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Genetic background of Prop1(df) mutants provides remarkable protection against hypothyroidism-induced hearing impairment.

Fang Q, Giordimaina AM, Dolan DF, Camper SA, Mustapha M - J. Assoc. Res. Otolaryngol. (2011)

Bottom Line: Using embryo transfer, we discovered that factors intrinsic to the fetus are the major contributor to this difference, not maternal effects.The endocochlear potential and KCNJ10 immunostaining in the stria vascularis are indistinguishable from wild type, and no differences in neurofilament or synaptophysin staining are evident in Prop1(df) mutants.Prop1(df) mutants exhibit persistent, abnormal expression of otoferlin in apical OHC, suggesting delayed maturation of synaptic function.

View Article: PubMed Central - PubMed

Affiliation: Department of Human Genetics, University of Michigan, 4945 Buhl, 1241 E Catherine St., Ann Arbor, MI 48109-5618, USA.

ABSTRACT
Hypothyroidism is a cause of genetic and environmentally induced deafness. The sensitivity of cochlear development and function to thyroid hormone (TH) mandates understanding TH action in this sensory organ. Prop1(df) and Pou1f1(dw) mutant mice carry mutations in different pituitary transcription factors, each resulting in pituitary thyrotropin deficiency. Despite the same lack of detectable serum TH, these mutants have very different hearing abilities: Prop1(df) mutants are mildly affected, while Pou1f1(dw) mutants are completely deaf. Genetic studies show that this difference is attributable to the genetic backgrounds. Using embryo transfer, we discovered that factors intrinsic to the fetus are the major contributor to this difference, not maternal effects. We analyzed Prop1(df) mutants to identify processes in cochlear development that are disrupted in other hypothyroid animal models but protected in Prop1(df) mutants by the genetic background. The development of outer hair cell (OHC) function is delayed, but Prestin and KCNQ4 immunostaining appear normal in mature Prop1(df) mutants. The endocochlear potential and KCNJ10 immunostaining in the stria vascularis are indistinguishable from wild type, and no differences in neurofilament or synaptophysin staining are evident in Prop1(df) mutants. The synaptic vesicle protein otoferlin normally shifts expression from OHC to IHC as temporary afferent fibers beneath the OHC regress postnatally. Prop1(df) mutants exhibit persistent, abnormal expression of otoferlin in apical OHC, suggesting delayed maturation of synaptic function. Thus, the genetic background of Prop1(df) mutants is remarkably protective for most functions affected in other hypothyroid mice. The Prop1(df) mutant is an attractive model for identifying the genes that protect against deafness.

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Neurite growth and synaptogenesis of OHCs are grossly unaffected in Prop1df mutants. A Synaptophysin, a presynaptic marker of efferent fibers, is stained on whole mount preparations of cochlear epithelia with an anti-synaptophysin antibody (green). B Neurofilament protein (NF-200) immunostaining was used to detect the neurite outgrowth in cochlea whole mounts of P28 mutants as well as wild-type controls. Prestin immunostaining was used to indicate the position of OHCs (red).
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Fig5: Neurite growth and synaptogenesis of OHCs are grossly unaffected in Prop1df mutants. A Synaptophysin, a presynaptic marker of efferent fibers, is stained on whole mount preparations of cochlear epithelia with an anti-synaptophysin antibody (green). B Neurofilament protein (NF-200) immunostaining was used to detect the neurite outgrowth in cochlea whole mounts of P28 mutants as well as wild-type controls. Prestin immunostaining was used to indicate the position of OHCs (red).

Mentions: The maturation of the nervous system in the rodent cochlea takes place during the first two postnatal weeks of life, which overlaps with the critical time window of TH function (Knipper et al. 2000). TH deprivation causes abnormalities in cochlear innervation and synaptogenesis in multiple hypothyroid animal models (Uziel et al. 1983; Brandt et al. 2007; Sendin et al. 2007). Abnormal efferent fibers have been observed by dye injections in hypothyroid rats even though the olivocochlear neurons, from which the efferent fibers arise, are normal in number and distribution (Cantos et al. 2000, 2003). Neuronal marker proteins are also frequently used for examination of the innervation patterns. We used antibodies that recognize neurofilament protein NF-200, which stains both afferent and efferent fibers, to detect neurite outgrowth in Prop1df/df mutant cochlea at 4 and 7 weeks. No significant differences were observed in neuronal fibers between mutants and wild types at 4 weeks (Fig. 5B) or 7 weeks (data not shown). Synaptophysin is a presynaptic marker of efferent fibers, which comprise 95% of the fibers innervating OHCs. A strong and normally organized pattern of synaptophysin immunostaining was observed in Prop1df/df mutants (Fig. 5A). Thus, neither the gross neurite outgrowth nor the efferent synaptogenesis of OHCs are apparently affected by low TH levels in DF/B-Prop1df/df mice.FIG. 5


Genetic background of Prop1(df) mutants provides remarkable protection against hypothyroidism-induced hearing impairment.

Fang Q, Giordimaina AM, Dolan DF, Camper SA, Mustapha M - J. Assoc. Res. Otolaryngol. (2011)

Neurite growth and synaptogenesis of OHCs are grossly unaffected in Prop1df mutants. A Synaptophysin, a presynaptic marker of efferent fibers, is stained on whole mount preparations of cochlear epithelia with an anti-synaptophysin antibody (green). B Neurofilament protein (NF-200) immunostaining was used to detect the neurite outgrowth in cochlea whole mounts of P28 mutants as well as wild-type controls. Prestin immunostaining was used to indicate the position of OHCs (red).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3298611&req=5

Fig5: Neurite growth and synaptogenesis of OHCs are grossly unaffected in Prop1df mutants. A Synaptophysin, a presynaptic marker of efferent fibers, is stained on whole mount preparations of cochlear epithelia with an anti-synaptophysin antibody (green). B Neurofilament protein (NF-200) immunostaining was used to detect the neurite outgrowth in cochlea whole mounts of P28 mutants as well as wild-type controls. Prestin immunostaining was used to indicate the position of OHCs (red).
Mentions: The maturation of the nervous system in the rodent cochlea takes place during the first two postnatal weeks of life, which overlaps with the critical time window of TH function (Knipper et al. 2000). TH deprivation causes abnormalities in cochlear innervation and synaptogenesis in multiple hypothyroid animal models (Uziel et al. 1983; Brandt et al. 2007; Sendin et al. 2007). Abnormal efferent fibers have been observed by dye injections in hypothyroid rats even though the olivocochlear neurons, from which the efferent fibers arise, are normal in number and distribution (Cantos et al. 2000, 2003). Neuronal marker proteins are also frequently used for examination of the innervation patterns. We used antibodies that recognize neurofilament protein NF-200, which stains both afferent and efferent fibers, to detect neurite outgrowth in Prop1df/df mutant cochlea at 4 and 7 weeks. No significant differences were observed in neuronal fibers between mutants and wild types at 4 weeks (Fig. 5B) or 7 weeks (data not shown). Synaptophysin is a presynaptic marker of efferent fibers, which comprise 95% of the fibers innervating OHCs. A strong and normally organized pattern of synaptophysin immunostaining was observed in Prop1df/df mutants (Fig. 5A). Thus, neither the gross neurite outgrowth nor the efferent synaptogenesis of OHCs are apparently affected by low TH levels in DF/B-Prop1df/df mice.FIG. 5

Bottom Line: Using embryo transfer, we discovered that factors intrinsic to the fetus are the major contributor to this difference, not maternal effects.The endocochlear potential and KCNJ10 immunostaining in the stria vascularis are indistinguishable from wild type, and no differences in neurofilament or synaptophysin staining are evident in Prop1(df) mutants.Prop1(df) mutants exhibit persistent, abnormal expression of otoferlin in apical OHC, suggesting delayed maturation of synaptic function.

View Article: PubMed Central - PubMed

Affiliation: Department of Human Genetics, University of Michigan, 4945 Buhl, 1241 E Catherine St., Ann Arbor, MI 48109-5618, USA.

ABSTRACT
Hypothyroidism is a cause of genetic and environmentally induced deafness. The sensitivity of cochlear development and function to thyroid hormone (TH) mandates understanding TH action in this sensory organ. Prop1(df) and Pou1f1(dw) mutant mice carry mutations in different pituitary transcription factors, each resulting in pituitary thyrotropin deficiency. Despite the same lack of detectable serum TH, these mutants have very different hearing abilities: Prop1(df) mutants are mildly affected, while Pou1f1(dw) mutants are completely deaf. Genetic studies show that this difference is attributable to the genetic backgrounds. Using embryo transfer, we discovered that factors intrinsic to the fetus are the major contributor to this difference, not maternal effects. We analyzed Prop1(df) mutants to identify processes in cochlear development that are disrupted in other hypothyroid animal models but protected in Prop1(df) mutants by the genetic background. The development of outer hair cell (OHC) function is delayed, but Prestin and KCNQ4 immunostaining appear normal in mature Prop1(df) mutants. The endocochlear potential and KCNJ10 immunostaining in the stria vascularis are indistinguishable from wild type, and no differences in neurofilament or synaptophysin staining are evident in Prop1(df) mutants. The synaptic vesicle protein otoferlin normally shifts expression from OHC to IHC as temporary afferent fibers beneath the OHC regress postnatally. Prop1(df) mutants exhibit persistent, abnormal expression of otoferlin in apical OHC, suggesting delayed maturation of synaptic function. Thus, the genetic background of Prop1(df) mutants is remarkably protective for most functions affected in other hypothyroid mice. The Prop1(df) mutant is an attractive model for identifying the genes that protect against deafness.

Show MeSH
Related in: MedlinePlus