Genomic stability is critical for the clinical use of human embryonic and induced pluripotent stem cells. We performed high resolution SNP (single nucleotide polymorphism) analysis on 186 pluripotent and 119 non-pluripotent samples. We report a higher frequency of subchromosomal copy number variations in pluripotent samples compared to non-pluripotent samples, with variations enriched in specific genomic regions. The distribution of these variations differed between hESCs and hiPSCs, characterized by large numbers of duplications found in a few hESC samples and moderate numbers of deletions distributed across many hiPSC samples. For hiPSCs, the reprogramming process was associated with deletions of tumor suppressor genes, while time in culture was associated with duplications of oncogenic genes. We also observed duplications that arose during a differentiation protocol. Our results illustrate the dynamic nature of genomic abnormalities in pluripotent stem cells and the need for frequent genomic monitoring to assure phenotypic stability and clinical safety.

Expansion of GAA x TTC triplets within an intron in FXN (the gene encoding frataxin) leads to transcription silencing, forming the molecular basis for the neurodegenerative disease Friedreich's ataxia. Gene silencing at expanded FXN alleles is accompanied by hypoacetylation of histones H3 and H4 and trimethylation of histone H3 at Lys9, observations that are consistent with a heterochromatin-mediated repression mechanism. We describe the synthesis and characterization of a class of histone deacetylase (HDAC) inhibitors that reverse FXN silencing in primary lymphocytes from individuals with Friedreich's ataxia. We show that these molecules directly affect the histones associated with FXN, increasing acetylation at particular lysine residues on histones H3 and H4 (H3K14, H4K5 and H4K12). This class of HDAC inhibitors may yield therapeutics for Friedreich's ataxia.

No abstract

Small molecules that target specific DNA sequences have the potential to control gene expression. Ligands designed for therapeutic application must bind any predetermined DNA sequence with high affinity and permeate living cells. Synthetic polyamides containing N-methylimidazole and N-methylpyrrole amino acids have an affinity and specificity for DNA comparable to naturally occurring DNA-binding proteins. We report here that an eight-ring polyamide targeted to a specific region of the transcription factor TFIIIA binding site interferes with 5S RNA gene expression in Xenopus kidney cells. Our results indicate that pyrrole-imidazole polyamides are cell-permeable and can inhibit the transcription of specific genes.

Histone deacetylase (HDAC) inhibitors, including various benzamides and hydroxamates, are currently in clinical development for a broad range of human diseases, including cancer and neurodegenerative diseases. We recently reported the identification of a family of benzamide-type HDAC inhibitors that are relatively non-toxic compared with the hydroxamates. Members of this class of compounds have shown efficacy in cellbased and mouse models for the neurodegenerative diseases Friedreich ataxia and Huntington disease. Considerable differences in IC 50 values for the various HDAC enzymes have been reported for many of the HDAC inhibitors, leading to confusion as to the HDAC isotype specificities of these compounds. Here we show that a benzamide HDAC inhibitor, a pimelic diphenylamide (106), is a class I HDAC inhibitor, demonstrating no activity against class II HDACs. 106 is a slow, tight-binding inhibitor of HDACs 1, 2, and 3, although inhibition for these enzymes occurs through different mechanisms. Inhibitor 106 also has preference toward HDAC3 with K i of ϳ14 nM, 15 times lower than the K i for HDAC1. In comparison, the hydroxamate suberoylanilide hydroxamic acid does not discriminate between these enzymes and exhibits a fast-on/fast-off inhibitory mechanism. These observations may explain a paradox involving the relative activities of pimelic diphenylamides versus hydroxamates as gene activators.The link between post-translational modifications by reversible histone acetylation and deacetylation and mRNA transcription has been shown to be one of the key mechanisms of epigenetic gene regulation (1). Acetylation of histone lysine residues, controlled by the histone acetyltransferases and histone deacetylases (HDACs), 2 has been a subject of intense recent research (2-5). Generally, histone hypoacetylation causes transcriptional silencing, whereas histone hyperacetylation results in transcriptional activation of various genes (6 -8). Eighteen HDACs have been identified in the human genome, including the zinc-dependent HDACs (class I, class II, and class IV), and the NAD ϩ -dependent enzymes (class III or sirtuins) (9, 10). HDACs 1, 2, 3, and 8 belong to class I, showing homology to the yeast enzyme RPD3. Class II is further divided into class IIa (HDACs 4, 5, 7, and 9) and IIb (HDAC 6 and 10), according to their sequence homology and domain organization. HDAC11 is the lone member of class IV (9, 11). The sirtuins (class III) are related to the yeast Sir2 protein and are involved in regulation of metabolism and aging (10).To date, a number of small molecule inhibitors of the zincdependent HDACs have been identified (12). These compounds can be broadly grouped in four chemical classes: the hydroxamates, the benzamides, butyrate analogs, and cyclic peptides, such as depsipeptide and related compounds (12, 13). Hydroxamate-based inhibitors, such as trichostatin A (TSA) and suberoylanilide hydroamic acid (SAHA; Fig. 1A) are believed to be pan-HDAC inhibitors (14 -16); however, recent studies have shown that TSA and SAHA...