Fig. 2. The 3.5-kb upstream region of Ciona Otx is capable of reproducing endogenous Otx expression pattern in Halocynthia embryos. (A) The structure of the 5' region of Ci-Otx. Boxes on the gray line indicate exons. ATG indicates the translation start site, which is located in the second exon. The light gray line represents the upstream region included in the construct –3541 (Bertrand et al., 2003). (B,B') Transcription of lacZ in 64-cell stage embryos injected with the reporter construct –3541, as visualized by whole-mount in situ hybridization. Animal (B) and vegetal (B') views are shown. Schematic representation of the in situ hybridization specimen is shown right (B,B'). Cells with endogenous Hr-Otx expression are colored as in Fig. 1. Blue dots indicate the cells in which lacZ transcripts were detected. Below the in situ hybridization specimens, the lacZ -positive cell line is indicated. (C) Frequency of lacZ-transcript-positive cells for the given cell line in embryos injected with the –3541 construct, examined at the 64-cell stage.