| It is reported that Meiosis activating sterol (MAS), an ubiquitous C29 product after lanosterol, is the intermediate of cholesterol biosynthesis, is an important substance to stimulate oocytes maturation in FSH-induced signal transduction pathway. Lanosterol 14α-demethy]ase (CYP51) converts lanosterol to MAS. Although MAS is firstly isolated from bovine testis, the information about bovine CYP51 expression is little. The present study was conducted to characterize the bovine CYP51 gene and its expression. It is revealed that the cDNA coding bovine CYP51 contains a 1509bp open reading frame and a 1119bp 3' untranslated region. The bovine CYP51 gene spans about 17kb and contains 10 exons. The promoter region is TATA-iess and contains several highly conserved regulatory elements, such as GC-box, cAMP-responsive elements (CRE), sterol regulatory element (SRE) at positions similar to those of human, rat, mouse and pig, suggesting an evolutionary conserved mechanism of CYP51 transcriptional regulation in mammals. No evidence of processed pseudogenes is found using long PCR and Southern blot. Northern blot analysis reveals that an approximately 2.7kb mRNA is expressed in all the examined bovine tissues, while a smaller size of mRNA (aboutl .8kb), arising from a more upstream polyadenylation site usage, is expressed only in the mature bovine testis where the MAS is accumulated. Using the anti-human CYP51 antibody, it is showed that leydig cells express the highest level of the CYP51 protein in testis. Among follicles of different stages, CYP51 protein is localized primarily to the oocytes with the level varying slightly. Granulosa cells of primordial, primary and secondary follicles show background staining. While granulosa cells facing the antrum and cumulus granulosa cells of antral follicles show considerably heavier staining. The highest level is expressed in corpus lutea. These data indicate a stage- and cell type-specific expression of CYP51 protein in bovine oogenesis.
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