. In the sections that follow, we review the role of these modifications within chromatin and their potential contributions to NR-mediated gene regulation. Ubiquitin and chromatin structure: implications for NR-mediated gene
H K Kinyamu, J Chen and T K Archer
Cissi Gardmo and Agneta Mode
. 2004 ). In this study, we have used the a1bg promoter to investigate molecular mechanisms of GH-mediated female-specific gene regulation. Materials and methods Animals and hormone therapy Normal Sprague
K J Oliveira, T M Ortiga-Carvalho, A Cabanelas, M A L C Veiga, K Aoki, H Ohki-Hamazaki, K Wada, E Wada and C C Pazos-Moura
acts to inhibit the TSH secretory mechanism. Here, studying mice lacking NB-R we were able to demonstrate the long-term role of NB in the regulation of pituitary–thyroid axis hormonal secretion and gene regulation. At basal state, NBR-KO mice
R Gruemmer, L Klein-Hitpaß and J Neulen
-5 (3.5-fold decrease) and elastin (14.9-fold decrease) could be observed. Up- and down-regulated genes in HUVECs treated with granulosa cell conditioned medium To analyze if the observed gene regulation induced by
R. K. Iles, B. H. Czepulkowski, B. D. Young and T. Chard
The β-subunit of human chorionic gonadotrophin (hCG) is coded on chromosome 19 by the β-hCG-hLH gene cluster. Genomic DNA has been isolated from bladder tumour cell lines which ectopically express β-hCG. The β-hCG—hLH gene cluster was probed for possible rearrangement or amplification and cells karyotyped for chromosome 19 abnormalities. No rearrangement or amplification of the gene cluster and no consistent abnormalities of chromosome 19 were found. The expression of β-hCG by bladder tumours is therefore likely to be the result of altered gene regulation and not a rearrangement or amplification of this gene cluster.
A. Levy and S. L. Lightman
We have examined the effects of human GH-releasing factor (1–44) (GRF), cortisol and somatostatin-(1–14) on GH gene expression in solid tissue and dispersed cells from human pituitary adenomas using quantitative in-situ hybridization histochemistry. Sections cut from tissue obtained at hypophysectomy from three acromegalic patients were hybridized to probes directed against mature α-subunit, GH, prolactin, pro-opiomelanocortin, TSHβ-subunit and LHβ-subunit mRNA. Only one biopsy contained GH mRNA in isolation. A second was found to co-exhibit GH, prolactin and α-subunit mRNA, and a third was found to contain prolactin, TSHβ-subunit, α-subunit and LHβ-subunit mRNA, with GH mRNA below the limit of specific detection, indicating that the sample was composed of normal rather than adenomatous pituitary tissue. GH mRNA in individual dispersed cells derived from the latter declined to barely detectable levels over 287 h, both in cultures containing GRF (10 ng/ml) or GRF (10 ng/ml) plus somatostatin (10 ng/ml) and in controls, but increased fourfold in cultures containing GRF (10 ng/ml) plus cortisol (0·5 μmol/l). GH mRNA remained unchanged in both adenoma samples over 138 and 450 h, irrespective of the addition of GRF or GRF plus hydrocortisone. In these samples, somatostatin plus GRF had no consistent effect. These studies confirm that quantitative in-situ hybridization histochemistry can be used to investigate hormone gene regulation in small samples of human tissue and should enable us to define more clearly the level at which abnormal gene regulation occurs.
Ayse Elif Erson-Bensan
Our understanding of the extent of microRNA-based gene regulation has expanded in an impressive pace over the past decade. Now, we are beginning to better appreciate the role of 3′-UTR (untranslated region) cis-elements which harbor not only microRNA but also RNA-binding protein (RBP) binding sites that have significant effect on the stability and translational rate of mRNAs. To add further complexity, alternative polyadenylation (APA) emerges as a widespread mechanism to regulate gene expression by producing shorter or longer mRNA isoforms that differ in the length of their 3′-UTRs or even coding sequences. Resulting shorter mRNA isoforms generally lack cis-elements where trans-acting factors bind, and hence are differentially regulated compared with the longer isoforms. This review focuses on the RBPs involved in APA regulation and their action mechanisms on APA-generated isoforms. A better understanding of the complex interactions between APA and RBPs is promising for mechanistic and clinical implications including biomarker discovery and new therapeutic approaches.
A. J. L. Clark, P. M. Lavender, G. M. Besser and L. H. Rees
As an approach to understanding the abnormalities of pro-opiomelanocortin (POMC) gene regulation in human ACTH-secreting tumours, we have analysed the POMC mRNA content of nine such tumours using the Northern blot technique. Most of the tumours and normal human pituitary contained easily detectable quantities of POMC mRNA. The length of this message in most tumours was similar to, or slightly larger than, that in the normal pituitary (1150–1200 bases). Ribonuclease H studies suggested that the origin of any size heterogeneity was a longer poly(A) tail in the tumour RNA. Some tumours, however, expressed a short POMC mRNA (800 bases) which may lack the first two exons of the POMC gene as has been described. A third POMC mRNA size variant (1500 bases) was also seen in low levels in two cases, and as the principal mRNA species in one case. Primer extension and S1 nuclease protection studies suggested that most transcripts in the tumours analysed originated from the conventional promoter, and thus the use of an alternative promoter is not an adequate explanation for the expression of this gene in ectopic ACTH-secreting tumours.
Elena Ivanova and Gavin Kelsey
Genomic imprinting is an important and enigmatic form of gene regulation in mammals in which one copy of a gene is silenced in a manner determined by its parental history. Imprinted genes range from those with constitutive monoallelic silencing to those, typically more remote from imprinting control regions, that display developmentally regulated, tissue-specific or partial monoallelic expression. This diversity may make these genes, and the processes they control, more or less sensitive to factors that modify or disrupt epigenetic marks. Imprinted genes have important functions in development and physiology, including major endocrine/neuroendocrine axes. Owing to is central role in coordinating growth, metabolism and reproduction, as well as evidence from genetic and knockout studies, the hypothalamus may be a focus for imprinted gene action. Are there unifying principles that explain why a gene should be imprinted? Conflict between parental genomes over limiting maternal resources, but also co-adaptation between mothers and offspring, have been invoked to explain the evolution of imprinting. Recent reports suggest there may be many more genes imprinted in the hypothalamus than hitherto expected, and it will be important for these new candidates to be validated and to determine whether they conform to current notions of how imprinting is regulated. In fully evaluating the role of imprinted genes in the hypothalamus, much work needs to be done to identify the specific neuronal populations in which particular genes are expressed, establish whether there are pathways in common and whether imprinted genes are involved in long-term programming of hypothalamic functions.
Y-J Y Wan, T Pan, L Wang, J Locker and T-C J Wu
In McA-RH 8994 rat hepatoma cells, all-transretinoic acid (t-RA) induces expression of the α-fetoprotein (AFP) and albumin genes and results in a phenotype similar to differentiated fetal hepatocytes. The present study elucidated the mechanism involved in AFP gene regulation mediated by retinoic acid. Northern blot analyses demonstrated that 9-cis-retinoic acid (c-RA), a ligand for retinoid x receptors (RXRs), also induced expression of the AFP gene in McA-RH 8994 cells. The induction was time- and dose-dependent. Northern blots and transfection assays using the 7·3 kb full-length regulatory region of the AFP gene demonstrated that c-RA was more effective than t-RA in regulating expression of the AFP gene. At 10−7 m, c-RA increased AFP mRNA 5-fold and chloramphenicol acetyltransferase (CAT) activity 2·5-fold. In contrast, t-RA at a concentration of 10−7 m exerted no significant effect; 10− 6 to 10−5 m t-RA was needed to affect AFP gene expression. These data suggested that activation of RXRs is essential for the regulation of the AFP gene. Co-transfection experiments revealed that overexpression of RXRα in McA-RH 8994 cells further enhanced the CAT activity induced by c-RA. In addition, c-RA did not alter the half-life of AFP mRNA. Thus, RXRα may play a crucial role in transcriptional regulation of the AFP gene and in controlling hepatocyte phenotype.