(A) Simplified schema of a normal thymus in a mouse expressing the transcription factor Foxn1.
(B) The same schema for a thymus of a nude mouse that does not express Foxn1; here the thymus lacks hematopoietic elements.
(C–F) By re-expressing individual signaling factors in the thymus of the nude mice—Ccl25 (C), Scf (D), Cxcl12 (E), and DLL4 (F)—Calderón and Boehm (2012) uncover a hierarchical restructuring of the thymus. The combined expression of factors leads to phenotypes as described in this Preview.