PRODUCTION OF TRANSGENIC TILAPIA (OREOCHROMIS-NILOTICUS) BY ONE-CELL-STAGE MICROINJECTION

Novel genes have been successfully introduced into fish of many species, chiefly by microneedle injection into fertilized eggs. Tilapia are important warm water food fishes with short generation times, but previous attempts to introduce transgenes into this species succeeded only with multicell embryo injection, a procedure that is likely to result in subsequent transgene mosaicism and probable failure of germline transmission to an F1 generation. We here report the successful production of transgenic tilapia (Oreochromis niloticus) by injection of transgenes (mouse metallothionein promoter/rat growth hormone gene) into the one-celled eggs. Slot blotting reveals the presence of transgene copies in many fish, and Southern blotting patterns suggest genomic integration in roughly 20% of fish developing from injected eggs. Most but not all of the transgenic fish appear to be mosaic in that copies are present only in some tissues. In some male fish analysed, this includes sperm. Introduction of DNA constructs in which a fish gene promoter is spliced to a bacterial CAT (chloramphenicol acetyl transferase) gene, together with subsequent CAT assays, were used to test for gene expression in the transgenic fish. A proportion (approximately 30%) gave positive results in these assays.