RGD Peptides, Integrins, and Cell Polarity in Danio rerio Mechanosensory Hair Cell Regeneration

Human hair cells in the inner ear use delicate molecular machinery to detect and process pressure changes in the air which we understand as sound. These cells die when exposed to dangers including loud noise and aminoglycoside antibiotics. Humans cannot replace these cells, leading to gradual hearing loss with age. Some species retain the ability to regenerate hearing including the zebrafish Danio rerio. Exposed neuromasts across the body of zebrafish produce hair cells entirely homologous to those of the inner ear which the fish uses to detect motion in water. Zebrafish hair cells must orient themselves precisely during regeneration to transmit information about the direction of water movement to the brain. Regeneration in zebrafish involves active movement by hair cell progenitors to preserve this orientation. Hair cells require the core planar cell polarity pathway and Notch signaling to orient themselves. However, the mechanisms of cellular movement during regeneration remain unknown. Integrins are a family of transmembrane proteins that function in cell adhesion to the extracellular matrix (ECM) and in signal transduction. Integrins are implicated in epidermal stem cell differentiation and some forms of cell motility. A subset of the integrins contain the RGD binding motif which binds to the Arg-Gly-Asp peptide sequence to attach to the ECM. The goal of this study was to determine whether external application of RGD peptides to zebrafish could interfere with integrin binding and thereby test the importance of integrins to hair cell regeneration. Fluorescence imaging of hair cells exposed to labeled RGD peptides confirms that RGD peptides can enter the neuromast