Schematic overview of GDF5-signalling and associated diseases
BDA2 is caused by heterozygous mutations in BMPR1B, whereas heterozygous NOG mutations lead to SYM1 or SYNS1. Heterozygous mutations in GDF5 cause BDC, while point mutations in GDF5 that interfere with specific protein-protein interactions lead to different phenotypes. The GDF5 mutant L441P does not interact efficiently with BMPR1B and causes BDA2 which cannot be discriminated by phenotype from an inherited BMPR1B mutation. The GDF5 mutant R438L binds additionally to BMPR1A. This gained function causes a clinical SYM1 phenotype, very similar to the one observed in patients with NOG loss-of-function mutations.

The Growth and Differentiation Factor 5 (GDF5) is a secreted signaling molecule that belongs to the TGFb superfamily. GDF5 has an essential function during embryonic development, especially during the formation of the distal limbs. GDF5 signals via binding to its cognate receptor Bone Morphogenetic Protein Receptor 1B (BMPR1B) and determine pattern formation in the developing hand. Mutations in GDF5 or BMPR1B cause different types of hand malformations, which are characterized by shortening of the phalanges and deviations of the finger joint regions. Our aim is to perform functional in vitro analysis and genotype-phenotype correlation of newly identified mutations in GDF5 (R438L, L441P) and BMPR1B (I200K, R486W). The molecular effects of these mutants were unknown and/or have led to atypical phenotypes in the patients. Functional analyses with a micromass culture system revealed a strong inhibition of chondrogenesis by both mutant receptors. These findings imply that both mutations identified in human BMPR1B affect cartilage formation in a dominant-negative manner. The L441P mutation in GDF5 causes a similar phenotype presumably because of a significantly reduced interaction with BMPR1B. Moreover, proximal symphalangism and the multiple synostosis syndrome, which were previously only associated with mutations in NOG, could be identified in patients with point mutations in GDF5. Here, the interaction of the GDF5 mutants with the inhibitor NOG were either disturbed or the mutant GDF5 displayed an additional activity by also binding to BMPR1A. The presented experiments with the newly identified mutations in GDF5 and BMPR1B have identified some of the main determinants of GDF5 for specific protein-protein interactions. Molecular details about the functional domains of GDF5 became apparent, e.g. the identification of those interfaces that are important for receptor binding specificity or for the GDF5-NOG interaction. Thus, these results broaden our understanding on the importance of GDF5 and BMPR1B during the complex process of early bone development. The analyzed mutations expand the knowledge about GDF5-dependent phenotypes, i.e., mutations in GDF5 or its interaction partners BMPR1B and NOG, respectively, can cause identical phenotypes if they impair their protein-protein interactions.

Selected publications:

Seemann P, Brehm A, Kulas J, Reissner C, Stricker S, Kuss P, Renninger S, Groppe JC, Plöger F, Pohl J, Schmidt-von Kegler M, Walther M, Gassner I, Rusu C, Janecke AR, Dathe K, Mundlos S. Mutations in GDF5 Reveal a Key Residue Mediating BMP Inhibition by NOGGIN. PLOS Genetics, in press;

Dathe K, Kjaer KW, Brehm A, Meinecke P, Nürnberg P, Neto JC, Brunoni D, Tommerup N, Ott CE, Klopocki E, Seemann P, Mundlos S. Duplications involving a conserved regulatory element downstream of BMP2 are associated with brachydactyly type A2. Am J Hum Genet. 2009 Apr;84(4):483-92;

Plöger F, Seemann P, Schmidt-von Kegler M, Lehmann K, Seidel J, Kjaer KW, Pohl J, Mundlos S. Brachydactyly Type A2 Associated with a Defect in proGDF5 Processing. Hum Mol Genet. 2008 Jan 18; [Epub ahead of print]

Lehmann K, Seemann P, Silan F, Goecke TO, Irgang S, Kjaer KW, Kjaergaard S, Mahoney MJ, Morlot S, Reissner C, Kerr B, Wilkie AO, Mundlos S. A New Subtype of Brachydactyly Type B Caused by Point Mutations in the Bone Morphogenetic Protein Antagonist NOGGIN. Am J Hum Genet. 2007 Aug;81(2):388-96. Epub 2007 Jun 8;

Lehmann K, Seemann P, Boergermann J, Morin G, Reif S, Knaus P, Mundlos S. A novel R486Q mutation in BMPR1B resulting in either a brachydactyly type C/symphalangism-like phenotype or brachydactyly type A2. Eur J Hum Genet. 2006 Sep 6;

Dawson K, Seeman P, Sebald E, King L, Edwards M, Williams J 3rd, Mundlos S, Krakow D., GDF5 Is a Second Locus for Multiple-Synostosis Syndrome. Am J Hum Genet. 2006 Apr;78(4):708-12. Epub 2006 Feb 24.

Seemann P, Schwappacher R, Kjaer KW, Krakow D, Lehmann K, Dawson K, Stricker S, Pohl J, Ploger F, Staub E, Nickel J, Sebald W, Knaus P, Mundlos S. Activating and deactivating mutations in the receptor interaction site of GDF5 cause symphalangism or brachydactyly type A2. J Clin Invest. 2005 Sep;115(9):2373-81.

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