In vivo drug testing in Tg:Pomc-Pttg zebrafish. (A) Pttg overexpression directed by zebrafish Pomc promoter induced cyclin E up-regulation in Tg:Pomc-Pttg transgenic pituitary at 3 mo. mRNA levels were assayed by quantitative real-time PCR (mean ± SE of relative expression; n = 30 pituitaries for each group). (B) Western blot of mouse corticotroph tumor AtT20 cells transfected with a control or PTTG siRNA. (C) In vivo treatment of Tg:Pomc-Pttg;Pomc-eGFP embryos with small-molecule CDK inhibitors (50 μM) or 0.2% DMSO as control from 18 to 40 hpf. One hundred to one hundred fifty embryos were treated with each compound. Representative images of live embryos are shown with gross morphology (Right) and pituitary Pomc-GFP–positive cells at higher magnification (Left) at 40 hpf. Embryos exposed to flavopiridol developed early developmental defect before pituitary POMC cell ontogeny occurs. (D) Relative expression of pituitary Pomc-eGFP fluorescence analyzed using Volocity 5.2 software (Improvision; mean ± SE of relative expression, n = 7). (E) R-roscovitine specifically suppresses expansion of pituitary POMC cells overexpressing zPttg from 18 to 48 hpf. Double transgenic Tg:Pomc-Pttg;Prl-RFP embryos were generated by breeding Tg:Pomc-Pttg fish with a previously generated PRL-RFP transgenic line, in which RFP was targeted to pituitary lactotrophs by a zebrafish Prolactin promoter (34). Representative fluorescent microscopy of pituitary POMC-eGFP (a and b) and PRL-RFP (c and d) expression in live Tg:Pomc-Pttg;Pomc-eGFP and Tg:Pomc-Pttg;Prl-RFP embryos treated with 0.2% DMSO (a and c) or 50 μM R-roscovitine (b and d). (F) Relative expression of pituitary POMC-eGFP or PRL-RFP fluorescence were analyzed (mean ± SE of relative expression; n = 10). Results represent one of three similar experiments; *P < 0.02 and **P < 0.000005. (Scale bar, 50 μm.)
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