Activates the canonical Wnt signaling pathway through FZD4 and LRP5 coreceptor. 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. Acts in concert with TSPAN12 to activate FZD4 independently of the Wnt-dependent activation of FZD4, suggesting the existence of a Wnt-independent signaling that also promote accumulation the beta-catenin (CTNNB1). May be involved in a pathway that regulates neural cell differentiation and proliferation. Possible role in neuroectodermal cell-cell interaction. Homodimer; disulfide-linked. Component of a complex, at least composed of TSPAN12, FZD4, LRP5/6 and norrin (NDP). Binds FZD4 with high affinity. Interacts with LRP6 (via Beta-propellers 1 and 2). Expressed in the outer nuclear, inner nuclear and ganglion cell layers of the retina, and in fetal and adult brain. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Retina International's Scientific Newsletter