Norrin precursor, also known as NDP, is a secreted regulatory protein. It activates the canonical Wnt signaling pathway through FZD4 and LRP5 coreceptor. This protein plays a central role in retinal vascularization by acting as a ligand for FZD4 that signals via stabilizing beta-catenin (CTNNB1) and activating LEF/TCF-mediated transcriptional programs. It may be involved in a pathway that regulates neural cell differentiation and proliferation. Recombinant human NDP protein, fused to His-tag at N-terminus, was expressed in E.coli.