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Biomedical subjects

N Dillon

Publications and source records attributed to N Dillon.

33 records · Page 2Linked to original sources
PubMed1993

Synthetic human beta-globin 5'HS2 constructs function as locus control regions only in multicopy transgene concatamers.

Transgenes linked to the beta-globin locus control region (LCR) are transcribed in a copy-dependent manner that is independent of the integration site. It has previously been shown that the LCR 5'HS2 region does not require its NF-E2 dimer binding site for LCR activity. In this paper we analyse synthetic 5'HS2 core constructs containing point mutations in the other factor binding sites 3' of the NF-E2 dimer site. The results show that 5'HS2 core is a partially active LCR that functions in a concatamer of at least two copies but not when present as a single copy in transgenic mice and that no single binding site within 5'HS2 is required for position-independent expression. In addition, the H-BP factor is identical to upstream stimulatory factor (USF) and full enhancement levels by 5'HS2 core in MEL cells require a combination of all the factor binding sites. We suggest that 5'HS2 cores in a concatamer interact with each other to establish an area of open chromatin and that this process may be the basis of LCR function.

Animals↗
PubMed1993

Transcriptional regulation of multigene loci: multilevel control.

Recent studies indicate that different levels of control operate within multigene loci. In addition to regulatory sequences immediately flanking the genes, there are also elements that act over long distances on more than one gene. Competition for these elements among genes can influence both the level and timing of gene expression during development.

Animals↗
PubMed1993

The regulation of human globin gene expression.

The haemopoietic system provides a well-characterized and accessible system for studying the mechanisms of developmental regulation and differentiation in higher eukaryotes. Our current understanding of the steps involved in the early stages of differentiation are poorly understood but a great deal is now known about the mechanisms by which globin expression is regulated in cells committed to the erythroid lineage. Many of the critical cis-acting sequences and some of the important trans-acting factors involved have been identified and current work is focusing on how these interact to produce high levels of tissue-specific and developmentally regulated expression of the human globin genes.

Animals↗
PubMed1992

A single point mutation is the cause of the Greek form of hereditary persistence of fetal haemoglobin.

In normal humans the fetal stage-specific gamma-globin genes are silenced after birth and not expressed in the adult. Exceptions are seen in cases of hereditary persistence of fetal haemoglobin (HPFH). These are clinically important because the elevated levels of gamma-globin can alleviate beta-thalassaemia and sickle cell anaemia. One class of mutations is associated with point mutations in the promoter of the gamma-globin genes (non-deletion HPFH), whereas others seem to be caused by large deletions 3' to the gamma-globin genes. To test whether the point mutation found in the Greek non-deletion HPFH (guanine to adenine at nucleotide position -117) is the cause of the raised gamma-globin levels in the adult stage and is not just a linked polymorphism, we engineered this mutation into a gamma-globin gene. When this gene was introduced into mice, the presence of the -117 mutation results in persistence of gamma-globin expression at a high level and a concomitant decrease in beta-globin expression in fetal and adult mice. We show that these changes correlate with the loss of binding of the transcription factor GATA1 to the gamma-globin promoter, suggesting that it may act as a negative regulator of the gamma-globin gene in adults.

Animals↗
PubMed1992

Developmental regulation of a complete 70-kb human beta-globin locus in transgenic mice.

We have used a linker-based ligation strategy to combine two 35-kb cosmid inserts from the human beta-globin locus into one linear fragment containing the entire locus. This 70-kb fragment was introduced into transgenic mice by microinjection of fertilized eggs. Southern blot analysis showed that a single complete transgene locus can be introduced into the germ line with high efficiency. Analysis of the expression patterns of the locus during development shows that the epsilon-globin gene behaves as a purely embryonic gene, the gamma-globin gene as an embryonic and early fetal gene, and the beta-globin gene as a fetal adult gene. Quantitation of expression showed that the levels of transcription of the epsilon- and gamma-globin genes are reversed relative to their mouse homologs but that the total output of the human and mouse loci is constant during development. These results suggest that multiple changes in DNA sequences and transcription factor balance must have occurred for the human gamma-globin gene to have evolved into a fetal gene.

Animals↗
PubMed1991

Expression of adult and tadpole specific globin genes from Xenopus laevis in transgenic mice.

Transgenic mice were generated which carried the adult alpha and beta-globin genes and the major tadpole specific beta-globin gene of Xenopus laevis. The adult specific alpha and beta genes were found to express in erythroid tissues in adult mice, while the major tadpole specific beta gene (beta T1) was expressed in blood from 12.5 day embryos. The pattern of expression of the beta T1 gene during mouse development was consistent with its being regulated as an embryonic globin gene in the mouse. This observation suggests that some of the factors mediating globin switching have been conserved during the evolution of modern amphibia and mammals and raises interesting questions concerning the evolution of vertebrate globin gene switching.

Aging↗
PubMed1991

Human gamma-globin genes silenced independently of other genes in the beta-globin locus.

Erythropoiesis during human development is characterized by switches in expression of beta-like globin genes during the transition from the embryonic through fetal to adult stages. Activation and high-level expression of the genes is directed by the locus control region (LCR), located 5' to the epsilon gene. The location of the LCR and its role in directing high-level expression of the globin genes has led to the suggestion that competition from the beta gene for interaction with the LCR has a major role in silencing the fetal gamma genes during adult life. We have now constructed lines of transgenic mice containing the human A gamma globin gene linked to the LCR. We observe high-level expression of the transgene in the embryonic stages but silencing of the gene in adult animals. We conclude that the gamma gene is not deregulated by the presence of the LCR and that competition from the beta gene is not required for silencing of the gamma genes in adult life. The silencing is therefore likely to be mediated by stage-specific factors binding to sequences immediately flanking the genes.

Animals↗
PubMed1991

Importance of globin gene order for correct developmental expression.

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.

Aging↗
PubMed1980

Age and beta adrenoceptor-mediated function.

Beta adrenoceptor-mediated responsiveness to isoproterenol was compared in young and old subjects using the production of cyclic adenosine monophosphate (cyclic AMP) by lymphocytes as an index. The mean log dose-response curve for the elderly group was displaced to the right and the mean maximum response was less than that for the young subjects. The results corroborate evidence of a decreased response to isoproterenol-induced increases in heart rate in the elderly and raise the possibility of a generalized decrease in beta adrenoceptor-mediated functions in old age.

Adolescent↗
PubMedDate not supplied

Induction and inactivation of a cytochrome P450 confering herbicide resistance in wheat seedlings.

Cytochrome P450-dependent enzymes from wheat catalyze the oxidation of endogenous compounds (lauric and oleic acids) and of several herbicides (diclofop, chlortoluron, bentazon). Treatment of wheat seedlings with the safener, naphthalic anhydride and with phenobarbital increases dramatically several P450-dependent enzyme activities including diclofop and lauric acid hydroxylation. The parallel induction of lauric acid (omega-1)-hydroxylase and diclofop hydroxylase activities suggests that both compounds proceeds from the same or very similar forms of P450. To test whether either one or multiple P450 forms are involved in these oxidations, we have designed selective irreversible inhibitors of lauric acid (omega-1)-hydroxylase. Results of in vivo and in vitro experiments with acetylenic analogs of lauric acid (10- and 11-dodecynoic acids) strongly suggest that a single P450 catalyzes both laurate and diclofop hydroxylation. Treatment of wheat seedlings with these acetylenes results in a strong inhibition of the in vivo metabolism of diclofop although oxidation of chlortoluron and bentazon are not affected. Our results suggest that at least three distinct P450 forms are involved in the detoxification process of the three herbicides. Interestingly, we also demonstrate that herbicides themselves are potent inducers of the amount of total P450 and laurate/diclofop hydroxylase activies. This increased capacity of wheat to detoxify the herbicide through the induction of P450 enzymes seems to be for a large extend the mechanism which confers a tolerance on various herbicides.

Benzothiadiazines↗