Induction of a RAR beta 2-lacZ transgene by retinoic acid reflects the neuromeric organization of the central nervous system.

The hormone retinoic acid (RA) has been implicated in the organization of the anteroposterior (AP) body axis. In this paper, we describe the effects of RA on the activity of the RA-inducible retinoic acid receptor-beta 2 (RAR beta 2) promoter. When transgenic embryos carrying a RAR beta 2-lacZ reporter gene were exposed to a single dose of RA between gestational days 8.5 to 10.5, lacZ expression was induced in the anterior central nervous system (CNS). Strikingly, the transgene was expressed in a segmented pattern reminiscent of that of Drosophila 'pair-rule' genes. RA treatment of midgastrulation embryos at day 7.5 disturbed the segmentation and produced severe craniofacial defects. We discuss the possibility that the entire anterior CNS is segmented and that this segmentation is reflected by the RAR beta 2-lacZ induction pattern.