200 Optimization of Individual Stages of Chicken Transgenesis to Increase Efficiency

Primordial germ cells (PGC) are the precursors of male and female progenitor cells. The cells are considered a valuable genetic material for the production of transgenic poultry. This technology includes isolation of the PGC from chick donor embryos, transformation of the cells, and injection into the dorsal aorta of recipient embryos. After injection, the PGC are involved in the process of embryo development and differentiate into male or female sex cells. The aim of the research was to optimize the individual stages of this technology to increase the efficiency of transgenesis. The PGC were extracted from embryo gonads at stage 26 to 27 (H&H) using the trypsinization process. The trypsin concentration and incubation time were determined experimentally. Treatment of chick embryos with a 0.05% trypsin solution for 5 min was optimal for obtaining culture of embryonic cells. Separation of the PGC from other types of embryonic cells was based on a differential adhesive capacity. The maximum homogeneity of the cell population for further cultivation was established by transfer (twice) of the supernatant containing unattached cells after 1 h of cultivation in a new culture dish. The cell population is represented mainly by the PGC (81 ± 4%). Additional purification of the PGC from other cell types using magnetic-activated cell sorting (MACS) increased the proportion of these cells up to 93 ± 2%. The lentiviral transduction (pHAGE vector, ZsGreen under CMV promotor) was used to transform the resulting culture of the PGC. The efficiency of infection of PGC with lentiviral particles (TU/mL = 2.5 × 108) was 70 ± 3%. The transformed cells were injected into the dorsal aorta of recipient embryos on Day 2.5 (n = 80). Before injecting donor PGC, recipient embryos were treated with busulfan to remove the endogenous PGC. The optimal dose of busulfan was selected experimentally. A series of experiments introducing busulfan in concentrations from 50 to 250 μg into chick embryos at 24 h of incubation showed that the optimal dose was 100 μg/embryo. The efficacy of colonization of gonads with donor PGC was assessed on Day-10 embryos (n = 32) and 4-week-old hatched chickens (n = 12). Cells from gonads were studied using fluorescence microscopy, fluorescence-activated cell sorting (FACS) and qPCR. The presence of fluorescent cells in the gonads of recipients was established in both embryos and hatched chickens. The relative number of the recombinant DNA copies and the relative level of expression were confirmed by qPCR. The FACS analysis of sex cells isolated from gonads of recipients showed that the percentage of transformed germ cells reached 55.8% in females (n = 5) and 31.9% in males (n = 7). Thus, the effectiveness of poultry transgenesis can be enhanced by preparation of donor PGC for injection into embryo recipients and elimination of endogenous PGC in recipients. Both the purification of PGC from other cell types based on adhesive capacity as well as treatment of embryo recipients at 24 h incubation with busulfan (100 μg/embryo) increased the effectiveness of transgenesis. Study supported by the RSF within project No. 16-16-10059.