Conley A, Corbin J, Smith T, Hinshelwood M, Liu Z, Simpson E
School of Veterinary Medicine, University of California, Davis 95616, U.S.A.
J Steroid Biochem Mol Biol. 1997 Apr;61(3-6):407-13.
Aromatase cytochrome P450 (P450arom) is expressed in a variety of tissues. Pigs express P450arom as bilaminar blastocysts in utero, and thereafter in the gonads, adrenal glands and placenta. Our studies also demonstrate the existence of porcine isozymes of P450arom which differ substantially in their amino acid composition and function. The placental isoform, most similar to P450arom in other mammals, consists of 503 amino acids. The ovarian isoform, expressed in both theca and granulosa cells, is a 501 amino acid protein exhibiting less than 20% of the activity of the placental isozyme. Furthermore, it is inhibited not only by CGS16949A but also by etomidate which does not inhibit the placental P450arom. Partial sequences generated by the rapid amplification of the cDNA ends (RACE) procedure indicate that the expression of a third isoform in the blastocyst is switched to the placental isozyme during differentiation of the fetal membranes. In addition, these transcripts, and others from the theca, granulosa, testes, adrenal glands and placenta demonstrate differences in the 5'-untranslated region (putative exon I) suggestive of tissue-specific alternative splicing. An identical 5'-untranslated sequence was obtained from transcripts expressed in the theca and granulosa. Testes and adrenal transcripts also have identical 5' ends, which differ substantially from the ovarian sequence. Blastocyst and placenta 5'-untranslated sequences differ from each other and from those expressed in the gonads and adrenals. Several tissue-specific transcripts thus encode porcine P450arom. Interestingly, distinct 5' sequences exist for ovarian and testes P450arom mRNAs, suggesting different promoters and therefore regulation in the male and female gonads. The molecular origins of the functional isoforms and the tissue-specific transcripts are uncertain, however partial genomic sequence and other genetic analyses suggest the existence of multiple genes. However, sequence alignment of the placental and ovarian isoforms indicates complete conservation of putative exon III, so that complex splicing remains a possibility. Clearly, the regulation of P450arom expression is more complex in the pig than in other vertebrates investigated to date.
芳香化酶细胞色素P450（P450arom）在多种组织中表达。猪在子宫内的双胚层胚泡中表达P450arom，此后在性腺、肾上腺和胎盘中表达。我们的研究还证明了猪P450arom同工酶的存在，它们在氨基酸组成和功能上有很大差异。胎盘同工型与其他哺乳动物的P450arom最相似，由503个氨基酸组成。卵巢同工型在卵泡膜细胞和颗粒细胞中均有表达，是一种由501个氨基酸组成的蛋白质，其活性不到胎盘同工酶的20%。此外，它不仅受到CGS16949A的抑制，还受到依托咪酯的抑制，而依托咪酯并不抑制胎盘P450arom。通过cDNA末端快速扩增（RACE）程序产生的部分序列表明，胚泡中第三种同工型的表达在胎膜分化过程中转换为胎盘同工酶。此外，这些转录本以及来自卵泡膜、颗粒细胞、睾丸、肾上腺和胎盘的其他转录本在5'-非翻译区（假定的外显子I）表现出差异，提示存在组织特异性可变剪接。从卵泡膜和颗粒细胞中表达的转录本获得了相同的5'-非翻译序列。睾丸和肾上腺转录本的5'端也相同，这与卵巢序列有很大差异。胚泡和胎盘的5'-非翻译序列彼此不同，也与性腺和肾上腺中表达的序列不同。因此，几种组织特异性转录本编码猪P450arom。有趣的是，卵巢和睾丸P450arom mRNA存在不同的5'序列，提示存在不同的启动子，因此在雄性和雌性性腺中存在不同的调控。然而，功能同工型和组织特异性转录本的分子起源尚不确定，不过部分基因组序列和其他遗传分析表明存在多个基因。然而，胎盘和卵巢同工型的序列比对表明假定的外显子III完全保守，因此复杂剪接仍然是一种可能性。显然，猪中P450arom表达的调控比迄今为止研究的其他脊椎动物更为复杂。
