Application of High Hybridization Stringency Technology to the Analysis of Putative Transgenic Fish and Their Progeny

Eight putative transgenic hybrid tilapia ( Oreochromis mossambicus × O. niloticus ) and their F, progeny were screened by Southern blot analysis for the presence of the bovine growth hormone transgene (bGH). Transgenic mice known to contain one copy of the bGH gene per genome were used as positive controls allowing for the determination of detection levels under high hybridization stringency conditions. At a sensitivity level of one copy per genome, the bovine growth hormone transgene was not detected in any of the experimental animals. The apparent lack of bGH transgene in the fish DNA at one copy per genome, coupled with no detectable levels of bovine growth hormone being found in either serum or whole blood of the original adults, indicates these fish are either not transgenic, or that they are mosaics and do not express the transgene. Results demonstrate the need for positive controls when conducting Southern blot analysis of potentially transgenic organisms. Mammalian models appear to be suitable positive controls and should be employed until transgenic piscine models are readily available. It is suggested that high hybridization stringency is necessary when analyzing for evolutionarily conserved transgenes such as those controlling growth hormones.