Reproductive-state dependent changes in inner ear gene expression in female plainfin midshipman fish.

Acoustic communication is vital for reproductive success in many vertebrates. In the plainfin midshipman fish (Porichthys notatus), females respond to low-frequency advertisement calls ("hums") produced by nesting type I males during the summer reproductive season, likely driving mate selection. Females exhibit seasonal, estrogen-mediated auditory plasticity that adaptively couples the sender and receiver to enhance reproductive success. Physiological plasticity in two regions of the inner ear, the saccule and the utricle, increases sensitivity to key features of the males' advertisement call in reproductive female midshipman. However, the mechanisms underlying this plasticity differ between inner ear regions. In the saccule, enhanced encoding of the male's call is correlated with an increase in cell proliferation and the number of sensory hair cells. By contrast, plasticity in auditory sensitivity in the utricle is independent of cell addition. In this study, we used nCounter technology to determine the transcriptional changes associated with auditory plasticity in the female midshipman inner ear. We found that the transcriptional profile of the saccule was distinct from the utricle. More of our target genes were differentially expressed in the saccule than the utricle, and more saccular transcripts showed seasonal changes in gene expression as compared to the other inner ear regions. Our results offer new insights into how gene expression differentially regulates auditory plasticity in the female midshipman inner ear and provides a framework for future studies of hormonally-mediated plasticity in other vertebrates.