A remote and highly conserved enhancer supports amygdala specific expression of the gene encoding the anxiogenic neuropeptide substance-P

The neuropeptide substance P (SP), encoded by the preprotachykinin-A (PPTA) gene, is expressed in the central and medial amygdaloid nucleus, where it plays a critical role in modulating fear and anxiety related behaviour. Determining the regulatory systems that support PPTA expression in the amygdala may provide important insights into the causes of depression and anxiety related disorders and will provide avenues for the development of novel therapies. In order to identify the tissue specific regulatory element responsible for supporting expression of the PPTA gene in the amygdala, we used long-range comparative genomics in combination with transgenic analysis and immunohistochemistry. By comparing human and chicken genomes, it was possible to detect and characterise a highly conserved long-range enhancer that supported tissue specific expression in SP expressing cells of the medial and central amygdaloid bodies (ECR1; 158.5 kb 5' of human PPTA ORF). Further bioinformatic analysis using the TRANSFAC database indicated that the ECR1 element contained multiple and highly conserved consensus binding sequences of transcription factors (TFs) such as MEIS1. The results of immunohistochemical analysis of transgenic lines were consistent with the hypothesis that the MEIS1 TF interacts with and maintains ECR1 activity in the central amygdala in vivo. The discovery of ECR1 and the in vivo functional relationship with MEIS1 inferred by our studies suggests a mechanism to the regulatory systems that control PPTA expression in the amygdala. Uncovering these mechanisms may play an important role in the future development of tissue specific therapies for the treatment of anxiety and depression.