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13.05.2020 News

It takes ears to understand: insights from zebrafish to help the hearing impaired

Myelinated neurons of the statoacoustic ganglion (green) connect the inner ear to the brain © CRTD

Neurons of the statoacoustic ganglion (purple) connect hair cells (green) of the inner ear to the brain (structure in the upper left corner) © CRTD

The inner ear is of central importance for hearing and balance. Sound waves and movements are registered by sensory hair cells. Neurons of the inner ear transmit this information to the brain, where it is processed and passed on to other organs. In humans, both hair cells and neurons are only generated during embryonic development. The capacity to replace damaged cells is lost soon after birth. This makes deafness irreversible. Currently, about five percent of the world's population is affected by hearing impairment or deafness, and it is estimated that this number continues to rise. Hence, there is a pressing need to develop new therapies restoring hearing abilities.

In contrast to humans, zebrafish continuously form new hair cells throughout life. However, it was unknown whether lifelong formation of new hair cell is accompanied by continued neuron production. Researchers at the Center for Regenerative Therapies (CRTD) at the TU Dresden have been investigating this question and published their findings in the scientific journal DEVELOPMENT.

For their study, the team led by Dr. Stefan Hans in the group of Prof. Dr. Michael Brand used marker analysis and a combination of genetic tools to characterize the statoacoustic ganglion (SAG) of the adult zebrafish on the anatomical and cellular level. They investigated whether zebrafish continue to produce new neurons after the larval stage - both in juvenile and adult age.

"Our most important finding is that the SAG is a highly heterogeneous structure containing mature, myelinated neurons and a neuronal progenitor cell pool as a source of newborn neurons. Moreover, we identified a stem cell population that replenishes the neuronal progenitor pool. With our study, we have comprehensively investigated for the first time the adult auditory and vestibular organ of the zebrafish. We were able to show that zebrafish - in contrast to mammals - display continuous neurogenesis within the inner ear," explains Dr. Stefan Hans, the last author of the study.

The knowledge gained about the cellular properties of progenitor cells during homeostasis is important for understanding the regeneration potential in the inner ear of mammals and for working on therapeutic options for hearing impaired and deaf humans.

This study was funded by the TU Dresden / CRTD through the German Excellence Initiative and a grant from the German Research Foundation to Dr. Stefan Hans (HA 6362/1).

Publication:

DEVELOPMENT: „Neurogenesis in the inner ear: the zebrafish statoacoustic ganglion provides new neurons from a Neurod/Nestin-positive progenitor pool well into adulthood” by Simone Schwarzer, Nandini Asokan, Oliver Bludau, Jeongeun Chae, Veronika Kuscha, Jan Kaslin and Stefan Hans. - https://dev.biologists.org/content/147/7/dev176750.long