David J. Grunwald, Ph.D.
Professor

Contribution to Society

The process by which the fertilized egg becomes a recognizable animal with many highly specialized and tightly organized cellular components has perplexed philosophers and scientists for millennia. Only in recent years have we developed the tools and understanding that allow us to perform informative experiments aimed at identifying the specific biochemical and cellular processes that contribute to formation of a normal embryo. Our present understanding of animal development indicates that essential processes are shared by all animals. Thus, we expect that our studies of the early zebrafish embryo will provide insight into how all animals develop and enlighten us about the primary defects likely to be the root causes of complex dysmorphologies in humans.

Research Summary

We are interested in the factors that determine the fates of tissue precursor cells in the vertebrate embryo. We investigate this question in the zebrafish, an organism with features that make it wonderfully suited for combining genetic, molecular, and cell biological methods of analysis.

One major focus of the laboratory is to determine how the precursors of the various mesodermal tissues are established in specific regional domains of the early gastrula. We have discovered that a small group of T-box genes, which encode a family of related transcription factors, are expressed in overlapping domains in the early mesoderm. The combined expression of these genes creates a code that assigns developmental fate to mesoderm precursors. Mis-expression of the T-box genes to alter the domains of overlap results in changes in the fates of the mesodermal precursor cells. Thus the functions and mode of action of T-box genes are reminiscent of HOX genes.

To understand how different T-box genes can interact when co-expressed, we have investigated how the transcription factors they encode regulate downstream target gene expression. We find that the T-domain proteins exhibit similar binding properties at some target sites but recognize other target sites differentially, allowing competition for regulation of some target genes. Furthermore, different T-domain transcription factors have different, and sometimes opposing, effects on the expression of target genes. Hence, a cell that expresses only one of the T-domain factors will activate a different repertoire of target genes than a cell that expresses multiple members of the family.

Analysis of T-box gene mutations in humans and other vertebrates has revealed important roles for T-box genes in the development of the limb, heart, tooth, and other complex organs. Since multiple T-box genes are known to be expressed at these developmental sites, we anticipate that T-box genes will generally function in a combinatorial manner. To understand how overlapping domains of T-box gene expression are established, we have begun to investigate the control of their expression in the early mesoderm of the zebrafish. We find that the nested pattern of T-box gene expression is generated in response to localized FGF and BMP growth factor signalling. Whereas one T-box gene, no tail, is activated solely by FGF signalling, another T-box gene, tbx6, requires both FGF and BMP signalling. Different requirements for the two growth factors fully accounts for why tbx6 is expressed by only a subset of the no tail-expressing cells. As T-box genes are often expressed at known sites of FGF and BMP signalling, differential response to these growth factors may be a general mechanism for establishing overlapping domains of T-box gene expression.

Recent Publications

Goering, L. M., K. Hoshijima, B. Hug, B. Bisgrove, A. Kispert and D. J. Grunwald. (2003). An interacting network of T-box genes directs gene expression and fate in the zebrafish mesoderm. Proceedings National Academy of Sciences (USA) 100: 9410-9415.

Hoshijima, K., Metherall, J. E., and Grunwald, D. J. (2002). A protein disulfide isomerase expressed in the embryonic midline is required for left/right asymmetries. Genes Dev 16, 2518-2529.

Grunwald, D. J., and Eisen, J. S. (2002). Headwaters of the zebrafish -- emergence of a new model vertebrate. Nat Rev Genet 3, 717-724.

Korzh, V., and Grunwald, D. (2001). Nadine Dobrovolskaia-Zavadskaia and the dawn of developmental genetics. Bioessays 23, 365-371.

Appel, B., Fritz, A., Westerfield, M., Grunwald, D. J., Eisen, J. S., and Riley, B. B. (1999). Delta-mediated specification of midline cell fates in zebrafish embryos. Curr Biol 9, 247-256.

Cretekos, C. J., and Grunwald, D. J. (1999). alyron, an insertional mutation affecting early neural crest development in zebrafish. Dev Biol 210, 322-338.

Dorsky, R. I., Snyder, A., Cretekos, C. J., Grunwald, D. J., Geisler, R., Haffter, P., Moon, R. T., and Raible, D. W. (1999). Maternal and embryonic expression of zebrafish lef1. Mech Dev 86, 147-150.

Dorsky RI, Snyder A, Cretekos CJ, Grunwald DJ, Geisler R, Haffter P, Moon RT, Raible DW. Maternal and embryonic expression of zebrafish lef1. Mech Dev. 1999 Aug;86(1-2):147-50.

Cretekos CJ, Grunwald DJ. alyron, an insertional mutation affecting early neural crest development in zebrafish. Dev Biol. 1999 Jun 15;210(2):322-38.

Appel B, Fritz A, Westerfield M, Grunwald DJ, Eisen JS, Riley BB. Delta-mediated specification of midline cell fates in zebrafish embryos. Curr Biol. 1999 Mar 11;9(5):247-56.

Bisgrove BW, Raible DW, Walter V, Eisen JS, Grunwald DJ. Expression of c-ret in the zebrafish embryo: potential roles in motoneuronal development.
J Neurobiol. 1997 Nov 20;33(6):749-68.

Hug B, Walter V, Grunwald DJ. tbx6, a Brachyury-related gene expressed by ventral mesendodermal precursors in the zebrafish embryo. Dev Biol. 1997 Mar 1;183(1):61-73.

Liao W, Bisgrove BW, Sawyer H, Hug B, Bell B, Peters K, Grunwald DJ, Stainier DY. The zebrafish gene cloche acts upstream of a flk-1 homologue to regulate endothelial cell differentiation. Development. 1997 Jan;124(2):381-9.