The abnormal medial positioning of the Pth’s in Tbx1 ^neo2/neo2 embryos corrected following in utero minoxidil administration. (A) Timed pregnant mice from Tbx1^+/neo2 intercrosses received carrier or minoxidil treatments as in Fig. 2 A. At E17–17.5, embryos from the indicated genotypes were sectioned and stained with H&E to visualize the trachea (Tr), thyroid (T), and Pth locations. The positions of the different organs are shown. Both 4× and 10× images were taken for the trachea (Tr), thyroids (Th), and Pth. Arrows are shown for the Pth structures in the 4× vs. 10× images. Data are representative of 8, 5, and 8 embryos from Tbx1^+/+ (carrier), Tbx1^neo2/neo2 (carrier), and Tbx1^neo2/neo2 (minoxidil) genotypes, respectively. (B) Pie charts reveal the lateral (blue) and medial (red) distributions of the Pth’s in the three groups of embryos. (C) Pie charts reveal the number of E13–13.5 embryos with a normal aortic arch (orange) or those with a visually detectable IAA-B (blue). This was shown for Tbx1^+/+, Tbx1^neo/neo2, and Tbx1^neo2/neo2 genotypes with carrier or minoxidil treatments. Tbx1^+/+-carrier (n = 15), Tbx1^neo2/neo2-carrier (n = 22), and Tbx1^neo2/neo2-minoxidil (n = 20). (D) Heart sections were prepared from the indicated E15–15.5 cohorts of embryos, obtained from pregnant mice with/without minoxidil administration, and stained with H&E. Sections were also processed for IHC to detect Col2a1 and Acan protein expression. The images are representation of >6 embryos/group. (E) Model depicting the formation of the thymus in normal and 22q11.2 settings. Minoxidil administration reduces the expression of chondrogenic collagens (Col2a1, Col9a1, and Col11a1) and ECM cross-linking enzymes (Plod and Lox), decreasing ECM stiffness. This reduces the chondrogenic potential of mesenchymal cells, enabling restoration of thymus growth.