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Figure 4. Liver Gene Expression in Transgenic Gut Preparations(A–C) Transthyretin (TTR) RNA expression. (A) In wild-type preparations, expression is only seen within the liver. (B and C) TTR-Xlhbox8-VP16 transgenics. (B) In this case, there is complete conversion of liver to pancreas, and transthyretin expression has been completely suppressed. (C) In this case, half the liver has changed into pancreas, and transthyretin expression is seen only in the other half. In all examples, nontransgenic guts were stained simultaneously with transgenic guts, and the staining reaction was stopped in both when the nontransgenic expression was clearly evident.(D) Liver differentiation begins normally in TTR-Xlhbox8-VP16 tadpoles. Xhex (blue) and GFP (magenta, driven by the elastase promoter) expression. GFP RNA is seen only in the dorsal and ventral pancreas at stage 40; no GFP expression is detected in the liver. Xhex expression is normal at this stage and is present throughout the whole liver.(E–H) Timing of liver differentiation in normal nontransgenic tadpoles: from 3 days, the liver has become a separate organ, with Xhex and AMBP expressed throughout. (E) Xhex RNA at stage 40 (3 days). (F) Xhex RNA at stage 45 (5 days). (G) AMBP RNA at stage 40 (3 days). (H) AMBP expression at stage 45 (5 days).(I and J) The TTR promoter becomes active in Xenopus tadpoles only after the liver has differentiated. This shows RNA in situ hybridization for GFP driven by the TTR promoter. (I) At stage 40 (3 days), no GFP expression is detected. (J) GFP expression is first detected at stage 44 (4 days). |
