Expression of the homeo box-containing gene En-2 delineates a specific region of the developing mouse brain

We have examined the pattern of expression of the homeo box-containing gene En-2 during mouse embryogenesis using in situ hybridization. Transcripts were first detected in the neural folds of 8.0-day, 5-somite embryos, and expression continued throughout development into adulthood. Hybridization occurred only in the central nervous system (CNS) and was limited to one band of the neural tube and to parts of those structures that later developed from it; the cerebellum, pons, periaqueductal gray, and colliculi. Expression in the germinal zone of the CNS was uniform within the hybridizing band. However, later in development, once cells had migrated out of the germinal zone, there was a reduction in the extent of hybridization and an increase in its spatial complexity. In the adult, expression of En-2 appeared to be limited to specific groups of neurons. The early, localized expression of En-2 within an apparently homogeneous tissue is consistent with the hypothesis that En-2 plays a role in defining a spatial domain within the developing brain.