Normal induction of early mesoderm-associated genes in control and scl-null EBs. (A through D) Expression of the early pan-mesodermal marker Brachyury, the ventral mesoderm inducing gene BMP-4, its type I receptor (BMP R1A), and the VEGF receptor tyrosine kinase flk-1 are shown at day 0, 4, 6, and 8 of embryoid body differentiation. At each time point, wild-type (+/+) or scl-heterozygous (+/−) lines are compared with three independent scl-null lines (−/−), except for day 0, when expression is shown for undifferentiated wild-type (+/+) ES cells only. RT-PCR amplification of three fivefold serial dilutions of cDNA is shown for each line. C, control lane with no cDNA added.