text: Differentiating EPL cells were analysed for the expression of established markers of the primitive streak (T, Bmp4, Tgfb1, Wnt3 and Fgf8) (Crossley and Martin, 1995; Dickson et al., 1995; Liu et al., 1999; Wilkinson et al., 1990; Winnier et al., 1995), ectoderm (Sox1 and Ascl1) (Guillemot et al.