In the wild-type thymus (Mcl1^WT), cortex (C) and medulla (M) architecture is well organized. In the cortex, cTECs interact with immature thymocytes (including DN and DP). In the medulla, mTECs interact with positively selected single positive (SP) thymocytes (including CD4SP and CD8SP). Specific deletion of MCL-1 in TECs (Mcl1^cKO) results in the deficiency of medulla formation and the disruption of thymic architecture with overpopulation by fibroblasts, which eventually leads to thymic hypoplasia (loss of the majority of thymocytes). Professional illustration by Somersault18:24.