Katie Kindt, Ph.D., Chief
The section on Sensory Cell Development and Function investigates how discrete subcellular signals, such as Ca2+ influx and vesicle release, shape hair cell development, and how these signals are required for proper physiological function.
In particular, our research is focused on the mechanosensory hair-cell synapse. Sensory hair-cell synapses or ribbon synapses are required to reliably transmit auditory and vestibular information to the brain. Recent evidence suggests that noise-induced and age-related hearing result from a loss of hair-cell synapses. Therefore, understanding how hair-cell synapses form and function is critical to understanding how to reform these structures after hearing loss. To study hair-cell synapse development and function, we use the zebrafish as a model system. Similar to mammals, zebrafish have sensory hair cells that enable them to sense sound and maintain proper balance. Previous work has shown that genes that cause deafness in zebrafish are also associated with hearing defects in humans and in mice. In contrast to mammals, the embryonic and larval zebrafish routinely studied are transparent and develop externally, allowing hair cells in zebrafish can be studied in vivo (figure 1).
Figure 1. Transgenic illuminates sensory hair cells in the larval zebrafish. Zebrafish have hair cells in their inner ear (A, B) and in their lateral line system (A,C). The lateral line system is composed of clusters of superficial hair cells called neuromasts that are readily visualized and physically stimulated.
In hair cells, synaptic responses are shaped by distinct sources of Ca2+: mechanosensitive Ca2+ -permeable channels in the hair bundle, voltage-gated Ca2+ channels at the synapse, and Ca2+ storage and release from mitochondria and ER. All of these Ca2+ signals shape vesicle release and are ultimately required for the proper formation and function of hair-cell synapses. To examine these complex signals in vivo, we use transgenic zebrafish to precisely monitor Ca2+ signals in the hair cell cytoplasm, hair bundle, presynaptic density, and monitor synaptic vesicle release (figure 2). We combine in vivo imaging of Ca2+ and vesicle fusion, confocal and electron microscopy, genetics, and pharmacology to characterize how discrete signals shape synapse function and development in an intact system. This long-term goal of this research is to improve our understanding of how hair-cell synapses functionally develop. This knowledge may provide insight into how to regenerate hair cell synapses after they are lost, a major barrier to restoring hearing loss.
Figure 2. Localized expression of genetically encoded indicators. Genetically encoded indicators localized to the ribbon synapse (A), hair bundle (B), and synaptic vesicles (green) and ribbon synapses (red) (C).
Left to right: Qiuxiang Zhang, Candy Wong, Mike Waltman, Sunita Warrier, Czarina Ramos, Katie Kindt, Alisha Beirl.