Integration of BMP and Wnt signalling in the developing zebrafish ear

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We are fascinated by the inner ear and the generation of its beautiful and intricate structure during embryonic development. In the adult, this complex sensory organ detects sound, gravity and motion, enabling us to hear and to maintain balance. In this project, we aim to uncover the mechanisms by which cells signal to one another in the embryo to ensure that the inner ear develops correctly.The inner ear develops in the embryo from the otic vesicle, a simple ball of cells that forms in close proximity to the developing brain. During embryonic development, cells of the otic vesicle and of the immature brain send and receive molecular signals, relaying instructions about when to activate the expression of different genes. This signalling activity results in cascades of gene activity, leading to the correct formation of different structures in the inner ear. We are particularly interested in the signals that instruct the otic vesicle to form the semicircular canals, curved ducts that function in the vestibular (balance) part of the ear.We will focus on two sets of signalling components, known as the BMP and Wnt pathways. We will disrupt individual proteins in these pathways either in ear or in developing brain tissue to examine the effects on ear development. Our preliminary studies indicate that a protein known as Bmper acts as a hub to integrate signalling information from both pathways in the developing ear. This is a new idea that has not yet been tested in any system, to our knowledge.Recent studies in the lab of our collaborator at the University of Exeter and others have shown that many signals are delivered to and received by cells on cytonemes, dynamic thin extensions of the cell membrane. The signalling molecules themselves are thought to be localised to the tips of these membrane protrusions. We hypothesise that cytonemes are involved in signalling to the developing ear, and part of our study will involve searching for these structures, and the signalling molecules within them, using high-resolution microscopy.We will use the zebrafish embryo as our model system, for two main reasons. Firstly, the zebrafish embryo is optically transparent, meaning that we can see internal organs such as the brain or ear in the live embryo under the microscope, without any need for dissection. We can label cells with fluorescently-tagged proteins, lighting up different structures as they develop. Secondly, a new technique known as CRISPR interference will allow us to block gene function in a very precise manner in either the ear or developing brain tissue, without affecting other tissues in the embryo. Our colleagues at the University of Sheffield are developing this technique as a community resource for those working on the zebrafish model system, and we will exploit this in our project.Our work aims to uncover fundamental developmental principles about how signalling molecules instruct the normal formation of a developing organ system in the embryo. However, the findings are likely to be of interest and relevance to medicine: in humans, mutations in BMP pathway genes are causative of congenital genetic disorders, while later in life, inappropriate activation of the Wnt signalling pathway underlies many cancers.