The eyes absent (EYA)-like genes are essential for the formation of sensory organs among fly (Drosophila melanogaster) and mammals. EYA4, one of the vertebrate genes of Eya family, is reported to be causative for late-onset mid-frequency sensorineural hearing loss in humans, while Eya4-deficient mice exhibited congenital profound deafness and otitis media with effusion due to the eustachian tube dysmorphology. Because of the species difference in the phenotype, the pathophysiology of EYA4 in the human cochlea has yet to be elucidated. Here, we examine the expression pattern of EYA4 in the cochlea of common marmoset (Callithrix jacchus), a non-human primate. The results indicated a distinct expression pattern of EYA4 in the adult marmoset cochleae, especially strong in all supporting cells, while in mouse their expressions were diminished. Interestingly, EYA4 expression in the hair cells, supporting cells and neurons was co-localized with sine oculis homeobox–SIX1, a transcription factor essential for the transcriptional activity of EYA4. The results revealed inter-species differences in the expression pattern of EYA4 gene in supporting cells between primates and rodents. The results also indicated a fundamental role of EYA4 in the primate auditory cells. Experiments with primate models such as marmosets or with human cochlear cells may provide cues about the unknown pathogenesis of EYA4-related hearing loss.
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