Estrogen receptors (ER) are ligand-induced transcription factors. In an Advanced Online Publication in Nature Medicine, Paolo Ciana and colleagues report their study of a transgenic mouse strain designed to follow ER activity in vivo (Nature Medicine, DOI:10.1038/nm809, 16 December 2002).

The ERE-luc mice express a luciferase reporter gene, under the control of estrogens, that can be monitored by injection of the substrate luciferine and bioluminescence measurements using a cooled charged device camera. There was a peak of luciferase activity detected at proestrus in ovaries and liver, corresponding with high levels of circulating estradiol. In other tissues and non-reproductive organs, there was a peak at diestrus. Ciana et al. also found evidence for ER activity in immature mice before gonadal production.

This model will be important for dissecting ER activation pathways that are dependent or independent of ligand, particularly in light of the use of estrogens in hormone replacement...

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