Fig. 9. Summary of Hh signaling and ventral spinal cord patterning in zebrafish. Arrows represent Hh ligands expressed by notochord (nc) and floor plate (triangle). The olig2^P/E domain (dark green) is formed at neural plate stage and expands to include the olig2^D/L domain (light green) by neural keel stage. Together, these comprise the pMN precursor domain. We propose that PMNs, KAs and VeLDs are produced first, from olig2^P/E, followed by SMNs and CiDs and, later, OPCs from olig2^D/L. Broken lines represent OPC dorsal migration.