Thymic development and lymphopoietic function in the absence of TGF-β signaling in thymic stromal cells. (A) Gross anatomic, histologic, and flow cytometric analysis of thymic tissue from 2-week-old TGFβRII^lox/lox::Foxn1-Cre and TGFβRII^lox/lox mice. (i,ii) Thymus in situ (T indicates thymus; H, heart; and L, lung). (iii,iv) H&E staining (magnification 4×). (v-x) Immunofluorescence microscopy; magnification, 20×. Cortical (v,vi) and medullary (vii-x) regions, stained for cytokeratin 8 (v-viii), cytokeratin 5 (v-x), ERTR7 (v-viii), and UEA-1 (ix,x). (xi,xii: representative fluorescence-activated cell sorting [FACS] profile for the cell surface expression of CD4 and CD8 [mean ± SD of 6 mice analyzed per group]). Percentages on plots are of total cells within gate. (B) Genomic deletion analysis of sorted thymic dendritic cells (CD45⁺ MHCII⁺, left lane) and epithelial cells (CD45⁻ MHCII⁺, right lane, purity ≥ 95) isolated from 4-week-old TGFβRII^lox/lox::Foxn1-Cre mice. The upper band denotes the undeleted allele, whereas the lower band represents the deleted allele. (C) Hoxa-controlled Cre expression pattern. Top: Sagittal section of an E10.25 Rosa26^lacZ::Hoxa3-Cre embryo, assayed for β-galactosidase expression and counterstained with nuclear fast red; PA indicates pharyngeal arch. Bottom: FACS analysis of E13.5 epithelial (left panel) and nonepithelial (right panel) thymic stromal cells from Z/EGLobe21 and Z/EGLobe21::Hoxa3-Cre mice for GFP expression. Percentages on graphs are of total cells within gate. (D) Thymocyte development in E12.5 FTOC of thymic lobes isolated from TGFβRII^lox/lox::Hoxa3-Cre and TGFβRII^lox/lox E12.5 embryos after a 12-day culture period. Representative dot blots of flow cytometric analysis for the cell surface expression of CD4 and CD8 (n = 3 for TGFβRII^lox/lox::Hoxa3-Cre; n = 4 for TGFβRII^lox/lox). Percentages on plots are of total cells within gate.