GRHL2 A frameshift mutation in the gene encoding the transcription factor grainyhead-like 2 (GRHL2) was identified as the cause of progressive deafness (DFNA28) segregating in a large pedigree (Peters et al., 2002). We have made the equivalent mutation in mouse (Grhl2-TMinsC/+) to model the cochlear pathology. GRHL2 is necessary for proper development of numerous epithelial tissues. Mice that are homozygous for inactivating alleles of Grhl2 die during embryogenesis, but heterozygous mice develop normally, including having normal cochlear development and initially normal hearing. However, we have discovered that the Grhl2-TMinsC mutation affects age-related hearing loss (AHL) in this mouse model, but the degree and rate of progression is influenced by the mouse strain background. Similarly, the mutation affects susceptibility to noise-induced hearing loss (NIHL), but in strain-specific ways. A goal of our present study is to understand the function of the GRHL2 transcription factor in the auditory system. We have performed ChIP-Seq experiments using our own and commercially available antibodies to GRHL2, in a variety of tissues and cell types. We have also conducted RNA-Seq experiments measuring gene-expression differences between mutant and normal cochleae. Finally, we have used shRNA to knock-down specific isoforms of GRHL2 and characterized the gene-expression differences in cultured kidney cells. By comparing the intersecting genes identified in these different experiments, we are identifying the GRHL2-regulated pathways that are disrupted by the DFNA28 mutation. A paper describing this work is in preparation. HGF Previously we identified three noncoding mutations of HGF associated with deafness in several families segregating nonsyndromic hearing loss (DFNB39) (Schultz et al., 2009). HGF encodes the multifunctional cytokine hepatocyte growth factor (HGF), which is secreted by mesenchymal cells and recognized by the tyrosine kinase receptor MET, expressed by epithelial cells. HGF is critical for cell signaling, cell motility, growth, and development. There are multiple isoforms of HGF whose expression, we hypothesize, are influenced by the DFNB39 noncoding mutations of HGF. We have created a mouse model which recapitulates a 10-bp intronic deletion found in some human DFNB39 patients. The 10 base pair deletion is located in intron 5 and founder lines retain a neomycin selection cassette, also located in intron 5 (Hgf tmdel10Neo). A comprehensive phenotypic assessment shows no obvious defects in Hgf tmdel10Neo/del10Neo mice other than cochlear abnormalities. Hearing loss was confirmed by ABR and DPOAE analyses. Hgf tmdel10Neo/del10Neo mice show severe-to-profound hearing loss, while heterozygotes Hgftmdel10Neo/+ show normal hearing. The hearing phenotype is changed when the Neomycin cassette is removed by crossing to a ubiquitously expressing Cre-recombinase line (Hgf tmdel10-). Hgftmdel10-/del10- mice show only mild-to-moderate hearing loss. Moreover, unlike their Hgf tmdel10-/+ and Hgf +/+ littermates, Hgf tmdel10-/del10- mice are resistant to noise-induced hearing loss. A full elucidiation of the HGF isoforms, and their relative abundances, produced from Hgf tmdel10Neo and Hgf tmdel10- alleles will further our understanding of the essential functions of HGF in the human and mouse auditory system. A paper describing this work is in preparation.
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