Fig. 4. TRX prevents re-establishment of repression. (A) BHL4G4PRE expression is maintained anterior to PS6 throughout embryonic development. In situ hybridization in late embryos shows that BX-driven expression ends in the ectoderm and H1-driven expression is limited to dorsolateral spots (arrows). In larvae, expression is repressed in the wing disc (w) and limited to the posterior haltere (h) and third leg (l) discs. (B) In homozygous trx embryos, the level of expression is reduced. In heterozygous trx larvae, expression in the posterior haltere is variegated and almost absent in the third leg disc. The arrows show the repressed domains in the haltere disc and the weak residual expression in the leg disc.