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Mutant huntingtin fragment selectively suppresses Brn-2 POU domain transcription factor to mediate hypothalamic cell dysfunction.

Yamanaka T, Tosaki A, Miyazaki H, Kurosawa M, Furukawa Y, Yamada M, Nukina N - Hum. Mol. Genet. (2010)

Bottom Line: We found a reduction of DNA binding of Brn-2, a POU domain transcription factor involved in differentiation and function of hypothalamic neurosecretory neurons.We provide evidence supporting that Brn-2 loses its function through two pathways, its sequestration by mutant Nhtt and its reduced transcription, leading to reduced expression of hypothalamic neuropeptides.Our data indicate that functional suppression of Brn-2 together with a region-specific lack of compensation by Brn-1 mediates hypothalamic cell dysfunction by mutant Nhtt.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Structural Neuropathology, RIKEN Brain Science Institute, Saitama 351-0198, Japan.

ABSTRACT
In polyglutamine diseases including Huntington's disease (HD), mutant proteins containing expanded polyglutamine stretches form nuclear aggregates in neurons. Although analysis of their disease models suggested a significance of transcriptional dysregulation in these diseases, how it mediates the specific neuronal cell dysfunction remains obscure. Here we performed a comprehensive analysis of altered DNA binding of multiple transcription factors using R6/2 HD model mice brains that express an N-terminal fragment of mutant huntingtin (mutant Nhtt). We found a reduction of DNA binding of Brn-2, a POU domain transcription factor involved in differentiation and function of hypothalamic neurosecretory neurons. We provide evidence supporting that Brn-2 loses its function through two pathways, its sequestration by mutant Nhtt and its reduced transcription, leading to reduced expression of hypothalamic neuropeptides. In contrast to Brn-2, its functionally related protein, Brn-1, was not sequestered by mutant Nhtt but was upregulated in R6/2 brain, except in hypothalamus. Our data indicate that functional suppression of Brn-2 together with a region-specific lack of compensation by Brn-1 mediates hypothalamic cell dysfunction by mutant Nhtt.

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Reduction of mRNA expression of Brn-2 but not Arnt2 in R6/2 hypothalamus. (A and B) Coronal sections from 12-week-old R6/2 (TG) or control (WT) mouse brain were subjected to in situ hybridization using antisense probe for Brn-2 (A) or Arnt2 (B). Three sections from front to back with 200 µm intervals were shown. (C) Brn-2 and Arnt2 signals in PVN were artificially labeled with blue and red, respectively, and merged. Note the drastic reduction of blue signals (Brn-2) compared with red signals (Arnt2) in R6/2 mouse. (D) Quantitative RT–PCR analysis of Brn-2, Arnt2, VP and OT of isolated hypothalamus from 12-week-old R6/2 (TG; n = 3) or control mice (WT; n = 3). As for VP and OT, RT–PCR data for other cerebral regions of one WT and one TG after removal of the hypothalamus are also shown. Values are means ± SD (*P < 0.05, **P < 0.01). Scale bars = 400 µm (A and B) and 100 µm (C).
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DDQ087F7: Reduction of mRNA expression of Brn-2 but not Arnt2 in R6/2 hypothalamus. (A and B) Coronal sections from 12-week-old R6/2 (TG) or control (WT) mouse brain were subjected to in situ hybridization using antisense probe for Brn-2 (A) or Arnt2 (B). Three sections from front to back with 200 µm intervals were shown. (C) Brn-2 and Arnt2 signals in PVN were artificially labeled with blue and red, respectively, and merged. Note the drastic reduction of blue signals (Brn-2) compared with red signals (Arnt2) in R6/2 mouse. (D) Quantitative RT–PCR analysis of Brn-2, Arnt2, VP and OT of isolated hypothalamus from 12-week-old R6/2 (TG; n = 3) or control mice (WT; n = 3). As for VP and OT, RT–PCR data for other cerebral regions of one WT and one TG after removal of the hypothalamus are also shown. Values are means ± SD (*P < 0.05, **P < 0.01). Scale bars = 400 µm (A and B) and 100 µm (C).

Mentions: Unexpectedly, in situ hybridization analysis showed reduction of Brn-2 mRNA in PVN and SON (Fig. 7A). This was confirmed by RT–PCR analysis using isolated hypothalamus; that is, in addition to reductions of VP and OT, Brn-2 mRNA was also reduced in R6/2 hypothalamus (Fig. 7D). Almost no VP or OT mRNAs were detected in the remaining cerebrum after removal of the hypothalamus, supporting the idea that the hypothalamic PVN and SON are contained in isolated tissues (Fig. 7D). The reduction of Brn-2 mRNA seems to be specific to hypothalamus because no alteration of Brn-2 mRNA was observed if we used cerebrum for RT–PCR as described earlier. In addition, in situ hybridization analysis showed no distinct reduction of Brn-2 mRNA in R6/2 cortex (data not shown). Thus, in hypothalamus, reduced transcription of Brn-2 may also contribute to the reduction of functional Brn-2 in R6/2 mice.


Mutant huntingtin fragment selectively suppresses Brn-2 POU domain transcription factor to mediate hypothalamic cell dysfunction.

Yamanaka T, Tosaki A, Miyazaki H, Kurosawa M, Furukawa Y, Yamada M, Nukina N - Hum. Mol. Genet. (2010)

Reduction of mRNA expression of Brn-2 but not Arnt2 in R6/2 hypothalamus. (A and B) Coronal sections from 12-week-old R6/2 (TG) or control (WT) mouse brain were subjected to in situ hybridization using antisense probe for Brn-2 (A) or Arnt2 (B). Three sections from front to back with 200 µm intervals were shown. (C) Brn-2 and Arnt2 signals in PVN were artificially labeled with blue and red, respectively, and merged. Note the drastic reduction of blue signals (Brn-2) compared with red signals (Arnt2) in R6/2 mouse. (D) Quantitative RT–PCR analysis of Brn-2, Arnt2, VP and OT of isolated hypothalamus from 12-week-old R6/2 (TG; n = 3) or control mice (WT; n = 3). As for VP and OT, RT–PCR data for other cerebral regions of one WT and one TG after removal of the hypothalamus are also shown. Values are means ± SD (*P < 0.05, **P < 0.01). Scale bars = 400 µm (A and B) and 100 µm (C).
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2865370&req=5

DDQ087F7: Reduction of mRNA expression of Brn-2 but not Arnt2 in R6/2 hypothalamus. (A and B) Coronal sections from 12-week-old R6/2 (TG) or control (WT) mouse brain were subjected to in situ hybridization using antisense probe for Brn-2 (A) or Arnt2 (B). Three sections from front to back with 200 µm intervals were shown. (C) Brn-2 and Arnt2 signals in PVN were artificially labeled with blue and red, respectively, and merged. Note the drastic reduction of blue signals (Brn-2) compared with red signals (Arnt2) in R6/2 mouse. (D) Quantitative RT–PCR analysis of Brn-2, Arnt2, VP and OT of isolated hypothalamus from 12-week-old R6/2 (TG; n = 3) or control mice (WT; n = 3). As for VP and OT, RT–PCR data for other cerebral regions of one WT and one TG after removal of the hypothalamus are also shown. Values are means ± SD (*P < 0.05, **P < 0.01). Scale bars = 400 µm (A and B) and 100 µm (C).
Mentions: Unexpectedly, in situ hybridization analysis showed reduction of Brn-2 mRNA in PVN and SON (Fig. 7A). This was confirmed by RT–PCR analysis using isolated hypothalamus; that is, in addition to reductions of VP and OT, Brn-2 mRNA was also reduced in R6/2 hypothalamus (Fig. 7D). Almost no VP or OT mRNAs were detected in the remaining cerebrum after removal of the hypothalamus, supporting the idea that the hypothalamic PVN and SON are contained in isolated tissues (Fig. 7D). The reduction of Brn-2 mRNA seems to be specific to hypothalamus because no alteration of Brn-2 mRNA was observed if we used cerebrum for RT–PCR as described earlier. In addition, in situ hybridization analysis showed no distinct reduction of Brn-2 mRNA in R6/2 cortex (data not shown). Thus, in hypothalamus, reduced transcription of Brn-2 may also contribute to the reduction of functional Brn-2 in R6/2 mice.

Bottom Line: We found a reduction of DNA binding of Brn-2, a POU domain transcription factor involved in differentiation and function of hypothalamic neurosecretory neurons.We provide evidence supporting that Brn-2 loses its function through two pathways, its sequestration by mutant Nhtt and its reduced transcription, leading to reduced expression of hypothalamic neuropeptides.Our data indicate that functional suppression of Brn-2 together with a region-specific lack of compensation by Brn-1 mediates hypothalamic cell dysfunction by mutant Nhtt.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Structural Neuropathology, RIKEN Brain Science Institute, Saitama 351-0198, Japan.

ABSTRACT
In polyglutamine diseases including Huntington's disease (HD), mutant proteins containing expanded polyglutamine stretches form nuclear aggregates in neurons. Although analysis of their disease models suggested a significance of transcriptional dysregulation in these diseases, how it mediates the specific neuronal cell dysfunction remains obscure. Here we performed a comprehensive analysis of altered DNA binding of multiple transcription factors using R6/2 HD model mice brains that express an N-terminal fragment of mutant huntingtin (mutant Nhtt). We found a reduction of DNA binding of Brn-2, a POU domain transcription factor involved in differentiation and function of hypothalamic neurosecretory neurons. We provide evidence supporting that Brn-2 loses its function through two pathways, its sequestration by mutant Nhtt and its reduced transcription, leading to reduced expression of hypothalamic neuropeptides. In contrast to Brn-2, its functionally related protein, Brn-1, was not sequestered by mutant Nhtt but was upregulated in R6/2 brain, except in hypothalamus. Our data indicate that functional suppression of Brn-2 together with a region-specific lack of compensation by Brn-1 mediates hypothalamic cell dysfunction by mutant Nhtt.

Show MeSH
Related in: MedlinePlus