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Real-Time Visualization of Human Prolactin Alternate Promoter Usage in Vivo Using a Double-Transgenic Rat Model

Molecular Physiology (S.S., N.K., G.B., J.J.M.), MRC Human Reproductive Sciences Unit (J.R.M., A.S.M.), and Research Animal Pathology Core (D.G.B.), University of Edinburgh, Edinburgh EH16 4TJ, Scotland, United Kingdom; Endocrine Sciences Research Group (S.F., J.R.E.D.), University of Manchester, Manchester M13 9NT, United Kingdom; and Centre for Cell Imaging (C.V.H., A.D.A., D.G.S., M.R.H.W.), University of Liverpool, Liverpool L69 7ZB, United Kingdom

Address all correspondence and requests for reprints to: Professor John J. Mullins, Molecular Physiology, University of Edinburgh, Queen’s Medical Research Institute, 47 Little France Crescent, Edinburgh EH16 4TJ, Scotland, United Kingdom. E-mail: j.mullins{at}ed.ac.uk.

We have generated a humanized double-reporter transgenic rat for whole-body in vivo imaging of endocrine gene expression, using the human prolactin (PRL) gene locus as a physiologically important endocrine model system. The approach combines the advantages of bacterial artificial chromosome recombineering to report appropriate regulation of gene expression by distant elements, with double reporter activity for the study of highly dynamic promoter regulation in vivo and ex vivo. We show first that this rat transgenic model allows quantitative in vivo imaging of gene expression in the pituitary gland, allowing the study of pulsatile dynamic activity of the PRL promoter in normal endocrine cells in different physiological states. Using the dual reporters in combination, dramatic and unexpected changes in PRL expression were observed after inflammatory challenge. Expression of PRL was shown by RT-PCR to be driven by activation of the alternative upstream extrapituitary promoter and flow cytometry analysis pointed at diverse immune cells expressing the reporter gene. These studies demonstrate the effective use of this type of model for molecular physiology and illustrate the potential for providing novel insight into human gene expression using a heterologous system.