Development of position-independent expression vectors and their transfer into transgenic fish.

Many genes have been transferred into fish for scientific and aquacultural purposes. We have been developing expression vectors containing regulatory sequences from the carp beta-actin gene enhancer/promoter for expression of genes or cDNAs in transgenic fish. Expression from these vectors varies over a 20-fold range in zebrafish, beginning within 12 hours of fertilization and continuing for at least two weeks. Expression can be found in nearly all tissues. The vectors have the following characteristics: (1) they contain either unique or polycloning restriction endonuclease sites for insertion of any gene or cDNA, and (2) the piscine sequences are flanked by restriction sites for easy removal of plasmid, or nonfish, sequences. We have tested the ability of special sequences, border elements, from other animals to confer position-independent expression of transgenes or enhance integration of transgenic constructs into fish chromosomes. Early results indicate that these elements do not act as enhancers and do not improve integration frequencies. However, both avian and insect border elements are able to confer position-independent expression as judged from expression of CAT genes in F1 generation fish.