Pituitary-specific expression and Pit-1 regulation of the rat growth hormone-releasing hormone receptor gene.
Mol Endocrinol
; 21(8): 1969-83, 2007 Aug.
Article
em En
| MEDLINE
| ID: mdl-17536003
ABSTRACT
The GHRH receptor is expressed in the somatotroph cell of the anterior pituitary, where it functions to mediate GHRH-stimulated GH release. To study pituitary and somatotroph cell-specific expression of this gene, a transgenic mouse model and complementary cell culture experiments were developed. The activity of the 1.6-kb proximal rat GHRH receptor promoter was examined in vivo by generating transgenic mice with the promoter directing expression of a luciferase reporter. The promoter directs tissue-specific expression; luciferase is highly expressed in the pituitary but absent from 14 other tissues. Immunocytochemistry experiments show that transgene expression is targeted to GH-expressing somatotroph cells. The transgene is 5-fold more highly expressed in males than females, and there is an increase in transgene expression leading up to the onset of puberty. The 1.6-kb promoter was further examined in cell culture experiments, which revealed that the promoter is selectively activated in pituitary cells and that promoter-reporter expression in nonpituitary cells can be enhanced by the pituitary-specific transcription factor Pit-1. EMSAs identified 10 short regions that specifically bind Pit-1 with highly variable relative affinities. The highest affinity site was previously identified and is required for Pit-1 activation of the promoter. Four additional sites contribute to Pit-1 regulation of the promoter and are important to achieving full activation of the gene. The results show that the 1.6-kb promoter is sufficient to direct tissue- and cell-specific expression in vivo and is regulated by Pit-1.
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Base de dados:
MEDLINE
Assunto principal:
Adeno-Hipófise
/
Regulação da Expressão Gênica
/
Receptores de Hormônios Reguladores de Hormônio Hipofisário
/
Receptores de Neuropeptídeos
/
Fator de Transcrição Pit-1
Tipo de estudo:
Prognostic_studies
Limite:
Animals
/
Humans
Idioma:
En
Ano de publicação:
2007
Tipo de documento:
Article