Construction and in vivo evaluation of a mammary gland-specific expression vector for human lysozyme.

A mammary gland-specific expression vector p205C3 was constructed with the 5'- and 3'-flanking regions of β-lactoglobulin gene and the first intron of β-casein gene of Chinese dairy goat as regulatory sequences. Human lysozyme (hLYZ) cDNA from mammary gland was cloned into p205C3 and the recombinant vector was used to generate transgenic mice by microinjection. Based on the lysoplate assay, four female offspring of one male founder were detected expressing recombinant hLYZ in their milk at the levels of 5-200 mg/l, and the expressed protein had the same molecular weight as that of normal hLYZ. Besides mammary glands, ectopic expressions were also found in the spleens and the small intestines of the transgenic mice. Among the offspring, the female transgenic mice maintained and expressed the transgene stably with a highest expression level of 750 mg/l. Therefore, p205C3 could be used to develop animal mammary gland bioreactors expressing hLYZ.