EVOLUTIONARY AND FUNCTIONAL-SIGNIFICANCE OF 2 CYP19 GENES DIFFERENTIALLY EXPRESSED IN BRAIN AND OVARY OF GOLDFISH

Remarkably high levels of cytochrome P450 aromatase (P450(arom)) enzym e are expressed in the brains of teleost fish when compared to the ova ries of the same fish, or to the brain or ovaries of other vertebrates . Northern analysis using a full-length P450(arom) cDNA from a goldfis h brain library indicates high accumulated levels of CYP19 mRNA in the brain but fails to detect P450(arom)mRNA in the ovary. The possibilit y of different brain and ovarian mRNA variants was investigated. Rever se transcription-polymerase chain reaction (RT-PCR) amplification of o varian RNA using degenerate primers led to the isolation of a 243 bp P 450(arom) cDNA fragment with approximate to 20% of nucleotide and amin o acid replacements when compared to the brain cDNA. Southern analysis with sequence-specific probes indicated two distinct CYP19 loci, and this was confirmed by PCR-restriction enzyme analysis of genomic DNA. Corresponding brain-and ovary-type genomic sequences were identified i n a second, diploid fish species (zebrafish), evidence that two genes are not caused per se by tetraploidy in goldfish. RT-PCR analysis of d ifferent tissues with sequence-specific primers showed high levels of the brain mRNA variant and much lower levels of the ovarian variant in neural tissues with high enzyme activity. In contrast, the ovary expr essed low levels of the ovarian mRNA variant exclusively. The data imp ly that the expression of two CYP19 genes in goldfish is controlled by distinct regulatory mechanisms. Further studies are required to deter mine whether the two genes lead to functionally distinct isozymes. (C) 1997 Elsevier Science Ltd.