RNase assays on tissues harvested from c-festransgenic mice.

(A) The Δ3-9 and Δ2-12 transgenic constructs are not expressed exclusively in myeloid cells. Ten micrograms of RNA from the indicated tissues were analyzed by RPAs. Southern blot analysis revealed that the Δ3-9 founder exhibited 2 copies of the transgene and the Δ2-12 transgenic mouse had 5 copies (data not shown). Various tissues obtained from both animals displayed ectopic expression: note the high levels of human c-fes in the spleen, brain, and lung of the Δ3-9 mouse and in the spleen, lung, and thymus in the Δ2-12 transgenic mouse. (B) The Δ6-18b construct exhibits LCR activity. Bone marrow RNAs from 3 founder animals with the indicated copy numbers of the Δ6-18b transgene are shown with Δ3′ founders for comparison. (C) The c-fes promoter linked to the human c-fescDNA (0.5-kb plasmid) is not sufficient for tissue-specific, copy-number–dependent transgene expression. The human c-fesriboprobe detects a 180-bp protected fragment in animals prepared with constructs based on the human c-fes cDNA because 93 bp fewer exon-19–encoded sequences are included in these plasmids (see “Materials and methods”). Note the inappropriately high levels of human c-fes transcripts apparent in the lung specimen.