Associate Professor of Neurobiology and Anatomy
Signaling pathways in zebrafish neural cell fate determination
During development of the central nervous system (CNS), cells are influenced by their environment to adopt specific fates. These environmental signals are crucial for the correct patterning of cell types and their subsequent functional connections. My laboratory is studying the role of the Wnt/β-catenin signaling pathway in CNS cell fate specification. We use zebrafish as a model organism, focusing on the regulation of Wnt/β-catenin target genes in the CNS by a family of transcription factors called Tcf proteins. Tcfs are required for β-catenin to regulate transcription, and can act as repressors or activators of target genes depending on the state of Wnt signaling. Three major questions are being addressed: (1) What cells in the CNS require β-catenin/Tcf signaling? (2) What is the function of Tcf proteins in these cells? (3) Which genes are Lef/Tcf targets during CNS cell differentiation?
(1) What cells in the CNS require β-catenin/Tcf signaling? We are using several approaches to address this question. We have generated transgenic zebrafish lines that express GFP under the control of a β-catenin-responsive promoter, and are now characterizing GFP-expressing cell populations in the CNS and determining whether transgene expression in these regions also requires β-catenin signals. We have also cloned all of the existing tcf genes in zebrafish and are systematically examining their expression during CNS development. Through these experiments we hope to identify novel β-catenin/Tcf-responsive cell populations in the CNS.
(2) What is the function of Tcf proteins in responsive cells? β-catenin/Tcf activity could affect proliferation, cell fate, differentiation, or multiple pathways. To determine the necessity for Tcf function in individual cells, we have generated transgenic lines that expresse inducible constitutive repressors and activators of Tcf target genes. We can activate the inducible promoters and follow the misexpressing cells in vivo to identify essential developmental roles played by β-catenin/Tcf function in CNS development. In addition, we are performing loss-of-function studies for tcf genes using either mutations or antisense gene knockdown. Our goal is to uncover novel roles for β-catenin/Tcf function in the development of specific CNS cell populations.
(3) What are the target genes? Tcf function can lead to the repression or activation of downstream genes, but particular targets in the CNS are unknown. We are using chromatin immunoprecipitation (ChIP) with our transgenic lines as well as specific Tcf antibodies to directly analyze candidate gene promoters as potential targets of Tcf in the CNS. The goal of this project is to identify Tcf target genes that are directly involved in cell fate determination and patterning of the CNS.
Kim, H.S., and Dorsky, R.I. (2011) Tcf7l1 is required for spinal cord progenitor maintenance. Developmental Dynamics, 240:2256-2264.
Lin, J., Wang, X., and Dorsky, R.I. (2011) Progenitor expansion in apc mutants is mediated by Jak/Stat signaling. BMC Developmental Biology, 11:73.
Wang, X., Lee, J.E., and Dorsky, R.I. (2009) Identification of Wnt-responsive cells in the zebrafish hypothalamus. Zebrafish, 6:49-58.
Gribble, S.L., Kim, H.S., Bonner, J., Wang, X., and Dorsky, R.I. (2009) Tcf3 inhibits spinal cord neurogenesis by regulating sox4a expression. Development, 136:781-789.
Veien, E.S., Rosenthal, J.S., Kruse-Bend, R.C., Chien, C.B., and Dorsky, R.I. (2008) Canonical Wnt signaling is required for the maintenance of dorsal retinal identity. Development, 135:4101-4111.
Bonner, J., Gribble, S.L., Veien, E.S., Nikolaus, O.B., Weidinger, G., and Dorsky, R.I. (2008) Distinct pathways mediate patterning and proliferation in the dorsal spinal cord downstream of canonical Wnt signaling. Developmental Biology, 313:398-407.
Gribble, S.L., Nikolaus, O.B., and Dorsky, R.I. (2008) Regulation and function of Dbx genes in the zebrafish spinal cord. Developmental Dynamics, 236:3472-3483.
Nyholm, M.K., Wu, S., Dorsky, R.I., and Grinblat, Y. (2007) The zebrafish zic2a-zic5 gene pair acts downstream of canonical Wnt signaling to control cell proliferation in the developing tectum. Development, 134:735-746.
Lee, J., Wu, S., Goering, L.M., and Dorsky, R.I. (2006) Canonical Wnt signaling through Lef1 is required for hypothalamic neurogenesis. Development, 133:4451-4461.
Veien, E.S., Grierson, M.J., Saund, R.S., and Dorsky, R.I. (2005) Expression pattern of zebrafish tcf7 suggests unexplored domains of Wnt/β-catenin activity. Dev Dyn., 233:233-239.
Lewis, J.L., Bonner, J., Modrell, M., Ragland, J.W., Moon, R.T., Dorsky, R.I., and Raible, D.W. (2004) Reiterated Wnt signaling during zebrafish neural crest development. Development, Mar;131(6):1299-1308.
Dorsky, R.I., Itoh, M., Moon, R.T., and Chitnis, A. (2003) Two tcf3 genes cooperate to pattern the zebrafish brain. Development, 130:1937-1947.
Dorsky, R.I., Sheldahl, L.C. and Moon, R.T. (2002) A Transgenic Lef1/β-catenin-Dependent Reporter is Expressed in Spatially -Restricted Domains Throughout Zebrafish Development. Developmental Biology, 241:229-237.
Dorsky, R.I., Raible, D.W. and Moon, R.T. (2000) Direct regulation of nacre, a zebrafish MITF homolog required for pigment cell formation, by the Wnt pathway. Genes and Development, 14:158-162.
Dorsky, R.I., Moon, R.T. and Raible, D.W. (1998) Control of neural crest cell fate by the Wnt signalling pathway. Nature, 396:370-373.