USE OF DIFFERENTIAL LYSIS FOR DNA ISOLATION TO CONFIRM SPERM TRANSFECTION
Authors: Pochernyaev A. K. , Denysiuk P. V. , Ilchenko M. O. , Lobchenko S. F. , Pochernyaev K. F. 
Published: July 2021

The purpose of the work. Despite some progress, the creation of transgenic pigs remains a long and inefficient process. One of the key points in the transfection of porcine generative cells is determining the event of the internalization of foreign DNA by cells. The methods currently used to determine the event of the internalization of foreign DNA by cells do not take into account the possibility of the presence of foreign DNA on the surface of sperm, even after washing from the culture medium. With this in mind, the purpose of this work is to develop a method for confirming the transfection of sperm with plasmid DNA.

Materials and methods of research. Sperm were washed four times with GCCS diluent. Sperm transfection was carried out in 0.6 ml polypropylene tubes with a lid in a volume of 50 μl of a suspension of protein-washed sperm in GCCS with a sperm concentration of 100 million/ml. To 50 μl of the suspension of washed sperm from proteins it was added 10 μl of the ring form of plasmid pET-28c (Novagen, France). Sperm were incubated in a thermostat at 37.7°C for two hours. Incubated sperm were stored at -20°C.

To isolate DNA, 60 μl of a suspension of washed sperm from proteins with plasmid pET-28c was transferred to 1.5 ml of a polypropylene tube with a lid and centrifuged for 5 min under conditions of 12 thousand vol. min, then 35 μl of supernatant was transferred into a clean 1.5 ml tube leaving at the bottom of approximately 25 μl of liquid with sediment.

Isolation of DNA from the supernatant: In a 1.5 ml tube containing 35 μl of supernatant, 2 μl of Proteinase K (20 mg/ml) and 5% aqueous suspension of Chelex-100 were added to a final volume of 100 μl. The contents of the tube were vortexed and incubated in a solid state thermostat for 30 min at +56°C and 8 min at +96°C. The supernatant containing the DNA of plasmid pET-28c was transferred to a clean 0.6 ml tube with a lid and stored at -20°C.

Isolation of DNA from the precipitate: To the precipitate it was added 100 μl of TE buffer and 2 μl of Proteinase K (20 mg/ml) and kept for 1.5 h at +56°C. After 5 minutes of centrifugation under conditions of 12 thousand vol. min the supernatant was removed, then to the precipitate was added 100 μl of TE buffer. The procedure of washing with TE buffer was repeated twice. To the purified precipitate it was added 7 μl of dithiothreitol (DTT), 2 μl of Proteinase K (20 mg/ml) and 5% aqueous suspension of Chelex-100 to a final volume of 100 μl. The contents of the tube were vortexed and incubated in a solid-state thermostat for 30 min at +56°C and 8 min at +96°C. The supernatant containing boar sperm DNA was transferred to a clean 0.6 ml tube with a lid and stored at -20°C.

The amplification was performed on a programmable thermostat TERTSIK-2 (DNA Technology, Russia). Oligonucleotide primers for the amplification of pET-28c DNA had the following structure: T7 promoter – TAATACGACTCACTATAGGG, T7 terminator – CGCTGAGCAATAACTAGC. This pair of oligonucleotide primers allows to obtain a PCR product with a size of 314 b.p. Tubes with PCR products were stored at -20°C.

The specificity of the PCR products was checked by 2% agarose gel electrophoresis in 1 × Tris-borate electrode buffer (TBE) for 2 h at a current of 50 mA in a horizontal electrophoretic chamber (Cleaver Scientific Ltd., UK). DNA of plasmid pUC19 hydrolyzed by Msp I endonuclease was used as a molecular weight marker. After electrophoresis, the gel was stained with ethidium bromide solution (10 mg / cm3), and the results of electrophoresis were photographed using a gel documentation system (Cleaver Scientific Ltd., UK).

Research results. The amplification of DNA of plasmid pET-28c, which was isolated using differential lysis, allowed to obtain a PCR product with a size of 314 b.p. The size of the PCR product using oligonucleotide primers (T7promoter/T7terminator) was as expected. Thus, evidence was obtained that plasmid DNA can enter sperm.

Conclusions. The time required to isolate DNA using differential lysis depends on the qualifications of the staff and the amount of researches and averages 5–6 hours. This method of DNA isolation does not require the complex equipment and significant costs for reagents, but fertilization of eggs with sperm with a confirmed transfection event will save in the next stages of transfection.