Identifying an optimal promoter sequence of goat β-lactoglobulin gene for constructing high-expression vectors in mammary epithelial cells

• We identified an optimal promoter sequence of goat β-lactoglobulin.
• A short promoter can effectively promote transgenic expression.
• Introns 1 and 2 are able to enhance promoter activity.

This study aimed to identify the highest efficiency promoter sequence of β-lactoglobulin (BLG) gene and construct a mammary-specific expression vector for expressing high level of transgene in goat mammary epithelial cells. We amplified 13 BLG proximal promoter fragments, 2 introns, and a 3′ untranslated region from goat genome. The dual-luciferase assay showed that the promoter activities of these BLG proximal promoter fragments were significantly higher in HC11 than those in 293T or GEF cells, and that BLG promoter region BLG11 (431 bp, −391/+40) was an optimal sequence to drive transgenic expression. Western blot analysis confirmed that the promoter sequence BLG11 had a higher promoter activity in goat mammary epithelial cells than other promoter sequences. Moreover, the expression levels of GFP were significantly increased by combining promoter region BLG11 and native intron 1 in transfected goat mammary epithelial cells, and increased further with introns 1 and 2. This study demonstrated that a short BLG promoter region BLG11 combined with introns 1 and 2 could promote transgenic expression in goat mammary epithelial cells. These mammary regulated elements may be useful for production of mammary gland bioreactor.