Pvalb8, a Type of Oncomodulin, Regulates Neuromast Development and Auditory Function in Zebrafish

Congenital hearing loss, frequently resulting from defective hair cells, remains poorly understood due to the incomplete identification of key pathogenic genes. Oncomodulin (OCM) is a kind of calcium-binding protein (CaBP) that regulates diverse cellular processes and is thought to play crucial roles in auditory function. In teleost fish, parvalbumin 8 (<i>pvalb8</i>) and parvalbumin 9 (<i>pvalb9</i>) belong to the oncomodulin lineage and are highly expressed in hair cells. In this study, we first reported the oncomodulin lineage function in fish and identified <i>pvalb8</i> as an essential regulator of hair cell development. Single-cell RNA sequencing (scRNA-seq) and whole-mount <i>in situ</i> hybridization (WISH) revealed that <i>pvalb8</i> is highly and specifically expressed in supporting cells and hair cells. Functional loss of <i>pvalb8</i>, achieved via CRISPR/Cas9 knockout or morpholino knockdown, resulted in reduced neuromast size and a significant decrease in neuromast hair cell number, leading to auditory behavioral deficits. In addition, <i>pvalb9</i> mutants exhibited hair cell defects similar to those observed in <i>pvalb8</i> mutants, including a significant reduction in hair cell number. Moreover, <i>pvalb8</i> loss strongly inhibited the proliferation of supporting cells, which likely accounts for the reduced number of differentiated hair cells. The expression levels of Wnt target genes, <i>axin2</i>, <i>ccnd1</i>, and <i>myca</i>, were all significantly reduced in <i>pvalb8</i> mutants compared to control zebrafish, while activation of the Wnt signaling pathway rescued the hair cell loss observed in <i>pvalb8</i> mutants, indicating that <i>pvalb8</i> promotes hair cell development via Wnt-dependent proliferative signaling. These findings highlight <i>pvalb8</i> as a critical factor in the regulation of auditory hair cell formation and function in zebrafish, offering new insights into the role of oncomodulin lineage in sensory cell development.