Browsing by Author "Burt, Rachel"

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    Anti-apoptotic gene Bcl2 is required for stapes development and hearing
    (Macmillan Publishers Limited, 2012-08-09) Carpinelli, Marina; Wise, Andrew; Arhatari, Benedicta; Bouillet, Phillipe; Manji, Shehnaaz; Manning, Michael; Cooray, Anne; Burt, Rachel
    In this paper we describe novel and specific roles for the apoptotic regulators Bcl2 and Bim in hearing and stapes development. Bcl2 is anti-apoptotic while Bim is pro-apoptotic. Characterization of the auditory systems of mice deficient for these molecules revealed that Bcl2 / mice suffered severe hearing loss. This was conductive in nature and did not affect sensory cells of the inner ear, with cochlear hair cells and neurons present and functional. Bcl2 / mice were found to have a malformed, often monocrural, porous stapes (the small stirrup-shaped bone of the middle ear), but a normally shaped malleus and incus. The deformed stapes was discontinuous with the incus and sometimes fused to the temporal bones. The defect was completely rescued in Bcl2 / Bim / mice and partially rescued in Bcl2 / Bimþ/ mice, which displayed high-frequency hearing loss and thickening of the stapes anterior crus. The Bcl2 / defect arose in utero before or during the cartilage stage of stapes development. These results implicate Bcl2 and Bim in regulating survival of second pharyngeal arch or neural crest cells that give rise to the stapes during embryonic development.
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    Organotypic Culture of Neonatal Murine Inner Ear Explants
    (Frontiers, 2019-05) Ogier, Jacqueline; Burt, Rachel; Drury, Hannah; Lim, Rebecca; Nayagam, Bryony
    The inner ear is a complex organ containing highly specialised cell types and structures that are critical for sensing sound and movement. In vivo, the inner ear is difficult to study due to the osseous nature of the otic capsule and its encapsulation within an intricate bony labyrinth. As such, mammalian inner ear explants are an invaluable tool for the study and manipulation of the complex intercellular connections, structures, and cell types within this specialised organ. The greatest strength of this technique is that the complete organ of Corti, or peripheral vestibular organs including hair cells, supporting cells and accompanying neurons, is maintained in its in situ form. The greatest weakness of in vitro hair cell preparations is the short time frame in which the explanted tissue remains viable. Yet, cochlear explants have proven to be an excellent experimental model for understanding the fundamental aspects of auditory biology, substantiated by their use for over 40 years. In this protocol, we present a modernised inner ear explant technique that employs organotypic cell culture inserts and serum free media. This approach decreases the likelihood of explant damage by eliminating the need for adhesive substances. Serum free media also restricts excessive cellular outgrowth and inter-experimental variability, both of which are side effects of exogenous serum addition to cell cultures. The protocol described can be applied to culture both cochlear and vestibular explants from various mammals. Example outcomes are demonstrated by immunohistochemistry, hair cell quantification, and electrophysiological recordings to validate the versatility and viability of the protocol.
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    Vitamin D-deficient diet rescues hearing loss in Klotho mice
    (Elsevier, 2010-12-08) Carpinelli, Marina; Wise, Andrew; Burt, Rachel
    Klotho-deficient mice exhibit a premature aging syndrome, a feature of which is mild hearing loss. In the present study, the hearing phenotype of Klotho mice was characterized to better determine how well this phenotype resembles presbycusis in humans. It was demonstrated that Klotho animals have auditory-evoked brainstem response (ABR) threshold shifts of 14e18 dB in response to pure tone stimuli of 4, 8, 16 and 32 kHz, and similarly, in response to clicks; however, cochlear histology and spiral ganglion neuron density appeared normal in these mice. It was further demonstrated that a vitamin D-deficient diet normalizes serum calcitriol (1,25(OH)2D3) levels and prevents hearing loss in Klotho mice. It is concluded that hearing loss in Klotho mice is caused by elevated renal 1a-hydroxylase expression and consequent excessive production of calcitriol. These findings implicate the vitamin D metabolic pathway in hearing loss and pose questions as to the mechanism by which elevated calcitriol levels mediate such hearing loss.