Identification of a Putative Nogo‐A Enhancer That is Active during Development

Abstract

Although Nogo‐A is best known for its role as an inhibitor of axon regeneration in the adult central nervous system (CNS), it also appears to have a role in defining neural identity and/or neural tube induction during development. Fibroblast growth factors (Fgfs) participate in the regulation of neural plate‐specific Nogo‐A expression, but the transcriptional activators and associated enhancer elements involved have yet to be defined.In an effort to identify Nogo‐A specific enhancer elements we searched for evolutionarily conserved regions (ECRs) surrounding the Nogo gene. We identified and isolated 5 ECRs within 250 kb of Nogo that are highly conserved across divergent species. Enhancer‐reporter constructs were generated by inserting ECRs upstream of a minimal TK‐HSV promoter coupled to green fluorescent protein (GFP). These constructs were co‐electroporated with red fluorescent protein (RFP) into whole chicken embryos at the early primitive streak stage (HH4). RFP fluorescence confirmed transfection efficiency, while GFP marked enhancer activity.A 125 bp ECR (Peak 1) showed GFP expression within the neural tube, coincident with Nogo‐A expression. Furthermore, this ECR is also activated in a human teratoma cell line (NTERA) that exhibits neural differentiation and Nogo‐A expression.Thus, we have identified a conserved neural‐specific enhancer element that may regulate Nogo‐A expression during development. Further studies are needed to characterize this regulatory module and define the neural‐related transcriptional activators that interact with this region.