ABSTRACT
The proliferation of cells in the various tissues of the animal body is normally controlled by exogenous or autocrine hormones and growth factors that bind to specific surface receptors. The proliferation of unicellular eukaryotes such as the budding yeast Saccharomyces cerevisiae is controlled by mechanisms which monitor the nutrient supply and cell size and, when appropriate, send signals to initiate the G1 buildup. The secretion of growth hormone and the proliferation of human pituitary somatotroph cells require the stimulation of adenylate cyclase by forskolin. Adrenocortical parenchymal cells can be stimulated by Adrenocroticotropic hormone to secrete steroids and proliferate both in the animal and primary cultures. Skin keratinocytes are by far the best studied of the lining cells and can serve as a model for the others. The yeast mutants producing an activated RAS2 protein are equivalent to many kinds of human cancer cells bearing mutated ras oncogenes and their activated oncogenic RAS proteins.
