Construction and functional study of pGN, a mammary gland-specific expression plasmid

The aim of this study was to construct a mammary gland-specific expression vector, pGN, and to validate its function in expressing growth hormone (GH) both in vitro and in vivo. First, the GH gene was amplified and inserted downstream of the b-casein 5'-arm. Next, the neo gene was cloned downstream of the b-casein 3'-arm as a selection marker. To analyze the bioactivity of the pGN plasmid, we expressed pGN in a Bcap-37 cell line and in the goat mammary gland. Quantitative PCR analysis revealed that the expression of GH mRNA in the pGN-transfected group was higher than that of the control group in Bcap-37 cells. Results of a radioimmunoassay and an enzyme-linked immunosorbent assay demonstrated that the pGN-transfected group expressed much more GH protein than the non-transfected group (P < 0.05). Upon injection of the pGN plasmid into the goat mammary gland, GH mRNA and growth hormone receptor mRNA expressions increased 2-fold. In vivo analyses revealed that GH protein expression was higher in the injected group than in the control group. Together, these results strongly demonstrated that the pGN plasmid was constructed correctly and exhibited favorable bioactivity in efficiently expressing GH both in vitro and in vivo.