Adult mice expressing aBrafQ241R mutation on an ICR/CD-1 background exhibit a cardio-facio-cutaneous syndrome phenotype

Abstract

Activation of the RAS pathway has been implicated in oncogenesis and developmental disorders called RASopathies. Germline mutations in BRAF have been identified in 50-75% of patients with cardio-facio-cutaneous (CFC) syndrome, which is characterized by congenital heart defects, distinctive facial features, short stature and ectodermal abnormalities. We recently demonstrated that mice expressing a Braf Q241R mutation, which corresponds to the most frequent BRAF mutation (Q257R) in CFC syndrome, on a C57BL/6J background are embryonic/neonatal lethal, with multiple congenital defects, preventing us from analyzing the phenotypic consequences after birth. Here, to further explore the pathogenesis of CFC syndrome, we backcrossed these mice onto a BALB/c or ICR/CD-1 genetic background. On a mixed (BALB/c and C57BL/6J) background, all heterozygous Braf(Q241R/+) mice died between birth and 24 weeks and exhibited growth retardation, sparse and ruffled fur, liver necrosis and atrial septal defects (ASDs). In contrast, 31% of the heterozygous Braf(Q241R/+) ICR mice survived over 74 weeks. The surviving Braf(Q241R/+) ICR mice exhibited growth retardation, sparse and ruffled fur, a hunched appearance, craniofacial dysmorphism, long and/or dystrophic nails, extra digits and ovarian cysts. The Braf(Q241R/+) ICR mice also showed learning deficits in the contextual fear-conditioning test. Echocardiography indicated the presence of pulmonary stenosis and ASDs in the Braf(Q241R/+) ICR mice, which were confirmed by histological analysis. These data suggest that the heterozygous Braf(Q241R/+) ICR mice show similar phenotypes as CFC syndrome after birth and will be useful for elucidating the pathogenesis and potential therapeutic strategies for RASopathies.

The impact of RASopathy-associated mutations on CNS development in mice and humans

“…Fewer animal models of CFCS have been reported likely due to its lower prevalence (1 in 810,000) compared to other RASopathies. Transgenic mouse models carrying gain of function mutations that are associated with CFCS recapitulate multiple aspects of human CFCS patients [108,192]. Since BRAF is the most prevalent gene that is mutated in CFCS, a majority of animal studies in CFCS have focused on Braf.…”

“…Mice expressing the conditional knock-in Braf L597V mutation also recapitulated CFCS symptoms of a short stature, facial dysmorphia, and cardiac enlargement [196]. The most prevalent CFCS mutation, Braf Q241R , induced embryonic/neonatal lethality with multiple congenital defects that included embryonic skeletal abnormalities, lymphatic defects, cardiac defects, and liver necrosis in the C57BL/6J background, and lethality between birth and 24 weeks, growth retardation, sparse and ruffled fur, liver necrosis, and atrial septal defects on the mixed background (BALB/c and C57BL/6J) [192,197]. In addition, Braf Q241R/mice showed growth retardation, a hunched appearance, craniofacial dysmorphism, and learning deficits on ICR background [192].…”

RAS and downstream RAF-MEK and PI3K-AKT signaling in neuronal development, function and dysfunction

“…Gain-of-function was achieved by low-level expression of the strongly kinase-activated B-RAF V600E (Urosevic et al , 2011), or by expression of the activating mutation B-RAF Q241R , the mouse equivalent of the human B-RAF Q257R found in CFC patients (Moriya et al , 2015). Loss-of-function mice were generated by genetic inactivation of B-RAF in essentially all neurons (Zhong et al , 2007; Galabova-Kovacs et al , 2008).…”

Impaired Osteogenesis of Disease-Specific Induced Pluripotent Stem Cells Derived from a CFC Syndrome Patient

“…Among them, no specific treatment has been developed for skeletal defects, including short stature, bone growth delay, low bone mineral density, short neck, craniofacial malformation, kyphosis, scoliosis, and funnel chest, though the majority of CFC syndrome patients suffer from diverse skeletal defects [ 8 ]. Although BRAF -mutant mice show several skeletal defects [ 9 ], they do not completely recapitulate the phenotypes of CFC syndrome patients because of interspecies differences.…”