RB plays dual roles in the regulation of cell proliferation and differentiation. The nervous tissue-specific gene Rig-1, a member of the roundabout (Robo) guidance receptor family, was identified as an RB-regulated gene in the mouse embryo. Herein, we report that a 2.3kb genomic DNA fragment, which contains the first 129 bases of the 5'-untranslated region and 2.2kb of the 5'-flanking region of Rig-1, has a cell type-specific promoter activity. Rig-1 promoter activity is downregulated by RB and upregulated by Pax-2. Furthermore, Rig-1 and Pax-2 mRNAs are coexpressed in the hindbrain and spinal cord of the E11.5 mouse embryo, suggesting that Pax-2 may regulate Rig-1 expression during the embryonic stage. Pax-2 interacts with RB and reverses its transcriptional suppression on the Rig-1 promoter. In summary, the ubiquitous tumor suppressor RB and the neuron-enriched transcription factor Pax-2 may play a role in the regulation of Rig-1 expression during embryogenesis.