• although anterior neuroectoderm is specified, mesoderm production is severely restricted
• analysis of nascent mesoderm markers shows that Lefty2 and Fgf4 are completely absent at E7.5 while Snail and Fgf8 expression is markedly reduced with weak areas of expression confined to the distal-most mesoderm at E7.0
• pharmacological inhibition of Nodal signaling with SB505124 partially restores mesoderm production: in culture, SB505124-treated embryos show increased mesodermal-like streak derivatives, a slight increase in T expression, a marked increase in mesodermal marker transcripts (Tbx6, Twist1 and Snail), a reduction of Nodal, Cer1, Eomes and Foxa2, but no effect on the loss of Lefty2 or Fgf4, suggesting that both Nodal-dependent and Nodal-independent events contribute to the gastrulation defects