Fig. 1. The upstream (5402-1473 bp) and the first intron (812-24 bp) regions are capable of directing Hr-Otx transcription during cleavage stages. (A) The structure of 5' region of Hr-Otx, including the putative endogenous promoter (TATAA) and intron 1. Boxes on the gray line indicate exons; ATG indicates the translation start site, which is located in the second exon. The light gray lines are the genomic regions examined for their transcription-driving activity. (B,B',D,D') Expression of Hr-Otx detected by whole-mount in situ hybridization. (C,C',E-F') Transcription of lacZ in embryos injected with the reporter construct harboring the upstream region 5402-1473 (C,C',E,E'), or the intron region 812-24 (F,F'), as visualized by in situ hybridization. In injected embryos, not all Hr-Otx-expressing cells are stained because of the mosaic inheritance of injected DNA. Specimens at the 32-cell stage (B-C') and 64-cell stage (D-F') are shown. (B-F) Animal view; (B'-F') vegetal view. A schematic representation of in situ hybridization is shown on the right side of each specimen (C,C',E-F'). Cells expressing Hr-Otx are colored, according to their derivation from the 8-cell embryo (H), as follows: a-line, dark green; b-line, light green; A-line, orange; and B-line, yellow. Blue dots indicate the cells in which lacZ transcripts were detected. Below the specimens of whole-mount in situ hybridization, the identity of the lacZ-transcribing cell line is indicated. (G) Frequency of lacZ -positive cells for a given cell line in embryos injected with the construct harboring the region 5402-1473bp or 812-23bp, examined at the 32-cell stage (top) and 64-cell stage (bottom). Color codes are as in H. Gray indicates ectopic expression. Number in parenthesis indicates number of embryos examined.