Prion diseases are caused by conversion of a normal cell-surface glycoprotein (PrP(C)) into a conformationally altered isoform (PrP(Sc)) that is infectious in the absence of nucleic acid. Although a great deal has been learned about PrP(Sc) and its role in prion propagation, much less is known about the physiological function of PrP(C). In this review, we will summarize some of the major proposed functions for PrP(C), including protection against apoptotic and oxidative stress, cellular uptake or binding of copper ions, transmembrane signaling, formation and maintenance of synapses, and adhesion to the extracellular matrix. We will also outline how loss or subversion of the cytoprotective or neuronal survival activities of PrP(C) might contribute to the pathogenesis of prion diseases, and how similar mechanisms are probably operative in other neurodegenerative disorders.

To identify sequence domains important for the neurotoxic and neuroprotective activities of the prion protein (PrP), we have engineered transgenic mice that express a form of murine PrP deleted for a conserved block of 21 amino acids (residues 105-125) in the unstructured, N-terminal tail of the protein. These mice spontaneously developed a severe neurodegenerative illness that was lethal within 1 week of birth in the absence of endogenous PrP. This phenotype was reversed in a dose-dependent fashion by coexpression of wild-type PrP, with five-fold overexpression delaying death beyond 1 year. The phenotype of Tg(PrPD105-125) mice is reminiscent of, but much more severe than, those described in mice that express PrP harboring larger deletions of the N-terminus, and in mice that ectopically express Doppel, a PrP paralog, in the CNS. The dramatically increased toxicity of PrPD105-125 is most consistent with a model in which this protein has greatly enhanced affinity for a hypothetical receptor that serves to transduce the toxic signal. We speculate that altered binding interactions involving the 105-125 region of PrP may also play a role in generating neurotoxic signals during prion infection.

We have defined the histone acetylation pattern of the endogenous murine ␤-globin domain, which contains the erythroidspecific ␤-globin genes. The ␤-globin locus control region (LCR) and transcriptionally active promoters were enriched in acetylated histones in fetal liver relative to fetal brain, whereas the inactive promoters were hypoacetylated. In contrast, the LCR and both active and inactive promoters were hyperacetylated in yolk sac. Hypersensitive site two of the LCR was also hyperacetylated in murine embryonic stem cells, whereas ␤-globin promoters were hypoacetylated. Thus, the acetylation pattern varied at different developmental stages. Histone deacetylase inhibition selectively increased acetylation at a hypoacetylated promoter in fetal liver, suggesting that active deacetylation contributes to silencing of promoters. We propose that dynamic histone acetylation and deacetylation play an important role in the developmental control of ␤-globin gene expression. Histone acetylation and deacetylation play important roles in transcriptional regulation (1-3). Allis and colleagues (4) proposed a model to explain how histone acetylation can regulate gene-specific transcription despite the ubiquitous distribution of nucleosomes in the genome. In this model, sequencespecific DNA binding proteins physically recruit histone acetylases (HATs) to chromosomal sites, which selectively target promoters for chromatin remodeling. The consequences of targeted HAT recruitment are evident from biochemical studies showing that histone acetylation increases the accessibility of nucleosomal DNA to trans-acting factors (5, 6). Thus, increased histone acetylation at a promoter may enhance the binding of factors that stimulate preinitiation complex assembly or may directly promote binding of the transcriptional machinery. Studies on the role of acetylation in transcription have been facilitated by the development of a chromatin immunoprecipitation (ChIP) assay (7), which allows one to measure the histone acetylation state of specific chromosomal sites in living cells. Analysis of histone acetylation by ChIP has shown that histone hyperacetylation at promoters correlates with transcriptional activity (8)(9)(10)(11)(12). Beyond the impact of local histone acetylation on promoter function, little is known about the importance of histone acetylation for long-range transcriptional control. Given that acetylation impairs higher-order chromatin folding (13), which can modulate the accessibility of cis-acting elements, histone acetylation could also control long-range activation. In addition, HATs recruited by enhancers and locus control regions (LCRs) may modify histones surrounding these elements, which could influence the function of the respective nucleoprotein complexes.An increasing number of genes have been shown to reside within chromosomal domains controlled by LCRs (14). The best example of a locus regulated by a LCR is the ␤-globin locus containing the embryonic, fetal, and adult ␤-globin genes. High-level transcription of t...

Histone acetylation precedes activation of many genes. However, the establishment and consequences of long-range acetylation patterns are poorly understood. To define molecular determinants of the developmentally dynamic histone acetylation pattern of the beta-globin locus, we compared acetylation of the locus in MEL and CB3 erythroleukemia cells. CB3 cells lack the beta-globin locus control region (LCR) binding protein p45/NF-E2. We found that p45/NF-E2 was required for histone hyperacetylation at adult beta-globin promoters approximately 50 kilobases downstream of the LCR, but not at the LCR. Surprisingly, RNA polymerase II associated with the LCR in a p45/NF-E2-independent manner, while its recruitment to the promoter required p45/NF-E2. We propose that polymerase accesses the LCR and p45/NF-E2 induces long-range transfer of polymerase to the promoter, resulting in transcriptional activation.

Agrobacterium-mediated sorghum transformation frequency has been enhanced significantly via medium optimization using immature embryos from sorghum variety TX430 as the target tissue. The new transformation protocol includes the addition of elevated copper sulfate and 6-benzylaminopurine in the resting and selection media. Using Agrobacterium strain LBA4404, the transformation frequency reached over 10% using either of two different selection marker genes, moPAT or PMI, and any of three different vectors in large-scale transformation experiments. With Agrobacterium strain AGL1, the transformation frequencies were as high as 33%. Using quantitative PCR analyses of 1,182 T0 transgenic plants representing 675 independent transgenic events, data was collected for T-DNA copy number, intact or truncated T-DNA integration, and vector backbone integration into the sorghum genome. A comparison of the transformation frequencies and molecular data characterizing T-DNA integration patterns in the transgenic plants derived from LBA4404 versus AGL1 transformation revealed that twice as many transgenic high-quality events were generated when AGL1 was used compared to LBA4404. This is the first report providing molecular data for T-DNA integration patterns in a large number of independent transgenic plants in sorghum.Electronic supplementary materialThe online version of this article (doi:10.1007/s11627-013-9583-z) contains supplementary material, which is available to authorized users.