- Human HOX genes are differentially activated by retinoic acid in embryonal carcinoma cells according to their position within the four loci. Stornaiuolo, A., Acampora, D., Pannese, M., D'Esposito, M., Morelli, F., Migliaccio, E., Rambaldi, M., Faiella, A., Nigro, V., Simeone, A. Cell Differ. Dev. (1990)