Endogenous RA activity in the developing forebrain.
Tissues were cultured as explants on a monolayer of F9 RARE-lacZ RA-reporter cells, then stained for β-galactosidase activity. (A–C) At E12.5, cortex and LGE were both negative, whereas eye was positive. (D–F) At E13.5, LGE and eye explants induced RA activity in the reporter cells, but not cortex. (G–I) At E14.5, meninges and LGE induced RA activity while the reporter cells surrounding E14.5 cortical explants remained negative. (J–L) For E14.5 Raldh2−/− (KO) tissues, meninges and cortex were negative, while LGE explants remained positive. (M–O) For E14.5 Raldh3−/− (KO) tissues, meninges explants remained positive, while cortex and LGE were negative. For each genotype and stage, tissues from at least three embryos were analyzed with similar results.