Fig. 2. (A) Representation of the domain of Xbh1 expression in comparison with those of other genes used as morphogenetic landmarks of different regions of the CMZ and central retina. (B) Xbh1 is positively regulated by Xath3 and Xath5, but not by XneuroD. RT-PCR was performed on animal caps injected with 1 ng of either Xath3 or Xath5 mRNA, or with 500 pg of XneuroD mRNA. Uninjected animal caps (uninj. caps) and stage 28 whole embryos (WE st. 28) were used as negative and positive controls, respectively; Xbrn3.0 and Xbrn3d were used as positive control markers. (C) Xbh1 mRNA injection (1 ng) is able to activate Xbrn3 genes and Xath3, but not Xath5.