EXPRESSION OF CYTOCHROME-P450 AROMATASE IN THE CHANNEL CATFISH, ICTALURUS-PUNCTATUS

The cDNA encoding the catfish ovarian aromatase has previously been is olated and described (accession number S75715). As demonstrated previo usly, the predicted amino acid sequence and enzymatic activity of the encoded protein share a significant degree of similarity to the forms of aromatase found in other vertebrates. Analyses utilizing reverse tr anscription coupled with the polymerase chain reaction (RT-PCR) demons trate the expression of aromatase mRNA in catfish brain, testis and ov ary. In spite of the evidence provided by Northern blot analysis for a single transcript encoding ovarian aromatase, RT-PCR analysis indicat ed transcript heterogeneity within the ovary, but not the testis or th e brain. Although not characterized, PCR analysis indicated that the t ranscript complexity of ovarian aromatase was within the encoding regi on. Until this study, the expression of aromatase and its correlation with the reproductive physiology of fish had not been studied at the m olecular level. In the catfish, significant changes in ovarian develop ment were evident following elevation of plasma estradiol titers durin g October and again in February. Seasonal changes in the expression of ovarian aromatase and 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD ) mRNA was reflected in estradiol plasma titers. Ovarian expression of 3 beta-HSD mRNA commenced a month before the message for aromatase wa s detected. Both transcripts were present from October to April. As th e female approached the time of spawning (in May), the abundance of bo th aromatase and 3 beta-HSD transcripts decreased. The aromatase messa ge was not detected in post-spawning females but 3 beta-HSD transcript s were evident. These data indicate that the timely synthesis of estra diol in catfish is caused by the regulation of both 3 beta-HSD and aro matase. (C) 1997 Elsevier Science Ltd.