Hussain S., Aponte-Rivera R., Barghout R.M., Trapani J.G., & Kindt K.S. (2022). In vivo analysis of hair cell sensory organs in zebrafish: From morphology to function. In Groves A.K. (Eds.) Developmental, Physiological, and Functional Neurobiology of the Inner Ear. Neuromethods (176). Humana, New York, NY.
Hair cells are the sensory receptors of the vertebrate auditory and vestibular systems. In aquatic vertebrates, hair cells are present in the inner ear, where they are required for hearing and balance, and in the lateral line, where they detect fluid flow. In mammals, hair cell epithelia are embedded within a bony labyrinth in the skull, which makes access challenging for in vivo studies. In larval zebrafish, however, both inner ear and lateral line hair cells can be easily studied in vivo as they are present in accessible locations and in transparent tissue. In addition, zebrafish hair cells have remarkable genetic conservation with humans, and recent advances in reverse genetics have streamlined the process to generate novel zebrafish mutants. Thus, zebrafish are suitable models for studying the genetics underlying hearing and balance and contributing a mechanistic understanding of human sensorineural hearing loss. This methods chapter serves as a guide to creating and studying novel zebrafish mutants, covering a range of topics from zebrafish breeding and propagation to embryo microinjections for targeted mutagenesis (morpholino, CRISPR-Cas9, and tol2-based transgenesis). Once these mutants are created, we discuss ways to test auditory-vestibular phenotypes. We also outline several powerful in vivo methods to study inner ear and lateral line morphology, assess hair cell function, and examine subcellular structures within hair cells. We showcase several previously characterized zebrafish mutants that can be used as controls and exemplars (emx2, cdh23, pcdh15a, myo7aa, caV1.3a) for these approaches. Finally, we discuss recent in vivo advances being applied to study and manipulate hair cells with optogenetics techniques such as genetically-encoded indicators and actuators for functional studies.
hair cells; zebrafish; lateral line; in vivo imaging; morpholino; CRISPR-Cas9; optophysiology; electrophysiology