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Lori L Wallrath

Publications and source records attributed to Lori L Wallrath.

11 recordsLinked to original sources
PubMed2007

Gene regulation by chromatin structure: paradigms established in Drosophila melanogaster.

Studies in Drosophila melanogaster have revealed paradigms for regulating gene expression through chromatin structure, including mechanisms of gene activation and silencing. Regulation occurs at the level of individual genes, chromosomal domains, and entire chromosomes. The chromatin state is dynamic, allowing for changes in gene expression in response to cellular signals and/or environmental cues. Changes in chromatin result from the action of ATP-dependent chromatin-remodeling complexes, reversible epigenetic histone modifications, and the incorporation of histone variants. Many of the chromatin-based transcriptional regulatory mechanisms discovered in D. melanogaster are evolutionarily conserved and therefore serve as a foundation for studies in other organisms.

Adenosine Triphosphatases↗
PubMed2006

TFIIIC boxes in the genome.

In this issue of Cell, Noma et al. (2006) show that B-boxes and TFIIIC limit the spread of heterochromatin at the silent mat region in the fission yeast genome. Global analysis of TFIIIC distribution revealed dispersed sites of association that coalesce at the nuclear periphery, suggesting that TFIIIC may act as a barrier throughout the genome.

Binding Sites↗
PubMed2006

A requirement for dimerization of HP1Hsalpha in suppression of breast cancer invasion.

The development and progression of cancer is controlled by gene expression, often regulated through chromatin packaging. Heterochromatin protein 1(Hsalpha) (HP1(Hsalpha)), one of three human HP1 family members, participates in heterochromatin formation and gene regulation. HP1(Hsalpha) possesses an amino-terminal chromodomain, which binds methylated lysine 9 of histone H3 (meK9 H3), and a carboxyl-terminal chromoshadow domain (CSD) that is required for dimerization and interaction with partner proteins. HP1(Hsalpha) is down-regulated in invasive metastatic breast cancer cells compared with poorly invasive nonmetastatic breast cancer cells. Expression of EGFP-HP1(Hsalpha) in highly invasive MDA-MB-231 cells causes a reduction in in vitro invasion, without affecting cell growth. Conversely, knock-down of HP1(Hsalpha) levels in the poorly invasive breast cancer cell line MCF-7 increased invasion, without affecting cell growth. To determine whether functions of the CSD were required for the regulation of invasion, mutant forms of HP1(Hsalpha) were expressed in MDA-MB-231 cells. A W174A mutation that disrupts interactions between HP1(Hsalpha) and PXVXL-containing partner proteins reduced invasion similar to that of the wild type protein. In contrast, an I165E mutation that disrupts dimerization of HP1(Hsalpha) did not decrease invasion. No gross changes in localization and abundance of HP1(Hsbeta), HP1(Hsgamma), and meK9 H3 were observed upon expression of wild type and mutant forms of HP1(Hsalpha) in MDA-MB-231 cells. Taken together, these data demonstrate that modulation of HP1(Hsalpha) alters the invasive potential of breast cancer cells through mechanisms requiring HP1 dimerization, but not interactions with PXVXL-containing proteins.

Breast Neoplasms↗
PubMed2005

Molecular genetic analysis of the nested Drosophila melanogaster lamin C gene.

Lamins are intermediate filaments that line the inner surface of the nuclear envelope, providing structural support and making contacts with chromatin. There are two types of lamins, A- and B-types, which differ in structure and expression. Drosophila possesses both lamin types, encoded by the LamC (A-type) and lamin Dm0 (B-type) genes. LamC is nested within an intron of the essential gene ttv. We demonstrate that null mutations in LamC are lethal, and expression of a wild-type LamC transgene rescues lethality of LamC but not ttv mutants. Mutations in the human A-type lamin gene lead to diseases called laminopathies. To determine if Drosophila might serve as a useful model to study lamin biology and disease mechanisms, we generated transgenic flies expressing mutant LamC proteins modeled after human disease-causing lamins. These transgenic animals display a nuclear lamin aggregation phenotype remarkably similar to that observed when human mutant A-type lamins are expressed in mammalian cells. LamC aggregates also cause disorganization of lamin Dm0, indicating interdependence of both lamin types for proper lamina assembly. Taken together, these data provide the first detailed genetic analysis of the LamC gene and support using Drosophila as a model to study the role of lamins in disease.

Alleles↗
PubMed2005

Role of Drosophila HP1 in euchromatic gene expression.

Heterochromatin protein 1 (HP1), a gene silencing protein, localizes to centric heterochromatin through an interaction with methylated K9 of histone H3, a modification generated by the histone methyl transferase SU(VAR)3-9. On Drosophila polytene chromosomes, HP1 also localizes to 200 sites scattered throughout euchromatin. To address the role of HP1 in euchromatic gene regulation, mRNAs from wild-type and Su(var)2-5 mutants lacking HP1 were compared. Genes residing within a 550-kb genomic region enriched in HP1 that show altered expression in the Su(var)2-5 mutant were analyzed in detail. Three genes within this region, Pros35, CG5676, and cdc2, were found to associate with HP1 by chromatin immunoprecipitation. Surprisingly, these genes require HP1 for expression, suggesting a positive role for HP1 in euchromatic gene expression. Of these genes, only cdc2 is packaged with methylated K9 H3. Furthermore, none of the genes show altered expression in a Su(var)3-9 mutant. Collectively, these data demonstrate multiple mechanisms for HP1 localization within euchromatin and show that some genes associated with HP1 are not affected by alterations in Su(var)3-9 dosage.

Animals↗
PubMed2004

Conserved properties of HP1(Hsalpha).

Heterochromatin protein 1 Hsalpha (HP1(Hsalpha)) is one of three human proteins that share sequence similarity with Drosophila HP1. HP1 proteins are enriched at centric heterochromatin and play a role in chromatin packaging and gene regulation. In humans, HP1(Hsalpha) is down-regulated in highly invasive/metastatic breast cancer cells, compared to poorly invasive/non-metastatic breast cancer cells. To gain insight into this differential regulation, we have cloned the HP1(Hsalpha) gene and characterized its genomic region. HP1(Hsalpha) is located on human chromosome 12q13.13, 589 bp upstream of the divergently transcribed hnRNPA1 gene. Analysis of the promoter region revealed that differential regulation of HP1(Hsalpha) between the two types of breast cancer cells is lost upon mutation of an USF/c-myc transcription factor binding site located 172 bp upstream of the predicted HP1(Hsalpha) transcription start site. These findings provide insights into the down-regulation of HP1(Hsalpha) in highly invasive/metastatic breast cancer cells. To examine the functional properties of HP1(Hsalpha), experiments were performed using Drosophila melanogaster as a genetic system. When human HP1(Hsalpha) was expressed in transgenic Drosophila, silencing of reporter genes inserted at centric and telomeric locations was enhanced. Furthermore, expression of HP1(Hsalpha) rescued the lethality of homozygous Su(var)2-5 mutants lacking HP1. Taken together, these results demonstrate the participation of HP1(Hsalpha) in silent chromatin formation and that HP1(Hsalpha) is a functional homologue of Drosophila HP1.

Adult↗
PubMed2004

Mechanisms of HP1-mediated gene silencing in Drosophila.

Heterochromatin Protein 1 (HP1) is a structural component of silent chromatin at telomeres and centromeres. Euchromatic genes repositioned near heterochromatin by chromosomal rearrangements are typically silenced in an HP1-dependent manner. Silencing is thought to involve the spreading of heterochromatin proteins over the rearranged genes. HP1 associates with centric heterochromatin through an interaction with methylated lysine 9 of histone H3, a modification generated by SU(VAR)3-9. The current model for spreading of silent chromatin involves HP1-dependent recruitment of SU(VAR)3-9, resulting in the methylation of adjacent nucleosomes and association of HP1 along the chromatin fiber. To address mechanisms of silent chromatin formation and spreading, HP1 was fused to the DNA-binding domain of the E. coli lacI repressor and expressed in Drosophila melanogaster stocks carrying heat shock reporter genes positioned 1.9 and 3.7 kb downstream of lac operator repeats. Association of lacI-HP1 with the repeats resulted in silencing of both reporter genes and correlated with a closed chromatin structure consisting of regularly spaced nucleosomes, similar to that observed in centric heterochromatin. Chromatin immunoprecipitation experiments demonstrated that HP1 spread bi-directionally from the tethering site and associated with the silenced reporter transgenes. To examine mechanisms of spreading, the effects of a mutation in Su(var)3-9 were investigated. Silencing was minimally affected at 1.9 kb, but eliminated at 3.7 kb, suggesting that HP1-mediated silencing can operate in a SU(VAR)3-9-independent and -dependent manner.

Animals↗
PubMed2003

Effects of tethering HP1 to euchromatic regions of the Drosophila genome.

Heterochromatin protein 1 (HP1) is a conserved non-histone chromosomal protein enriched in heterochromatin. On Drosophila polytene chromosomes, HP1 localizes to centric and telomeric regions, along the fourth chromosome, and to specific sites within euchromatin. HP1 associates with centric regions through an interaction with methylated lysine nine of histone H3, a modification generated by the histone methyltransferase SU(VAR)3-9. This association correlates with a closed chromatin configuration and silencing of euchromatic genes positioned near heterochromatin. To determine whether HP1 is sufficient to nucleate the formation of silent chromatin at non-centric locations, HP1 was tethered to sites within euchromatic regions of Drosophila chromosomes. At 25 out of 26 sites tested, tethered HP1 caused silencing of a nearby reporter gene. The site that did not support silencing was upstream of an active gene, suggesting that the local chromatin environment did not support the formation of silent chromatin. Silencing correlated with the formation of ectopic fibers between the site of tethered HP1 and other chromosomal sites, some containing HP1. The ability of HP1 to bring distant chromosomal sites into proximity with each other suggests a mechanism for chromatin packaging. Silencing was not dependent on SU(VAR)3-9 dosage, suggesting a bypass of the requirement for histone methylation.

Animals↗
PubMed2002

Does heterochromatin protein 1 always follow code?

Heterochromatin protein 1 (HP1) is a conserved chromosomal protein that participates in chromatin packaging and gene silencing. A loss of HP1 leads to lethality in Drosophila and correlates with metastasis in human breast cancer cells. On Drosophila polytene chromosomes HP1 is localized to centric regions, telomeric regions, in a banded pattern along the fourth chromosome, and at many sites scattered throughout the euchromatic arms. Recently, one mechanism of HP1 chromosome association was revealed; the amino-terminal chromo domain of HP1 interacts with methylated lysine nine of histone H3, consistent with the histone code hypothesis. Compelling data support this mechanism of HP1 association at centric regions. Is this the only mechanism by which HP1 associates with chromosomes? Interest is now shifting toward the role of HP1 within euchromatic domains. Accumulating evidence in Drosophila and mammals suggests that HP1 associates with chromosomes through interactions with nonhistone chromosomal proteins at locations other than centric heterochromatin. Does HP1 play a similar role in chromatin packaging and gene regulation at these sites as it does in centric heterochromatin? Does HP1 associate with the same proteins at these sites as it does in centric heterochromatin? A first step toward answering these questions is the identification of sequences associated with HP1 within euchromatic domains. Such sequences are likely to include HP1 "target genes" whose discovery will aid in our understanding of HP1 lethality in Drosophila and metastasis of breast cancer cells.

Animals↗