Expression of the Cyp19 gene, encoding aromatase cytochrome P450, is driven by 
several tissue-specific promoters. The underlying mechanisms of this complex 
regulation have not yet been elucidated in detail. In the present report we 
investigate a possible link between chromatin structure and tissue-specific 
regulation of the bovine Cyp19 gene. We analysed the DNA methylation status and 
mapped DNaseI hypersensitive sites in the region encompassing the Cyp19 promoter 
1.1 (P1.1) which controls Cyp19 expression in the bovine placenta. We show that 
P1.1 is hypomethylated in placental cotyledons (foetal layer) whereas it is 
methylated in placental caruncles (maternal layer), testis and corpus luteum. 
Furthermore, two placenta-specific DNaseI hypersensitive sites, HS1 and HS2, 
were observed within P1.1. Both DNA hypomethylation and the presence of DNaseI 
hypersensitive sites correlate with transcriptional activity of P1.1. Sequence 
analysis of hypersensitive sites revealed potential cis-regulatory elements, an 
E-box in HS1 and a trophoblast-specific element-like sequence in HS2. It could 
be demonstrated by electrophoretic mobility shift assays that both sequence 
motifs are specific targets for placenta-derived nuclear factors. In conclusion, 
observed tissue-specific differences of the chromatin structure which correlate 
with tissue-specific promoter activity suggest that chromatin might be an 
important regulator of aromatase expression in cattle.