Receptor for WNT2 that is coupled to the beta-catenin canonical signaling pathway, which leads to the activation of disheveled proteins, inhibition of GSK-3 kinase, nuclear accumulation of beta-catenin and activation of Wnt target genes (By similarity). Plays a role in neuromuscular junction (NMJ) assembly by negatively regulating the clustering of acetylcholine receptors (AChR) through the beta-catenin canonical signaling pathway (PubMed:24860427). May play a role in neural progenitor cells (NPCs) viability through the beta-catenin canonical signaling pathway by negatively regulating cell cycle arrest leading to inhibition of neuron apoptotic process (By similarity). During hippocampal development, regulates neuroblast proliferation and apoptotic cell death (PubMed:15930120). Controls bone formation through non canonical Wnt signaling mediated via ISG15 (PubMed:21402791). Positively regulates bone regeneration through non canonical Wnt signaling (PubMed:24391920). Relocalizes DVL1 to the cell membrane leading to phosphorylation of DVL1 and AXIN1 relocalization to the cell membrane. In the embryo, found in the neural tube, trunk skeletal muscle precursors (myotomes), limb skeletal anlagen, craniofacial regions and nephric ducts. In the adult, expression is abundant in heart, brain, testis and skeletal muscle. In the testis, expressed in all spermatogenic cell types. Lower levels in adult lung, liver and kidney. Barely detectable in spleen. Expressed also in chondrocytes. Not detected at 7 dpc, weakly at 11 dpc and strongly at 15 dpc and 17 dpc. Expression covers the entire neural tube at 9.5 dpc, decreases at 10.5 dpc and becomes detectable only in the lumbar to tail regions at 11.5 dpc. In the somites, expression begins at 10.5 dpc to become up-regulated all along the rostrocaudal trunk axis at 11.5 dpc. In craniofacial territories, expression is first detected at 11.5 dpc in restricted areas of the nose, the maxillar mandibular and second branchial arch anlagen. At 11.5 dpc, predominantly expressed in restricted areas of the nose, dorsally to the eye and in the caudal pharyngeal region. Highly expressed at early stages of neuromuscular junction assembly (14.5 dpc) and gradually decreases as development proceeds, being more than about 4-fold less expressed in 19.5 dpc. Increases during the initial stages of osteoblast differentiation. Lys-Thr-X-X-X-Trp motif interacts with the PDZ domain of Dvl (Disheveled) family members and is involved in the activation of the Wnt/beta-catenin signaling pathway. The FZ domain is involved in binding with Wnt ligands. Ubiquitinated by ZNRF3, leading to its degradation by the proteasome. Homozygous Fzd9 knockout mice show deficits in spatial memory behaviors. Heterozygous and homozygous Fzd9 knockout mice appear healthy, develop normally, and are fertile (PubMed:15930120). Homozygous Fzd9 knockout mice display osteopenia (PubMed:21402791). Belongs to the G-protein coupled receptor Fz/Smo family. Has been first described as FZD3 in literature.