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Research areas:

Developmental Biology, Molecular Cell Biology

Research interests:

We use zebrafish and medaka models to investigate fundamental processes of embryonic development and to approach the molecular basis of different human disorders. This includes:

• Formation and patterning of the central nervous system
• Molecular mechanisms of neural degeneration
• Development of somites and bones
• Fish models for human neurodegenerative disorders and bone diseases

Pattern formation in the embryonic spinal cord

The spinal cord of vertebrates consists of millions of different neurons that are interconnected in a highly coordinated fashion to allow proper function of our nervous system. During embryogenesis, these neurons are formed at specific positions in the developing neural tube. We have studied Midkine growth factors and could show that they regulate formation of two important organizer regions in the spinal cord, the floor and the roof plate. Both structures secrete factors that build up morphogen gradients and induce neural differentiation at distinct positions. Our present projects aim to elucidate the signalling cascades that are activated by Midkine growth factors.

Defects in RNA metabolism as cause of neurodegenerative diseases: A zebrafish model for Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is a common motoneuron disease in humans. It is characterized by the degeneration of a-motoneurons in the spinal cord, which results in progressive paralysis of the trunk and limbs. SMA patients carry mutations in the survival of motor neuron 1 (SMN1) gene, which encodes a protein that interestingly is implicated in the assembly of spliceosomal UsnRNPs. It remains unclear, whether the neuronal defects in SMA patients reflect a particular sensitivity of motoneurons to general splicing deficiencies or a motoneuron specific function of the SMN protein. Our recent findings in the zebrafish model favour the first hypothesis and suggest that motoneuron degeneration in SMA patients is a direct consequence of impaired UsnRNP production. Using the zebrafish model, we thus gain novel insight into the pathomolecular mechanisms leading to this neurodegenerative disease in humans.

Fig. 1: Motor axonal defects in the spinal cord of zebrafish embryos after knock-down of snRNP assembly components. Motor axons are truncated (arrow) or bifurcated (arrowheads) and do not reach their proper targets in the musculature (top). These defects can be rescued by supplementation of intact spliceosomal UsnRNPs into zebrafish embryos (bottom).

Laboratory fish as models for human bone disease

Osteoporosis and other related bone diseases are a major public health concern and have increasing impact onto our human society. We use medaka fish to characterize regulatory networks that have been implicated in human bone diseases. Bone forming cells (osteoblasts) and bone resorbing cells (osteoclasts) of teleosts share many features with those of mammals. Also the underlying genetic pathways are highly conserved. As partner of the ENFORM (European Network using Fish as Osteoporosis Research Model) consortium, we characterized several fish homologs of human genes, which play important regulatory roles during bone formation. We also use stable transgenic fish that express fluorescent reporters in early bone precursor cells or differentiated bones. This approach allows to follow bone formation by real time imaging in genetically altered individuals. In addition, these fish will be used for high-throughput in vivo screens for bone anabolic compounds. This will generate targets for future therapeutic evaluation in humans.

 

Fig. 2.Transgenic medaka fish expressing green fluorescent protein in osteoblasts of the larval head skeleton (ventral view, anterior to the top). The transparency of embryos allows monitoring of bone development in real time in vivo.

Selected publications (2003-2007):

1. Liedtke, D. and Winkler, C. (2007). Midkine-b regulates cell specification at the neural plate border in zebrafish. Dev Dyn. (in press)

2. Herpin, A., Schindler, D., Kraiss, A., Hornung, U., Winkler, C., and Schartl, M. (2007). Inhibition of germ cell proliferation by the medaka male determining gene Dmrt1bY. BMC Dev Biol. 7, 99.

3. Schaefer, M., Kinzel, D., and Winkler, C. (2007). Discontinuous organization and specification of the lateral floor plate in zebrafish. Dev Biol. 301, 117-129.

4. To, T.T., Hahner, S., Nica, G., Rohr, K.B., Hammerschmidt, M., Winkler, C., and Allolio, B. (2007). Pituitary-interrenal interaction in zebrafish interrenal organ development. Mol Endocrinol. 21, 472-485.

5. Renn, J., Schaedel, M., Volff, J.N., Goerlich, R., Schartl, M., and Winkler, C. (2006). Dynamic expression of Sparc precedes formation of skeletal elements in the Medaka (Oryzias latipes). Gene 372, 208-218.

6. Gajewski, M., Elmasri, H., Girschick, M., Sieger, D., and Winkler, C. (2006). Comparative analysis of her genes during fish somitogenesis reveals a mouse/chick-like mode of oscillation in medaka. Dev Genes Evol 216, 315-332.

7. Sieger, D., Ackermann, B., Winkler, C., Tautz, D., and Gajewski, M. (2006). her1 and her13.2 are jointly required for somitic border specification along the entire axis of the fish embryo. Dev Biol 293, 242 - 251.

8. Winkler, C., Eggert, C., Gradl, D., Meister, G., Giegerich, M., Wedlich, D., Laggerbauer, B. and Fischer, U. (2005). Reduced RNP assembly causes motor axon degeneration in an animal model for spinal muscular atrophy. Genes & Development 19, 2320-2330.

9. Schaefer, M., Rembold, M., Wittbrodt, J., Schartl, M., and Winkler, C. (2005). Medial floor plate formation in zebrafish consists of two phases and requires trunk-derived Midkine-a. Genes & Development 19, 897-902.

10. Schaefer, M., Kinzel, D., Neuner, C., Schartl, M., Volff, J.N., and Winkler, C. (2005). Hedgehog and retinoid signalling confines nkx2.2b expression to the lateral floor plate of the zebrafish trunk. Mech Dev 122, 43-56.

11. Winkler, C., Hornung, U., Kondo, M., Neuner, C., Duschl, J., Shima, A. and Schartl, M. (2004). Developmentally regulated and non-sex-specific expression of autosomal dmrt genes in embryos of the Medaka fish (Oryzias latipes). Mech Dev 121, 997-1005.

12. Schoft, V.K., Beauvais, A.J., Lang, C., Gajewski, A., Prufert, K., Winkler, C., Akimenko, M.-A., Paulin-Levasseur, M., and Georg Krohne, G. (2003). The lamina-associated polypeptide 2 (LAP2) isoforms b , g , and w of zebrafish: developmental expression and behavior during the cell cycle. J Cell Science 116, 2505-2517.

13. Winkler, C. , Elmasri, H., Klamt, B., Volff, J-N., and Gessler, M. (2003). Characterization of hey bHLH genes in teleost fish. Dev Genes Evol 213, 541-553.

14. Winkler, C. , Schafer, M., Duschl, J., Schartl, M., and Volff, J.-N. (2003). Functional divergence of two zebrafish midkine growth factors following fish-specific gene duplication. Genome Res 13, 1067-1081.