DYNAMIC MONITORING AND QUANTIFICATION OF GENE-EXPRESSION IN SINGLE, LIVING CELLS - A MOLECULAR-BASIS FOR SECRETORY-CELL HETEROGENEITY

Progress in understanding the dynamics of gene expression has been ham pered by lack of a strategy for continuously monitoring this process w ithin normal, living cells. Here, we employed a modification of conven tional luciferase technology to make single and repeated real-time mea surements of PRL gene expression from individual, living lactotropes f rom nursing rats. Cells were individually transfected by microinjectio n with a PRL promoter/luciferase reporter construct. Levels of PRL gen e transcription were quantified by photonic imaging in the same cells before and after 24 h of culture in the presence or absence of the dop amine agonist bromocryptine or epidermal growth factor, two well known regulators of PRL gene transcription. We found these cells to be rema rkably heterogeneous with respect to basal PRL gene expression and tha t the degree of activity within a single cell could fluctuate greatly over time under basal culture conditions. Treatment with bromocryptine or epidermal growth factor induced predictable and reversible changes in the average responses observed, yet individual cells displayed mar ked differences in response to these agents. These findings demonstrat e the utility of this paradigm for monitoring dynamics of gene express ion within normal, living cells of any type. Moreover, they provide a molecular basis for the secretory heterogeneity and plasticity that ha ve come to be known as hallmarks of lactotrope cell function.