Expression of whey acidic protein (WAP) genes in tissues other than the mammary gland in normal and transgenic mice expressing mWAP/hGH fusion gene.

Whey acidic protein (WAP) is a major whey protein secreted in rodents' milk. Murine WAP (mWAP) genes have been assumed to be expressed solely in the mammary gland. However, several heterologous genes fused with the mWAP promoter and artificially introduced into animal genomes as transgene were expressed not only in the mammary gland but also in other tissues as well. In the present study, we investigated, by means of the reverse transcription polymerase chain reaction (RT-PCR), the patterns of expression of endogenous WAP genes in tissues of normal mice and in transgenic mice carrying hGH gene coupled to the mWAP promoter sequence. The results revealed that the genes driven by the mWAP promoter, regardless of whether they are endogenous genes or transgenes, were transcribed in a variety of tissues other than the mammary gland of lactating normal female mice, although the expression levels are generally low. The expression of WAP genes in the cerebrum and the liver is regulated, as in the mammary gland, according to the reproductive stages. However, the tissue distribution of endogenous WAP gene expression in mature virgin transgenic female mice was the same as that in lactating normal female mice.