Fig. 4. Analysis of TSC potential in the 9 s.p. ChE. (A) RT-PCR analysis of TSC markers in late-streak and 9 s.p. ExRs. ß-actin is a positive control. The sizes of the PCR products are indicated on the left. (B) Photomicrograph of a 40 XX chromosome spread from a representative cell of the polyclonal TSC line, derived from a single 9 s.p. ChE after approximately 2 months in culture, used for chimaeric analysis. Numbers represent specific chromosomes. Scale bar: 10 µm. (C) Photomicrograph of a late-headfold stage TSC chimaera produced by blastocyst injection of the 9 s.p. TSC line in B. Arrows indicate contribution of blue staining ROSA26 +/– TSCs to the ChE and EPC. Scale bar: 500 µm.