Expression of corticotropin-releasing hormone transgenes in neurons of adult and developing mice.

The DNA sequences important for cell-specific expression and developmental regulation of corticotropin-releasing hormone (CRH) were analyzed in transgenic mice. A construct containing 0.5 kb of CRH 5' flanking DNA linked to the chloramphenicol acetyltransferase reporter gene was expressed in many brain regions and in several ectopic peripheral sites, suggesting that this portion of the CRH gene contains basal promoter activity but lacks DNA elements necessary for appropriate tissue specificity. Cell specificity of transgene expression was examined with a CRH-beta-galactosidase reporter construct containing the same 0.5-kb CRH promoter fragment, but also including the CRH structural gene and 2 kb of CRH 3' flanking DNA. Transgene expression was observed in inappropriate regions of the brain, but no expression was detected in peripheral tissues, suggesting that these additional CRH sequences suppress inappropriately high levels of peripheral expression. Cell-specific expression improved significantly with the inclusion of 8.7 kb of CRH 5' flanking DNA. Individual transgenic lines exhibited expression in a number of the major CRH neuronal groups including the paraventricular nucleus, medial geniculate nucleus, inferior olivary nucleus, and Barrington's nucleus. Transgene expression was properly activated in Barrington's nucleus during development. This study demonstrates that the regulatory control of cell-specific and developmentally appropriate CRH expression is complex, utilizing multiple DNA sequence elements located upstream and downstream of the CRH transcription start site.