Features of the preparation of biological material for genome editing in cattle

Abstract

Abstract. To carry out genome editing in cattle, an effective and well-functioning system for obtaining gametes, fertilizing eggs and their cryopreservation is necessary. Aim of the work: review and research of present-day existing methods of obtaining, insemination and cryopreservation of donor material, in order to provide genome editing in cows. Methods and materials. The work is completed according to the theme No. 0532-2019-0001 “Development of complex technology of marker-based genome selection of agricultural animals” within State Order of Ministry of Education and Science of the Russian Federation. The analysis of open scientific literature on the issues of in vitro fertilization in animals, cryopreservation of oocytes and embryons, sperm preparation and methods of insemination of cows’ oocytes, and cryopreservation of oocytes and embryons of animals is done. Features of the preparation of biological material of cattle for genome editing by microinjection into ooplasm are described. Results of research and duscussion. At present time there are two ways to obtain donor material from cattle: from live animals and taking ovaries after slaughtering cows. Material transportation is carried out at a temperature of 30–37 °C depending on the distance to the laboratory and expected time period of transportation. Oocyte-cumulus complexes can be removed by ovarian dissection and aspiration of visible follicles. In both cases, immature eggs are predominantly obtained. Subsequent ripening is carried out in vitro using special media in a CO2 incubator. The culture medium for oocyte maturation should contain hormones that mimic the peak of LH (luteinizing hormone), which occurs in vivo during the maturation of oocytes before ovulation. To accumulate a certain number of eggs at the stage of MII, it is recommended to carry out their cryopreservation by the method of vitrification, having previously released the oocyte from the cumulus cells. After thawing, oocytes need to be incubated for 2–3 hours 38.5 °C in 5–6.5% CO2 to restore the spindle. In order to make editing more effective, the introduction of genetic material is recommended to be carried out in parallel with the fertilization method “icsi”. In humans, mice and rabbits, an injection of sperm into the cytoplasm is sufficient to activate the oocyte, however, in cattle, just micro-injection of the sperm is not enough and often the male pronucleus does not form. To solve the problem, various methods are used, including freezing-thawing of sperm, resulting in damage of a membrane, or addition of heparin-glutathione into the medium that increases decondensation of the sperm DNA.