Comparison of gene expression in pre-implantation bovine embryos either injected or transfected with a siRNA targeted against E-cadherin

The ability to create transgenic livestock is a tremendous benefit in scientific research for many disciplines including functional genomics, pharmaceutical synthesis and development of enhanced production animals. Transgenes can either be stably or transiently expressed to alter gene function and obtain a specifically engineered phenotype. To create a transgenic bovine embryo, genetically altered somatic cells must be used in somatic cell nucleus transfer, or early 1-cell embryos (zygotes) must be microinjected with plasmid DNA or small interfering RNA (siRNA). Given the cost and skill associated with both methods, a preliminary investigation exploring alternative delivery techniques of siRNA (transient expression) into bovine zygotes with a nonhomologous Cy3 labeled siRNA (Cy3-siRNA) was first performed. It was discovered that zygotes injected with more than 50 Bmol L-1 of Cy3-siRNA fail to form a blastocoel and that, although bovine zygotes are not susceptible to chemical transfection, the trophectoderm cells of the blastocyst are. Based on this information, bovine E-cadherin gene expression was compared in day 9 blastocysts derived from either injected zygotes (day 1) or transfected blastocysts (day 7) with a Cy3 labeled E-cadherin specific siRNA (Cy3-siEcad) to determine 1) if gene suppression in zygotes injected with 25 Bmol L-1 Cy3-siEcad continues during embryo development up to hatching, and 2) if blastocysts transfected at a ratio of 9:6 with GeneJammer? truly experience gene knock down after siRNA transfection capable of maintaining suppression to day 9. Quantitative PCR indicated blastocysts transfected with Cy3-siEcad had a significant 15.3% decrease (P < 0.05) in E-cadherin mRNA at day 9 compared to the injected zygotes. Protein fluorescence analysis from immunocytochemistry of whole mounted day 9 blastocysts revealed injected zygotes accumulated significantly less E-cadherin protein (67.7%) than the transfected blastocysts (P < 0.05). From these data, it can be concluded that although siRNA injection may be capable of knocking down gene expression for the first 7 days of embryonic development, it does not persist to the hatching stage; however, blastocysts transfected at day 7 do express altered gene expression in the trophectoderm which can continue through embryonic hatching events.