Fig. 6. Partial rescue of primitive erythropoiesis by the Scl transgene (Scl^tg). (A) Analysis of Scl expression in Sil-Scl transgenic E9.5 yolk sacs. Individual yolk sacs were analyzed for endogenous and transgenic expression of Scl using quantitative SYBR Green PCR. Histogram represents the average amount of Scl mRNA±s.d., normalized according to the internal control (S16). To estimate the relative levels of Scl expression from the transgene and endogenous source, the molar amount of endogenous Scl in wild-type mice was taken as 1. Scl^+/+, n=4; Scl^tg, n=6. (B) Apoptosis in TER119-positive cells. TER119, Annexin V and 7-AAD staining were performed as in Fig. 5. Data shown are from three independent litters and are expressed as % of TER119-positive cells. Note that the level of apoptotic death depends on the number of Vegf^lo alleles and is attenuated by the Scl transgene. *P<0.05; n is the number of embryos of a corresponding genotype. (C) Analysis of erythroid genes in individual yolk sacs was performed as described in Fig. 4. (D) Plots illustrate the level of gene expression within individual yolk sacs as ratio of the indicated genes and the L32 internal control. Horizontal bars represent median values. Note that the Scl^tg increases the level of Gata1 and ßH1 in homozygous Vegf^lo/lo yolk sacs. P<0.01.