Fig. 7. HES1 exerts a dominant-negative effect upon the ATH5 promoter. (A) Retinal cells at stages 22-23 or 29-30 were transfected with an ATH5-promoter/CAT-reporter plasmid alone or with different combinations of the ATH5, NGN2 and HES1 expression vectors. NGN2 and HES1 expression vectors were co-transfected in different ratios, as indicated. (B) Peripheral and central regions of retina were dissected at stage 22-23. They were electroporated with NGN2 and control expression vectors and cultured as explants for 24 hours. The presence of ATH5 mRNA was detected by northern blot hybridisation. Overexpression of NGN2 upregulated ATH5 expression in the central but not in the peripheral retina. (C) Retinal cells at stages 24 or 29-30 were transfected with an ATH5-promoter/lacZ-reporter plasmid singly or in combinations with ATH5 or NGN2 expression vectors. lac⁺ cells were revealed and processed for in situ hybridization with a HES1-specific riboprobe. Overexpression of NGN2 increased the relative number of double-labelled cells, indicating that the NGN2 protein can activate the ATH5 promoter in cells that express HES1 (a), unlike the ATH5 protein (b).