Fig. 7. Differentiation of ostiae in svp mutant embryos. (A-D) Confocal sections of late stage 16 embryos double labeled with anti-Prc (red) and either anti--Spectrin (green) (A,B) or anti-D-Mef2 (green) (C,D). Differentiation into aorta and heart occurs correctly but the change in morphology (A,B) or in the shape of nuclei (C,D) of the svp-expressing cells (arrowhead and open arrowhead) is not apparent, in either the heart or the aorta. The asterisks mark the alary muscles. (E) In svp mutant embryos, expression of Abd-A (red) in all cardioblasts in segments A5-A7, including svp-positive cells (arrowheads) is similar to that in wild-type embryos. (F,G) In vivo observation of the cardiac tube in svp mutant embryos. The heart starts beating normally but almost completely stops after 22 hours of development. The ostiae cells (arrows) differentiate after an initial delay; differentiation, however, remains incomplete and they do not function (or open and close). Double arrows mark the internal limit of the lumen.