Understanding cochlear development : insights from a notch disease model and lineage tracing of In utero barcoded otic progenitors

The organ of Corti, located in the cochlea of the inner ear, is the organ for auditory perception in mammals. Proper auditory function depends on the formation of a precise mosaic of mechanosensory inner hair cells (IHCs), outers hair cells (OHCs) and different subtypes of associated supporting cells (SCs), a process guided by Notch signaling during development. Although previous research has increased our understanding of inner ear development, lineage progression and mechanisms of cell fate specifications in the inner ear are not fully understood.

The overall aim of this thesis is to investigate signalling mechanisms guiding cochlear development, focussing on lineage and cell fate specifications. This thesis deploys a wide array of wet and dry lab methods, the use of animal models, and various conventional and state-of-the-art technologies to study cochlear development during normal development and upon dysregulation of Notch signaling.

In Project _, we reveal lineage specifications and clonal relationships between cell types in the mouse cochlea. To overcome previous technical barriers to perform these analyses, we first refined an in utero injection method to target and manipulate ectoderm and neural crest derived otic progenitors. Next, we used this method to in utero label otic progenitors with heritable barcodes and performed next-generation lineage tracing and clonal analysis. Our data revealed several early lineage restrictions in the inner ear, including specification of cochlear floor and roof populations, and the compartmentalization of the cochlear floor into three separate domains. Together, this project demonstrates the high potential for in utero injections for otic progenitor manipulation and provides an atlas of clonal relationships between cell types in the mouse cochlea.

In Project __, we zoom in on signaling mechanisms guiding organ of Corti patterning and studied the effect of hypomorphic Jag1-mediated Notch activation on signaling, patterning and hearing outcomes using the Nodder mouse model for Alagille Syndrome (ALGS). This project revealed a novel role for Jag1 in repressing Notch activation in lateral SCs and highlighted the involvement for Notch signaling in hair cell (HC) development, subtype specification, and positioning. Additionally, we showed that the Nodder mouse model is a suitable model to study inner ear defects in ALGS and may be utilized as a model to study therapeutic interventions to combat hearing deficits. Together, work in this thesis increased our understanding of cochlear development.

List of scientific papers

_. Sandra de Haan, Jingyan He, Agustin A. Corbat, Lenka Belicova, Michael Ratz, Jonas Frisen, Matthew W. Kelley, Emma R. Andersson. Otic placode and neural crest barcoding reveals cochlear compartmentalization. [Submitted]

__. Sandra de Haan, Agustin A. Corbat, Christopher R. Cederroth, Lisa G. Autrum, Simona Hankeova, Elizabeth C. Driver, Barbara Canlon, Matthew W. Kelley, Emma R. Andersson. Jag1 represses Notch activation in lateral supporting cells and inhibits an outer hair cell fate in the medial compartment of the developing cochlea. Preprint at bioRxiv. 2024.02.02.577075. [Accepted]
https://doi.org/10.1101/2024.02.02.577075