@article{ascenzi_ulker_todd_sowinski_schimeneck_allen_weissinger_thompson_2003, title={Analysis of trans-silencing interactions using transcriptional silencers of varying strength and targets with and without flanking nuclear matrix attachment regions}, volume={12}, ISSN={["1573-9368"]}, DOI={10.1023/A:1023310118231}, abstractNote={We investigated the effect of the Rb7 matrix attachment region (MAR) on trans-silencing in tobacco plants, comparing the effects of three transgene silencer loci on ten target loci. Two of the silencer loci, C40 and C190, contain complex and rearranged transgene arrays consisting of 35S:GUS or NOS:NPTII containing plasmids. The third silencer locus, V271, was previously characterized as a complex locus containing rearranged 35S:RiN sequences. Each of these silencers can reduce 35S promoter-driven expression at other loci, albeit with varying efficiencies. The presence of MARs at a target locus does not prevent trans-silencing by the V271 silencer. However, four of seven MAR-containing loci were at least partially resistant to silencing by the C40 and C190 loci. One MAR locus was unaffected by C40, our weakest silencer, and three were silenced only when the silencer locus was maternally inherited. Silencing is progressive in the F1 and F2 generations; two days after germination there is little or no difference between seedlings derived from crosses to silencing or control lines, but seedlings containing silencer loci slowly lose expression during subsequent development. These observations are compatible with the hypothesis that a product of the silencer locus must accumulate before unlinked loci can be affected. However, our silencer loci are themselves silenced for GUS transcription, and coding region homology is not required for their effects on target loci. Our results are consistent with a model in which transcriptional silencing is triggered by transcription of sequences during the early stages of embryo or seedling development.}, number={3}, journal={TRANSGENIC RESEARCH}, author={Ascenzi, R and Ulker, B and Todd, JJ and Sowinski, DA and Schimeneck, CR and Allen, GC and Weissinger, AK and Thompson, WF}, year={2003}, month={Jun}, pages={305–318} }
 @article{ascenzi_ingram_massel_thompson_spiker_weissinger_2001, title={The role of cell differentiation state and HMG-I/Y in the expression of transgenes flanked by matrix attachment regions}, volume={10}, ISSN={["0962-8819"]}, DOI={10.1023/A:1012082602587}, abstractNote={The tobacco nuclear matrix attachment region (MAR), RB7, has been shown to have a much greater effect on transgene expression in cultured cells than in transgenic plants. This is comparable to work in mouse systems showing that MARs have a positive effect on transgene expression in embryonic tissues but not adult tissues. There are several possible explanations for these observations. One is that cell differentiation state and proliferation rate can affect MAR function. We tested this possibility by initiating suspension cell cultures from well-characterized transgenic plants transformed with 35S::GUS with and without flanking MARs and then comparing GUS specific activity in the cell lines to those of the transgenic plants from which the cell lines were derived. If cell differentiation state and proliferation rate do affect MAR function, we would expect the ratio of transgene expression (cell suspensions : plants) to be greater in MAR lines than in control lines. This turned out not to be the case. Thus, it appears that MAR function is not enhanced simply because cells in culture divide rapidly and are not differentiated. Because in animal systems the chromosomal protein HMG-I/Y has been shown to be upregulated in proliferating cells and may have a role in MAR function, we have also examined the levels of the tobacco HMG-I/Y homolog by immunoblotting. The level of this protein does not differ between primary transformant cultured cells (NT-1) and Nicotiana tabacum plants (SR-1). However, a higher molecular weight cross-reacting polypeptide was found in nuclei from the NT-1 cell suspensions but was not detected in SR-1 leaf nuclei or cell suspensions derived from the SR-1 plants.}, number={5}, journal={TRANSGENIC RESEARCH}, author={Ascenzi, R and Ingram, JL and Massel, M and Thompson, WF and Spiker, S and Weissinger, AK}, year={2001}, pages={465–470} }
 @article{ascenzi_gantt_1999, title={Molecular genetic analysis of the drought-inducible linker histone variant in Arabidopsis thaliana}, volume={41}, number={2}, journal={Plant Molecular Biology}, author={Ascenzi, R. and Gantt, J. S.}, year={1999}, pages={159–169} }
 @article{ascenzi_gantt_1999, title={Subnuclear distribution of the entire complement of linker histone variants in Arabidopsis thaliana}, volume={108}, ISSN={["0009-5915"]}, DOI={10.1007/s004120050386}, abstractNote={Linker histones (e.g. H1, H5, H1 degrees ) are thought to exert control on chromatin function by restricting nucleosomal dynamics. All higher eukaryotes possess a diverse family of linker histones, which may exhibit functional specialization. Arabidopsis thaliana apparently contains a minimal complement of linker histone structural variants and therefore is an ideal model for investigating functional differentiation among linker histones. Histones H1-1 and H1-2 are relatively similar proteins that are expressed in a wide variety of tissues and make up the majority of linker histone while H1-3 is a highly divergent minor variant protein that is induced by drought stress. We are interested in determining whether the in vivo distribution of each of these proteins also differs. To this end, we have produced subtype-specific antibodies and have localized each of the three proteins at the intranuclear and DNA sequence levels by indirect immunofluorescence and immunoprecipitation, respectively. Antibodies against linker histones H1-1 and H1-2 decorate nuclei in patterns very similar to 4',6-diamidino-2-phenylindole (DAPI) staining, but different than the staining pattern of total histones. In contrast, antibodies made against two regions of H1-3 bind to chromatin in a diffuse pattern distinct from the DAPI-staining pattern. We also describe a technique to determine the localization of plant linker histone variants along regions of chromatin, employing in vivo chemical DNA-protein cross-linking to preserve native associations followed by immunoprecipitation with subtype-specific antibodies. We use this technique to demonstrate that, in contrast to the major linker histones, H1-3 does not bind the repetitive sequences pAL1 and 5S rDNA. In addition, we show that linker histones are bound to the compacted nucleosomal arrays at the telomere but with reduced stoichiometry. Taken together, our results suggest that plants, as has been shown for animals, possess a variant linker histone that is differentially localized.}, number={6}, journal={CHROMOSOMA}, author={Ascenzi, R and Gantt, JS}, year={1999}, month={Nov}, pages={345–355} }