FIG. 4.

Anatomy of interventricular septum and outflow tract of the hearts of E16.5 wild-type and Pax3-FKHR heterozygous embryos and Pax3 expression. (A to D) Hematoxylin and eosin staining of transverse sections of wild-type (A and C) and mutant (B and D) hearts. The muscular component of the interventricular septum of the heterozygous mutant is already abnormally thickened (asterisk in panel B); the outflow tract of the heart of the Pax3-FKHR mouse is appropriately divided, but the lumen of the pulmonary trunk portion of the outflow tract is dilated (compare panels C and D). (E) Pax3 plus Pax3-FKHR expression in the heart of an E16.5 Pax3-FKHR embryo. (F) Higher magnification of the boxed region of panel E. Green, nuclear staining with methylene green; purple, staining with α-myosin heavy chain; brown, staining with anti-Pax3.