Fig. 6. Fate mapping with Pitx2 abc^creneo and Rosa26 reporter allele. (A,B) lacZ staining of 10.5 dpc Pitx2 abc^creneo+/- (A) and Pitx2 abc^creneo;abc^null (B), and Rosa26 reporter trans-heterozygous embryo. Arrow indicates the lacZ-positive cells in the OFT that have crossed the midline (broken line). (C,D) lacZ staining (C) and Pitx2c whole-mount in situ (D) of 12.5 dpc Pitx2 abc^creneo+/- and Rosa26 reporter trans heterozygous embryos. Signal is indicated by the arrows. (E-H) lacZ staining (E,G) and Pitx2c whole-mount in situ (F,H) of 14.5 dpc (E,F) and 16.5 dpc (G,H) Pitx2 abc^creneo+/- and Rosa26 reporter trans heterozygotes. lacZ-positive cells are indicated by arrows (E,G). Pitx2c expression has been extinguished in Pitx2 daughter cells that would be lacZ positive and are marked with and asterisk (F,H). (I,J) Coronal sections through a 16.0 dpc Pitx2 abc^creneo+/- and Rosa26 reporter trans-heterozygotes at slightly different dorsoventral planes. Arrows indicate lacZ-positive cells in myocardium (I) and in interatrial and interventricular septum (J). (K,L) Whole-mount lacZ staining of 14.5 dpc wild-type (K) and Pitx2 abc^creneo;c Pitx2 mutant (L), and Rosa26 reporter trans-heterozygous embryos. Arrows indicate lacZ-positive cells. Circled area in L indicates region with fewer lacZ-positive cells. (M,N)Whole-mount lacZ staining of 16.5 dpc wild-type (M) and Pitx2 abc^crenoe;c Pitx2 mutant (N), and Rosa26 reporter trans-heterozygotes. Arrows indicate lacZ-positive cells. Circled area in N indicates region with fewer lacZ-positive cells. (O-R) Transverse sections through a 16.5 dpc Pitx2 abc^creneo+/- (O,Q) and Pitx2 abc^creneo;c (P,R) and Rosa26 reporter trans-heterozygous embryo. More rostral sections show lacZ-positive Pitx2 daughter cells (arrow) in myocardium of both Pitx2 abc^creneo+/- (O) and abc^creneo;c mutants (P), while more caudal sections near cardiac apex show lacZ-positive cells in abc^creneo+/- (Q) but not in abc^creneo;c mutants (R) as denoted by the asterisk. (S,T) Transverse sections through a 12.5 dpc Pitx2 abc^creneo+/- (S) and Pitx2 abc^creneo;abc^null (T) and Rosa26 reporter trans-heterozygote showing lacZ expression in AV cushion in heterozygote (arrow) but absent in the mutant (asterisk). (U) Coronal section through a 14.5 dpc Pitx2 abc^creneo;abc^null and Rosa26 reporter trans-heterozygote showing exclusion of lacZ-positive cells from AV cushion (asterisk). (V,W) Coronal section through a 16.5 dpc Pitx2 abc^creneo+/- (V) and abc^creneo;c (W) and Rosa26 reporter trans-heterozygote showing lacZ-positive cells within valve leaflet in the Pitx2 abc^creneo+/- embryo (arrows) but exclusion of lacZ-positive cells from the AV valve leaflets of Pitx2 mutants(asterisk). rv, right ventricle; lv, left ventricle; ivs, interventricular septum; scv, superior caval vein.

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