Calcium dynamics and resting transcriptional activity regulates prolactin gene expression.

Research on the regulation of hormone gene expression by calcium signaling is hampered by the difficulty of monitoring both parameters within the same individual, living cells. Here we achieved concurrent, dynamic measurements of both intracellular Ca(2+) concentration ([Ca(2+)](i)) and prolactin (PRL) gene promoter activity in single, living pituitary cells. Cells were transfected with the luciferase reporter gene under control of the PRL promoter and subjected to bioluminescence and fluorescence imaging before and after presentation of TSH-releasing hormone (TRH), a prototypic regulator of PRL secretion and gene expression that induces a transient Ca(2+) release, followed by sustained Ca(2+) influx.

PRL gene expression in individual living mammotropes displays distinct functional pulses that oscillate in a noncircadian temporal pattern.

PRL gene expression in the anterior pituitary has been the focus of intensive investigation for many years, but very little information is available on the actual dynamics by which this process occurs in individual mammotrope cells. Here, we used single cell bioluminescent imaging microscopy and a recently refined reporter gene strategy to measure PRL promoter-driven gene expression (PRL-GE) in individual living primary mammotropes. Using this approach we report a new phenomenon involving repetitive on/off gene expression bursts that occurred in a distinctly noncircadian oscillatory pattern.