Forming Connections: The Cell-Autonomous Roles of GATA3 and NEUROD1 in Developing Auditory Neurons
Date of Award
Doctor of Philosophy
Jeremy Duncan, Ph.D.
Wendy Beane, Ph.D.
John Jellies, Ph.D.
Cindy Linn, Ph.D.
Cochlea, gata3, hearing, inner ear afferent, neurod1, spiral ganglion neurons
Hearing loss is the most prevalent sensory disorder, yet current treatment options are restricted to hearing aids and cochlear implants. Both treatment options require the presence and proper formation of inner ear auditory afferent neurons, known as spiral ganglion neurons (SGNs). In many patients with hearing loss, these neurons are either not present or are improperly organized, making current therapeutic options nonviable. Although it would be ideal to preserve functioning SGNs or to regenerate them, we are still learning how SGNs develop and form their projections to their peripheral and central targets. Therefore, a better understanding of the genes involved in their development is needed before major improvements can be made to treat hearing loss.
Two genes that have been suggested to have a role in SGN development include the zinc-finger transcription factor Gata3 and the basic helix-loop-helix transcription factor Neurod1. Previous studies regarding Gata3 in Mus musculus demonstrated that Gata3 is necessary immediately after specification of cells to a SGN fate for the neurons to correctly form projections to their target cells in the periphery, and for their long-term survival. However, Gata3 expression persists in SGNs until at least two weeks after birth. Therefore, the role of Gata3 after initial specification of cells to a neuronal fate was previously uninvestigated. The role of Neurod1 has been studied in Neurod1-null mice and in mice where Neurod1 has been conditionally deleted from multiple cell types within the inner ear. These studies suggested a role for Neurod1 in SGN survival, formation of projections towards peripheral cell targets, and in formation of projections towards central targets in the cochlear nucleus. However, no study has looked at the role of Neurod1 within only SGNs to determine whether Neurod1 has a cell-autonomous role or if the deletion from multiple cell types is leading to previously reported phenotypes.
In this study, the Cre-loxP system in mice was used to conditionally delete Gata3 or Neurod1 from only SGNs. Gata3 was eliminated from neurons at later developmental timepoints than previously examined to determine the role of Gata3 at later stages in SGN development. Neurod1 was eliminated during the initial stages of cell specification but its deletion was restricted to only SGNs. Using immunohistochemistry, lipophilic dye tracing, and quantitative-PCR, I provide evidence that both Gata3 and Neurod1 have cell-autonomous roles in SGN development. My findings support the hypothesis that Gata3 has a cell-autonomous role in the formation of SGN peripheral, but not central, projections. This is the first report of the effects of deleting Neurod1 from only SGNs. My findings support the hypothesis that Neurod1 has a cell-autonomous role in the development of SGNs, particularly in formation of central projections. This work provides further evidence for the need of Gata3 throughout SGN development for proper formation of peripheral projections and a cell-autonomous role for Neurod1 in SGN development. This study lays a foundation for further research where downstream targets of Gata3 or Neurod1 can be examined to enhance our understanding of the complex gene network involved in SGN formation.
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Ketchum, Elizabeth Madison, "Forming Connections: The Cell-Autonomous Roles of GATA3 and NEUROD1 in Developing Auditory Neurons" (2022). Dissertations. 3843.