ANALYSIS OF GLUCOCORTICOID SIGNALING BY GENE TARGETING

Glucocorticoids are involved in the regulation of numerous physiologic al processes. The majority of these effects are thought to be mediated by the glucocorticoid receptor (GR) via activation and repression of gene expression. In most cases activation requires binding of a recept or-dimer to DNA while repression is mediated by protein-protein-intera ction of GR-monomers with other transcription factors. To analyse the molecular mechanisms that underlie glucocorticoid effects, mouse mutat ions in the GR gene were generated and analysed. In order to address t he role of glucocorticoid receptor signalling during development and i n physiology, the gene was disrupted by gene targeting. Most of the mi ce homozygous for the mutation die shortly after birth due to severe l ung atelectasis. Additional defects were found in the adrenals, Liver, brain, bone marrow and thymus as well as in the feedback-regulation o f the HPA-axis. To approach the question which functions of the GR are regulated by DNA-binding and which by protein-protein-interaction, a point mutation was introduced into the dimerization domain of the GR w hich is located in the DNA-binding domain. By homologous recombination in ES-cells using the Cre/loxP-system, mice carrying this mutation we re generated [GR(dim) mice]. The mice are fully viable although they s how impaired inducibility of gluconeogenetic enzymes in liver, defects in longterm renewal of erythroid progenitors and increased expression of POMC and ACTH in the pituitary. However neither in the lung nor th e adrenals were any histological abnormalties found. In conclusion GR( dim)-mice represent a valuable tool to further analyse mechanisms of p hysiological effects of the GR. (C) 1998 Elsevier Science Ltd. All rig hts reserved.