The focus of this laboratory is on the role of intercellular signaling in the early developing vertebrate embryo, specifically focussing on the frog and zebrafish embryos. The work ranges from biochemical studies aimed at understanding the proteins involved in the intracellular signaling pathways to genetic studies aimed at understanding how these signals function to create embryonic structures.

One area of major interest is the role of the Wnt pathway in regulating the formation of the head and dorsal axis in the frog embryo in response to the entry of the sperm. We have determined several of the key intracellular interactions that regulate this pathway including the kinase GSK3 and a novel inhibitor of GSK3 (GBP) that we cloned in a 2-hyrid screen. Together with Randall Moon's group (Pharmacology), we showed that GSK3 acts by phosphorylating the protein ß-catenin causing it to be degraded. We showed that ß-catenin works to activate the transcription of the siamois gene, which is the master regulator of head and dorsal axis formation. In our recent work, we found that GBP is transported in the frog egg by binding kinesin, demonstrating that GBP acts as an interface between the sperm directed microtubule network and the regulators of ß-catenin.

Together with Dr. Wenqing Xu's group (Biostructure), we have used crystallography to understand the interactions between different proteins in the Wnt pathway, and used this structural information to test new hypotheses about the workings of this pathway, and to reveal potential drug targets since misregulation of ß-catenin levels leads to a variety of cancers. We recently determined the structures of ß-catenin bound to Axin and to APC, which are key members of the complex of proteins that regulates ß-catenin levels. This structure suggested a new mechanism for ß-catenin turnover within the complex. Using biochemical and structural approaches, we are continuing to analyze this complex.

In zebrafish, we have been working to understand how intercellular signals pattern the formation of the mesoderm, taking advantage of the genetics available in this system. We are particularly focused on the role of Bmp in regulating the formation of the tail, and the downstream genes regulated by Bmp signals. We have also discovered the molecular nature of two important patterning mutations, floating head and spadetail. Floating head mutants lack the notochord, and are due to a mutation in a homeobox transcription factor. Spadetail mutants lack the trunk muscle and are due to a mutation in a T-box transcription factor. We are actively continuing our studies on the interplay of intercellular signals and transcription factors in forming the trunk and tail.

In the foreground of the picture is ß-catenin (yellow) bound to a fragment of Axin (red). In the background is a picture of a two-headed tadpole, created by altering ß-catenin levels in the embryo.

Selected Publications

Graham, T. A., Weaver, C., Mao, F., Kimelman, D., and Xu, W. (2000). Crystal structure of a ß-catenin/Tcf complex. Cell 103, 885-896.

Griffin, K. J. P., Amacher, S. L., Kimmel, C. B., and Kimelman, D. (1998). Molecular identification of spadetail: regulation of zebrafish trunk and tail mesoderm formation by T-box genes. Development 125, 3379-3388.

Griffin, K. J. P., and Kimelman, D. (2002). One-eyed pinhead and the T-box transcription factor Spadetail are essential for heart and somite formation. Nat Cell Biol 4, 821-825.

Lee, H., and Kimelman, D. (2002). A dominant negative form of p63 is required for epidermal proliferation in zebrafish. Dev Cell 2, 607-616.

Pyati, U.J., Webb A.E., and Kimelman, D. (2005) Transgenic zebrafish reveal stage-specific roles for Bmp signaling in ventral and posterior mesoderm development. Development 132, 2333-2343

Szeto, D. P., and Kimelman, D. (2004). Combinatorial gene regulation by Bmp and Wnt in zebrafish posterior mesoderm formation. Development 131, 3751-3760.

Talbot, W. S., Trevarrow, B., Halpern, M. E., Melby, A. E., Farr, G., Postlethwait, J. H., Jowett, T., Kimmel, C. B., and Kimelman, D. (1995). A homeobox gene essential for zebrafish notochord development. Nature 378, 150-157.

Weaver, C., Farr, G. H. I., Pan, W., Rowning, B. A., Wang, J., Mao, J., Wu, D., Li, L., Larabell, C. A., and Kimelman, D. (2003). GBP binds kinesin light chain and translocates during cortical rotation in Xenopus eggs. Development 130, 5425-5436.

Xing, Y., Clements, W. K., Kimelman, D., and Xu, W. (2003). Crystal structure of a ß-catenin/Axin complex suggests a mechanism for the ß-catenin Destruction complex. Genes Dev 17, 2753-2764.

Xing, Y., Clements, W. K., Le Trong, I., Hinds, T. R., Stenkamp, R., Kimelman, D., and Xu, W. (2004). Crystal Structure of a ß-catenin/APC complex reveals a critical role for APC phosphorylation in APC function. Mol Cell 15, 523-533.

Yost, C., Farr, G. H. I., Pierce, S. B., Ferkey, D. M., Chen, M. M., and Kimelman, D. (1998). GBP, an inhibitor of GSK-3, is implicated in Xenopus development and oncogenesis. Cell 93, 1031-1041.

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Revised 5/7/2005