RU38486 blocks the steroid regulation of transmitter choice in cultured rat sympathetic ganglia

Genetically manipulated mice: a powerful tool with unsuspected caveats

Although genetic manipulations in mice have provided a powerful tool for investigating gene function in vivo, recent studies have uncovered a number of developmental phenomena that complicate the attribution of phenotype to the specific genetic change. A more realistic approach has been to modulate gene expression and function in a temporal and tissue-specific manner. The most common of these methods, the CreLoxP and tetracycline response systems, are surveyed here and their recently identified shortcomings discussed, along with a less well known system based on the E. coli lac operon and modified for use in mammals. The potential for further complications in interpretation due to hitherto unexpected epigenetic effects involving transfer of RNA or protein in oocytes or sperm is also explored. Given these problems we reiterate the necessity for the use of completely reversible methods that will allow each experimental group of animals to act as their own control. Using these methods with a number of specific modifications to eliminate non-specific effects from random insertion sites and inducer molecules, the full potential of genetic manipulation studies should be realized.

The antiglucocorticoid action of mifepristone

Glucocorticoid hormones influence the physiological activity of almost all cell types in the mammal. This is accomplished via a soluble receptor that, in the presence of an appropriate steroid, modifies the activity of RNA polymerase by binding to the site where different factors assemble for the initiation of cell transcription. The development of antiglucocorticoids has permitted the molecular elucidation of a number of underlying events. Contrary to the classical view, it is now clear that the affinity, stability and activability of the glucocorticoid receptor in the presence of a steroid are cell- and/or tissue-dependent events. The antiglucocorticoid RU 38486 can even activate transcription by binding to sites distinct from those that process transactivation by the agonist. Furthermore, glucocorticoids can sometimes activate the mineralocorticoid receptor, whereas mineralocorticoids can bind the glucocorticoid receptor. Since mifepristone is devoid of adverse toxicity, it has been used for the paraclinical diagnosis of the hypothalamus-pituitary-adrenal axis in normal volunteers, subjects with disorders of the behaviour, and the treatment of Cushing's disease. However, the whole spectrum of cell-specific processes that are antagonized by RU 38486 suggests wide ranging possibilities in the eventual application of antigluco-corticoids.