http://repub.eur.nl/res/aut/2009/ List of Publications en http://repub.eur.nl/static-eur/img/logo.png http://repub.eur.nl http://repub.eur.nl/res/pub/12952/ 2001-09-17T00:00:00Z During the switch from human gamma- (fetal) to beta- (adult) globin gene expression, the gamma and beta genes are expressed competitively by an alternating transcription mechanism. The -50 region of the gamma gene promoter has been proposed to be responsible for the early competitive advantage of the gamma genes and to act as a stage selector element (SSE) in hemoglobin switching. We analyzed the effect of mutating the -50 region of the gamma gene in the presence of a competing beta gene in transgenic mice. This shows that the -50 region does not affect silencing of the beta gene in early development and does not act as a stage selector. However, it affects the ratio of gamma versus beta gene expression in the early, but not later, stages of fetal development. Interestingly, both the wild-type and mutant minilocus constructs show a higher frequency of alternate transcription than observed in the complete locus, suggesting that sequences normally present between the gamma and beta genes facilitate the interaction of the locus control region (LCR) and beta-globin gene in the complete locus. http://repub.eur.nl/res/pub/12807/ 1999-02-15T00:00:00Z The analysis of a number of cases of beta-globin thalassemia and hereditary persistence of fetal hemoglobin (HPFH) due to large deletions in the beta-globin locus has led to the identification of several DNA elements that have been implicated in the switch from human fetal gamma- to adult beta-globin gene expression. We have tested this hypothesis for an element that covers the minimal distance between the thalassemia and HPFH deletions and is thought to be responsible for the difference between a deletion HPFH and deltabeta-thalassemia, located 5' of the delta-globin gene. This element has been deleted from a yeast artificial chromosome (YAC) containing the complete human beta-globin locus. Analysis of this modified YAC in transgenic mice shows that early embryonic expression is unaffected, but in the fetal liver it is subject to position effects. In addition, the efficiency of transcription of the beta-globin gene is decreased, but the developmental silencing of the gamma-globin genes is unaffected by the deletion. These results show that the deleted element is involved in the activation of the beta-globin gene perhaps through the loss of a structural function required for gene activation by long-range interactions. http://repub.eur.nl/res/pub/2527/ 1996-10-01T00:00:00Z Locus control regions (LCRs) are responsible for initiating and maintaining a stable tissue-specific open chromatin structure of a locus. In transgenic mice, LCRs confer high level expression on linked genes independent of position in the mouse genome. Here we show that an incomplete LCR loses this property when integrated into heterochromatic regions. Two disruption mechanisms were observed. One is classical position-effect variegation, resulting in continuous transcription in a clonal subpopulation of cells. The other is a novel mechanism resulting in intermittent gene transcription in all cells. We conclude that only a complete LCR fully overcomes heterochromatin silencing and that it controls the level of transcription by ensuring activity in all cells at all times rather than directly controlling the rate of transcription. http://repub.eur.nl/res/pub/2497/ 1996-01-01T00:00:00Z Single-copy human beta-globin transgenes are very susceptible to suppression by position effects of surrounding closed chromatin. However, these position effects are overcome by a 20 kbp DNA fragment containing the locus control region (LCR). Here we show that the 6.5 kbp microlocus LCR cassette reproducibly directs full expression from independent single-copy beta-globin transgenes. By testing individual DNase I-hypersensitive sites (HS) present in the microlocus cassette, we demonstrate that the 1.5 kbp 5'HS2 enhancer fragment does not direct beta-globin expression from single-copy transgenes. In contrast, the 1.9 kbp 5'HS3 fragment directs beta-globin expression in five independent single-copy transgenic mouse lines. Moreover, the 5'HS3 core element and beta-globin proximal promoter sequences are DNase I hypersensitive in fetal liver nuclei of these expressing transgenic lines. Taken together, these results demonstrate that LCR activity is the culmination of at least two separable functions including: (i) a novel activity located in 5'HS3 that dominantly opens and remodels chromatin structure; and (ii) a recessive enhancer activity residing in 5'HS2. We postulate that the different elements of the LCR form a 'holocomplex' that interacts with the individual globin genes. http://repub.eur.nl/res/pub/2516/ 1996-01-01T00:00:00Z Hereditary persistence of fetal haemoglobin (HPFH) is a clinically important condition in which a change in the developmental specificity of the gamma-globin genes results in varying levels of expression of fetal haemoglobin in the adult. The condition is benign and can significantly alleviate the symptoms of thalassaemia or sickle cell anaemia when co-inherited with these disorders. We have examined structure-function relationships in the -117 HPFH gamma promoter by analysing the effect of mutating specific promoter elements on the functioning of the wild-type and HPFH promoters. We find that CCAAT box mutants dramatically affect expression from the HPFH promoter in adult blood but have little effect on embryonic/fetal expression from the wild-type promoter. Our results suggest that there are substantial differences in the structure of the wild-type gamma promoter expressed early in development and the adult HPFH promoter. Together with previous results, this suggests that gamma silencing is a complex multifactorial phenomenon rather than being the result of a simple repressor binding to the promoter. We present a model for gamma-globin gene silencing that has significant implications for attempts to reactivate the gamma promoters in human adults by pharmacological means. http://repub.eur.nl/res/pub/2528/ 1996-01-01T00:00:00Z BACKGROUND: In recent years, interest has been revived in the possibility of transplanting organs into humans from a phylogenetically disparate species such as the pig (xenotransplantation). Such discordant xenografts, however, are subject to hyperacute rejection (HAR) and activation of host complement plays a major role in this rejection. This problem may be solved through the use of transgenic technology by providing the grafted tissue with molecules that down-regulate the action of host complement. RESULTS: Transgenesis with a yeast artificial chromosome (YAC) was used to produce transgenic mice with the complete genomic gene of the human complement regulator membrane cofactor protein (MCP). Transgenic mice were obtained that exhibit full regulation of MCP as normally observed in humans. Hearts from these mice were shown to be significantly protected from HAR caused by human serum in an in vivo experimental procedure. CONCLUSIONS: We conclude that MCP can protect discordant xenografts from HAR caused by human serum and that transgenic mice can be used effectively as in vivo models for the study of the role of human complement regulatory molecules in xenotransplantation. http://repub.eur.nl/res/pub/2496/ 1994-01-01T00:00:00Z The entire chicken lysozyme gene locus including all known cis-regulatory sequences and the 5' and 3' matrix attachment sites defining the borders of the DNase I sensitive chromatin domain, is expressed at a high level and independent of its chromosomal position in macrophages of transgenic mice. It was concluded that the lysozyme gene locus carries a locus control function. We analysed several cis-regulatory deletion mutants to investigate their influence on tissue specificity and level of expression. Position independent expression of the gene is lost whenever one of the upstream tissue specific enhancer regions is deleted, although tissue specific expression is usually retained. Deletion of the domain border fragments has no influence on copy number dependency of expression. However, without these regions an increased incidence of ectopic expression is observed. This suggests that the domain border fragments may help to suppress transgene expression in inappropriate tissues. We conclude, that position independent expression of the lysozyme gene is not controlled by a single specific region of the locus but is the result of the concerted action of several tissue specific upstream regulatory DNA elements with the promoter. http://repub.eur.nl/res/pub/2461/ 1991-01-01T00:00:00Z We have used transgenic mice to study the influence of position of the human globin genes relative to the locus control region (LCR) on their expression pattern during development. The LCR, which is located 5' of the globin gene cluster, is normally required for the activation of all the genes. When the human beta-globin gene is linked as a single gene to the LCR it is activated prematurely in the embryonic yolk sac. We show that the correct timing of beta gene activation is restored when it is placed farther from the LCR than a competing human gamma- or alpha-globin gene. Correct timing is not restored when beta is the globin gene closest to the LCR. Similarly, the human gamma-globin gene is silenced earlier when present farthest from the LCR. On the basis of this result, we propose a model of developmental gene control based on stage-specific elements immediately flanking the genes and on polarity in the locus. We suggest that the difference in relative distance to the LCR, which is a consequence of the ordered arrangement of the genes, results in nonreciprocal competition between the genes for activation by the LCR.