Projects

Maturation and sensory hair cell regeneration potential

In humans, as with all mammals, the loss of auditory sensory hair cells is irreversible. However, different degrees of hair cell regeneration occur in vestibular sensory epithelia, at early developmental stages, or in non-mammalian species. Hair cell regeneration results from division and/or trans-differentiation of neighbouring supporting cells. It is generally accepted that poor, or absent, hair cell regeneration relates to the differentiation state reached by supporting cells and hair cells, but the mechanisms behind this are unknown.

What dictates hair cell regeneration potential? Taking on a multi-layered approach, combining single-cell multi-omics, spatial transcriptomics and transcriptional manipulations, we are studying the vestibular utricle to evaluate the connection between maturation and HC regeneration potential.

We are taking on a comparative approach to identify the cell/tissue level factors that interact during maturation to distinguish the mouse (marginally-regenerating) and chick (fully-regenerating) utricle. Additionally, we are studying the regeneration trajectories of postnatal and adult mouse utricle to zoom-in on the factors driving the age-related decrease in regeneration potential. Finally, our aim is to perform simultaneous transcriptional manipulation of identified targets aiming to overturn the poor HC regeneration of the adult mammalian utricle.

Legend: VC_research_image_legends

Credit V. Castagna

 

Evolution and development of brainstem sound localisation circuits

Our view of the world, how we move around, how we process the sound information that comes in through our ears or the visual information we detect with our eyes, is all done by circuits of neurons in the brain. These are groups of specific types of neurons, that are connected to each other in specific ways and that receive and send specific inputs and outputs. How are these circuits built during development? How have they evolved? How are the different neuronal types born and become their adult selves?, how do they migrate to their final positions? and how do they extend projections to build the circuit’s connections? These are all crucial questions in neuroscience. Knowing how a circuit is built teaches us a lot about its function, and how and why it may not be working properly.

We are addressing these questions by studying the development and evolution of sound localisation circuits in the brainstem. We are using fate mapping techniques in developing chicken embryos, to trace the different neuronal lineages and combining this with gene expression profiling to better follow their development. We are then comparing the differences and similarities of how sound localisation circuits develop in birds (chicken) and mammals (mouse) to better understand how circuits that perform similar functions have evolved independently.

Legend: One side of chicken embryo hindbrain transverse section. The sample was collected from chicken embryo at embryonic day 10. The hindbrain is an

essential structure in the developing embryo which give rise to the cerebellum and the brainstem in chicken. Neurons that are developed from progenitor cells which express transcription factor, Atoh1, are labelled by green fluorescent protein through electroporation, and are shown in green color here. Cell nuclei are counterstained with DAPI and are shown in gray color.

How the brain protects the ear: the role of the efferent system during noise-induced trauma

Worldwide, almost half a billion people have disabling hearing loss and 1.1 billion young people (12-35 years old) are at risk of losing their hearing due to recreational noise. In particular for loud sound exposure, noise-induced hearing loss (NIHL) can result from a loss of synapses between sensory cells and auditory nerve fibres, even before either cell type is terminally damaged, making this a crucial target for hearing protection therapies.

The auditory system is unique in receiving modulation from the CNS directly onto sensory cells. Medial olivocochlear (MOC) efferent neurons form a negative feedback gain-control system that inhibits the amplification of sounds by specialised sensory cells (outer hair cells - OHCs), mediated by α9α10 nicotinic acetylcholine receptors (nAChRs) located at the base of OHCs.

The MOC system has an important role in the protection from NIHL. We are exploring the molecular actors driving this protection, by studying changes in gene expression landscape, upon noise-induced trauma, in mouse models with different levels of α9α10 nAChR activity.

Legend: VC_research_image_legends

Credit V. Castagna

The transcriptomic state of spiral ganglion neurons in different types of hearing loss

In the inner ear, spiral ganglion neurons (SGNs) are essential for transmitting sound information to the brain. Morphological, electrophysiological and transcriptomic characterisation subdivides them into two types: type I SGNs contact the inner hair cells that transduce and transmit sound information, while type II SGNs contact outer hair cells that have a critical role in sound amplification and tuning. Type I SGNs are further subdivided into types Ia, Ib, and Ic.

The success of any therapeutic intervention aimed at recovering, enhancing or replacing auditory function rests on the presence of healthy and functional SGNs. To this end, general approaches like anti-inflammatory drugs are routinely used in the clinic, but these do not directly target SGNs.

Using single-nuclei transcriptomics and smFISH, we are studying how each subtype of SGN is affected by acute or chronic hearing loss, including congenital hearing loss (Otof knock mouse), aminoglycoside-induced hair cell damage and noise-induced hearing loss. Our aim is to identify targets to potentially mitigate their indirect damage and improve their function.

Legend: Image of transverse section of Nucleus Magnocellularis (NM) and Nucleus Laminiaris (NL). Collected from chicken embryo at embryonic day 10. Neurons are labelled with green fluorescence protein through electroporation. They are the auditory nuclei in chicken brainstem, take part in sound localization, which allows chicken to determine where a sound is coming from. The solid line represents the border of the hindbrain section, the dash lines indicate the border of NM and the NL respectively.

Understanding the neural mechanisms of mating in malaria mosquitoes

Each year, malaria transmitted by mosquitoes causes around 600,000 deaths. Despite its global health priority, the neuroscience of mosquito mating behaviour is not well understood. The malaria mosquitoes mating behaviour is sexually dimorphic, occurring at dusk in male-dominated swarms, where males locate females acoustically.

The role of audition in mating is behaviourally and sexually dimorphic. At dusk, male mosquitoes retune their ears to amplify female sounds, increase their own flight tones to enhance audibility of the females’, and show phonotactic responses. In contrast, female mosquitoes do not morphologically alter their ears, flight tones, nor show phonotactic responses, and their ears contain half as many neurons as males.

Given the importance of the auditory pathways for mosquito reproduction, a deeper understanding of the underlying circuit could offer novel vector control strategies. Furthermore, this project will shed light on a fundamental neuroscience question: how auditory modulations influence behavioural outcomes.

In the lab, we are using single-nuclei RNA sequencing, spatial transcriptomics, genetic manipulation, and behavioural studies to uncover which neuronal populations are involved in auditory-based mating behaviour, where such populations are located, and how they orchestrate distinct behaviours.

Legend: Cross section of the malaria-transmitting mosquito inner ear labelling GABAA receptor (red), neuronal tracks (green), and nuclei (blue).

Credit A Suppermpool.