Green fluorescent protein-glucocorticoid receptor knockin mice reveal dynamic receptor modulation during thymocyte development.
To delineate the cellular targets and mechanisms by which glucocorticoids (GCs) exert their actions, we generated mice in which a green fluorescent protein (GFP)-GC receptor (GR) fusion gene is knocked into the GR locus. In these mice, the GFP-GR protein, which is functionally indistinguishable from endogenous GR, allows the tracking and quantitation of GR expression in single living cells. In GFP-GR thymus, GR expression is uniform among embryonic thymocyte subpopulations but gradually matures over a 3-wk period after birth. In the adult, GR is specifically induced to high levels in CD25(+)CD4(-)CD8(-) thymocytes and returns to basal levels in CD4(+)CD8(+) thymocytes of wild-type and positively selecting female HY TCR-transgenic mice, but not negatively selecting male HY TCR-transgenic mice. In GFP-GR/recombinase-activating gene 2(-/-) thymocytes, GR expression is down-regulated by pre-TCR complex stimulation. Additionally, relative GR expression is dissociated from GC-induced apoptosis in vivo. Results from these studies define differential GR expression throughout ontogeny, suggest pre-TCR activation as a specific mechanism of GR down-regulation, define immature CD8(+) thymocytes as novel apoptosis-sensitive GC targets, and separate receptor abundance from susceptibility to apoptosis across thymocyte populations.
Department of Pediatrics, Washington University School of Medicine, St. Louis, MO 63110, USA.
Judson A
JA
Brewer
Barry P
BP
Sleckman
Wojciech
W
Swat
Louis J
LJ
Muglia
D000818:Animals; D017252:CD3 Complex; D003907:Dexamethasone / Q000494:pharmacology; D005786:Gene Expression Regulation; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D011948:Receptors, Antigen, T-Cell / Q000502:physiology; D011965:Receptors, Glucocorticoid / Q000235:genetics / Q000502:physiology*; D013601:T-Lymphocytes / Q000502:physiology*
D017252:CD3 Complex; C115335:CD3E protein, human; D008164:Luminescent Proteins; D011948:Receptors, Antigen, T-Cell; D011965:Receptors, Glucocorticoid; D049452:Green Fluorescent Proteins; D003907:Dexamethasone