Figure 2. A beating heart is required for HSC formation and artery development.

(A-H) Effect of sih mutation on HSC and vascular formation at 36hpf.

(A,E) runx1/cmyb expression is greatly reduced in sih^-/- embryos compared to WT siblings.

(B,F) flk1 expression reveals a grossly normal vascular pattern in sih^-/- embryos; changes in the development of the intersomitic vessels and vascular plexus were noted in some animals.

(C,F) ephB2 expression is diminished in sih^-/- embryos.

(D,H) flt4 expression is expanded in sih^-/- embryos.

(L) The expression levels of HSC (runx1, cmyb), vascular (flk) and arterial (ephB2) markers are significantly decreased in sih^-/- embryos compared to sibling controls (t-test, p<0.05, n=3), as measured by qPCR at 36hpf.

(J,K) The sih mutation has no effect on primitive hematopoiesis as seen by benzidine staining at 36hpf; in the absence of a heartbeat blood is pooled in the major vessels.