craniosynostosis syndromes, including premature coronal suture closure and midface flattening (retrusion). [22][23][24][25][26][27][28][29][30][31] Pathogenic variants in TWIST1 (twist family basic Helix-Loop-Helix transcription factor 1) gene, another transcription factor associated with craniosynostosis, [32][33][34] directly affect BMP signaling of skull preosteoblasts, leading to variations in cerebral brain angiogenesis. 35 These animal models as well as studies of cellular behavior in human craniosynostosis cell lines provide the means to examine the structural, cellular, and molecular changes that occur during prenatal development.…”