Closely Related Genes Encode Developmental and Tissue Isoforms of Porcine Cytochrome P450 Aromatase

Abstract

We examined the chromosomal basis for the synthesis of tissue (ovary, endometrium/placenta, and peri-implantation blastocyst) isoforms of cytochrome P450 aromatase in the pig. DNA fragments derived from three distinct porcine aromatase chromosomal genes were cloned and characterized. The porcine type III aromatase gene encoding the blastocyst aromatase isoform was found to consist of nine coding exons and two mutually exclusive, 5' untranslated exons (designated E1A and E1B), collectively spanning 30 kb or more. The porcine type II aromatase gene, encoding the endometrial/placental aromatase isoform, was identified by cloning of a genomic DNA fragment spanning the corresponding exons 7, 8, and 9. The DNA inserts of two other phage clones encompassed exons 2, 3, and 4 of a third chromosomal gene (type I) encoding the ovarian aromatase isoform. All intron-exon junctions in these genomic fragments were found to be identical in relative positions to those of the single-copy human aromatase gene. Comparisons of cDNA and genomic sequences indicated that nucleotide sequence variation was not uniform across the corresponding exons of these genes and that the corresponding intronic sequences were conserved. The type II and type III aromatase genes were localized to the same regional location (q16-17) on swine chromosome 1, which is homologous to the human chromosome 15 region (q21.1) in which the human aromatase gene resides. Results demonstrate that the three aromatase genes characterized in the present study appear to be similar in their overall structural organization and most likely are clustered, which could have resulted from at least two independent gene duplication events. The presence of multiple aromatase genes constitutes a newly described mechanism by which aromatase enzyme biosynthesis and functional activity can be regulated in a tissue and temporal fashion and serves to highlight further the complexity of aromatase gene expression in mammals. Moreover, the presence of a unique aromatase gene that is highly expressed in pig blastocysts may constitute a paradigm for other mammals (e.g., equids, rabbit, hamster) whose peri-implantation blastocysts are estrogenic.

A 500-bp region, ≈40 kb upstream of the human CYP19 (aromatase) gene, mediates placenta-specific expression in transgenic mice

“…Results of studies using RACE (rapid amplification of cDNA ends) cDNA libraries made from cattle, horse, and pig placental tissues have indicated that tissue-specific promoters upstream of placenta-specific exons also regulate placental expression of the CYP19 gene in these species (25). In those species in which the 5Ј flanking regions of the CYP19 placenta-specific promoters have been cloned, there is low sequence identity among species (25,26). Furthermore, in the human CYP19 gene, the placenta-specific promoter lies Ϸ40 kb upstream of the start site of translation, whereas in the bovine CYP19 gene, the placenta-specific promoter lies Ϸ19 kb upstream of the translation start site (27).…”

“…Furthermore, in the human CYP19 gene, the placenta-specific promoter lies Ϸ40 kb upstream of the start site of translation, whereas in the bovine CYP19 gene, the placenta-specific promoter lies Ϸ19 kb upstream of the translation start site (27). In the pig, there is even greater complexity, because there may be as many as three CYP19 genes encoding tissue-specific isoforms with multiple promoter usage for some of the isoforms (26,28). Because of this complexity, it is not possible to begin to define the genetic basis for placenta-specific expression of human aromatase by comparison of promoter sequences.…”

Two cytochrome P450 aromatase genes in the hermaphrodite ricefield eel Monopterus albus: mRNA expression during ovarian development and sex change

“…In mammals, with the exception of pig (Choi et al 1997, Graddy et al 2000, CYP19 is encoded by a single copy of the CYP19 gene, and the tissuespecific expression was achieved by the use of tissue-specific promoters and alternative splicing of 5 0 untranslated exons (Simpson 2003). However, two distinct CYP19 genes, namely cyp19a1a and cyp19a1b, which were expressed mainly in the ovary and brain respectively, were identified in teleosts, such as Carassius auratus (Tchoudakova & Callard 1998), Oncorhynchus mykiss (Tanaka et al 1992, Valle et al 2002, Danio rerio (Kishida & Callard 2001), Oreochromis niloticus (Kwon et al 2001), Dicentrarchus labrax (Blázquez & Piferrer 2004), Halichoeres tenuispinis (Choi et al 2005), Fundulus heteroclitus (Greytak et al 2005), and Epinephelus coioides (Zhang et al 2004).…”

Dual Regulation of Promoter II- and Promoter 1f-Derived Cytochrome P450 Aromatase Transcripts in Equine Granulosa Cells during Human Chorionic Gonadotropin-Induced Ovulation: A Novel Model for the Study of Aromatase Promoter Switching

“…Placental expression of P450AROM has also been documented in cows (9,10), pigs (11)(12)(13), and horses (9). A single CYP19 gene spanning more that 75 kb and containing nine coding exons (exons II-X) has been identified in humans (5,14,15), but there is evidence for multiple distinct, but closely related, aromatase genes in pigs (13,16,17).…”