Fig. 3. Efficient Tbx20 mRNA knockdown in embryonic stem (ES) cells (A) and ES cell-derived embryos (B,C). (A) Quantitative RT-PCR of Tbx20 mRNA levels in wild-type ES cells (wt) or ES cells stably transfected with constructs expressing Tbx20 shRNA a or b. Tetraploid aggregations were performed with ES cells with a 95% reduction in Tbx20 mRNA levels (b12), an 85% reduction in Tbx20 mRNA levels (a5, a6, b2) or a 65% reduction in Tbx20 mRNA levels (a4, b3). (B) Western analysis of protein extract from whole E9.5 embryos derived from lines a4, a6 and b12, and from wild-type embryos. (C) In situ hybridization for Tbx20 on wild-type, a6 and b12 embryos.