Molecular and Cellular Endocrinology 149 (1999) 221 – 228 Rapid communication Medaka (Oryzias latipes ) FTZ-F1 potentially regulates the transcription of P -450 aromatase in ovarian follicles: cDNA cloning and functional characterization Masatada Watanabe a,b , Minoru Tanaka b , Daisuke Kobayashi b , Yasutoshi Yoshiura b , Yuichi Oba b , Yoshitaka Nagahama b, * a Department of Molecular Biomechanics, School of Life Science, The Graduate Uniersity for Adanced Studies, Okazaki 444 -8585, Japan b Laboratory of Reproductie Biology, Department of Deelopmental Biology, National Institute for Basic Biology, Okazaki 444 -8585, Japan Received 24 August 1998; accepted 24 December 1998 Abstract Our previous findings suggest the activity of cytochrome P -450 aromatase (P -450arom), the enzyme which converts testosterone to estradiol-17, in the ovarian follicle of medaka (Oryzias latipes ) is regulated at the transcriptional level. In this study, we cloned a cDNA encoding a FTZ-F1-like protein (mdFtz -F1 ) from ovarian follicles of medaka. In vitro translated mdFTZ-F1, and nuclear extract from medaka ovarian follicles, formed complexes with oligonucleotide probes containing putative orphan nuclear receptor binding motifs, which are present in the promoter region of the medaka P -450arom gene. The expression pattern of mdFtz -F1 transcripts during oogenesis coincides with that of P -450arom transcripts. Transfection assays further suggest a potential transcriptional regulatory activity of mdFTZ-F1 upon the medaka P -450arom promoter. Taken together, these results suggest a potential role of mdFTZ-F1 in the transcriptional regulation of P -450arom in the ovarian follicle of medaka. © 1999 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Cytochrome P -450 aromatase; FTZ-F1-like protein; Promoter; Transcriptional regulation; Fish ovarian follicles; medaka: Oryzias latipes 1. Introduction Cytochrome P-450 aromatase (P-450arom), the en- zyme that catalyzes the conversion of testosterone to estradiol-17, plays an important role in the course of ovarian development. The mechanism of P-450arom activation has been investigated during oogenesis of a teleost fish, the medaka (Oryzias latipes ). In medaka, events such as vitellogenesis, oocyte maturation, and ovulation can be timed accurately (Sakai et al., 1987). A progressive increase in P-450arom activity occurs in vitellogenic follicles isolated between 28 and 20 h before the onset of light (Fukada et al., 1994). The activity of P-450arom is markedly enhanced by pregnant mare serum gonadotropin (PMSG). The enhancement of P- 450arom activity by PMSG, forskolin, and/or dbcAMP is completely inhibited by actinomycin D (Nagahama et al., 1991). Furthermore, there is a close correlation between changes in the level of P -450arom transcripts and P-450arom enzyme activity during oogenesis (Fukada et al., 1996). These results suggest that P- 450arom activity in medaka ovarian follicles is regu- lated at the transcriptional level. * Corresponding author. Tel.: +81-564-557550; fax: +81-564- 557556. E-mail address: nagahama@nibb.ac.jp (Y. Nagahama) 0303-7207/99/$ - see front matter © 1999 Elsevier Science Ireland Ltd. All rights reserved. PII:S0303-7207(99)00006-4