FTZ-F1alpha is expressed in the developing gonad of frogs

Fushi tarazu transcription factor-1 (FTZ-F1), a member of the nuclear hormone receptor superfamily, is a regulator for fushi tarazu gene expression in Drosophila. Its expression pattern during organogenesis in vertebrates, however, is not known yet. In this study, we cloned a frog FTZ-F1 homologue (rrFTZ-F1alpha) and analyzed its expression and localization during gonadal development of the frog Rana rugosa. Cloned rrFTZ-F1alpha cDNA encoded a protein of 501 amino acids including the regions I-III and FTZ-F1 box that are evolutionally conserved in the FTZ-F1 superfamily. rrFTZ-F1alpha shared high similarity at the amino acid level with mouse LRH-1 (76%), human FTF (92%), chicken OR2.0 (92%), Xenopus laevis FF1rA (94%) and zebrafish FF1A (82%). Northern blot analysis showed that the rrFTZ-F1alpha mRNA at a size of 7.4 kb was the most prominent in the testis among various tissues of adult frogs examined. The RT-PCR analysis revealed that the expression of rrFTZ-F1alpha was weak in the gonad of tadpoles before stage XVI, but it became stronger in the testis of froglets at stage XXV and much higher in the testis of frogs 2 months after metamorphosis. In addition, in situ hybridization analysis revealed that the rrFTZ-F1alpha gene was transcribed in germ cells except for sperm in the testis, and in oocytes at stage A in the ovary of frogs 2 months after metamorphosis. Together, these results suggest that FTZ-F1alpha probably plays an important role in differentiation of germ cells in the gonad of frogs in both sexes.