Mutant Huntingtin Causes a Selective Decrease in the Expression of Synaptic Vesicle Protein 2C / 神经科学通报·英文版

Huntington's disease (HD) is a neurodegenerative disease caused by a polyglutamine expansion in the huntingtin (Htt) protein. Mutant Htt causes synaptic transmission dysfunctions by interfering in the expression of synaptic proteins, leading to early HD symptoms. Synaptic vesicle proteins 2 (SV2s), a family of synaptic vesicle proteins including 3 members, SV2A, SV2B, and SV2C, plays important roles in synaptic physiology. Here, we investigated whether the expression of SV2s is affected by mutant Htt in the brains of HD transgenic (TG) mice and Neuro2a mouse neuroblastoma cells (N2a cells) expressing mutant Htt. Western blot analysis showed that the protein levels of SV2A and SV2B were not significantly changed in the brains of HD TG mice expressing mutant Htt with 82 glutamine repeats. However, in the TG mouse brain there was a dramatic decrease in the protein level of SV2C, which has a restricted distribution pattern in regions particularly vulnerable in HD. Immunostaining revealed that the immunoreactivity of SV2C was progressively weakened in the basal ganglia and hippocampus of TG mice. RT-PCR demonstrated that the mRNA level of SV2C progressively declined in the TG mouse brain without detectable changes in the mRNA levels of SV2A and SV2B, indicating that mutant Htt selectively inhibits the transcriptional expression of SV2C. Furthermore, we found that only SV2C expression was progressively inhibited in N2a cells expressing a mutant Htt containing 120 glutamine repeats. These findings suggest that the synaptic dysfunction in HD results from the mutant Htt-mediated inhibition of SV2C transcriptional expression. These data also imply that the restricted distribution and decreased expression of SV2C contribute to the brain region-selective pathology of HD.

Investigation of optimum concentrations of betaine for improving the resolution of sequencing G-C rich DNA with trinucleotide repeats / 中华医学遗传学杂志

<p><b>OBJECTIVE</b>To develop an optimal sequencing system which can improve the resolution of sequencing G-C rich DNA with abundant trinucleotide repeats by applying concentration gradients of betaine to the Sanger sequencing system.</p><p><b>METHODS</b>Concentration gradients of betaine were introduced into the sequencing system by taking the 5' terminal of Nogo-B cDNA (Am-Nogo-B) (G-C%=72%, without trinucleotide repeats) and 5' terminal of Huntingtin cDNA (Am-HTT) (G-C%=74%, with abundant CAG and CCG repeats) the results of sequencing were compared.</p><p><b>RESULTS</b>The optimum concentration of betaine for sequencing Am-Nogo-B has differed from that for Am-HTT. Result of sequencing Am-Nogo-B has achieved the best quality when the concentration of betaine was at 0.8-1.2 mol/L, whereas the result of sequencing Am-HTT obtained the best quality when the concentration of betaine was at 1.6 -2.4 mol/L. The results were reproducible.</p><p><b>CONCLUSION</b>G-C rich DNA with similar G-C% required different concentrations of betaine in the sequencing system due to base pair compositions. The sequencing system developed for improving the resolution of sequencing of G-C rich DNA with abundant trinucleotide repeats can be used as a reference for similar studies.</p>

Clinical characteristics and genetic mutation analysis in a Hui family with Huntington disease / 中华医学遗传学杂志

<p><b>OBJECTIVE</b>To perform clinical analysis and gene diagnosis of Huntington disease (HD) in a Hui pedigree from Xinjiang.</p><p><b>METHODS</b>The IT15 gene mutation of the Hui family was analyzed by touchdown PCR, molecular cloning and gene sequencing.</p><p><b>RESULTS</b>The proband carried 46 CAG repeats. Pain in bilateral lower limb was the first symptom, followed by symptoms such as dance like involuntary movements, mood disorders, impaired memory and intelligence. Asymptomatic son of the proband carried 44 CAG repeats.</p><p><b>CONCLUSION</b>This family showed reduced CAG trinucleotide repeats of IT15 gene during maternal transmission. A CAA variation is also detected within the CAG repeat region.</p>

Intergeneration CAG expansion in a Wuhan juvenile-onset Huntington disease family / 神经科学通报·英文版

<p><b>OBJECTIVE</b>To make early diagnosis of IT15 gene mutation in a Wuhan juvenile-onset Huntington disease (HD) family, for providing them with genetic counseling, and making preparation for the further research on pathogenesis and experimental therapy of HD.</p><p><b>METHODS</b>According to the principle of informed consent, we extracted genomic DNA from peripheral blood samples and carried genetic diagnosis of pathogenic exon 1 of IT15 gene by modified touchdown PCR and DNA sequencing methods.</p><p><b>RESULTS</b>Eight of twenty-five family members carried abnormal allele: III(10), III(12), III(14), IV(3), and V(2) carried (CAG) (48), IV(11) and IV(12) carried (CAG) (67), and IV(14) carried (CAG) (63), in contrast with the 8-25 CAG trinucleotides in the members of control group. IV(14) carried 15 more CAG trinucleotides than her father III(10).</p><p><b>CONCLUSION</b>The results definitely confirm the diagnosis of HD and indicate the CAG trinucleotide repeat expansion of IT15 gene in this HD family. In addition, CAG expansion results in juvenile-onset and anticipation (characterized by earlier age of onset and increasing severity) of the patient IV(12).</p>