Neuron-Glia Interactions in the Cochlea

Project Summary In this project, we will investigate the cellular and molecular events that allow cochlear glia to shape and sustain auditory circuits for a lifetime of hearing. Like the other glia of the peripheral nervous system, cochlear glia develop from the neural crest, a highly migratory and plastic population of progenitors that produce neurons and connective tissue as well as satellite glia and Schwann cells. Despite their common origin with other peripheral glia, the glia that ultimately populate the cochlea take on some unique properties that are essential for the sense of hearing, such as the ability to myelinate spiral ganglion neuron (SGNs) cell bodies. In addition, cochlear glia provide crucial trophic support for the highly active SGNs and also clear away excess ions and transmitter that could otherwise be damaging. Finally, whereas glial precursors generally migrate along axons, in the cochlea, the glial precursors migrate ahead of the SGN neurites and appear to facilitate efficient formation of orderly radial bundles along the tonotopic axis. Our overall goal is to learn how cochlear glia acquire these properties. Based on data from our lab and others, we hypothesize that the transcription factors Gata2 and Gata3 act separately in developing glia and SGNs to coordinate interactions needed for cochlear wiring and function. In support of this idea, we found that Gata2 is expressed by cochlear glia but not by glia of the somatosensory system. Additionally, previous analysis of Gata2 mutant mice revealed hearing deficits and SGN loss that could be due to unrecognized effects on the glia. On the other hand, we observed that Gata3 mutant SGNs extend their neurites as if they are unable to interact with the glia, resulting in disorderly wiring that mimics what occurs when glia are depleted from the developing cochlea. We will follow up on these observations by using molecular genetic approaches in the mouse to characterize glial organization and its effects on SGN neurite outgrowth (Aim 1), to determine the role of Gata2 in cochlear glia development (Aim 2), and to compare GATA-dependent programs of gene expression in SGNs and glia (Aim 3). For Aim 1, we will use genetic and viral approaches to visualize glia and disrupt their ability to interact with developing SGN neurites, as assessed in fixed tissue and by time-lapse imaging. For Aim 2, we will delete Gata2 from cochlear glia and assess effects on cochlear wiring, on glial differentiation and function, on SGN survival, and on auditory function, as assessed by recording ABRs and DPOAEs. For Aim 3, we will perform scRNA-sequencing of embryonic Gata2 and Gata3 mutant cochleas, both to identify downstream genes that may mediate neuron-glia interactions and to learn how neurons and glia are affected by each other during development. Together, these studies will advance our knowledge of cochlear glia development and function, with direct implications for hearing loss, including that associated with Gata2 (Emberger Syndrome) and Gata3 (HDR Syndrome) mutations in humans.