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D Garrick

Publications and source records attributed to D Garrick.

12 recordsLinked to original sources
PubMed2005

Understanding alpha-globin gene regulation: Aiming to improve the management of thalassemia.

Over the past 50 years, many advances in our understanding of the general principles controlling gene expression during hematopoiesis have come from studying the synthesis of hemoglobin. Discovering how the alpha- and beta-globin genes are normally regulated and documenting the effects of inherited mutations that cause thalassemia have played a major role in establishing our current understanding of how genes are switched on or off in hematopoietic cells. Previously, nearly all mutations causing thalassemia have been found in or around the globin loci, but rare inherited and acquired trans-acting mutations are being found more often. Such mutations have demonstrated new mechanisms underlying human genetic disease. Furthermore, they are revealing new pathways in the regulation of globin gene expression that, in turn, may open up new avenues for improving the management of patients with common types of thalassemia.

Chromosomes, Human, Pair 11↗
PubMed2001

An integrated model for adolescent inpatient group therapy.

This paper proposes an integrated group therapy model to be utilized by psychiatric and mental health nurses; one innovatively designed to meet the therapeutic needs of adolescents admitted to inpatient psychiatric programs. The writers suggest a model of group therapy primarily comprised of interpersonal approaches within a feminist perspective. The proposed group focus is on active therapeutic engagement with adolescents to further interpersonal learning and to critically examine their contextualized lived experiences. Specific client and setting factors relevant to the selection of therapeutic techniques are reviewed. Selected theoretical models of group therapy are critiqued in relation to group therapy with adolescents. This integrated model of group therapy provides a safe and therapeutic forum that enriches clients' personal and interpersonal experiences as well as promotes healthy exploration, change, and empowerment.

Adolescent↗
PubMed2000

Mutations in ATRX, encoding a SWI/SNF-like protein, cause diverse changes in the pattern of DNA methylation.

A goal of molecular genetics is to understand the relationship between basic nuclear processes, epigenetic changes and the numerous proteins that orchestrate these effects. One such protein, ATRX, contains a highly conserved plant homeodomain (PHD)-like domain, present in many chromatin-associated proteins, and a carboxy-terminal domain which identifies it as a member of the SNF2 family of helicase/ATPases. Mutations in ATRX give rise to characteristic developmental abnormalities including severe mental retardation, facial dysmorphism, urogenital abnormalities and alpha-thalassaemia. This circumstantial evidence suggests that ATRX may act as a transcriptional regulator through an effect on chromatin. We have recently shown that ATRX is localized to pericentromeric heterochromatin during interphase and mitosis, suggesting that ATRX might exert other chromatin-mediated effects in the nucleus. Moreover, at metaphase, some ATRX is localized at or close to the ribosomal DNA (rDNA) arrays on the short arms of human acrocentric chromosomes. Here we show that mutations in ATRX give rise to changes in the pattern of methylation of several highly repeated sequences including the rDNA arrays, a Y-specific satellite and subtelomeric repeats. Our findings provide a potential link between the processes of chromatin remodelling, DNA methylation and gene expression in mammalian development.

Blotting, Southern↗
PubMed1999

The chicken beta-globin 5'HS4 boundary element blocks enhancer-mediated suppression of silencing.

A constitutive DNase I-hypersensitive site 5' of the chicken beta-globin locus, termed 5'HS4 or cHS4, has been shown to insulate a promoter from the effect of an upstream enhancer and to reduce position effects on mini-white expression in Drosophila cells; on the basis of these findings, it has been designated a chromatin insulator. We have examined the effect of the cHS4 insulator in a system that assays both the level of gene expression and the rate of transcriptional silencing. Because transgenes flanked by insulator elements are shielded from position effects in Drosophila cells, we tested the ability of cHS4 to protect transgenes from position effects in mammalian cells. Flanking of an expression vector with the cHS4 insulator in a colony assay did not increase the number of G418-resistant colonies. Using lox/cre-based recombinase-mediated cassette exchange to control integration position, we studied the effect of cHS4 on the silencing of an integrated beta-geo reporter at three genomic sites in K562 erythroleukemia cells. In this assay, enhancers act to suppress silencing but do not increase expression levels. While cHS4 blocked enhancement at each integration site, the strength of the effect varied from site to site. Furthermore, at some sites, cHS4 inhibited the enhancer effect either when placed between the enhancer and the promoter or when placed upstream of the enhancer. These results suggest that the activity of cHS4 is not dominant in all contexts and is unlikely to prevent silencing at all genomic integration sites.

Animals↗
PubMed1998

Repeat-induced gene silencing in mammals.

In both plants and Drosophila melanogaster, expression from a transgenic locus may be silenced when repeated transgene copies are arranged as a concatameric array. This repeat-induced gene silencing is frequently manifested as a decrease in the proportion of cells that express the transgene, resulting in a variegated pattern of expression. There is also some indication that, in transgenic mammals, the number of transgene copies within an array can exert a repressive influence on expression, with several mouse studies reporting a decrease in the level of expression per copy as copy number increases. However, because these studies compare different sites of transgene integration as well as arrays with different numbers of copies, the expression levels observed may be subject to varying position effects as well as the influence of the multicopy array. Here we describe use of the lox/Cre system of site-specific recombination to generate transgenic mouse lines in which different numbers of a transgene are present at the same chromosomal location, thereby eliminating the contribution of position effects and allowing analysis of the effect of copy number alone on transgene silencing. Reduction in copy number results in a marked increase in expression of the transgene and is accompanied by decreased chromatin compaction and decreased methylation at the transgene locus. These findings establish that the presence of multiple homologous copies of a transgene within a concatameric array can have a repressive effect upon gene expression in mammalian systems.

Animals↗
PubMed1996

Variegated expression of a globin transgene correlates with chromatin accessibility but not methylation status.

There are now many mammalian examples in which single cell assays of transgene activity have revealed variegated patterns of expression. We have previously reported that transgenes in which globin regulatory elements drive the lacZ reporter gene exhibit variegated expression patterns in mouse erythrocytes, with transgene activity detectable in only a sub-population of circulating erythroid cells. In order to elucidate the molecular mechanism responsible for variegated expression in this system, we have compared the chromatin structure and methylation status of the transgene locus in expressing and non-expressing populations of erythrocytes. We find that there is a difference in the chromatin conformation of the transgene locus between the two states. Relative to active transgenes, transgene loci which have been silenced exhibit a reduced sensitivity to general digestion by DNase I, as well as a failure to establish a transgene-specific DNase I hypersensitive site, suggesting that silenced transgenes are situated within less accessible chromatin structures. Surprisingly, the restrictive chromatin structure observed at silenced transgene loci did not correlate with increased methylation, with transgenes from both active and inactive loci appearing largely unmethylated following analysis with methylation-sensitive restriction enzymes and by sequencing PCR products derived from bisulphite-converted genomic DNA.

Animals↗
PubMed1996

Age-dependent silencing of globin transgenes in the mouse.

Variegation of transgene expression, a heterocellular or mosaic pattern of expression seen in all mice in a given transgenic line, is a frequently observed but unexplained phenomenon. We have encountered variegation with globin transgenes; when lacZ expression is driven by globin control elements a proportion of erythrocytes express beta-galactosidase (beta-gal), while the remaining erythrocytes express none. The percentage of expressing cells is constant within each line (at any particular developmental stage), but varies between lines. Such variation may account for much of the line-to-line variability which has been reported in the expression of a transgene construct. We have now extended these observations by studying expression of several globin/lacZ transgenes with increasing age. Expression of beta-gal is variegated in all lines in adult mice, including those made with a beta-globin promoter and locus control region driving lacZ. The extent of variegation differs widely between lines, but in all lines there is a marked decline in the number of erythrocytes expressing beta-gal with increasing age. Progression of silencing continues long past the point at which globin switching is complete, suggesting that it is not related to this process. We observe that age-dependent silencing is most severe in high copy number animals. Increasing variegation of transgene expression with ageing of mice is likely to complicate interpretation of the developmental regulation of transgenes. We speculate that it reflects a general mechanism of epigenetic regulation.

Aging↗
PubMed1995

Position-dependent variegation of globin transgene expression in mice.

Expression of genes in eukaryotes has commonly been analyzed in a whole tissue, and levels of expression have been interpreted as the result of equivalent rates of transcription in every cell. We have produced transgenic mouse lines that express beta-galactosidase under the control of globin promoters linked to the major tissue-specific regulatory element of the alpha-globin locus, which permits the analysis of transgene expression in individual red blood cells. We find that expression of the transgene within all mouse lines is heterocellular. Individual cells either do not express the transgene at all or express it at a level characteristic of that line. The number of beta-galactosidase-expressing cells varies greatly between different lines of transgenic mice at any defined stage of development, but within a transgenic line, individual mice have strikingly similar numbers of expressing cells. This suggests that the degree of heterocellular expression is determined by the site of integration, as is seen in position-effect variegation.

Animals↗
PubMedDate not supplied

Scurvy: forgotten but not gone.

Scurvy is still seen sporadically in the developed world. At a time when subclinical vitamin C deficiency in the general population is being recognized increasingly, the need for clinicians to be aware of this disease remains. We present the case of a 9-year-old boy admitted to hospital with musculoskeletal pain, weakness and changes in the skin and gums. After extensive investigation, he was found to have vitamin C deficiency resulting from a restricted eating pattern. Musculoskeletal complaints are a common mode of presentation of scurvy in children. Failure to appreciate this fact and the risk factors for poor vitamin C intake in the paediatric age group can result in unnecessary and invasive investigations for apparent 'multisystem' disease.

Ascorbic Acid↗