Active Wnt/beta-catenin signaling is required for embryonic thymic epithelial development and functionality ex vivo

The Wnt/beta-catenin signaling pathway plays an important role in the commitment and development of thymic epithelial precursors. Here we document similarities of thymic epithelial development during embryogenesis in human and mouse. We stained for thymic epithelial surface markers (EpCAM1, Ly51, K8) and ligand/receptor pair (Wnt4, Fz4). Our results confirm the relevance of using murine test systems to model human embryonic thymic epithelial cell development. We have efficiently transduced murine embryonic epithelial cells using mock (GFP) and Wnt/beta-catenin-inhibiting (ICAT-encoding) recombinant adenoviral vectors. The effect of Wnt4 was assayed in the form of Wnt4-containing supernatant. Gene expressional changes were assessed by Q-PCR and also morphology using conventional and confocal fluorescent microscopy. Functional aberration caused by ICAT was assessed through evaluation of thymocyte maturation. Our results demonstrate that ICAT and Wnt4 have reciprocal effects during embryonic thymic epithelial cell development. While Wnt4 is capable of increasing the expression level of characteristic intracellular (FoxN1), surface (MHCII) and secreted (IL7) molecules, Wnt/beta-catenin inhibition through ICAT can moderately decrease their expression. Morphological changes induced by ICAT resulted in the development of hollow, inflated thymic lobes with reduced epithelial cell numbers. The ICAT-treated thymic lobes also showed significant impairment in supporting thymocyte development and maturation.