Regulation of the NOGO‐Associated Enhancer

NOGO-A has been characterized as a neurite outgrowth inhibitor with the capacity to block axonal regeneration in the adult central nervous system (CNS); however, NOGO-A is also expressed during embryonic development when neurite outgrowth is essential and regeneration is possible. We have identified a conserved noncoding region 88.5Kb upstream of the  NOGO-A / RTN4  gene. This sequence exhibits enhancer activity in neuroectoderm during neural tube development coincident with  NOGO-A  expression. Specifically, enhancer activity localizes to the myelencephalon and the spinal cord in stage 10 chick embryos, with increased activity at the level of somites 1-6. Several putative transcription factor binding sites are found in this NOGO-associated enhancer (NAE) which may contribute to activity, including Pit-1a, HNF3b and Sox3. Site-directed mutagenesis of all three binding sites leads to a complete loss in enhancer activity. Isolated mutation of the Pit-1a or HNF3b binding site results in no apparent change in enhancer activity, while isolated mutation of the Sox3 binding site results in decreased activity. These data suggest that regulation requires Sox3 in concert with either Pit-1a or HNF3b binding sites for full activity. Additional studies are needed to confirm the functional role of this enhancer during CNS development.