The thymus is seeded by very small numbers of progenitor cells that undergo massive proliferation before differentiation and rearrangement of TCR genes occurs. Various signals mediate proliferation and differentiation of these cells, including Wnt signals. Wnt signals induce the interaction of the cytoplasmic cofactor beta-catenin with nuclear T cell factor (TCF) transcription factors. We identified target genes of the Wnt/beta-catenin/TCF pathway in the most immature (CD4-CD8-CD34+) thymocytes using Affymetrix DNA microarrays in combination with three different functional assays for in vitro induction of Wnt signaling. A relatively small number (approximately 30) of genes changed expression, including several proliferation-inducing transcription factors such as c-fos and c-jun, protein phosphatases, and adhesion molecules, but no genes involved in differentiation to mature T cell stages. The adhesion molecules likely confine the proliferating immature thymocytes to the appropriate anatomical sites in the thymus. For several of these target genes, we validated that they are true Wnt/beta-catenin/TCF target genes using real-time quantitative PCR and reporter gene assays. The same core set of genes was repressed in Tcf-1-null mice, explaining the block in early thymocyte development in these mice. In conclusion, Wnt signals mediate proliferation and cell adhesion, but not differentiation of the immature thymic progenitor pool.

*Oligonucleotide Array Sequence Analysis, *Zebrafish Proteins, Animals, Antigens, CD34/*biosynthesis, Cell Adhesion/genetics/immunology, Cell Differentiation/genetics/immunology, Cell Division/genetics/immunology, Cell-Free System/physiology, Child, Cytoskeletal Proteins/genetics/physiology, DNA-Binding Proteins/genetics/physiology, Genes, Reporter, Humans, Lithium Chloride/pharmacology, Lymphoid Enhancer-Binding Factor 1, Mice, Mice, Inbred C57BL, Protein Biosynthesis, Proteins/genetics/physiology, Proto-Oncogene Proteins/biosynthesis/*genetics/isolation & purification/physiology, Research Support, Non-U.S. Gov't, Retroviridae/genetics, Signal Transduction/drug effects/genetics/immunology, T Cell Transcription Factor 1, T-Lymphocyte Subsets/cytology/*immunology/*metabolism, Thymus Gland/cytology/*immunology/*metabolism, Trans-Activators/genetics/physiology, Transcription Factors/genetics/physiology, Transduction, Genetic, Transfection, Wnt Proteins, beta Catenin
Journal of Immunology
Erasmus MC: University Medical Center Rotterdam

Staal, F.J.T, Weerkamp, F, Baert, M.R.M, van den Burg, C.M, van Noort, M, de Haas, E.F, & van Dongen, J.J.M. (2004). Wnt target genes identified by DNA microarrays in immature CD34+ thymocytes regulate proliferation and cell adhesion. Journal of Immunology. Retrieved from