May play a central role in the initial events of axis formation and in particular in specifying anterior head regions and their spatial relationship with trunk structures. Activates the head organizer gene cer1 by acting synergistically with siamois and mix-A/mix.1 through the 5'-TAATCT-3' element of the cer1 promoter. Also binds as a complex with lhx1/lim1 and ldb1 to the gsc promoter to stimulate expression. Shows a localized expression in the dorsal region of the marginal zone at stage 9.5. At stage 10.5, expressed in dorsal bottle cells of the dorsal deep zone fated to give rise to prechordal mesendoderm. Also begins to be expressed in presumptive anterior neuroectoderm where expression persists in subsequent stages. At stage 14, expression is confined to mesendoderm and ectoderm cells of anterior dorsal regions. Expressed at low levels throughout early development from unfertilized egg to late blastula when its expression level significantly increases. Belongs to the paired homeobox family. Bicoid subfamily.