PMC

Branchial arch artery defects in MRTF-B mutant embryos. (A–C) Wild-type and MRTF-B mutant embryos at E10.5 (A) and E11.5 (B and C). Hematoxylin/eosin sections show hypoplastic sixth arch arteries in mutant embryos. Abnormal communication between the fourth and sixth arteries at E10.5 is indicated (*). Histological sections stained for SM α-actin show smooth muscle differentiation within the wall of branchial arch arteries and dorsal aortae in the wild-type embryo. In contrast, SM α-actin expression is not detected in the branchial arch arteries of the mutant embryo, but expression is seen in the dorsal aorta and heart. Branchial arch arteries are numbered as 3, 4, and 6. da, dorsal aorta. (D) Schematic of branchial arch arteries. The plane of section in the embryos shown in A–C is indicated by a dashed line. as, aortic sac; lda, left dorsal aorta; rda, right dorsal aorta. (E) Transverse section through the heart shows incomplete ventricular septation (arrowhead) and thin myocardial wall in the mutant embryo at E13.5. lv, left ventricle; rv, right ventricle.

LacZ staining of MRTF-B mutant embryos. Embryos were stained for lacZ expression. At E8.5, staining was apparent in the ventral neural tube and two distinct stripes (arrowheads) in the developing hindbrain (A). LacZ staining is observed in the otic vesicle, heart, dorsal aorta, and branchial arch arteries 1, 2, and 3 at E9.5 (B and C). At E10.5, lacZ expression becomes more widespread, with high level of expression in the first branchial arch (D). LacZ expression is also detected in the third and fourth arch arteries of MRTF-B mutant embryos as shown in the right and left lateral view (E and F). Branchial arch arteries are numbered. ba1, first branchial arch; nt, neural tube; ov, otic vesicle, h, heart; da, dorsal aorta.

(A-F) Angiographic casting of wild-type (A,C) and Pbx1^-/- (B,D-F) E14.5 mouse embryos. (A,B) The position of the aortic arch (arrow) is indicated relative to the forelimbs (arrowheads). (G,H) India ink casting of the branchial arch arteries in wild-type (G) and Pbx1^-/- (H) E11.5 embryos. The branchial arch arteries are numbered according to branchial arch origin. (I,J) Whole-mount in situ hybridization staining for Msx2 (blue) on wild-type (I) and Pbx1^-/- (J) E10.5 embryos. The arrowhead indicates the groove separating the third and fourth branchial arches in the wild-type embryo. The arrow indicates Msx2 expression in the fourth branchial arch. CCA, common carotid artery; ICA, internal carotid artery; ECA, external carotid artery; DA, ductus arteriosus; BCA, brachiocephalic artery; RSA and LSA, right and left subclavian arteries; LPA, left pulmonary artery; PA, right and left pulmonary arteries; IVA, internal vertebral artery; AA, axillary artery; IMA, internal mammary artery; SVC, superior vena cava; DLSCA, developmentally left, but anatomically right subclavian artery; DRSCA, developmentally right, but anatomically left subclavian artery.

Persistence of left-sided fifth arch with normal arch arising from the fourth branchial arch and patent ductus arising from the distal sixth arch