Formation of new neurons in the adult zebrafish inner ear during homeostasis and regeneration

• Applicant: Dr. Stefan Hans
• Subject Area: Developmental Neurobiology ; Developmental Biology ; Cognitive, Systems and Behavioural Neurobiology
• Term: since 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 256131635

Sensorineural hearing loss affects millions of people worldwide. In the mammalian inner ear, the underlying cell types, namely sensory hair cells and neurons, are only produced during fetal stages and the capacity to replace damaged cells is lost soon after birth, making deafness irreversible. In contrast, zebrafish display continuous neurogenesis throughout life and more over robust regeneration after lesion. The aim of the project is to identify genes underlying inner ear neurogenesis during homeostasis and regeneration using adult zebrafish as a model organism. In the first funding period, we conducted a transcriptome analysis of cells undergoing inner ear induction at early stages of development. We generated a novel dataset of genes regulated by Dlx3b/4b, a competence factor essential for proper inner ear induction. Besides numerous novel genes, we identified an Atoh1b-dependent module acting downstream of Dlx3b/4b. In the adult zebrafish, we performed the first anatomical and cellular characterization of the statoacoustic ganglion (SAG), the sensory ganglion connecting the inner ear to the brain. In contrast to mammals, zebrafish exhibit adult neurogenesis also in the peripheral nervous system and new neurons arise from a Neurod/Nestin-positive progenitor pool. Furthermore, the Neurod/Nestin-positive progenitor pool is not exhausted and is replenished by a proliferating but otherwise so far marker-negative stem cell population. Our single cell transcriptome analysis provides first insights into the nature of the stem cell population as well as a preliminary differentiation trajectory in the zebrafish SAG. Moreover, we established a mechanical lesion to the SAG, which rekindles progenitor proliferation resulting in the production of new neurons and robust regeneration. Finally, we developed Cre-Controlled CRISPR (3C) as an easy method for conditional gene inactivation that will allow loss-of-function studies at adult stages. In the next funding period, we will focus on the stem cell population in the SAG giving rise to new neurons during homeostasis and regeneration. We will determine the identity of the stem cell population and characterize it using transcriptome analysis, immunohistochemistry and Cre-mediated lineage tracing. Moreover, using our newly 3C system, we will address the contribution of identified genes in the production of new neurons. Studying the molecular and cellular basis of adult inner ear neurogenesis in zebrafish will allow comparative studies with mammalian species which might provide valuable insights into developing cures for human deafness.

• DFG Programme: Research Grants