xlim1 and lim domain binding protein 1 cooperate with various transcription factors in the regulation of the goosecoid promoter the homeobox genes xlim1 and goosecoid gsc are coexpressed in the spemann organizer and later in the prechordal plate that acts as head organizer based on our previous finding that gsc is a possible target gene for xlim1 we studied the regulation of gsc transcription by xlim1 and other regulatory genes expressed at gastrula stages by using gscluciferase reporter constructs injected into animal explants a 492bp upstream region of the gsc promoter responds to xlim13m an activated form of xlim1 and to a combination of wildtype xlim1 and ldb1 a lim domain binding protein supporting the view that gsc is a direct target of xlim1 footprint and electrophoretic mobility shift assays with gsthomeodomain fusion proteins and embryo extracts overexpressing flagtagged fulllength proteins showed that the xlim1 homeodomain or xlim1ldb1 complex recognize several taatxy core elements in the 492bp upstream region where xy is ta tg ca or gg some of these elements are also bound by the ventral factor pv1 whereas a taatct element did not bind xlim1 or pv1 but did bind the anterior factors otx2 and gsc these proteins modulate the activity of the gsc reporter in animal caps otx2 activates the reporter synergistically with xlim1 plus ldb1 whereas gsc and pv1 strongly repress reporter activity we show further using animal cap assays that the endogenous gsc gene was synergistically activated by xlim1 ldb1 and otx2 and that the endogenous otx2 gene was activated by xlim13m and this activation was suppressed by the posterior factor xbra based on these data we propose a model for gene interactions in the specification of dorsoventral and anteroposterior differences in the mesoderm during gastrulation