Scl is a critical regulator of PLM development. (A-H) Whole-mount embryos (12 × magnification); posterior views; dorsal, top; numbers of embryos represented in gray. Gata1 expression was never observed in the PLM of morphant embryos (A). Runx1 was at first dependent on Scl, initiated weakly in the PLM of morphants at 6 somites (12 hpf) (B, arrow), and by the 10- to 12-somite stage (14 hpf-15 hpf) appeared almost as robust as wt (B, arrowheads). dra was initially expressed normally in morphants, but appeared reduced from 7 somites (12.5 hpf) (C, arrows). The posterior-most region of dra expression was unaffected (C, arrowhead). biKLF expression was lost in morphants by 10 somites (14 hpf) (D). Hhex expression initiated as normal, appeared reduced at 7 somites (12.5 hpf) (E, arrows) and was lost by 10 somites (14 hpf) (E). Gata2, fli1, and lmo2 expression in the PLM was unaffected in 10-somite (14 hpf) morphants (F-H). (I) Data from in situ analyses are summarized schematically. Bars represent the changing expression of genes over time. Bars marked by asterisks represent gene expression in morphants. Purple, Scl-independence; red, Scl-dependence; green, scl expression.