Wnt4 regulates thymopoiesis at multiple stages. Working model depicting the different levels of Wnt4 action on T-cell development. (1) Wnt4 in the BM increases lymphoid-primed multipotential progenitor (LMPP) survival in a paracrine manner.^23,25  (2) Wnt4 facilitates ETP/DN2 expansion in a paracrine manner (Figures 2–3). (3) Wnt4 facilitates TEC expansion, in particular that of mTECs in the fetal and early postnatal period, probably in an autocrine manner (Figures 4–5). (4) Wnt4 is likely to increase the clonal expansion capacity of precursor TECs (Figures 4,6). HSC indicates hematopoietic stem cell; CLP, common lymphoid precursor; CMP, common myeloid precursor; TESC, thymic epithelial stem/progenitor cell; CMJ, corticomedullary junction.