REGULATION OF EXPRESSION OF TRANSGENES IN DEVELOPING FISH

The transcriptional regulatory elements of the beta-actin gene of carp (Cyprinus carpio) have been examined in zebrafish and goldfish harbou ring transgenes. The high sequence conservation of the putative regula tory elements in the beta-actin genes of animals suggested that their function would be conserved, so that transgenic constructs with the sa me transcriptional control elements would promote similar levels of tr ansgene expression in different species of transgenic animals. To test this assumption, we analysed the temporal expression ot a reporter ge ne under the control of transcriptional control sequences from the car p beta-actin gene in zebrafish (Brachydanio rerio) and goldfish (Carra sius auratus). Our results indicated that, contrary to expectations, c ombinations of different transcriptional control elements affected the level, duration, and onset of gene expression differently in developi ng zebrafish and goldfish. The major differences in expression of beta -actin/CAT (chloramphenicol acetyltransferase) constructs in zebrafish and goldfish were: (1) overall expression was almost 100-fold higher in goldfish than in zebrafish embryos, (2) the first intron had an enc hancing effect on gene expression in zebrafish but not in goldfish, an d (3) the serum-responsive/CArG-containing regulatory element in the p roximal promoter was not always required for maximal CAT activity in g oldfish, but was required in zebrafish. These results suggest that in the zebrafish, but not in the goldfish, there may he interactions betw een motifs in the proximal promoter and the first intron which appear to be required for maximal enhancement of transcription.