Abstract
The Notch signaling pathway is thought to regulate multiple stages of inner ear development. Mutations in the Notch signaling pathway cause disruptions in the number and arrangement of hair cells and supporting cells in sensory regions of the ear. In this study we identify an insertional mutation in the mouse Sfswap gene, a putative splicing factor, that results in mice with vestibular and cochlear defects that are consistent with disrupted Notch signaling. Homozygous Sfswap mutants display hyperactivity and circling behavior consistent with vestibular defects, and significantly impaired hearing. The cochlea of newborn Sfswap mutant mice shows a significant reduction in outer hair cells and supporting cells and ectopic inner hair cells. This phenotype most closely resembles that seen in hypomorphic alleles of the Notch ligand Jagged1 (Jag1). We show that Jag1; Sfswap compound mutants have inner ear defects that are more severe than expected from simple additive effects of the single mutants, indicating a genetic interaction between Sfswap and Jag1. In addition, expression of genes involved in Notch signaling in the inner ear are reduced in Sfswap mutants. There is increased interest in how splicing affects inner ear development and function. Our work is one of the first studies to suggest that a putative splicing factor has specific effects on Notch signaling pathway members and inner ear development.
Highlights
The organ of Corti is an excellent system to study mechanisms of cell patterning due to its highly organized array of sensory cells
Reverse transcriptase PCR (RT-PCR), followed by sequencing, reveals that some of the Sfswap mRNA produced in SfswapTg/Tg mice includes sequences from the lentiviral insert and exclusion of exons surrounding the insert
We found that SfswapTg/Tg; Jag1+/2 mutants have a more pronounced cochlear phenotype than either single mutant alone, showing a loss of outer hair cells extending into the second and first rows, increased inner hair cells throughout the length of the cochlea and the addition of a fourth row of outer hair cells in the apex (Figure 6C)
Summary
The organ of Corti is an excellent system to study mechanisms of cell patterning due to its highly organized array of sensory cells. Mutations in members of the Hes and Hey family of downstream Notch effectors cause an increase in hair cell numbers at the expense of supporting cells, with mutations of multiple Hes/Hey family members causing progressively more severe phenotypes [10,11]. These studies suggest that lateral inhibition mediated by Notch signaling acts to regulate and maintain the correct proportion of hair cells and supporting cells in inner ear sensory organs
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