The Frizzled family: receptors for multiple signal transduction pathways
© BioMed Central Ltd 2004
Published: 14 June 2004
Frizzled genes encode integral membrane proteins that function in multiple signal transduction pathways. They have been identified in diverse animals, from sponges to humans. The family is defined by conserved structural features, including seven hydrophobic domains and a cysteine-rich ligand-binding domain. Frizzled proteins are receptors for secreted Wnt proteins, as well as other ligands, and also play a critical role in the regulation of cell polarity. Frizzled genes are essential for embryonic development, tissue and cell polarity, formation of neural synapses, and the regulation of proliferation, and many other processes in developing and adult organisms; mutations in human frizzled-4 have been linked to familial exudative vitreoretinopathy. It is not yet clear how Frizzleds couple to downstream effectors, and this is a focus of intense study.
Gene organization and evolutionary history
The frizzled genes were first identified in Drosophila in a screen for mutations that disrupt the polarity of epidermal cells in the adult fly . Subsequently, frizzleds have been found in diverse metazoans , including at least ten in vertebrates, four in Drosophila, and three in Caenorhabditis elegans. Frizzleds have also been identified in primitive metazoans, including the sponge Suberites domuncula  and in Hydra vulgaris , but they have not been described in protozoans. They have been shown to encode receptors for Wnt proteins . The smoothened (smo) gene, which functions in the Hedgehog signaling pathway in various developmental processes, is distantly related to frizzled genes. Additional information on the Wnt pathway can be found on the Wnt gene homepage  and in various comprehensive reviews [1, 7–9].
Characteristic structural features
The CRD, which is necessary and sufficient for binding to Wnt molecules, consists of 120-125 residues with ten conserved cysteines, all of which form disulphide bonds [5, 11]. The crystal structures of the CRDs from mouse Frizzled 8 (mFz8) and mouse secreted Frizzled-related protein 3 (sFRP-3) reveal that CRDs are predominantly α-helical and form a previously unknown protein fold . A ligand-binding interface, involving a single region of the CRD surface, was predicted from analysis of the crystal structure integrated with comprehensive mutagenesis. Within the crystal, the CRDs form a conserved dimer interface, although in solution they appear to exist as monomers. Whether dimerization of the CRD has a role in ligand binding in vivo is not yet known .
The presence of seven hydrophobic domains has raised speculation that these receptors are related to the GPCR super-family. The sequence similarity to GPCRs is low, however, and is limited to the hydrophobic domains, which might be expected to have some similarity because of the shared higher frequency of hydrophobic residues. An intriguing sequence similarity, potentially derived from evolutionary conservation, has been described between Frizzleds and members of the Taste2 subfamily of taste receptors (which are GPCRs) .
A motif (KTXXXW) located two amino acids after the seventh hydrophobic domain is highly conserved in Frizzleds and is essential for activation of the Wnt/β-catenin pathway . Point mutations affecting any of the three conserved residues are defective in Wnt/β-catenin signaling (see below for more details on this pathway). A peptide derived from this conserved motif interacts in vitro with a peptide from the PDZ domain of mouse Dishevelled 1 - an intracellular signal-transduction protein - suggesting that this motif might mediate interaction between Frizzled proteins and Dishevelled proteins, although an interaction between the full-length proteins has not yet been demonstrated . Apart from the KTXXXW motif, the carboxy-terminal tail is not well conserved among Frizzleds. The carboxy-terminal S/T-X-V motif found in some Frizzleds is apparently not required for Frizzled function . The distantly related protein Smo also contains an amino-terminal CRD and seven hydrophobic domains, but it lacks the KTXXXW motif and does not bind Wnts [5, 15].
Localization and function
Frizzled proteins are found exclusively at the plasma membrane. They are located at the surface of Wnt-responsive cells, although recent evidence has suggested that they may be internalized as part of a mechanism for regulating the extracellular level of Wnt protein and/or the cellular response to Wnts [16, 17]. The tissue-specific expression of frizzled genes is complex, given that numerous frizzleds have been described in metazoans. In general, frizzleds are widely and dynamically expressed and, indeed, it is rare to find a cell that does not express one or more frizzleds. Specific expression patterns of frizzleds in model organisms have been described [2, 6, 14, 18].
Loss-of-function phenotypes of frizzled genes
Disruption of planar cell polarity in sensory bristles, dorsal epidermis, and ommatidia
 (see also [40-42])
Wg signal transduction is abolished in embryos and the wing imaginal disk
fz-/-; Dfz2 deficiency
Mimics loss of wg in embryonic epidermal patterning, neuroblast specification, midgut morphogenesis, and heart formation
fz RNAi ; Dfz2 RNAi
Defects in embryonic patterning that mimic wg loss of function
Suppresses a hypomorphic wg mutation
Embryos lack endoderm and overproduce pharyngeal tissue
Abnormal migration of the Q neuroblast
Disruption of a variety of asymmetric cell divisions
Severe defects in major axon tracts within the forebrain
Defects in cell survival in the cerebellum; vascular defects in retina, cochlea, and cerebellum
Embryonic lethal (at day 10.75) because of defects in yolk-sac angiogenesis
Familial exudative vitreoretinopathy
Loss of neural crest induction
Depletion of maternal Xfz7 disrupts dorsal anterior development
Severe gastrulation defect arising from inability of involuted anterior mesoderm to separate from the ectoderm
The first evidence that Frizzled proteins can function as receptors for canonical Wnt signaling was the observations that Drosophila frizzled-2 (Dfz2) can make Drosophila S2 cells responsive to the Wnt protein Wingless (Wg); these cells normally do not respond to Wg . Although fz interacts genetically with dishevelled in the PCP pathway, a fz loss-of-function mutant does not disrupt canonical Wnt signaling in the fly, as fz and Dfz2 are functionally redundant for canonical signaling . Evidence that frizzleds are required for Wnt signaling therefore required removing both fz and Dfz2, which was accomplished by RNA interference against Dfz2 in an fz mutant background, by analysis of chromosomal deficiencies that delete Dfz2 (see Table 1), and by identifying mutations in Dfz2 and crossing these mutants to fz flies . In vertebrates, overexpression studies suggest that different Frizzleds function in either the canonical or the noncanonical pathways , but at least some vertebrate frizzleds appear to function in multiple pathways, including the PCP, Wnt/calcium, and canonical Wnt/β-catenin pathways .
Description of the Wnt/calcium pathway derives originally from the observations that overexpression of Wnt5a or rat frizzled2 can cause an increase in intracellular calcium in zebrafish and can activate protein kinase C and calcium/calmodulin-dependent protein kinase (CaM kinase) in Xenopus . This pathway appears to require G proteins and Dishevelled, although a distinct Wnt/calcium pathway has also been proposed to regulate protein kinase C independently of Dishevelled in a frizzled7 pathway that maintains the separation of mesoderm and ectoderm during gastrulation in Xenopus .
The specific functions of Frizzled proteins are as varied as the number of cell types that express them. In addition to Drosophila and C. elegans, frizzled mutants have also been described in mouse and humans, and interference with frizzled function using antisense or dominant-interfering constructs has been described in Xenopus and zebrafish. Some of the phenotypes associated with loss of function of Frizzleds in various organisms are listed in Table 1. Of particular note is the fact that mutations in human FZD4 are found in familial exudative vitreoretinopathy (FEVR), an inherited form of retinal degeneration with associated progressive hearing loss ; investigation into the related Nome's disease, which arises from mutations in a novel, secreted protein called Norrin, led to the exciting recent discovery that Norrin is a ligand for Fz4 that can activate canonical Wnt signaling and yet is distinct from the Wnt proteins .
Wnts bind to Frizzleds with high affinity (where tested) through the Frizzled CRD [5, 15, 27, 28]. Furthermore, expression of the CRD alone antagonizes Wnt/β-catenin signaling , as does expression of secreted Frizzled-like proteins, such as Frzb-1, which have sequence similarity to the extracellular CRD domain of Frizzleds . The amino-terminal extracellular region, including the CRD, has also been proposed to play a role in dimerization of the receptor and activation of canonical Wnt/β-catenin signaling; Carron et al.  reported that Xenopus Frizzled3 (Xfz3) dimerizes to activate canonical signaling and that Xfz7, which is monomeric, can activate Wnt/β-catenin signaling if artificially forced to dimerize but not when it is a monomer. In Drosophila, the CRD of Fz has an approximately ten-fold lower affinity for Wg protein than does the CRD of Dfz2, and ligand affinity is one determinant in the specificity of different Frizzled proteins for different pathways downstream of Wnt signaling .
The mechanism by which Frizzled proteins transduce signals once ligand has bound is largely unknown for any of the Frizzled-mediated signaling pathways. Screens for Drosophila mutations that disrupt canonical Wnt signaling in embryonic segments and in imaginal disks identified a number of downstream components, including dishevelled, shaggy/zeste-white-3 (homologous to vertebrate glycogen synthase kinase 3), and armadillo (homologous to β-catenin), but none of the proteins encoded by these genes has been shown to interact directly with Frizzled proteins. Dishevelled is recruited to the membrane if Frizzleds are overexpressed (reviewed in [7, 9, 30]), and it has been proposed to interact directly, through its PDZ domain, with the carboxyl terminus of Frizzleds, but this interaction has not yet been demonstrated with full-length proteins and the physiological significance of Dishevelled membrane recruitment is not known . Xenopus Kermit, a PDZ domain protein of previously unknown function , interacts directly with the cytoplasmic domain of Frizzled proteins and is recruited to the cell surface specifically by Fz3. Kermit is required for Wnt1/Fz3-mediated induction of neural crest, but it is not yet known whether Kermit functions in other settings involving Wnt/Fz signaling, and corresponding Kermit-like molecules for Frizzleds other than Fz3 have not yet been identified. PSD-95, a mouse PDZ-domain protein, can interact with mouse Fz1, Fz2, Fz4, and Fz7 , and the fly PDZ-domain protein GOPC interacts with the carboxyl terminus of Drosophila fz , but the functional significance of these interactions is not yet known.
The arrow gene of Drosophila, which is required for canonical Wnt signaling, was recently found to encode a type-1 membrane receptor similar to low-density lipoprotein receptor-related proteins 5 and 6 (LRP5 and LRP6; ). Disruption of LRP6 in mouse causes multiple phenotypes consistent with loss of Wnt signaling . A dominant negative form of LRP6 inhibits Wnt signaling in Xenopus, and human LRP6 protein co-immunoprecipitates with the Fz8 CRD in a Wnt-dependent manner, suggesting that binding of Wnt to Frizzleds generates a ternary signaling complex of ligand (Wnt), receptor (Frizzled), and coreceptor (LRP) . Co-immunoprecipitation of Wnts with LRPs has also been described by others using vertebrate proteins , but not with Drosophila Frizzled, Arrow, and Wg proteins . Expression of a chimeric molecule in which the carboxyl terminus of Arrow has been fused to Dfz2 robustly activates canonical Wnt signaling in the wing, supporting the hypothesis that binding of Wnts to Frizzleds somehow leads to interaction with and activation of Arrow/LRPs . In addition, LRP5 and Arrow interact directly with Axin, a cytoplasmic scaffold protein that is the hub of cytoplasmic regulation of Wnt signaling, recruiting Axin to the membrane [35, 36]. These observations are consistent with the idea that the Wnt signal is transduced through Frizzled proteins to Arrow/LRP, which then modulates cytoplasmic signaling through recruitment of the Axin complex. Arrow is not apparently required for PCP signaling .
In Drosophila, no ligand has been identified for activation of the PCP pathway. As discussed above, a number of components have been shown to be required for PCP signaling, and many localize at either the posterior region of the cell (Frizzled and Dishevelled) or in the anterior of the adjacent cell (for example, Strabismus, a novel transmembrane protein, and Prickle, a LIM-domain protein). Many of these components have been implicated in the regulation of convergent-extension movements in vertebrate embryos, and a role for Wnts, including Wnt11 and Wnt5a, is supported by genetic evidence in zebrafish and by the use of dominant-negative ligands in Xenopus . The mechanism by which Frizzleds communicate with other components of the PCP pathway remains an intriguing mystery, however.
Regarding Wnt/calcium signaling, overexpression of rat Fz2 by injection of mRNA causes an increase in intracellular calcium in zebrafish embryos, and overexpression of Frizzleds in Xenopus can lead to activation of protein kinase C (PKC) ; these effects are sensitive to pertussis toxin and other G-protein antagonists . In addition, a complex chimeric molecule that incorporates the extracellular and ligand binding domains of the β-adrenergic receptor and the intracellular sequence of rat Fz2 was shown to cause intracellular calcium release within minutes after addition of adrenergic agonists . Although this chimeric receptor is artificial, this was an important experiment because purified Wnts were not available until recently and the chimera provided a clever and novel approach to activate the pathway rapidly.
A similar chimeric receptor involving rat Fz1 and the β-adrenergic receptor has also been used to support a role for G proteins in canonical Wnt signaling ; additional support for a role of G proteins was provided by the observation that overexpressed RGS4, a G-protein antagonist, appears to block canonical Wnt signaling in Xenopus axis-duplication assays. These indirect assays support a potential role of G proteins in mediating the canonical and Wnt/calcium pathways, although a requirement for G proteins has not yet been established by loss-of-function experiments . A new, noncanonical pathway involving Dwnt4, Frizzleds, and PKC has also recently been described in Drosophila in the developing ovary .
An important remaining question is how Frizzleds transduce a signal upon binding of the ligand. For the canonical Wnt pathway, as discussed above, ligand binding may initiate interaction with Arrow/LRPs, but the nature of the interaction is not known. Arrow/LRP does not appear to be involved in the PCP pathway, and other potential coreceptors have not been identified for this pathway. Whether Frizzleds are regulated by a secreted ligand in the PCP pathway also remains an open question, at least in Drosophila. The mechanism of signal transduction in the Wnt/calcium pathway is also an area of intense research, and the exciting possibility that Frizzleds couple directly to G proteins is still a controversial area, perhaps in part because of the lack of genetic data to support the idea of this interaction.
Information on the specificity of ligand-receptor interaction is also limited. Direct binding assays have been performed for a limited number of ligands, although this is likely to change now that a purification protocol has been established for Wnt proteins . A classification of Wnt proteins has suggested that some ligands, such as Wg, Wnt1, and Wnt3a, function as ligands that activate the canonical pathway, whereas others, such as Wnt5a, Wnt11, and Dwnt4, function in noncanonical pathways. Whether this distinction applies to Frizzleds remains to be resolved. In Drosophila, Fz functions in both pathways but Dfz2 functions only in canonical signaling; in vertebrates, this distinction is less clear (compare  with ).
Frizzled proteins are asymmetrically distributed in tissues that exhibit planar polarity in the fly, and PCP signaling has been proposed to regulate oriented cell movements in vertebrate gastrulation; so far, however, an asymmetric subcellular distribution of vertebrate Frizzled proteins has not been demonstrated, largely because of the difficulty in generating antibodies sensitive enough to detect the endogenous protein. In addition, the biochemistry of PCP signaling is in its early stages, mainly because a biochemical readout for this pathway has not been clearly established, and it remains unclear whether PCP is regulated by a ligand-receptor interaction.
Finally, Wnt/Frizzled signaling clearly plays important roles in adult tissues as well as embryonic development. The limited number of human diseases found so far to be linked to mutations in frizzled genes is likely to expand in the near future.
The authors thank members of the Klein lab for helpful discussions. P.S.K. is supported by the NIH and the Howard Hughes Medical Institute.
- Adler PN: Planar signaling and morphogenesis in Drosophila. Dev Cell. 2002, 2: 525-535. 10.1016/S1534-5807(02)00176-4. An excellent recent review on planar cell polarity.PubMedView ArticleGoogle Scholar
- Wang Y, Macke JP, Abella BS, Andreasson K, Worley P, Gilbert DJ, Copeland NG, Jenkins NA, Nathans J: A large family of putative transmembrane receptors homologous to the product of the Drosophila tissue polarity gene frizzled. J Biol Chem. 1996, 271: 4468-4476. 10.1074/jbc.271.8.4468. The first large-scale analysis of vertebrate frizzled genes.PubMedView ArticleGoogle Scholar
- Adell T, Nefkens I, Muller WE: Polarity factor 'Frizzled' in the demosponge Suberites domuncula: identification, expression and localization of the receptor in the epithelium/pinacoderm. FEBS Letters. 2003, 554: 363-368. 10.1016/S0014-5793(03)01190-6. Identification of a Frizzled in a marine sponge, representing the most primitive metazoan phylum (Porifera); the Sd-fz protein is proposed to be involved in tissue polarity.PubMedView ArticleGoogle Scholar
- Minobe S, Fei K, Yan L, Sarras M, Werle M: Identification and characterization of the epithelial polarity receptor "Frizzled" in Hydra vulgaris. Dev Genes Evol. 2000, 210: 258-262. 10.1007/s004270050312. This primitive frizzled gene, expressed in the endoderm in adult hydra, is estimated to have diverged from other frizzled genes about one billion years ago.PubMedView ArticleGoogle Scholar
- Bhanot P, Brink M, Samos CH, Hsieh JC, Wang Y, Macke JP, Andrew D, Nathans J, Nusse R: A new member of the frizzled family from Drosophila functions as a Wingless receptor. Nature. 1996, 382: 225-230. 10.1038/382225a0. A landmark paper showing that Frizzleds are Wnt receptors.PubMedView ArticleGoogle Scholar
- The Wnt Gene Homepage. The definitive web resource for information on Wnts and Frizzleds, with many links, interactive models, reviews, and comprehensive information. The best starting point for information on Frizzleds., [http://www.stanford.edu/~rnusse/wntwindow.html]
- Veeman MT, Axelrod JD, Moon RT: A second canon. Functions and mechanisms of beta-catenin-independent Wnt signaling. Dev Cell . 2003, 5: 367-377. 10.1016/S1534-5807(03)00266-1. An excellent recent review on noncanonical Wnt/Frizzled signaling.PubMedView ArticleGoogle Scholar
- Strutt D: Frizzled signalling and cell polarisation in Drosophila and vertebrates. Development . 2003, 130: 4501-4513. 10.1242/dev.00695. An excellent recent review on noncanonical Wnt/Frizzled signaling.PubMedView ArticleGoogle Scholar
- He X, Semenov M, Tamai K, Zeng X: LDL receptor-related proteins 5 and 6 in Wnt/β-catenin signaling: arrows point the way. Development. 2004, 131: 1663-1677. 10.1242/dev.01117. An excellent recent review on Frizzled-LRP interactions.PubMedView ArticleGoogle Scholar
- Fredriksson R, Lagerstrom MC, Lundin LG, Schioth HB: The G-protein-coupled receptors in the human genome form five main families. Phylogenetic analysis, paralogon groups, and fingerprints. Mol Pharmacol. 2003, 63: 1256-1272. 10.1124/mol.63.6.1256. A thorough sequence comparison of the hydrophobic domains in GPCRs and Frizzleds.PubMedView ArticleGoogle Scholar
- Dann CE, Hsieh JC, Rattner A, Sharma D, Nathans J, Leahy DJ: Insights into Wnt binding and signalling from the structures of two Frizzled cysteine-rich domains. Nature. 2001, 412: 86-90. 10.1038/35083601. The crystal structure of two CRDs reveals a novel protein fold.PubMedView ArticleGoogle Scholar
- Umbhauer M, Djiane A, Goisset C, Penzo-Mendez A, Riou JF, Boucaut JC, Shi DL: The C-terminal cytoplasmic Lys-thr-X-X-X-Trp motif in frizzled receptors mediates Wnt/beta-catenin signalling. EMBO J . 2000, 19: 4944-4954. 10.1093/emboj/19.18.4944. Identification of a highly conserved motif in all Frizzleds that is required for canonical signaling.PubMedPubMed CentralView ArticleGoogle Scholar
- Wong HC, Bourdelas A, Krauss A, Lee HJ, Shao Y, Wu D, Mlodzik M, Shi DL, Zheng J: Direct binding of the PDZ domain of Dishevelled to a conserved internal sequence in the C-terminal region of Frizzled. Mol Cell. 2003, 12: 1251-1260. 10.1016/S1097-2765(03)00427-1. An NMR study of peptide binding in solution suggests that the KTXXXW peptide can interact with a peptide derived from Dishevelled.PubMedPubMed CentralView ArticleGoogle Scholar
- Thorpe CJ, Schlesinger A, Bowerman B: Wnt signalling in Caenorhabditis elegans: regulating repressors and polarizing the cytoskeleton. Trends Cell Biol. 2000, 10: 10-17. 10.1016/S0962-8924(99)01672-4. An excellent recent review on Wnt signaling in nematodes.PubMedView ArticleGoogle Scholar
- Hsieh JC, Rattner A, Smallwood PM, Nathans J: Biochemical characterization of Wnt-frizzled interactions using a soluble, biologically active vertebrate Wnt protein. Proc Natl Acad Sci USA. 1999, 96: 3546-3551. 10.1073/pnas.96.7.3546. Using soluble Wnt proteins to measure affinity constants for binding to Frizzled proteins.PubMedPubMed CentralView ArticleGoogle Scholar
- Chen W, ten Berge D, Brown J, Ahn S, Hu LA, Miller WE, Caron MG, Barak LS, Nusse R, Lefkowitz RJ: Dishevelled 2 recruits beta-arrestin 2 to mediate Wnt5A-stimulated endocytosis of Frizzled 4. Science. 2003, 301: 1391-1394. 10.1126/science.1082808. Evidence for Frizzled endocytosis mediated by a well characterized regulatory component of GPCR signaling.PubMedView ArticleGoogle Scholar
- Dubois L, Lecourtois M, Alexandre C, Hirst E, Vincent JP: Regulated endocytic routing modulates wingless signaling in Drosophila embryos. Cell. 2001, 105: 613-624. 10.1016/S0092-8674(01)00375-0. The first suggestion that endocytosis of Wnt ligands may shape the Wnt morphogen gradient.PubMedView ArticleGoogle Scholar
- Gradl D, Kuhl M, Wedlich D: Keeping a close eye on Wnt-1/wg signaling in Xenopus. Mech Dev. 1999, 86: 3-15. 10.1016/S0925-4773(99)00129-X. An excellent and thorough review of Wnt/Frizzled signaling in Xenopus.PubMedView ArticleGoogle Scholar
- Deardorff MA, Tan C, Conrad LJ, Klein PS: Frizzled-8 is expressed in the Spemann organizer and plays a role in early morphogenesis. Development. 1998, 125: 2687-2700. The first evidence that Frizzleds play a role in orienting vertebrate gastrulation movements.PubMedGoogle Scholar
- Moon RT, Campbell RM, Christian JL, McGrew LL, Shih J, Fraser S: Xwnt-5A: a maternal Wnt that affects morphogenetic movements after overexpression in embryos of Xenopus laevis. Development. 1993, 119: 97-111. The first evidence that Wnts play a role in controlling vertebrate gastrulation movements.PubMedGoogle Scholar
- Sokol SY: Analysis of Dishevelled signalling pathways during Xenopus development. Curr Biol. 1996, 6: 1456-1467. The first evidence for a role for dishevelled in coordinating gastrulation movements in vertebrates.PubMedView ArticleGoogle Scholar
- Chen CM, Struhl G: Wingless transduction by the Frizzled and Frizzled2 proteins of Drosophila. Development. 1999, 126: 5441-5452. Identification of a mutant allele of Dfz2 allowed definitive demonstration that fz and Dfz2 are redundant in and required for wg signaling in Drosophila.PubMedGoogle Scholar
- Sheldahl LC, Park M, Malbon CC, Moon RT: Protein kinase C is differentially stimulated by wnt and frizzled homologs in a G-protein-dependent manner. Curr Biol. 1999, 9: 695-698. 10.1016/S0960-9822(99)80310-8. Early evidence that Frizzleds can activate PKC.PubMedView ArticleGoogle Scholar
- Winklbauer R, Medina A, Swain RK, Steinbeisser H: Frizzled-7 signalling controls tissue separation during Xenopus gastrulation. Nature. 2001, 413: 856-860. 10.1038/35101621. A later function for Frizzled-7, acting through PKC, in cell sorting during Xenopus gastrulation; see Table 1.PubMedView ArticleGoogle Scholar
- Robitaille J, MacDonald ML, Kaykas A, Sheldahl LC, Zeisler J, Dube MP, Zhang LH, Singaraja RR, Guernsey DL, Zheng B, et al: Mutant frizzled-4 disrupts retinal angiogenesis in familial exudative vitreoretinopathy. Nat Genet. 2002, 32: 326-330. 10.1038/ng957. The first description of an inherited disease in humans linked to a mutation in a frizzled gene.PubMedView ArticleGoogle Scholar
- Xu Q, Wang Y, Dabdoub A, Smallwood PM, Williams J, Woods C, Kelley MW, Jiang L, Tasman W, Zhang K, et al: Vascular development in the retina and inner ear: control by Norrin and Frizzled-4, a high-affinity ligand-receptor pair. Cell. 2004, 116: 883-895. 10.1016/S0092-8674(04)00216-8. Identification of a novel Frizzled ligand and extension of phenotypic characterization of Fz4 knockout in mice.PubMedView ArticleGoogle Scholar
- Rulifson EJ, Wu C-H, Nusse R: Pathway specificity by the bifunctional receptor Frizzled is determined by affinity for Wingless. Molecular Cell. 2000, 6: 117-126. 10.1016/S1097-2765(00)00013-7. An important paper showing that ligand affinity plays a role in determining which pathway is activated by a Frizzled that can function in the PCP and canonical pathways.PubMedView ArticleGoogle Scholar
- Wu CH, Nusse R: Ligand receptor interactions in the Wnt signaling pathway in Drosophila. J Biol Chem. 2002, 277: 41762-41769. 10.1074/jbc.M207850200. Describes a reverse binding assay using membrane-tethered neurotactin-Wnt chimeras to bind soluble CRDs derived from Frizzled proteins.PubMedView ArticleGoogle Scholar
- Carron C, Pascal A, Djiane A, Boucaut JC, Shi DL, Umbhauer M: Frizzled receptor dimerization is sufficient to activate the Wnt/beta-catenin pathway. J Cell Sci. 2003, 116: 2541-2550. 10.1242/jcs.00451. Suggestions that Frizzled CRD dimerization plays a role in canonical signaling.PubMedView ArticleGoogle Scholar
- Boutros M, Mihaly J, Bouwmeester T, Mlodzik M: Signaling specificity by frizzled receptors in Drosophila. Science. 2000, 288: 1825-1828. 10.1126/science.288.5472.1825. A careful structure/function analysis of the domains from Fz and Dfz2 involved in either canonical or PCP signaling in Drosophila.PubMedView ArticleGoogle Scholar
- Tan C, Deardorff MA, Saint-Jeannet JP, Yang J, Arzoumanian A, Klein PS: Kermit, a frizzled interacting protein, regulates frizzled 3 signaling in neural crest development. Development. 2001, 128: 3665-3674. The first identification of a protein that interacts with the cytoplasmic face of Frizzled proteins.PubMedGoogle Scholar
- Hering H, Sheng M: Direct interaction of Frizzled-1, -2, -4, and -7 with PDZ domains of PSD-95. FEBS Lett. 2002, 521: 185-189. 10.1016/S0014-5793(02)02831-4. Shows direct binding between PSD-95 and the carboxyl termini of several Frizzleds.PubMedView ArticleGoogle Scholar
- Yao R, Maeda T, Takada S, Noda T: Identification of a PDZ domain containing Golgi protein, GOPC, as an interaction partner of Frizzled. Biochem Biophys Res Commun. 2001, 286: 771-778. 10.1006/bbrc.2001.5430. GOPC binds to Frizzled and may have a role in its transport from the Golgi apparatus to the plasma membrane.PubMedView ArticleGoogle Scholar
- Wehrli M, Dougan ST, Caldwell K, O'Keefe L, Schwartz S, Vaizel-Ohayon D, Schejter E, Tomlinson A, DiNardo S: arrow encodes an LDL-receptor-related protein essential for Wingless signalling. Nature. 2000, 407: 527-530. 10.1038/35035110. The identification of arrow (also known as LRP5/6) as an essential gene for canonical Wnt signaling.PubMedView ArticleGoogle Scholar
- Tolwinski NS, Wehrli M, Rives A, Erdeniz N, DiNardo S, Wieschaus E: Wg/Wnt signal can be transmitted through arrow/LRP5,6 and Axin independently of Zw3/Gsk3beta activity. Dev Cell. 2003, 4: 407-418. 10.1016/S1534-5807(03)00063-7. This paper confirmed the interaction of Arrow/LRP with Axin and demonstrated the constitutive activity of an Arrow-Frizzled fusion protein.PubMedView ArticleGoogle Scholar
- Mao J, Wang J, Liu B, Pan W, Farr GH, Flynn C, Yuan H, Takada S, Kimelman D, Li L, et al: Low-density lipoprotein receptor-related protein-5 binds to Axin and regulates the canonical Wnt signaling pathway. Mol Cell. 2001, 7: 801-809. 10.1016/S1097-2765(01)00224-6. The first demonstration of interaction between the carboxyl terminus of LRP C and Axin, suggesting a new mechanism for canonical Wnt signaling.PubMedView ArticleGoogle Scholar
- Malbon CC, Wang H, Moon RT: Wnt signaling and heterotrimeric G-proteins: strange bedfellows or a classic romance?. Biochem Biophys Res Commun. 2001, 287: 589-593. 10.1006/bbrc.2001.5630. An excellent recent review of the evidence for involvement of G proteins in Wnt/Frizzled signaling.PubMedView ArticleGoogle Scholar
- Cohen ED, Mariol MC, Wallace RM, Weyers J, Kamberov YG, Pradel J, Wilder EL: DWnt4 regulates cell movement and focal adhesion kinase during Drosophila ovarian morphogenesis. Dev Cell. 2002, 2: 437-448. 10.1016/S1534-5807(02)00142-9. Identification of a novel, noncanonical pathway utilizing Frizzleds, Dishevelled, and PKC in the developing ovary.PubMedView ArticleGoogle Scholar
- Gubb D, Garcia-Bellido A: A genetic analysis of the determination of cuticular polarity during development in Drosophila melanogaster. J Embryol Exp Morphol. 1982, 68: 37-57. An early description of a frizzled mutant in Drosophila.PubMedGoogle Scholar
- Muller H, Samanta R, Wieschaus E: Wingless signaling in the Drosophila embryo: zygotic requirements and the role of the frizzled genes. Development. 1999, 126: 577-586. See Table 1.PubMedGoogle Scholar
- Bhanot P, Fish M, Jemison JA, Nusse R, Nathans J, Cadigan KM: Frizzled and DFrizzled-2 function as redundant receptors for Wingless during Drosophila embryonic development. Development. 1999, 126: 4175-4186. See Table 1.PubMedGoogle Scholar
- Bhat KM: frizzled and frizzled 2 play a partially redundant role in wingless signaling and have similar requirements to wingless in neurogenesis. Cell. 1998, 95: 1027-1036. 10.1016/S0092-8674(00)81726-2. See Table 1.PubMedView ArticleGoogle Scholar
- Kennerdell JR, Carthew RW: Use of dsRNA-mediated genetic interference to demonstrate that frizzled and frizzled 2 act in the wingless pathway. Cell. 1998, 95: 1017-1026. 10.1016/S0092-8674(00)81725-0. The first use of RNAi in Drosophila; see Table 1.PubMedView ArticleGoogle Scholar
- Sato A, Kojima T, Ui-Tei K, Miyata Y, Saigo K: Dfrizzled-3, a new Drosophila Wnt receptor, acting as an attenuator of Wingless signaling in wingless hypomorphic mutants. Development. 1999, 126: 4421-4430. See Table 1.PubMedGoogle Scholar
- Rocheleau CE, Downs WD, Lin R, Wittmann C, Bei Y, Cha YH, Ali M, Priess JR, Mello CC: Wnt signaling and an APC-related gene specify endoderm in early C. elegans embryos. Cell. 1997, 90: 707-716. 10.1016/S0092-8674(00)80531-0. Identification of canonical Wnt signaling pathway in early cell-fate specification in C. elegans; see Table 1.PubMedView ArticleGoogle Scholar
- Harris J, Honigberg L, Robinson N, Kenyon C: Neuronal cell migration in C. elegans: regulation of Hox gene expression and cell position. Development. 1996, 122: 3117-3131. See Table 1; early evidence for role of Wnts and Frizzleds in cell migration.PubMedGoogle Scholar
- Sawa H, Lobel L, Horvitz HR: The Caenorhabditis elegans gene lin-17, which is required for certain asymmetric cell divisions, encodes a putative seven-transmembrane protein similar to the Drosophila frizzled protein. Genes Dev . 1996, 10: 2189-2197. A role for Frizzleds in asymmetric divisions in C. elegans; see Table 1.PubMedView ArticleGoogle Scholar
- Wang Y, Thekdi N, Smallwood PM, Macke JP, Nathans J: Frizzled-3 is required for the development of major fiber tracts in the rostral CNS. J Neurosci. 2002, 22: 8563-8573. See Table 1.PubMedGoogle Scholar
- Wang Y, Huso D, Cahill H, Ryugo D, Nathans J: Progressive cerebellar, auditory, and esophageal dysfunction caused by targeted disruption of the frizzled-4 gene. J Neurosci. 2001, 21: 4761-4771. See Table 1.PubMedGoogle Scholar
- Ishikawa T, Tamai Y, Zorn AM, Yoshida H, Seldin MF, Nishikawa S, Taketo MM: Mouse Wnt receptor gene Fzd5 is essential for yolk sac and placental angiogenesis. Development. 2001, 128: 25-33. See Table 1.PubMedGoogle Scholar
- Deardorff MA, Tan C, Saint-Jeannet JP, Klein PS: A role for frizzled 3 in neural crest development. Development. 2001, 128: 3655-3663. See Table 1.PubMedGoogle Scholar
- Sumanas S, Strege P, Heasman J, Ekker SC: The putative wnt receptor Xenopus frizzled-7 functions upstream of beta-catenin in vertebrate dorsoventral mesoderm patterning. Development. 2000, 127: 1981-1990. The first loss-of-function evidence for upstream components of Wnt/Frizzled signaling in dorsal ventral axis determination; see Table 1.PubMedGoogle Scholar
- HBG006977 phylogenetic tree in Hoverplot. A tree of Frizzled proteins generated by the Pôle Bio-Informatique Lyonnais., [http://pbil.univ-lyon1.fr/cgi-bin/acnuc-link-ac2tree?db=Hoverprot&query=O00144]