Fig. 3. Dlx2a can bind and activate transcription through the intergenic I12b enhancer. (A) In a transient transfection assay, zebrafish Dlx2a upregulates transcription of a CAT reporter construct containing the I12b enhancer (mI12b-pBLCAT2) by a factor of 11. By comparison, expression of a CAT reporter gene under control of the I56i enhancer (Zerucha et al., 2000) was activated 5.6-fold in the presence of Dlx2a. (B) The disruption of the Dlx2a homeodomain completely abolishes this activation. In the presence of zebrafish Dlx2a, a 9.03-fold increase in CAT activity was observed, whereas the Dlx2a homeodomain mutant showed only a basal level of CAT activity. Values shown represent the mean of relative CAT activity obtained from two to three independent experiments ± s.e.m.