Non-Cell Autonomous and Epigenetic Mechanisms of Huntington’s Disease

Huntington’s disease (HD) is a rare neurodegenerative disorder caused by an expansion of CAG trinucleotide repeat located in the exon 1 of Huntingtin (HTT) gene in human chromosome 4. The HTT protein is ubiquitously expressed in the brain. Specifically, mutant HTT (mHTT) protein-mediated toxicity leads to a dramatic degeneration of the striatum among many regions of the brain. HD symptoms exhibit a major involuntary movement followed by cognitive and psychiatric dysfunctions. In this review, we address the conventional role of wild type HTT (wtHTT) and how mHTT protein disrupts the function of medium spiny neurons (MSNs). We also discuss how mHTT modulates epigenetic modifications and transcriptional pathways in MSNs. In addition, we define how non-cell autonomous pathways lead to damage and death of MSNs under HD pathological conditions. Lastly, we overview therapeutic approaches for HD. Together, understanding of precise neuropathological mechanisms of HD may improve therapeutic approaches to treat the onset and progression of HD.

High-throughput genotyping assays for identification of glycophorin B deletion variants in population studies

Glycophorins are the most abundant sialoglycoproteins on the surface of human erythrocyte membranes. Genetic variation in glycophorin region of human chromosome 4 (containing GYPA, GYPB, and GYPE genes) is of interest because the gene products serve as receptors for pathogens of major public health interest, including Plasmodium sp., Babesia sp., Influenza virus, Vibrio cholerae El Tor Hemolysin, and Escherichia coli. A large structural rearrangement and hybrid glycophorin variant, known as Dantu, which was identified in East African populations, has been linked with a 40% reduction in risk for severe malaria. Apart from Dantu, other large structural variants exist, with the most common being deletion of the whole GYPB gene and its surrounding region, resulting in multiple different deletion forms. In West Africa particularly, these deletions are estimated to account for between 5 and 15% of the variation in different populations, mostly attributed to the forms known as DEL1 and DEL2. Due to the lack of specific variant assays, little is known of the distribution of these variants. Here, we report a modification of a previous GYPB DEL1 assay and the development of a novel GYPB DEL2 assay as high-throughput PCR-RFLP assays, as well as the identification of the crossover/breakpoint for GYPB DEL2. Using 393 samples from three study sites in Ghana as well as samples from HapMap and 1000 G projects for validation, we show that our assays are sensitive and reliable for genotyping GYPB DEL1 and DEL2. To the best of our knowledge, this is the first report of such high-throughput genotyping assays by PCR-RFLP for identifying specific GYPB deletion types in populations. These assays will enable better identification of GYPB deletions for large genetic association studies and functional experiments to understand the role of this gene cluster region in susceptibility to malaria and other diseases.

Epigenetic Regulation of Varicella-Zoster Virus Open Reading Frames 62 and 63 in Latently Infected Human Trigeminal Ganglia

ABSTRACT Open reading frames (ORFs) 21, 29, 62, 63, and 66 of varicella-zoster virus (VZV) are transcribed during latency in human ganglia. ORF 63 is the most frequently expressed gene, and ORF 62 encodes a transcriptional activator. The mechanisms regulating the expression of these genes are not well understood, although analyses of other alphaherpesviruses indicate a role for chromatin in virus gene regulation during latent infection. Using chromatin immunoprecipitation (ChIP) assays to analyze the euchromatic state of ORFs 62 and 63 compared to the centromere from human chromosome 4 (heterochromatic) and the human glyceraldehyde-3-phosphate dehydrogenase promoter (euchromatic), we show that the promoters of ORFs 62 and 63 are associated with the histone protein H3K9(Ac) and thus maintained in a euchromatic state during latency. Conversely, the promoters of ORF 36 (thymidine kinase) and ORF 14 (glycoprotein C), genes expressed during lytic but not latent infection, were not enriched in the fraction of latently infected ganglia that bound to anti-H3K9(Ac) antibody. A ChIP assay using productively infected MeWo cells revealed that VZV ORFs 62, 63, 36, and 14 are all euchromatic. Together, these data indicate that the expression of the two latency-related VZV genes, ORFs 62 and 63, is regulated epigenetically through chromatin structure.