Fig. 2. Mesoderm spreading in mutant embryos. (A-F) Ectodermal cell fate and
mesoderm morphogenesis. Cross sections of embryos showing the development of
the mesoderm in embryos with altered ectodermal cell fates. The embryos have
been stained to reveal the di-phosphorylated form of the MAP kinase ERK. Each
set of panels show an early and late timepoint during the flattening of the
mesoderm. (A,B) Sections of brk, sog mutant embryos. (C,D) Sections
of Egfr (top18A) mutant embryos. (E,F) Sections
of brk, sog; Egfr (top18A) triple mutant embryos.
Arrowheads indicate mesodermal cells in which high levels of the
di-phosphorylated form of ERK are present. (G,H) Sections of embryos stained
with antibodies directed against Twist to reveal mesodermal cells. (G) A
section of a late dof, stg double mutant embryo. (H) Mesoderm
development in a late htl mutant embryo expressing an activated form
of Htl throughout the mesoderm.