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Mitochondrial Dysfunction and Hearing Loss
Published in Shamim I. Ahmad, Handbook of Mitochondrial Dysfunction, 2019
The epithelium of the inner ear is derived from otic placodes. Recent studies show that FGF-19 (fibroblast growth factor 19) causes the expression of Wnt-8c (Wingless/Integrated 8c) in the rhombencephalon neuroepithelium, which stimulates to form FGF-3 (fibroblast growth factor 3). The FGF family members have many activities, especially around mitogenic and cell survival functions that involve processes that include embryonic development, for example the initiation of inner ear when the FGF-19 chick homolog and Wnt-8c interact.7–9 The FGF-3 gene will act at the end of the 4th week in the embryogenic period, in the transformation of the otic placode first into the otic cup, after that, this one closes off creating the otic vesicle. (see Fig. 3). The Pax-2 homeobox is involved in the early stages of the development of the otic vesicle. If this gene fails, the formation of the cochlea or the spiral ganglion is not possible. For the Semicircular ducts formation, the action of Otx-1 is necessary for the lateral one, and for the rest of them, anterior and posterior, the homeobox Dlx-5.7,9,10
Anatomy of the Cochlea and Vestibular System: Relating Ultrastructure to Function
Published in John C Watkinson, Raymond W Clarke, Christopher P Aldren, Doris-Eva Bamiou, Raymond W Clarke, Richard M Irving, Haytham Kubba, Shakeel R Saeed, Paediatrics, The Ear, Skull Base, 2018
The vestibular system can be generally divided into two parts: the saccule is anatomically a separate chamber from the utricle and the three semicircular canals which arise from and terminate in the utricle and run in orthogonal planes – horizontal (lateral), posterior and superior (anterior) (Figures 47.1a and 47.2a). Not only is there anatomical separation; the utricle and semicircular canals are evolutionarily and developmentally separate from the saccule. In the evolutionarily most primitive extant vertebrates (e.g. hag fish), the inner ear is composed of only two semicircular canals that are continuous with a single utricle-like chamber with a macula.50,51 During ontogenetic development, the utricle and semicircular canals arise on one side of the embryonic otic vesicle, opposite to that of the saccule which develops close to the site at which the cochlea is defined.52 There is thus an anatomical and developmental relationship between the saccule and the cochlea, and in fish and some amphibia, the saccule does have an auditory function.53,54 This biological relationship may be an underlying factor in the sound-induced vertigo and dizziness characteristic of Tullio syndrome.
Growth of the Ear Capsule
Published in D. Dixon Andrew, A.N. Hoyte David, Ronning Olli, Fundamentals of Craniofacial Growth, 2017
Sperber (1989) described the formation of the otic placode. The hindbrain (vestibulocochlear nerve) induces surface ectodermal cells to form the placode, by 21-24 days of intrauterine life (i.u.L). This later, by the 4th week, forms a pit (the otic cup), then an otic vesicle or otocyst, which sinks below the surface ectoderm, (Figure 12.3 traces the developmental stages from otocyst to membranous labyrinth). The cartilaginous otic capsule is induced by the otocyst from surrounding mesenchyme, and this will later form the bony labyrinth, in which the membranous labyrinth is deeply embedded.
Lead and lead–arsenic combined exposure induces mortality and developmental impairments in zebrafish embryos: a study using wild-caught zebrafish from Bangladesh
Published in Drug and Chemical Toxicology, 2022
Nusrat Jahan Toma, Saeed Anwar, Tamanna Kabir, Mohammad Jakir Hosen
Previous reports show that lead, even at low concentrations, causes damage to the inner ear receptor cells and auditory neuronal function resulting in impaired hearing ability in children, physical workers, and older adults (Counter and Buchanan 2002, Chuang et al.2007, Liu and Yan 2007, Carlson and Neitzel 2018, Jamesdaniel et al.2018). Our study observed deformation in the otic vesicle involved in inner ear development in lead-treated embryos. Lead exposure results in irregularities in tailbud formation and growth retardation during the very early embryonic developmental stage. Dorsal curvature in the lead-treated embryos, together with the observations mentioned above, provides a notion that lead disrupts the homeostasis resulting in the dorsal-ventral pattern of embryos.
Transgenic zebrafish larvae as a non-rodent alternative model to assess pro-inflammatory (neutrophil) responses to nanomaterials
Published in Nanotoxicology, 2022
Suzanne Gillies, Rachel Verdon, Vicki Stone, David M. Brown, Theodore Henry, Lang Tran, Carl Tucker, Adriano G. Rossi, Charles R. Tyler, Helinor J. Johnston
All images were analyzed using ImageJ software (Schneider, Rasband, and Eliceiri 2012). For the tail fin injury experiments, a selection area measuring 250 µm in length was applied to the tail fin injury region in ImageJ, so that the right vertical line of the selected area was in line with the transected edge of the tail fin, and all neutrophils within this region were counted manually. For the microinjection images, the otic vesicle was identified by eye and the neutrophils within the vesicle were counted manually using the ImageJ multi-point tool. The neutrophil counts in each image were scored ‘blind’ such that the researcher was not aware of what treatment what being assessed.
Novel compounds protect auditory hair cells against gentamycin-induced apoptosis by maintaining the expression level of H3K4me2
Published in Drug Delivery, 2018
Ao Li, Dan You, Wenyan Li, Yingjie Cui, Yingzi He, Wen Li, Yan Chen, Xiao Feng, Shan Sun, Renjie Chai, Huawei Li
Epigenetic modifications play an important role in the regulation of many chromosomal functions and are closely linked to certain biological events such as transcriptional regulation, cancer development, and cell death (Reik, 2007; Greer & Shi, 2012; Rizzi et al., 2012). More recently, epigenetic factors and non-coding RNAs have emerged as an additional layer of gene regulation in the hearing research field (Doetzlhofer & Avraham, 2017). In inner ear development, recent studies have shown that histone deacetylases 1 and 3 (HDAC1 and HDAC3) are expressed in the developing otic vesicles and play an important role in otic vesicle formation. Knockdown of HDAC1 or HDAC3 in zebrafish embryos induces smaller otic vesicles, abnormal otoliths, malformed or absent semicircular canals, and fewer sensory HCs (He et al., 2016a, 2016b), indicating that epigenetic regulation plays crucial roles in the development of auditory organs. Previous studies of inner ear disease and injury have shown that after exposure to traumatic noise histone H3 lysine 9 acetylation (H3K9ac) is decreased in the nuclei of outer HCs (OHCs), while HDAC1, HDAC2, and HDAC3 are increased in OHCs, and that HDAC inhibitors can significantly reduce OHC loss and attenuate noise-induced hearing loss (Chen et al., 2016). Histone methylation is a major covalent modification that epigenetically regulates cell-specific gene expression patterns (Shi et al., 2004; Wang et al., 2011). Recent studies have highlighted specific functional roles of histone methylation in a variety of cellular processes such as cell differentiation, survival, and death (Rugg-Gunn et al., 2010; Greer & Shi, 2012). Our previous studies showed that the G9a inhibitor BIX01294 protects against neomycin-induced HC loss by inhibiting dimethylation of H3K9 (Yu et al., 2013).