Fig. 8. Defective heart morphogenesis in both ephrinB2 conventional and conditional mutant embryos. (A-C) EphrinB2 is primarily expressed in the endocardial lining (arrows) of the heart, as revealed by sections of E9.5 ephrinB2^lacZ/+ embryos stained for PECAM1 (A,C, green channel) and ß-gal (A,B, red channel). Some non-endocardial staining is seen (A-C, red channel not overlapping with green, arrowheads). (D-F) In the heart, restriction of Tie2-Cre activity to the endocardial lining is revealed by E9.5 sections of Tie2-Cre X R26R lacZ reporter cross embryos double-labeled for PECAM1 (D,F, green channel) and ß-gal (D,E, red channel). A merged image (D) shows Tie2-Cre activity is found only in the PECAM1-positive endocardial lining (arrows). (G-I) EphrinB2 conventional and conditional embryos show swelling and defective looping of the heart compared with control ephrinB2^lacZ/+ embryos (compare H and I with G), revealed by whole-mount anti-PECAM1 staining at E9.5. (J-L) PECAM1 stained sections of hearts reveal little or no myocardial trabeculation (arrowheads) in both the conditional and conventional mutants (compare L with K) compared with control embryos (compare K and L with J, arrowheads) at E9.5.