Morphological comparison of the craniofacial phenotypes of mouse models expressing the Apert FGFR2 S252W mutation in neural crest- or mesoderm-derived tissues

Abstract

Bones of the craniofacial skeleton are derived from two distinct cell lineages, cranial neural crest and mesoderm, and articulate at sutures and synchondroses which represent major bone growth sites. Premature fusion of cranial suture(s) is associated with craniofacial dysmorphogenesis caused in part by alteration in the growth potential at sutures and can occur as an isolated birth defect or as part of a syndrome, such as Apert syndrome. Conditional expression of the Apert FGFR2 S252W mutation in cells derived from mesoderm was previously shown to be necessary and sufficient to cause coronal craniosynostosis. Here we used micro computed tomography images of mice expressing the Apert mutation constitutively in either mesoderm- or neural crest-derived cells to quantify craniofacial shape variation and suture fusion patterns, and to identify shape changes in craniofacial bones derived from the lineage not expressing the mutation, referred to here as secondary shape changes. Our results show that at postnatal day 0: (i) conditional expression of the FGFR2 S252W mutation in neural crest-derived tissues causes a more severe craniofacial phenotype than when expressed in mesoderm-derived tissues; and (ii) both mesoderm- and neural crest-specific mouse models display secondary shape changes. We also show that premature suture fusion is not necessarily dependent on the expression of the FGFR2 S252W mutation in the sutural mesenchyme. More specifically, it appears that suture fusion patterns in both mouse models are suture-specific resulting from a complex combination of the influence of primary abnormalities of biogenesis or signaling within the sutures, and timing.

Keywords: Apert syndrome; Craniosynostosis; FGFR2; Mesoderm; Neural crest; Suture fusion pattern.

Fig. 1

Suture fusion pattern in four groups of mice. Four stages were defined: patent (white); bridging (light grey); partially fused (dark grey); fused (black) (for the stages definition see Materials and methods section)

Fig. 2

Facial sutures are derived from neural crest. The heads of E16.5 Wnt1-Cre/R26R (A–E) or Mesp1-Cre/R26R (A′–E′) were coronally sectioned and stained for β-galactosidase activity (blue). Sutures shown are (A, A′) Inter-premaxillary; (B, B′) Inter-maxillary; (C, C′) Inter-palatine; and (D, D′) Maxillary-Palatine. (E, E′) Sections through the mesoderm-derived basioccipital bone at the posterior of each head is shown. Slides are counter-stained with eosin (pink). Scale bars = 100 μm (A–D) and 200 μm (E, E′).

Fig. 3

Skull shape differences between Meso^+/S252W and NC^+/S252W mutants and unaffected mice. Cellular origin of the skull at P0 is shown in lateral and ventral views in panel A (mesoderm-derived bones in pink, neural crest-derived bones in green) [1,2]. Lateral views of a wild type mouse, Meso^+/S252W mutant (note the fused coronal suture), and NC^+/S252W mutant from μCT reconstruction (panel B). Midsagittal section of the cranial base of a wild type mouse, Meso^+/S252W mutant, and NC^+/S252W mutant (note the retroflexion of the cranial base and vomer) from μCT reconstruction (panel C). Placement of the 77 Meso^+/S252W, Meso^+/+, NC^+/S252W, and NC^+/+ P0 mice on PC1 and PC2 in the skull shape space (principal component analysis of the landmarks Procrustes shape coordinates) (panel D). Shape changes visualized by wireframes associated with negative and positive scores on PC1 and PC2 (panel E).

Fig. 4

Comparison of the consensus shapes (PAS) of the NC^+/S252W and Meso^+/S252W mutants. Superior (with base removed), superior (with vault removed), inferior (with vault removed), anterior, and lateral views (reading from left to right) of the PAS of the NC^+/S252W (panel A) and Meso^+/S252W mutants (panel B). Color map representing the anatomical regions displaying the most and least intense shape differences (in red and dark blue respectively) between the NC^+/S252W and Meso^+/S252W mutants (panel C). Wireframes corresponding to the NC^+/S252W (green) and Meso^+/S252W (orange) mutants in lateral view when compared to the consensus shape of the unaffected mice (black) and to each other (panel D).