Glucocorticoids (GC) produced by the adrenal cortex mediate the body's adaptive response to stress. The synthesis and secretion of these steroids is regulated by the hypothalamic-anterior pituitary system. In response to stressful stimuli, the hypothalamus is induced to secrete corticotrophin releasing hormone (CRH) . CRH is transported via the blood to the anterior pituitary where it stimulates the secretion of the neurohormone ACTH, which then stimulates the adrenal cortex to synthesize and secrete GC. Feedback inhibition by GC on both the anterior pituitary and the hypothalamus completes the regulatory loop. Abnormalities in hypothalamic-pituitary-adrenal (HPA) axis function can result in a number of clinical disorders including depression. Depressed patients show hypersecretion of CRH, consistent with the findings that CRH influences motor activity, feeding, and sexual behaviors, all functions which are altered by depression. Knowledge of the regulation of CRH gene expression will provide the groundwork for understanding both normal and abnormal responses to stress. The first step will be to establish the basis for tissue-specific activation of the CRH gene in the paraventricular nucleus of the hypothalamus and other localized regions of the brain and periphery. Transgenic mice bearing the rat CRH gene and varied amounts of 5' flanking DNA will be constructed and tissues analyzed by in situ hybridization in order to locate the cis-acting DNA sequences necessary and sufficient for appropriate expression of the transgene. Immortalized cell lines producing gene products characteristic of differentiated hypothalamic cells would be invaluable for studying CRH gene regulation. To achieve this, tissue-specific elements from the CRH gene will be engineered onto a gene encoding a selectable marker (neomycin) as well as an oncogene (temperature sensitive SV40 T-antigen) and the hybrid genes used to produce transgenic mice. Cell lines will be derived from these animals at a young age using the selective agent and expression studies done at the nonpermissive temperature. CRH transgenic mouse studies will shed light on the intricacies of cell-specific expression in the brain and hypothalamus, develop cell lines necessary to study regulation of gene expression, and thus provide the basis for understanding clinically important syndromes such as depression.
| Keegan, C E; Karolyi, I J; Knapp, L T et al. (1994) Expression of corticotropin-releasing hormone transgenes in neurons of adult and developing mice. Mol Cell Neurosci 5:505-14 |
