GNRH1 and Kallmann syndrome: Starting from profile data obtained from a mouse model of Kallmann syndrome, we functionally examined this pathway in zebrafish showing that miR-9 and miR-200-class are required for normal differentiation of the ORNs, for the extension and connectivity of the olfactory axons, and for the migration of the GnRH neurons from the nasal primordium to the forebrain.