Fig. 6. Model for Delta-Notch-mediated induction of hypochord fate. At early gastrula stage, ntl-expressing midline precursors occupy the dorsal margin. During gastrulation, Delta signaling, primarily from paraxial mesoderm expression of DeltaD and DeltaC, induce ntl-positive midline precursors to express her4. These cells downregulate ntl expression and, after completion of gastrulation, migrate beneath notochord to form hypochord.