Fushi tarazu transcription factor-1 (FTZ-F1) was originally found as a regulator of fushi tarazu gene expression in Drosophila. The frog homologue (FTZ-F1α) and the 3.5 kb 5′-flanking region of the FTZ-F1α gene have been cloned, and it has been shown by reverse transcription-polymerase chain reaction that FTZ-F1α expression begins in embryos at stage 11 and becomes stronger after that. By in situ hybridization analysis, the FTZ-F1α mRNA was also found in immature frog oocytes. In this study, immunohistology revealed that the product of FTZ-F1α was localized in the cytoplasm of the immature oocyte. To analyze the promoter activity of the Rana rugosa FTZ-F1α gene, transgenic Xenopus were produced carrying the fusion construct, consisting of truncated 5′-flanking regions (3.0, 1.8 and 0.3 kb) of the FTZ-F1α gene and the green fluorescent protein (GFP) open reading frame. The 0.3 kb 5′-flanking region could drive GFP expression in Xenopus embryos at stage 20 and in immature oocytes in the ovary 2 months after metamorphosis. Gel mobility shift assay was used to test whether proteins in extracts from Xenopus embryos and ovaries bound to the 0.3 kb DNA. The extract from embryos at stage 11 formed one retarded band. The extract from ovaries formed a different retarded band. The results, taken together, indicate that production of transgenic Xenopus is very useful for the analysis of the promoter activity of genes in amphibians. The results also suggest that at least two proteins (one in the embryo and the other in the ovary of 2-month-old postmetamorphosing Xenopus) bind the 0.3 kb 5′-flanking region of the FTZ-F1α gene. These proteins may be involved in the regulation of FTZ-F1α gene expression in amphibians.
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