Title: To turn it up or to turn it down? Characterising the role of different levels of Wnt and Hedgehog signalling activity in the formation of auditory and vestibular hair cell types
Funder: Dunhill Medical Trust

Abstract: Auditory and vestibular organs originate from a pool of prosensory cells that segregate into separate territories during development. The sensory organs are populated with hair cells, which have certain differences allowing them to specialize in either auditory or vestibular function. However, the molecular mechanisms regulating which type of hair cell is formed are unclear. The initial formation of sensory organs relies on several signalling pathways that position them along the dorso-ventral axis of the inner ear. One of them is the canonical Wnt pathway. It forms a high to low activity gradient in the otocyst; high levels act as a dorsalizing factor and low levels maintain the ventrally confined prosensory cells. The ventrally localised organs are also influenced by a high activity of Hedgehog pathway. It has not yet been investigated whether the activity of both pathways regulates in a dose-dependent manner the formation of different hair cell types and for how long the prosensory cells have to be exposed to certain levels of their activity to become an auditory or vestibular hair cell. To test this, I will combine signalling pathway reporter assay and genetic manipulation with inducible gene expression system in the developing chicken inner ear. I will also test if manipulating Wnt and Hedgehog activty can triger the formation of an auditory epithelium in stem cell organoids. Findings of my project could help to improve the existing protocols for hair cell formation and facilitate generation of platforms for modelling inner ear diseases or drug screening.

Lay abstract: The inner ear houses the auditory organ that recognises sounds and vestibular system that detects head movement, body balance and acceleration. Auditory and vestibular organs are populated with specialised sensory cells called hair cells. Even though auditory hair cells share functional and structural similarities with vestibular hair cells, they also have features that set them apart and allow them to specialise in sound detection. Hair cells are vulnerable and can disappear due to various reasons, e.g. age, treatment with certain drugs or exposure to noise. Their loss is the leading cause of hearing loss and current experimental approaches towards hair cell regeneration in the adult inner ear, in particular by stem cell use, have one main limitation, they mainly generate vestibular-like hair cells or very immature hair cells lacking characteristics typical for auditory cells. It is therefore essential to understand the molecular mechanisms guiding cells towards vestibular or auditory fate in the inner ear. Wnt and Hedgehog pathways are two signalling cascades used by cells to communicate with each other during inner ear development. They are known to influence the early formation of auditory and vestibular organs, but they direct role in the specification of different hair cell types of the inner ear has not yet been investigated. Therefore, the aim of this project is to test if Wnt and Hedgehog signalling pathways are part of the mechanism deciding whether an auditory or vestibular hair cell is formed. The activity of both pathways will be monitored in the developing inner ear to establish their pattern of activity in vestibular and auditory elements and then modulated using genetic tools in the developing ear. The knowledge gained from these experiments will be then applied to stem cell systems to probe if manipulating the activity of Wnt and/or Hedgehog can trigger auditory hair cell formation. The findings of this project could help to improve existing protocols for auditory hair cell regeneration and develop new tools for testing drugs and regenerative therapies.

Research activity codes: 1.1 NORMAL BIOLOGICAL DEVELOPMENT AND FUNCTIONING
Health categories: EAR;GENERIC HEALTH RELEVANCE