160 ATTEMPTS TO CULTURE BIOPSIED CELLS FROM IN VITRO BOVINE BLASTOCYSTS FOR GENOTYPING

Abstract

Genomic tools have now become available for most livestock species and are being used routinely for marker-assisted selection in cattle. One major challenge in bovine selection is the possibility to detect multiple markers from biopsies of pre-implantation stage embryos which allows to transfer only selected embryos following genotyping. Preliminary studies have shown that 2 ng of DNA collected from 200 embryonic cells (hatched blastocyst) may be sufficient for genotyping based on few markers (<100). However, the present genotyping techniques are much more demanding in terms of DNA. The aim of this work was to test different in vitro culture conditions of biopsied cells issued from bovine blastocysts to produce a large number of cells for genotyping. Bovine embryos were produced in vitro according to a standard protocol (Menck M et al. 1997 Reprod. Nutr. Dev. 37, 141-150). Only grade 1 embryos were biopsied using a microblade under a stereomicroscope. Biopsies had from 5 to 10 cells. Biopsied embryos were in vitro cultured in B2 + 2.5% FCS seeded with VERO cells for 48 h to assess the survival rate. Individual biopsies were cultured in vitro in 4-well culture dishes (Nunc) coated with collagen type 1 at 39°C in a humidified air atmosphere and 5% CO₂ under 3 medium conditions. Intact hatched Days 8 to 10 blastocysts were cultured under the same conditions as controls. In condition 1, 43 biopsies and 35 control blastocysts were cultured in DMEM/F12 + 10% FCS and 0.25% ITS (insulin, rransferrin, selenium). In condition 2, 30 biopsies and 35 control blastocysts were cultured in DMEM/F12 + 20% FCS supplemented with 1 mM sodium pyruvate, 1 μg mL^-1 of heparin, and 1 μg mL^-1 of FGF4. In condition 3, 30 biopsies and 43 control blastocysts were cultured in a complex medium composed of 30% of [DMEM/F12 + 20% FCS] and 70% [DMEM/F12 + 20% FCS conditioned medium using mitomycined VERO cells] supplemented with 1 mM sodium pyruvate, 1.5 μg mL^-1 of heparin, and 1.5 μg mL^-1 of FGF4 (adapted from Oda et al. 2006 Methods Enzymol. 419, 387-400). Medium was replaced every 3 days. Outgrowths were physically detached and isolated cells were cultured using condition 3. For further passages, monolayers were trypsinized (0.025%) and cells were analyzed by immunofluorescence using anti-cytokeratin 1-8 antibodies. After biopsy and 48 h of in vitro culture, 97.1% (100/103) of embryos survived. For all culture conditions, none of the biopsied cells attached to the coated dishes and no colony were observed after culture. Control intact blastocysts adhered and formed significantly lower rate of outgrowths for condition 1 v. 2 and 3: 77.1% v. 85.7% and 93%, respectively (P < 0.05). After several passages, 3 cell lines were produced and we observed a network of cytokeratin filaments by immunofluorescence suggesting an epithelial cell type for this network. These results show that production of a large number of cells from biopsies was not efficient enough for genotyping. However, the 3 tested culture conditions are favorable for the production and multiplication of cells from intact bovine blastocysts and condition 3 seems to be a suitable medium condition for embryonic cell culture.