Fate mapping of Tbx1-expressing cells in the mesentery. (A and A′) X-gal staining of isolated intestines at E14.5 shows extensive contribution of Tbx1-traced cells to the mesenteric vessels of control (A; Tbx1^Cre/+; R26R) and mutant (Tbx1^Cre/ΔE5; R26R) embryos (A’). Black lines indicate the angle of sections in B and B′. (B and B′) In the proximal mesentery of E14.5 embryos, X-gal staining and anti-Lyve1 colocalize in mesenteric LECs in control (B) and mutant (B′) embryos. Note the abnormal anatomy of the mutant lymphatic vessels (B’, red arrowheads). (C and C’) At E15.5, in the proximal mesentery, highly abnormal lymphatic vessels in mutant embryos (C’, red arrowheads) are both X-gal⁺ and Lyve1⁺. (D and D’) In the distal mesentery, lymphatic vessels were present in control embryos (D, arrowhead) but not mutant embryos (D’). Insets show the boxed area at higher magnification. (E and E’) At E16.5, very few X-gal⁺/Lyve1⁺ vessels are identifiable (E’, red arrowhead). Note that the vasa vasorum (E′, black arrows) is X-gal⁺/Lyve1 negative. A, mesenteric artery; V, mesenteric vein; L, lymphatic vessel; P, proximal; D, distal. Black arrowheads indicate lymphatic vessels. Bars, 100 µm.