187 EMBRYO GENOTYPING FROM IN VIVO BIOPSIED BOVINE EMBRYOS AFTER WHOLE GENOME AMPLIFICATION

Abstract

Genomic tools are now available for most livestock species and used routinely for marker-assisted selection (MAS) in cattle. The detection of a large number of markers that are widespread over the genome is generally limited by the amount of genomic DNA available in an embryo biopsy of a small size not to be detrimental to embryonic survival. Amplification of DNA from such a biopsy is then necessary. In this study, the efficiency of embryo genotyping for 45 microsatellites (MS) following whole-genome amplification (WGA) was evaluated from samples of a variable number of cells isolated from cattle embryos. In a second part, this work aims to test the reliability of the MAS method for 45 MS and 13 single nucleotide polymorphisms (SNP) from bovine embryo biopsies under field conditions. In experiment 1, in vitro bovine morulae (n = 10) were produced, and 1, 5, and 10 embryonic cells were removed from each morula. Cells were dry frozen in tubes before further processing. Whole-genome amplification was performed using the commercial Qiagen REPLI-g^® Mini Kit according to the manufacturer instructions (Qiagen, Valencia, CA, USA). WGA solution was then diluted, processed by PCR with 45 markers, and the resulting data were genotyped with GeneMapper software^® (Applied Biosystems Europe). Accuracy and reliability of genotyping were assessed using different samples of cells from the same embryo. In experiment 2, after superovulation (10 cows), bovine embryos were in vivo-produced and collected at day 6 or day 7 of pregnancy. Only grade 1 embryos were washed and biopsied using a microblade. Biopsied embryos were either frozen or transferred back to synchronized recipients. Individual biopsies were transferred as dry samples to the laboratory. Genomic DNA was amplified using WGA, and embryos were genotyped. The results of experiment 1 clearly indicate that a conventional biopsy of 5 to 10 cells was sufficient for multi-markers detection after whole-genome amplification as 98% of the 45 markers were detected compared to 45% of marker detection using 1 cell (P < 0.01). In experiment 2, from 123 collected embryos, 79 were classified as grade I or II transferable embryos (64.2%) and 57 were biopsied (34 were classified as stage 4–5 and 23 as stage 5–6, according to the IETS criteria). Using the stereomicroscopic analysis, 44 biopsies had a number of cells ranging from 4 to 7 (5.6 ± 1.4) and 13 biopsies from 8 to 10 (8.4 ± 1.6). Overall, at least 95% of markers (MS + SNP) were detected in 49.1% of biopsies (28/57). The total detection rate for SNP was significantly higher than for MS; 70.2% (40/57) v. 31.6% (18/57), respectively, (chi-square, P < 0.01). The detection rate of the markers was not significantly affected by the embryo stage or the biopsy size. Our results confirm that genotyping a large number of markers from biopsy samples after whole-genome amplification is possible under field conditions. A larger number of biopsies is required to assess the reliability of this method that may allow the development of MAS from early embryo.

This work has been performed through the programme TYPAGENAE (GENANIMAL 4-03) with the financial support of FRT/ANR and Apis-Genes.