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It has been demonstrated that electroporated salmon sperm can be used as a vector to transfer foreign genes into salmon ova. When 1- to 11-day old embryos were analyzed using the polymerase chain reaction for the presence of the transgene, over 95% of the embryos were found to contain the transgene (Walker et al., 1995). However, when 12 weeks old alevin were analyzed, the percentage of alevins containing the transgene was highly variable between experiments, ranging from zero to over 85% (Symonds et al., 1994). The variability of transgene retention may be caused by the DNase I activity of the host cells. Alternatively, the delivered DNA may fail to enter the nucleus and, thus, be unable to be stably integrated into the fish genome. Weinhues et al. (1987) first demonstrated that DNA-protamine complex enhances the translocation of the DNA into the nucleus. Recently, Page et al. (1995) co-injected DNA-polylysine complex into the mouse pronuclei. These authors found an increase in integration of the transgene from 0 to 12%. These experiments suggest that the DNA-protein complex may prevent access of the nucleases to the foreign DNA, and hence prevent the foreign DNA from degradation and enhance the chances for the foreign DNA to enter the nucleus. |
