Abstract
Nitric oxide synthase is ubiquitously present in metazoans and is involved in a wide range of biological processes. Three distinctNosgenes have been so far identified in vertebrates exhibiting a complex expression pattern and transcriptional regulation. Nevertheless, although independent events ofNosduplication have been observed in several taxa, only few studies described the regulatory mechanisms responsible for their activation in non-vertebrate animals. To shed light on the mechanisms underlying neuronal-typeNosexpression, we focused on two non-vertebrate chordates: the cephalochordateBranchiostoma lanceolatumand the tunicateCiona robusta. Here, throughout transphyletic and transgenic approaches, we identified genomic regions in both species acting asNosfunctional enhancers during development.In vivoanalyses ofNosgenomic fragments revealed their ability to recapitulate the endogenous expression territories. Therefore, our results suggest the existence of evolutionary conserved mechanisms responsible for neuronal-typeNosregulation in non-vertebrate chordates. In conclusion, this study paves the way for future characterization of conserved transcriptional logic underlying the expression of neuronal-typeNosgenes in chordates.