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B Pichon

Publications and source records attributed to B Pichon.

23 records · Page 2Linked to original sources
PubMed1996

Induction of nerve growth factor-induced gene-B (NGFI-B) as an early event in the cyclic adenosine monophosphate response of dog thyrocytes in primary culture.

We investigated the induction of nerve growth factor-induced gene-B (NGFI-B) in dog thyrocytes in primary culture stimulated by different agents. The dog NGFI-B complementary DNA (cDNA) was cloned from a cDNA library of dog thyrocytes and used to study, by Northern blotting, the level of NGFI-B messenger RNA (mRNA) in those cells. We have shown that TSH and forskolin, which both induce proliferation and differentiation of the thyroid cells by activation of the protein kinase A pathway, lead to a strong and transient expression of two NGFI-B mRNA species, which differ in the length of the poly(A) tail. In contrast, 12-O-tetradecanoyl-13-phorbol-acetate (TPA) and epidermal growth factor, which induce proliferation and dedifferentiation of those cells by activation of the protein kinase C and the protein tyrosine kinase cascade, respectively, lead to a weaker expression of NGFI-B mRNA. In parallel, we studied the transactivation capacity of NGFI-B in the same cell system by transient transfection of a chloramphenicol acetyl transferase reporter construction containing a NGFI-B-dependent synthetic promoter. The highest transactivation was observed after forskolin stimulation, whereas transactivation after TPA stimulation was weak and no significant transactivation was observed after epidermal growth factor stimulation. Taken together, these results show that NGFI-B is an immediate early gene product that is mainly induced by the cAMP-dependent pathway in dog thyrocytes. Moreover they suggest that NGFI-B expression could be one of the early transcriptional changes induced specifically by this cascade and leading to differentiation and/or proliferation of these cells.

Amino Acid Sequence↗
PubMed1994

Unmethylated thyroglobulin promoter may be repressed by methylation of flanking DNA sequences.

The thyroglobulin gene, like many other tissue-specific genes, appears to be specifically less methylated in the differentiated cell type where it is transcribed. The thyroglobulin gene promoter elements themselves are highly CG-deficient and do not contain any HpaII/MspI sites. In this study, using DNA constructs that were methylated in vitro with HpaII or MspI methylases, we show that DNA methylation of vector sequences is sufficient to repress the activity of the thyroglobulin gene promoter in transient transfection experiments. Reporter-gene expression from a plasmid containing only the proximal thyroglobulin gene promoter is sensitive to DNA methylation even in fully differentiated thyrocytes. Transcription from methylated plasmids containing the thyroglobulin gene enhancer and proximal promoter is also clearly reduced when the transfected cells are maintained under less-differentiated conditions. These results indicate that DNA methylation can influence, from a distance, the activity of an unmodified promoter. Our results also agree with the view that loss of DNA methylation does not constitute a prerequisite for thyroglobulin gene expression in differentiated thyrocytes, where the thyroglobulin gene enhancer and promoter are activated. However, the production of thyroglobulin transcripts could be severely impaired when this activation is not maximal, as is the case in less-differentiated cells or when the enhancer element is lacking. We suggest that DNA methylation helps to maintain the thyroglobulin gene in an inactive state unless all of the conditions required for its expression are fulfilled, and that the thyroid-specific demethylation events are a consequence of the activation state of the gene.

Animals↗
PubMed1988

Fully automated analytical system using liquid-solid extraction and liquid chromatography for the determination of CGP 6140 in plasma.

Liquid-solid extraction on disposable extraction columns (DECs) and liquid chromatography can be combined in a completely automated analyser. The Gilson ASPEC system was used to develop a procedure for the determination of CGP 6140 in plasma. Both sample preparation via C8 Bond-Elut DECs and injection were fully automatic. The fully automated system prepared the samples by performing the same operations as for a manual procedure. The DEC was first wetted with methanol, then with water. A 400-microliters volume of plasma and 40 microliters of the internal standard solution, diluted with 1 ml of water, were applied to the DEC, rinsed with 10(-2) mol/l dipotassium hydrogenphosphate and eluted from the DEC with 300 microliters of acetonitrile-methanol (50:50, v/v). The eluting strength of the eluate was reduced by dispensing 1 ml of water into each vial prior to direct injection into a Spherisorb ODS column via a 1-ml loop. This allowed the reconcentration of the extracted compounds on the top of the column, as they were injected in a large volume of solvent of lower eluting strength than the mobile phase [acetonitrile-methanol-4 x 10(-3) mol/l ammonia solution (54.5:5:40.5, v/v/v)]. Reproducibility results are presented.

Chemical Phenomena↗