EGFR confers exquisite specificity of Wnt9a-Fzd9b signaling in hematopoietic stem cell development

Summary The mechanisms of Wnt-Frizzled (Fzd) signaling selectivity and their biological implications remain unclear. We demonstrate for the first time that the epidermal growth factor receptor (EGFR) is required as a co-factor for Wnt signaling. Using genetic studies in zebrafish, paired with in vitro cell biology and biochemistry, we have determined that Fzd9b signals specifically with Wnt9a in vivo and in vitro to elicit β-catenin dependent Wnt signals that regulate hematopoietic stem and progenitor cell (HSPC) development in the dorsal aorta. This requirement is conserved in the derivation of HSPCs from human embryonic stem cells. Wnt9a-Fzd9b specificity requires two intracellular domains in Fzd9b, which interact with EGFR as a required co-factor to promote signal transduction. EGFR phosphorylates one tyrosine residue on Fzd9b, a requirement for the Wnt signal. These findings indicate that Wnt signaling interactions can be exquisitely specific and inform protocols for derivation of HSPCs in vitro . Highlights An in vitro signaling screen identifies Fzd9b as a Wnt9a-specific receptor. Fzd9b and Wnt9a regulate hematopoietic stem cell development as a cognate pair. WNT9A and FZD9 are required for HSPC derivation from human pluripotent cells in vitro . EGFR confers specificity to Wnt9a-Fzd9b signaling in zebrafish and human cells.