Delta-like 1 (DLL1), an activating ligand of NOTCH, is expressed in paraxial (presomitic) mesoderm and then becomes confined to caudal halves of somites during somitogenesis (inferred from the mouse homolog). Expression of DLL1 is activated by WNT signaling in paraxial mesoderm via LEF1, which binds multiple sites in the DLL1 promoter and recruits beta-catenin (CTNNB1) (inferred from mouse homologs). TBX6 also directly activates DLL1 expression in paraxial mesoderm (inferred from mouse homologs). Expression of DLL1 on the cell surface of paraxial mesoderm cells is oscillatory (inferred from the mouse homolog). Presenilin 1 (PSEN1) is required for expression of DLL1 and NOTCH1 in the paraxial mesoderm (inferred from mouse homologs).