Secretion of Biologically Active Human Granulocyte Colony-Stimulating Factor (G-CSF) in Milk of Transgenic Mice

Expression of the human granulocyte-macrophage colony stimulating factor (hGM-CSF) gene under control of the 5'-regulatory sequence of the goat alpha-S1-casein gene with and without a MAR element in transgenic mice

Expression of the human granulocyte-macrophage colony-stimulating factor (hGM-CSF) gene under the control of the 5'-regulatory sequence of the goat alpha-S1-casein gene with and without a matrix attachment region (MAR) element from the Drosophila histone 1 gene was studied in four and eight transgenic mouse lines, respectively. Of the four transgenic lines carrying the transgene without MAR, three had correct tissues-specific expression of the hGM-CSF gene in the mammary gland only and no signs of cell mosaicism. The concentration of hGM-CSF in the milk of transgenic females varied from 1.9 to 14 μg/ml. One line presented hGM-CSF in the blood serum, indicating ectopic expression. The values of secretion of hGM-CSF in milk of 6 transgenic lines carrying the transgene with MAR varied from 0.05 to 0.7 μg/ml, and two of these did not express hGM-CSF. Three of the four examined animals from lines of this group showed ectopic expression of the hGM-CSF gene, as determined by RT-PCR and immunofluorescence analyses, as well as the presence of hGM-CSF in the blood serum. Mosaic expression of the hGM-CSF gene in mammary epithelial cells was specific to all examined transgenic mice carrying the transgene with MAR but was never observed in the transgenic mice without MAR. The mosaic expression was not dependent on transgene copy number. Thus, the expected "protective or enhancer effect" from the MAR element on the hGM-CSF gene expression was not observed.

A 3,387 bp 5'-flanking sequence of the goat alpha-S1-casein gene provides correct tissue-specific expression of human granulocyte colony-stimulating factor (hG-CSF) in the mammary gland of transgenic mice

A new expression vector containing the 1,944 bp 5'-flanking regulatory region together with exon 1 and intron 1 of the goat alpha-S1-casein gene (CSN1S1), the full-sized human granulocyte colony-stimulating factor gene (hGCSF) and the 3'-flanking sequence of the bovine CSN1S1, was created. The vector DNA was used for generation of four mouse transgenic lines. The transgene was integrated into chromosomes 8 and 12 of two founders as 2 and 5 copies, respectively. Tissue-specific secretion of hG-CSF into the milk of transgenic mice was in the range of 19-40 μg/ml. RT-PCR analysis of various tissues of the transgenic mice demonstrated that expression of hGCSF was detected in only the mammary gland in the progeny of all founders. Moreover, cells were shown to be positive for hG-CSF by immunofluorescent analysis in the mammary glands but not in any other tissues. There were no signs of mosaic expression in the mammary gland. Trace amounts of hG-CSF were detected in the serum of females of two transgenic lines during lactation only. However, no transgenic mice showed any changes in hematopoiesis based on the number of granulocytes in blood. Immunoblotting of hG-CSF in the milk of transgenic mice revealed two forms, presumably the glycosylated and non-glycosylated forms. The hematopoietic activity of hG-CSF in the milk of transgenic females is comparable to that of recombinant G-CSF. In general, the data obtained in this study show that the new expression vector is able to provide correct tissue-specific expression of hG-CSF with high biological activity in transgenic mice.