Fig. 7

A model for the establishment of PPE and NC at the NPB. Spatial distribution of expression levels of TFs in the ectoderm from dorsal (D) to ventral (V) is shown at the beginning of gastrulation (upper panel) and after completion of gastrulation (lower panel). Faint colors indicate weak expression. TFs are grouped according to shared expression patterns. BMP activity levels are also shown for the early stage. Arrows indicate positive regulatory relationships, while lines with bars indicate negative regulatory relationships. Solid lines indicate relationships that have been verified in loss of function (and usually also in gain of function) experiments, while hatched lines indicate relationships that are only supported by gain of function experiments. Temporal changes of regulatory relationships are proposed based on changing TF expression patterns.The context-dependent regulation of Six1 and Eya1 as well as of FoxD3 by Dlx3 and Zic1 is shown by converging arrows. The question marks in the lower panel indicate that TFs probably cooperate with other as yet unknown factors in a context-dependent way to either activate or repress target genes. Cross-regulation of TFs by Six1 and Eya1 is not depicted for clarity. See text for details