Tissue-specific promoter methylation coincides with Cyp19 gene expression in buffalo (Bubalus bubalis) placenta of different stages of gestation

Aromatase is the key enzyme for estrogen biosynthesis and is encoded by Cyp19 gene. Placental cotyledons are the main site of Cyp19 gene expression during pregnancy. The present study was aimed to investigate if DNA methylation and thus epigenetic mechanisms play a potential role in stage-specific regulation of Cyp19 expression in placental cotyledons of pregnant water buffaloes (Bubalus bubalis). Significantly higher expression of Cyp19 gene (p < 0.05) in placental cotyledons of early gestation period and post parturition period was found in comparison to mid-gestation placenta. Tissue-specific promoter driven transcript analyses showed that the change in expression was mainly due to change in the relative abundance of transcripts from exon I.1 while the transcripts from exon II showed comparatively less variation. Methylation analysis of 5 CpG dinucleotides of placenta-specific promoter I.1 and proximal promoter, PII showed hypo-methylation of PI.1 in early and term placenta while hyper-methylation in mid-placenta. However, PII was found to be hypomethylated in all the three tissues. In conclusion, result of the present study demonstrated that stage-specific methylation status of PI.1, the major promoter responsible for aromatase expression in buffalo placental cotyledons, coincides with the change in expression of Cyp19 gene in different stages of pregnancy.

Research highlights
► First report of significantly higher expression of Cyp19 gene (p < 0.05) in buffalo placental cotyledons of early gestation period and post parturition period was found in comparison to mid-gestation placenta.
► First report of differential promoter usage for Cyp19 gene expression in placental cotyledons of different stages of buffalo placenta.
► First report on the role of differential methylation of PI.1 in stage-specific differential expression of Cyp19 gene during pregnancy.
► A direct association between promoter methylation and stage-specific promoter choice, a remarkable feature of Cyp19 gene regulation, has been elucidated for the first time in the present report.