Expression of a chimeric VIP gene is targeted to the intestine in transgenic mice

We showed previously that a gene construction that consisted of 5.2 kb of 5' flanking sequence, the first exon, and part of the first intron of the human gene encoding vasoactive intestinal peptide (VIP) fused to the reporter gene chloramphenicol acetyltransferase (CAT) fully mimicked the diverse behavior of the endogenous VIP gene when transfected into subclones of the human neuroblastoma cell line SK-N-SH (Waschek et al., 1988). To determine if the same sequences were sufficient to target expression of a reporter to VIP-producing tissues in the mouse, we initiated a pilot study in which we generated four transgenic mice or mouse lines that contained the VIPCAT fusion gene. Detectable levels of CAT were found in the ileum of either founder or offspring of each of the transgenic mouse lines. In all other tissues tested, CAT activity was either below the level of detection or the transgene was not expressed, with the exception of one mouse in which ectopic expression in the cerebellum was observed. The results indicate that the VIP sequences utilized were sufficient to direct expression of the transgene to the intestine, but not necessarily to other sites of VIP expression. To investigate what specific DNA sequences might confer VIP expression in the intestine and other sites, we analyzed further the VIP gene in SK-N-SH subclones using VIP/luciferase fusion gene constructions. A 0.6 kb DNA fragment located between 4.0 kb and 4.6 kb upstream from the VIP transcriptional start site was found to impart a high level of expression in one subclone and an increased degree of phorbol ester induction in another. These and other data indicate that multiple transcriptional elements control VIP expression in neuroblastoma cells and are candidates as mediators of VIP gene expression in the intact animal.