Fig. 5. Normal AP patterning and endoderm specification in Nodal^600/600 embryos. (A) Whole-mount analysis of endogenous Nodal mRNA expression in WT embryos at 6.5 dpc. The box indicates the position of the sagittal section shown in B. (B) Nodal expression in the epiblast (epi) and visceral endoderm (VE) is indicated by black arrowheads. (C) Nodal ^600/600 mutants show markedly reduced expression within the epiblast. (D) Sagittal section shows loss of expression within the VE (white arrowheads). (E) In WT embryos at 7.5 dpc, Nodal mRNA is confined to the node (n). (F) Nodal ^600/600 mutants are morphologically indistinguishable from WT and display robust Nodal expression in the node. (G) Asymmetric Nodal expression in the node and left lateral plate mesoderm (llpm) of WT embryos at 8.5 dpc. (H) Posterior views of embryos shown in G. (I) Transverse section shows asymmetric Nodal expression. (J) Nodal ^600/600 mutant embryos strongly express Nodal in the node. A proportion of embryos exhibit a very low level of expression in the left LPM. Posterior view (K) and section (L) of the Nodal ^600/600 mutant embryo shown on the right in J, confirming node expression is equivalent on both sides. s, somite. All panels are lateral views with anterior towards left, except H and K, which show posterior views.

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