The Ptch1^DL mouse: A new model to study lambdoid craniosynostosis and basal cell nevus syndrome‐associated skeletal defects

Abstract

Mouse models provide valuable opportunities for probing the underlying pathology of human birth defects. Employing an ENU-based screen for recessive mutations affecting craniofacial anatomy we isolated a mouse strain, Dogface-like (DL), with abnormal skull and snout morphology. Examination of the skull indicated that these mice developed craniosynostosis of the lambdoid suture. Further analysis revealed skeletal defects related to the pathology of basal cell nevus syndrome (BCNS) including defects in development of the limbs, scapula, ribcage, secondary palate, cranial base, and cranial vault. In humans, BCNS is often associated with mutations in the Hedgehog receptor PTCH1 and genetic mapping in DL identified a point mutation at a splice donor site in Ptch1. Using genetic complementation analysis we determined that DL is a hypomorphic allele of Ptch1, leading to increased Hedgehog signaling. Two aberrant transcripts are generated by the mutated Ptch1DL gene, which would be predicted to reduce significantly the levels of functional Patched1 protein. This new Ptch1 allele broadens the mouse genetic reagents available to study the Hedgehog pathway and provides a valuable means to study the underlying skeletal abnormalities in BCNS. In addition, these results strengthen the connection between elevated Hedgehog signaling and craniosynostosis.

MEMO1 drives cranial endochondral ossification and palatogenesis

“…Following ENU treatment of C57BL/6J male mice, we generated founder males that were used in a three-generation cross to screen for recessive mutations that lead to defects in head morphology at embryonic day 18.5 (E18.5) 18 . From this, we identified a mutant line that we originally termed F1-9-13FP in which ~25% of the offspring from heterozygous matings displayed a variety of craniofacial defects including a misshapen nasal bridge, a downward positioned cranium, a domed skull (Fig 1A, C), and a fully penetrant cleft palate (Fig 1B, D).…”

“…To identify genes and alleles affecting mouse craniofacial formation we have recently conducted a recessive N-ethyl-N-nitrosourea (ENU) screen 18 . Here we report the phenotypic and molecular characterization of one mutant from this screen that displayed a combination of craniofacial defects including cleft secondary palate, a domed cranium, and cranial base defects.…”

The Morphogenesis of Cranial Sutures in Zebrafish

“…Sutures are identified with respect to their adjacent bones, i.e., the interfrontal suture (metopic in humans) lies in between the frontal bones. The coronal suture separates the frontal and parietal bones, the sagittal suture separate the parietal bones, and the lambdoid sutures separate the occipital and parietal bones [10]. Because mutations in genes encoding FGF receptors and transcription factors like Twist1 and Msx2 cause premature suture obliteration and fusion of cranial bones, it is accepted that sutures serve both as growth and signaling centers [11–15].…”

The old and new face of craniofacial research: How animal models inform human craniofacial genetic and clinical data

“…The experimental protocol has been amenable to both large and small-scale screens, but none have reached genome-wide saturation due to the considerable resources that would be required. Nevertheless, screens focusing on dysmorphic head and/or craniofacial phenotypes such as cranial neural tube closure, holoprosencephaly, micrognathia, agnathia, and orofacial clefting have identified many new genes and alleles that affect craniofacial development (Caruana et al, 2013; Feng et al, 2013; Nolan et al, 2000; Sandell et al, 2011). Perhaps one of the most important insights that has come from mouse ENU mutagenesis is the unexpected link between cilia formation and function in Hedgehog-dependent pathologies such as holoprosencephaly.…”

“…This intraflagellar transport protein gene is also mutated in one type of human ciliopathy termed Short-Rib Thoracic Dysplasia (Norris and Grimes, 2012). Additional ENU mutations have provided new alleles that impact facial development by disrupting signaling through the Wnt, Hh, Tgfb, Fgf, and retinoic acid pathways and are valuable models to understand genetic and environmental influences on human craniofacial birth defects (Bjork et al, 2010; Feng et al, 2013; Handschuh et al, 2014; Sandell et al, 2011; Sandell et al, 2007). Of particular note, a dominant ENU screen identified the mouse line batface (Bfc), which presented with a shorter and broader face and was caused by a mutation in Ctnnb1, the gene encoding β-catenin (Nolan et al, 2000).…”