Pathomechanism of BDB: for this purpose we are analysing the function of Ror2 in different animal models such as mouse and chick. In the chicken, overexpression of truncated forms of Ror2 resulted in a severe chondrodysplasia phenotype comparable with the Ror2-null mouse. However, no brachydactyly-like phenotype was observed (Stricker et al. 2006).

Retroviral overexpression of truncated Ror2-constructs in the chick resulted in severe cartilage growth plate abnormalities but not a brachydactyly phenotype. Skeletal preparations from 11 day old chicken embryos; cartilage stains blue, bone stains red.

In collaboration with Aris N. Econimides (Regeneron Inc, Tarrytown, USA) we have analysed a knock-in mouse mutant harbouring an exact copy of a human BDB mutation (Raz et al. 2008). The mutant exhibited a brachydactyly phenotype with missing medial phalanges. We are currently analysing this phenotype molecularly.

Phenotype of the Ror2-W749X knock-in mouse mutant. Skeletal preparations of forelimbs from newborn mice, cartilage stains blue, bone stains red. Note the missing medial phalanges in the W749X mutant (arrows).

Ror2 signalling, interacting pathways: we and others have found evidence that implicate Ror2 in both, BMP and Wnt signalling cascades. In collaboration with P. Knaus (FU Berlin) we found that Ror2 interacts with the Bmp receptor type 1b on the cell surface (Sammar et al. 2004). In collaboration with G. Gross (GBF, Braunschweig) we found that Ror2 can modulate the canonical Wnt pathway dependent on its interaction with an intracellular kinase, TAK1 (Winkel et al. 2008). We are currently analysing the interaction of Ror2 with the Wnt pathway(s) in collaboration with A. Schambony (University of Erlangen-Nürnberg) and V. Bryja (Masaryk University Brno, Czech Republic). In order to find intracellular interaction partners of Ror2 we performed a yeast-two hybrid screen with the intracellular part of Ror2. Candidates from this screen are currently being analysed.

Ror2 interacts with the Wnt and Gdf5/Bmp pathways. Intracellular interaction partners of Ror2 identified so far are depicted at the bottom.

A picture evolves that places Ror2 as a connecting/modifying factor at the junction between pathways that are traditionally thought to represent independent functional modules. According to this hypothesis, perturbations of this intricate network cause a variety of features that are displayed in the syndrome family of inherited hand malformations. This leads to the question:

Is there a common pathomechanism for the brachydactylies as a molecular disease family? The brachydactylies are a syndrome family that shares overlapping features. Intriguingly, many of the mutations causing the different brachydactyly subtypes are found in members of the bone morphogenetic protein (Bmp) pathway (see figure). In addition to that, BDA1 is caused by mutations in Indian hedgehog (IHH).

Brachydyctyly mutations are found in members of the Bmp signalling pathway, in Ror2 and Ihh. Ror2 interacts with the Wnt and Bmp signalling pathways, phenotypic overlap of human syndromes as well as mouse mutants suggests interaction of Ror2 with the Ihh pathway as well.

Syndromes exhibiting overlapping features are often caused by mutations in genes whose products are involved in a common pathway or are integrated in a protein-protein interaction network (concept of so-called molecular disease families).

For this purpose, we analyse of mouse mutants representative for different human brachydactylies and perform crossing experiments to analyse genetic interactions.

Selected publications:

Witte F, Chan D, Economides AN, Mundlos S, Stricker S.
Receptor tyrosine kinase-like orphan receptor 2 (ROR2) and Indian hedgehog regulate digit outgrowth mediated by the phalanx-forming region.
Proceedings of the National Academy of Sciences U.S.A. , in press. Epub Jul 26. 2010. doi: 10.1073/pnas.1009314107

Witte F, Bernatik O, Kirchner K, Masek J, Mahl A, Krejci P, Mundlos S, Schambony A, Bryja V, Stricker S.
Negative regulation of Wnt signaling by CK1 phosphorylated Dishevelled via Ror2.
FASEB J. 2010, 24, 2417-2426.

Verhey van Wijk N, Witte F, Feike AC, Schambony A, Birchmeier W, Mundlos S, Stricker S.
The LIM domain protein Wtip interacts with the receptor tyrosine kinase Ror2 and inhibits canonical Wnt signalling.
Biochem. Biophys. Res. Commun. 2009, 390, 211-216.

Schwarzer W, Witte F,Rajab A, Mundlos S,Stricker S.
A gradient of ROR2 protein stability and membrane localization confers brachydactyly type B or Robinow syndrome phenotypes.
Hum Mol Genet 2009, 18(21), 4013-4021.

Kurth I, Klopocki E, Stricker S, van Oosterwijk J, Vanek S, Altmann J, van Harssel J, de Ravel T, Wilkie A, Gal A, Mundlos S.
Duplications of non-coding elements 5´ of SOX9 are associated with brachydactyly anonychia.
Nat Genet 2009, 41(8), 862-863.

Gao B, Hu J, Stricker S, Cheung M, Ma G, Law KF, Witte F, Briscoe J, Mundlos S, He L, Cheah KS, Chan D.
A mutation in Ihh that causes digit abnormalities alters its signalling capacity and range.
Nature 2009, 458(7242), 1196-1201.

Witte F, Dokas J, Neuendorf F, Mundlos S, Stricker S.
Comprehensive expression analysis of all Wnt genes and their major secreted antagonists during mouse limb development and cartilage differentiation.
Gene Expr Patterns 2009, 9, 215-223.

Winkel A, Stricker S, Tylzanowski P, Seiffart V, Mundlos S, Gross G, Hoffmann A.
Wnt-ligand-dependent interaction of TAK1 (TGF-beta-activated kinase-1) with the receptor tyrosine kinase Ror2 modulates canonical Wnt-signalling.
Cell Signal 2008, 20(11), 2134-44.

Raz R, Stricker S, Gazzerro E, Clor JL, Witte F, Nistala H, Zabski S, Pereira RC, Stadmeyer L, Wang X, Gowen L, Sleeman MW, Yancopoulos GD, Canalis E, Mundlos S, Valenzuela DM, Economides AN.
The mutation ROR2W749X, linked to human BDB, is a recessive mutation in the mouse, causing brachydactyly, mediating patterning of joints and modeling recessive Robinow syndrome.
Development 2008, 135(9), 1713-23.

Stricker S, Verhey van Wijk N, Witte F, Brieske N, Seidel K, Mundlos S.
Cloning and expression pattern of chicken Ror2 and functional characterization of truncating mutations in Brachydactyly type B and Robinow syndrome.
Dev Dyn 2006, 235(12), 3456-65.

Woods CG, Stricker S, Seemann P, Stern R, Cox J, Sherridan E, Roberts E, Springell K, Scott S, Karbani G, Sharif SM, Toomes C, Bond J, Kumar D, Al-Gazali L, Mundlos S
Mutations in WNT7A cause a range of limb malformations, including Fuhrmann syndrome and Al-Awadi/Raas-Rothschild/Schinzel phocomelia syndrome.
Am J Hum Genet 2006, 79(2), 402-8. *co-first authors

Sammar M, Stricker S, Schwabe GC, Sieber C, Hartung A, Hanke M, Oishi I, Pohl J, Minami Y, Sebald W, Mundlos S, Knaus P.
Modulation of GDF5/BRI-b signalling through interaction with the tyrosine kinase receptor Ror2.
Genes Cells 2004, 9(12), 1227-38.

Lehmann K, Seemann P,Stricker S, Sammar M, Meyer B, Süring K, Majewski F, Tinschert S, Grzeschik KH, Müller D, Knaus P, Nürnberg P, Mundlos S.
Mutations in bone morphogenetic protein receptor 1B cause brachydactyly type A2.
Proc Natl Acad Sci U S A 2003, 100(21), 12277-82.