A minimal c-fes cassette directs myeloid-specific expression in transgenicmice

The c-fes proto-oncogene encodes a 92-kd protein tyrosine kinase whose expr ession is restricted largely to myeloid and endothelial cells in adult mamm als. A 13.2-kilobase (kb) human c-fes genomic fragment was previously shown to contain cis-acting element(s) sufficient for a locus control function i n bone marrow macrophages. Locus control regions (LCRs) confer transgene ex pression in mice that is integration site independent, copy number dependen t, and similar to endogenous murine messenger RNA levels. To identify seque nces required for this LCR, c-fes transgenes were analyzed in mice. Myeloid -cell-specific, deoxyribonuclease-1-hypersensitive sites localized to the 3 ' boundary of exon 1 and intron 3 are required to confer high-level transge ne expression comparable to endogenous c-fes, independent of Integration si te. We define a minimal LCR element as DNA sequences (nucleotides +28 to +2 523 relative to the transcription start site) located within intron 1 to in tron 3 of the human locus. When this 2.5-kb DNA fragment was linked to a c- fes complementary DNA regulated by its own 446-base-pair promoter, integrat ion-site-independent, copy-number-dependent transcription was observed in m yeloid cells in transgenic mice. Furthermore, this 2.5-kb cassette directed expression of a heterologous gene (enhanced green fluorescent protein) exc lusively in myeloid cells. The c-fes regulatory unit represents a novel rea gent for targeting gene expression to macrophages and neutrophils in transg enic mice. (C) 2000 by The American Society of Hematology.