A missense mutation in Fgfr1 causes ear and skull defects in hush puppy mice

Abstract

The hush puppy mouse mutant has been shown previously to have skull and outer, middle, and inner ear defects, and an increase in hearing threshold. The fibroblast growth factor receptor 1 (Fgfr1) gene is located in the region of chromosome 8 containing the mutation. Sequencing of the gene in hush puppy heterozygotes revealed a missense mutation in the kinase domain of the protein (W691R). Homozygotes were found to die during development, at approximately embryonic day 8.5, and displayed a phenotype similar to null mutants. Reverse transcription PCR indicated a decrease in Fgfr1 transcript in heterozygotes and homozygotes. Generation of a construct containing the mutation allowed the function of the mutated receptor to be studied. Immunocytochemistry showed that the mutant receptor protein was present at the cell membrane, suggesting normal expression and trafficking. Measurements of changes in intracellular calcium concentration showed that the mutated receptor could not activate the IP3 pathway, in contrast to the wild-type receptor, nor could it initiate activation of the Ras/MAP kinase pathway. Thus, the hush puppy mutation in fibroblast growth factor receptor 1 appears to cause a loss of receptor function. The mutant protein appears to have a dominant negative effect, which could be due to it dimerising with the wild-type protein and inhibiting its activity, thus further reducing the levels of functional protein. A dominant modifier, Mhspy, which reduces the effect of the hush puppy mutation on pinna and stapes development, has been mapped to the distal end of chromosome 7 and may show imprinting.Electronic supplementary materialThe online version of this article (doi:10.1007/s00335-011-9324-8) contains supplementary material, which is available to authorized users.

Mature middle and inner ears express Chd7 and exhibit distinctive pathologies in a mouse model of CHARGE syndrome

“…Fgfr1 mutant mice have abnormal stapes anatomy, increased compound action potentials and skeletal defects (Calvert et al, 2011). Fgfr1 expression is decreased in Chd7 mutant olfactory placodes (Layman et al, 2011), and may also have roles in inner and middle ear development.…”

Genetic insights into the mechanisms of Fgf signaling

“…However, this phenotype is dependent on genetic background, since Fgfr1 was shown to regulate primitive endoderm formation on a 129S4 genetic background, while the same null allele caused mesoderm defects on a mixed genetic background (Hoch and Soriano 2006;Brewer et al 2015). Other studies have also demonstrated that ear defects caused by an ENU-induced mutation in Fgfr1 are also modified by genetic background (Pau et al 2005;Calvert et al 2011). For Fgfr2, different targeting strategies have produced distinct phenotypes.…”

Fgfr1 regulates development through the combinatorial use of signaling proteins

“…Fgfr1-related phenotypes are subject to variation depending on the genetic background (Hoch and Soriano 2006;Calvert et al 2011). To minimize phenotypic variability, we analyzed mouse mutants on 129S4 coisogenic or congenic genetic backgrounds.…”

“…−/− studies due to differences in genetic backgrounds, which have been shown to influence Fgfr1-associated phenotypes (Calvert et al 2011).…”