PMC:3886832 / 28272-36541 JSONTXT

{"project":"2_test","denotations":[{"id":"24416530-19416898-69475142","span":{"begin":122,"end":124},"obj":"19416898"},{"id":"24416530-19416898-69475142","span":{"begin":122,"end":124},"obj":"19416898"},{"id":"24416530-15919954-69475143","span":{"begin":125,"end":127},"obj":"15919954"},{"id":"24416530-15919954-69475143","span":{"begin":125,"end":127},"obj":"15919954"},{"id":"24416530-20203184-69475144","span":{"begin":128,"end":130},"obj":"20203184"},{"id":"24416530-20203184-69475144","span":{"begin":128,"end":130},"obj":"20203184"},{"id":"24416530-16904081-69475145","span":{"begin":131,"end":133},"obj":"16904081"},{"id":"24416530-16904081-69475145","span":{"begin":131,"end":133},"obj":"16904081"},{"id":"24416530-16904081-69475146","span":{"begin":243,"end":245},"obj":"16904081"},{"id":"24416530-16904081-69475146","span":{"begin":243,"end":245},"obj":"16904081"},{"id":"24416530-20203184-69475147","span":{"begin":300,"end":302},"obj":"20203184"},{"id":"24416530-20203184-69475147","span":{"begin":300,"end":302},"obj":"20203184"},{"id":"24416530-19363479-69475148","span":{"begin":386,"end":388},"obj":"19363479"},{"id":"24416530-19363479-69475148","span":{"begin":386,"end":388},"obj":"19363479"},{"id":"24416530-16904081-69475149","span":{"begin":562,"end":564},"obj":"16904081"},{"id":"24416530-16904081-69475149","span":{"begin":562,"end":564},"obj":"16904081"},{"id":"24416530-20467336-69475150","span":{"begin":869,"end":871},"obj":"20467336"},{"id":"24416530-20467336-69475150","span":{"begin":869,"end":871},"obj":"20467336"},{"id":"24416530-15919954-69475151","span":{"begin":917,"end":919},"obj":"15919954"},{"id":"24416530-15919954-69475151","span":{"begin":917,"end":919},"obj":"15919954"},{"id":"24416530-20467336-69475152","span":{"begin":1138,"end":1140},"obj":"20467336"},{"id":"24416530-20467336-69475152","span":{"begin":1138,"end":1140},"obj":"20467336"},{"id":"24416530-16904081-69475153","span":{"begin":1337,"end":1339},"obj":"16904081"},{"id":"24416530-16904081-69475153","span":{"begin":1337,"end":1339},"obj":"16904081"},{"id":"24416530-19416898-69475154","span":{"begin":1510,"end":1512},"obj":"19416898"},{"id":"24416530-19416898-69475154","span":{"begin":1510,"end":1512},"obj":"19416898"},{"id":"24416530-20203184-69475155","span":{"begin":1659,"end":1661},"obj":"20203184"},{"id":"24416530-20203184-69475155","span":{"begin":1659,"end":1661},"obj":"20203184"},{"id":"24416530-20203184-69475156","span":{"begin":2027,"end":2029},"obj":"20203184"},{"id":"24416530-20203184-69475156","span":{"begin":2027,"end":2029},"obj":"20203184"},{"id":"24416530-10706289-69475157","span":{"begin":2215,"end":2217},"obj":"10706289"},{"id":"24416530-10706289-69475157","span":{"begin":2215,"end":2217},"obj":"10706289"},{"id":"24416530-17765873-69475158","span":{"begin":2337,"end":2339},"obj":"17765873"},{"id":"24416530-17765873-69475158","span":{"begin":2337,"end":2339},"obj":"17765873"},{"id":"24416530-17765873-69475159","span":{"begin":2654,"end":2656},"obj":"17765873"},{"id":"24416530-17765873-69475159","span":{"begin":2654,"end":2656},"obj":"17765873"},{"id":"24416530-23472202-69475160","span":{"begin":2762,"end":2764},"obj":"23472202"},{"id":"24416530-23472202-69475160","span":{"begin":2762,"end":2764},"obj":"23472202"},{"id":"24416530-23646144-69475161","span":{"begin":3103,"end":3105},"obj":"23646144"},{"id":"24416530-23646144-69475161","span":{"begin":3103,"end":3105},"obj":"23646144"},{"id":"24416530-19416898-69475162","span":{"begin":3232,"end":3234},"obj":"19416898"},{"id":"24416530-19416898-69475162","span":{"begin":3232,"end":3234},"obj":"19416898"},{"id":"24416530-16904081-69475163","span":{"begin":3372,"end":3374},"obj":"16904081"},{"id":"24416530-16904081-69475163","span":{"begin":3372,"end":3374},"obj":"16904081"},{"id":"24416530-16904081-69475164","span":{"begin":3727,"end":3729},"obj":"16904081"},{"id":"24416530-16904081-69475164","span":{"begin":3727,"end":3729},"obj":"16904081"},{"id":"24416530-21316421-69475165","span":{"begin":3861,"end":3863},"obj":"21316421"},{"id":"24416530-21316421-69475165","span":{"begin":3861,"end":3863},"obj":"21316421"},{"id":"24416530-20634979-69475166","span":{"begin":4078,"end":4080},"obj":"20634979"},{"id":"24416530-20634979-69475166","span":{"begin":4078,"end":4080},"obj":"20634979"},{"id":"24416530-16904081-69475167","span":{"begin":4220,"end":4222},"obj":"16904081"},{"id":"24416530-16904081-69475167","span":{"begin":4220,"end":4222},"obj":"16904081"},{"id":"24416530-23646144-69475168","span":{"begin":4330,"end":4332},"obj":"23646144"},{"id":"24416530-23646144-69475168","span":{"begin":4330,"end":4332},"obj":"23646144"},{"id":"24416530-23472202-69475169","span":{"begin":4732,"end":4734},"obj":"23472202"},{"id":"24416530-23472202-69475169","span":{"begin":4732,"end":4734},"obj":"23472202"},{"id":"24416530-23472202-69475170","span":{"begin":4830,"end":4832},"obj":"23472202"},{"id":"24416530-23472202-69475170","span":{"begin":4830,"end":4832},"obj":"23472202"},{"id":"24416530-23646144-69475171","span":{"begin":4984,"end":4986},"obj":"23646144"},{"id":"24416530-23646144-69475171","span":{"begin":4984,"end":4986},"obj":"23646144"},{"id":"24416530-23472202-69475172","span":{"begin":5578,"end":5580},"obj":"23472202"},{"id":"24416530-23472202-69475172","span":{"begin":5578,"end":5580},"obj":"23472202"},{"id":"24416530-19363478-69475173","span":{"begin":5703,"end":5705},"obj":"19363478"},{"id":"24416530-19363478-69475173","span":{"begin":5703,"end":5705},"obj":"19363478"},{"id":"24416530-19363479-69475174","span":{"begin":5706,"end":5708},"obj":"19363479"},{"id":"24416530-19363479-69475174","span":{"begin":5706,"end":5708},"obj":"19363479"},{"id":"24416530-19363479-69475175","span":{"begin":6073,"end":6075},"obj":"19363479"},{"id":"24416530-19363479-69475175","span":{"begin":6073,"end":6075},"obj":"19363479"},{"id":"24416530-19363478-69475176","span":{"begin":6366,"end":6368},"obj":"19363478"},{"id":"24416530-19363478-69475176","span":{"begin":6366,"end":6368},"obj":"19363478"},{"id":"24416530-16904081-69475177","span":{"begin":6987,"end":6989},"obj":"16904081"},{"id":"24416530-16904081-69475177","span":{"begin":6987,"end":6989},"obj":"16904081"},{"id":"24416530-23472202-69475178","span":{"begin":7011,"end":7013},"obj":"23472202"},{"id":"24416530-23472202-69475178","span":{"begin":7011,"end":7013},"obj":"23472202"},{"id":"24416530-17765873-69475179","span":{"begin":7041,"end":7043},"obj":"17765873"},{"id":"24416530-17765873-69475179","span":{"begin":7041,"end":7043},"obj":"17765873"},{"id":"24416530-23472202-69475180","span":{"begin":7598,"end":7600},"obj":"23472202"},{"id":"24416530-23472202-69475180","span":{"begin":7598,"end":7600},"obj":"23472202"},{"id":"24416530-19363478-69475181","span":{"begin":7696,"end":7698},"obj":"19363478"},{"id":"24416530-19363478-69475181","span":{"begin":7696,"end":7698},"obj":"19363478"},{"id":"24416530-23472202-69475182","span":{"begin":7750,"end":7752},"obj":"23472202"},{"id":"24416530-23472202-69475182","span":{"begin":7750,"end":7752},"obj":"23472202"},{"id":"24416530-15846349-69475183","span":{"begin":7876,"end":7878},"obj":"15846349"},{"id":"24416530-15846349-69475183","span":{"begin":7876,"end":7878},"obj":"15846349"},{"id":"T35364","span":{"begin":122,"end":124},"obj":"19416898"},{"id":"T64240","span":{"begin":122,"end":124},"obj":"19416898"},{"id":"T24698","span":{"begin":125,"end":127},"obj":"15919954"},{"id":"T85948","span":{"begin":125,"end":127},"obj":"15919954"},{"id":"T40458","span":{"begin":128,"end":130},"obj":"20203184"},{"id":"T66935","span":{"begin":128,"end":130},"obj":"20203184"},{"id":"T21325","span":{"begin":131,"end":133},"obj":"16904081"},{"id":"T55661","span":{"begin":131,"end":133},"obj":"16904081"},{"id":"T10959","span":{"begin":243,"end":245},"obj":"16904081"},{"id":"T88767","span":{"begin":243,"end":245},"obj":"16904081"},{"id":"T38967","span":{"begin":300,"end":302},"obj":"20203184"},{"id":"T77891","span":{"begin":300,"end":302},"obj":"20203184"},{"id":"T91621","span":{"begin":386,"end":388},"obj":"19363479"},{"id":"T74853","span":{"begin":386,"end":388},"obj":"19363479"},{"id":"T56614","span":{"begin":562,"end":564},"obj":"16904081"},{"id":"T70415","span":{"begin":562,"end":564},"obj":"16904081"},{"id":"T67782","span":{"begin":869,"end":871},"obj":"20467336"},{"id":"T2037","span":{"begin":869,"end":871},"obj":"20467336"},{"id":"T91931","span":{"begin":917,"end":919},"obj":"15919954"},{"id":"T96310","span":{"begin":917,"end":919},"obj":"15919954"},{"id":"T33992","span":{"begin":1138,"end":1140},"obj":"20467336"},{"id":"T31485","span":{"begin":1138,"end":1140},"obj":"20467336"},{"id":"T95445","span":{"begin":1337,"end":1339},"obj":"16904081"},{"id":"T55368","span":{"begin":1337,"end":1339},"obj":"16904081"},{"id":"T47472","span":{"begin":1510,"end":1512},"obj":"19416898"},{"id":"T82500","span":{"begin":1510,"end":1512},"obj":"19416898"},{"id":"T50495","span":{"begin":1659,"end":1661},"obj":"20203184"},{"id":"T6935","span":{"begin":1659,"end":1661},"obj":"20203184"},{"id":"T45537","span":{"begin":2027,"end":2029},"obj":"20203184"},{"id":"T40891","span":{"begin":2027,"end":2029},"obj":"20203184"},{"id":"T52949","span":{"begin":2215,"end":2217},"obj":"10706289"},{"id":"T61649","span":{"begin":2215,"end":2217},"obj":"10706289"},{"id":"T41636","span":{"begin":2337,"end":2339},"obj":"17765873"},{"id":"T15900","span":{"begin":2337,"end":2339},"obj":"17765873"},{"id":"T10567","span":{"begin":2654,"end":2656},"obj":"17765873"},{"id":"T9160","span":{"begin":2654,"end":2656},"obj":"17765873"},{"id":"T68646","span":{"begin":2762,"end":2764},"obj":"23472202"},{"id":"T60212","span":{"begin":2762,"end":2764},"obj":"23472202"},{"id":"T67528","span":{"begin":3103,"end":3105},"obj":"23646144"},{"id":"T13077","span":{"begin":3103,"end":3105},"obj":"23646144"},{"id":"T54974","span":{"begin":3232,"end":3234},"obj":"19416898"},{"id":"T52997","span":{"begin":3232,"end":3234},"obj":"19416898"},{"id":"T4367","span":{"begin":3372,"end":3374},"obj":"16904081"},{"id":"T63180","span":{"begin":3372,"end":3374},"obj":"16904081"},{"id":"T13503","span":{"begin":3727,"end":3729},"obj":"16904081"},{"id":"T157","span":{"begin":3727,"end":3729},"obj":"16904081"},{"id":"T9575","span":{"begin":3861,"end":3863},"obj":"21316421"},{"id":"T94046","span":{"begin":3861,"end":3863},"obj":"21316421"},{"id":"T15126","span":{"begin":4078,"end":4080},"obj":"20634979"},{"id":"T11805","span":{"begin":4078,"end":4080},"obj":"20634979"},{"id":"T87142","span":{"begin":4220,"end":4222},"obj":"16904081"},{"id":"T16971","span":{"begin":4220,"end":4222},"obj":"16904081"},{"id":"T10806","span":{"begin":4330,"end":4332},"obj":"23646144"},{"id":"T145","span":{"begin":4330,"end":4332},"obj":"23646144"},{"id":"T59252","span":{"begin":4732,"end":4734},"obj":"23472202"},{"id":"T21103","span":{"begin":4732,"end":4734},"obj":"23472202"},{"id":"T23261","span":{"begin":4830,"end":4832},"obj":"23472202"},{"id":"T54410","span":{"begin":4830,"end":4832},"obj":"23472202"},{"id":"T97040","span":{"begin":4984,"end":4986},"obj":"23646144"},{"id":"T30825","span":{"begin":4984,"end":4986},"obj":"23646144"},{"id":"T17932","span":{"begin":5578,"end":5580},"obj":"23472202"},{"id":"T9987","span":{"begin":5578,"end":5580},"obj":"23472202"},{"id":"T66187","span":{"begin":5703,"end":5705},"obj":"19363478"},{"id":"T31453","span":{"begin":5703,"end":5705},"obj":"19363478"},{"id":"T37696","span":{"begin":5706,"end":5708},"obj":"19363479"},{"id":"T40401","span":{"begin":5706,"end":5708},"obj":"19363479"},{"id":"T52520","span":{"begin":6073,"end":6075},"obj":"19363479"},{"id":"T16107","span":{"begin":6073,"end":6075},"obj":"19363479"},{"id":"T61722","span":{"begin":6366,"end":6368},"obj":"19363478"},{"id":"T63005","span":{"begin":6366,"end":6368},"obj":"19363478"},{"id":"T17962","span":{"begin":6987,"end":6989},"obj":"16904081"},{"id":"T85551","span":{"begin":6987,"end":6989},"obj":"16904081"},{"id":"T67802","span":{"begin":7011,"end":7013},"obj":"23472202"},{"id":"T54766","span":{"begin":7011,"end":7013},"obj":"23472202"},{"id":"T84325","span":{"begin":7041,"end":7043},"obj":"17765873"},{"id":"T49895","span":{"begin":7041,"end":7043},"obj":"17765873"},{"id":"T6895","span":{"begin":7598,"end":7600},"obj":"23472202"},{"id":"T85528","span":{"begin":7598,"end":7600},"obj":"23472202"},{"id":"T97675","span":{"begin":7696,"end":7698},"obj":"19363478"},{"id":"T54266","span":{"begin":7696,"end":7698},"obj":"19363478"},{"id":"T51054","span":{"begin":7750,"end":7752},"obj":"23472202"},{"id":"T37573","span":{"begin":7750,"end":7752},"obj":"23472202"},{"id":"T92630","span":{"begin":7876,"end":7878},"obj":"15846349"},{"id":"T31134","span":{"begin":7876,"end":7878},"obj":"15846349"}],"text":"4.2. Important miRNA Clusters in the Inner Ear\nOne of the most widely studied miRNA groups is the miR-183/182/96 cluster [73,74,77,78]. miR-183, miR-182 and miR-96 are expressed from the cluster as a polycistronic unit in the mouse inner ear [78]. miR-183 controls the differentiation of hair cells [77], while mutations in the miR-96 seed region are associated with hearing disorders [89]. This cluster showed strong expression of mature miR-183, miR-182 and miR-96 in the hair cells of both mouse cochlea and vestibule at P0, but the levels of pri-miR-183/96 [78] and miR-183 [88] varied between the hair cells in the apex and base of the cochlea. This signifies that hair cells at different locations in the inner ear may process miRNAs differently. Expression of the miRNAs from this cluster has also been identified in the embryonic stages of the mouse inner ear [79] and in zebrafish hair cells and neuromasts [74], indicating a high degree of conservation between organisms. Interestingly, the expression pattern of miR-182 was broad in many embryonic tissues, but confined specifically to the inner ear during post-natal periods [79]. In mouse, the levels of miR-183, miR-182 and miR-96 changed over developmental time between P0 and P100. Notably, miR-183 and miR-96 were upregulated during adult stages, while miR-182 was not [78]. Another group identified the expression of antisense miR-182 in the mouse cochlea and vestibule at P0, suggesting potential downregulation of miR-182 in the inner ear [73]. Inhibition of miR-183 in zebrafish using morpholinos decreased the number of hair cells in sensory macula in both the inner ear and neuromasts [77]. Overexpression of either miR-182 or miR-96 in zebrafish embryos showed duplicated otic vesicles and an increase in the number of ectopic hair cells, suggesting that these miRNAs can control hair cell fate during development. Morpholinos targeted towards either miR-182/miR-183, miR-96 or miR-183/182/96 all decreased hair cell numbers in the zebrafish inner ear [77].\nLet-7 family members are another class of widely studied miRNAs in the inner ear, and members of this family specify transition of cells from larval to the adult stage in C. elegans [90]. In salamanders, let-7 family members were found to be regulated during regeneration of a labyrinth culture in vitro [86]. Treatment of adult newt labyrinth with gentamicin caused hair cell death, and gene expression studies indicated let-7g and let-7c were downregulated while let-7a and let-7e were upregulated at day 7 following gentamicin treatment. All members from let-7a through let-7g were found to be downregulated at day 12 [86]. Adult mice exposed to acoustic overstimulation showed expression of let-7a, 7b, 7d, 7e, 7f, 7g and 7i [83]. Since both antibiotic treatment and acoustic overexposure regulate let7 miRNAs, this indicates a common pathway for hair cell degeneration. miRNA profiling in normal aging mice revealed upregulation of let-7a, 7b, 7c, 7e, 7f, 7g and 7i miRNAs, suggesting they may regulate pro-apoptotic pathways, leading to degeneration of hair cells [82]. In another study, let-7a and let-7b showed opposite expression profiles between cochlea and vestibule in the newborn mouse [73]. During the development of the mouse inner ear, members of let7 family (let7a–let7i) were differentially expressed between P0 and P100 [78]. An interesting observation from this study is that all the let7 members were downregulated at the P21 developmental time point, while most let7 members were upregulated in the P35 and P100 adult stages. Let-7e was downregulated at all five time points analyzed, suggesting it may be a negative regulator for the growth of auditory sensory epithelia [78].\nMiR-181 is known to cause proliferation of hair cells in the chicken inner ear and inhibition of miR-181a reduces proliferation [85]. Consistent with this, overexpression of miR-181a in the chick basilar papillae in vitro showed an increase in the number of hair cells, and this proliferative effect can be enhanced by the addition of forskolin [84]. Upregulation of miR-181a and miR-181b in the chick inner ear was found at P0 and P8, and it gradually decreases towards the adult stage [78]. miR-181a, miR-181c and miR-181d were downregulated in two normal aging mouse models, C57BL/6J and CBA/J [82], implying that aging can lead to decreased levels of miR-181, which then inhibits proliferation. This suggests that during the early post-natal growth of the inner ear, miR-181 is required, but may not be necessary during the adult stage. However, adult rats showed expression levels of miR-181a that were different from the mouse inner ear, suggesting species-specific differences may also exist [83]. \nAcoustic trauma caused downregulation of miR-183 approximately three-fold in rat inner ear [83]. Age-related hearing loss was associated with the downregulation of miR-183 at three months of age in C57BL/6J mice and at nine months in CBA/J mice [82]. The discrepancies in the onset of downregulation of miR-183 can partly be attributed to the different genetic backgrounds of these mouse models. C57BL/6J mice have the presence of the Ahl gene, which causes deficiencies in cadherin23. This suggests that interference with genes essential for normal hair cell functioning can cause rapid loss of hair cells in these models. miR-183 was downregulated in the cochlea of acoustically-overexposed rats, and then, computational analyses predicted that this downregulation could be potentially associated with cell death and apoptotic functions [83]. \nMutations in the seed regions of miRNAs are reported to segregate with hearing disorders and cause Mendelian diseases [71,89]. Any changes to the conserved seed region in the miRNA cause disruptions in base pairing to its target mRNAs. A study of Spanish patients reported mutations identified in the seed region of miR-96 in the fourth (G \u003e A) and fifth (C \u003e A) nucleotides that are highly conserved between 14 different organisms. These mutations were associated with hearing disorders [89]. The diminuendo (Dmdo) mouse model has an N-ethyl-N-nitrosourea-induced mutation at the sixth nucleotide (A \u003e T) within the seed region of miR-96. This mutation caused a severe hair cell degeneration phenotype in both heterozygotes and homozygotes, with the latter having a quicker onset [71]. Mutations in miR-96 caused a shift in the global gene expression profile with almost 90 direct, indirect and acquired target genes. A novel mutation in the stem region of miR-96 (+57T \u003e C) was identified in non-syndromic sensorineural hearing loss patients [91]. Although this mutation is not in the seed region, it was reported to decrease the levels of both miR-96 and antisense miR-96. \nIn summary, miRNAs can regulate mRNAs at the post-transcriptional level by binding to their target molecules. Global change in miRNA expression profiles have been documented with both pre- and mature forms during development [78], acoustic exposure [83] and antibiotic treatment [86]. Studies using conditional Dicer knockout in the mouse inner ear clearly demonstrated that mature miRNAs are important for the morphology and development of hair cells. A single miRNA can have multiple target mRNAs, which indirectly controls the expression of many genes and affects many cellular pathways. Bioinformatic analyses have revealed many potential targets for miRNAs expressed in the inner ear that can be categorized into functions, such as cell death, cell proliferation, RNA metabolic processes, Wnt signaling and protein kinase cascades [83]. For example, the targets for miR-96 were identified to be Aqp5, Celsr2, Odf2, Myrip and Ryk [71] and for miR-182, Sox2 [88], Egr1, Irs1 and Taok1 [83], using luciferase assays. Reduced Sox2 levels in the mouse inner ear causes hearing impairments and severe malformations [92]. It is quite clear from these studies that non-coding miRNAs play an important role in regulating mRNA transcripts post-transcriptionally. Currently, only a handful of targets are known for miRNAs. Although profiling studies and computational analyses can predict mRNA targets, further experimental validation is required to show if they are indeed true targets of the miRNAs of interest.\n"}