Association of foreign DNA with porcine spermatozoa

The aim of this project was to establish if DNA molecules bind to porcine spermatozoa after incubation in vitro. In an initial experiment, the DNA was mixed with porcine spermatozoa to test for the presence of DNases. From bacterial transformation and gel electrophoresis studies, it was established that the presence of DNases within the sperm or in the sperm suspension was negligible. By the addition of radiolabeled DNA, spanning a large size range, it was demonstrated that the DNA molecules interacted with the sperm during a 15 to 20 min period of incubation. These samples were centrifuged and washed extensively to confirm that the DNA was closely associated with the sperm. Under the experimental conditions used, it was calculated that approximately 3.8 × 10² DNA molecules were associated with each spermatozoon. Percoll gradient experiments, which allowed differentiation between motile and nonmotile sperm, showed that motile sperm were more efficient at capturing DNA molecules than nonmotile sperm. In situ hybridization studies revealed that approximately 30% of the motile sperm carried the DNA on their surface, and the associated DNA was attached only to the sperm head with no attachment to the sperm tails. Heterologous foreign DNA can become closely associated in a nonran-dom manner with porcine spermatozoa.