A hybrid bovine ss-casein/bGH gene directs transgene expression to the lung and mammary gland of transgenic mice

We investigated spatial and temporal expression of bGH controlled by two di fferent sizes (1.8 kb and 15 kb) of 5'-flanking sequences of the bovine ss- casein in transgenic mice. In the 1.8-kb promoter-containing mice, bGH expr ession was specifically confined to lung and mammary gland at lactation. Wh ile mammary gland expression was highly variable depending on the lines, lu ng expression was relatively constant with a high level in most lines. More over, this dual-tissue specificity of bGH expression was consistently retai ned in all of the 15 kb-promoter-containing mice, although a low ectopic ex pression was sometimes detected in salivary gland or brain. During mammary gland development in the 1.8-kb promoter-containing mice was mammary gland expression first detected at lactation, following the bovine rather than mu rine pattern of ss-casein expression. In contrast, lung expression was almo st constant regardless of mammary gland developmental state or sex. Therefo re, it can be concluded that a combination of the bovine ss-casein promoter and bGH gene directs a distinct dual-tissue specific bGH expression with d ifferent regulatory mechanisms between mammary gland and lung and as little as 1.8-kb promoter is sufficient for the proper regulation of the bovine s s-casein gene in mammary gland.