Fig. 4. cNanog expression during chick embryo development. (A-J) Whole-mount in situ hybridisation to cNanog transcripts. Nanog transcripts are localised in the epiblast of the area pellucida and area opaca of the pre-streak embryo (A, stage XI; B, stage XII), but not in the hypoblast (B'). From stage XIV, cNanog mRNA disappears from the posterior area pellucida (C,C') and from the growing primitive streak (D, stage 3; E,E', stage 3+; F, stage 4+). cNanog transcripts are downregulated in the epiblast from stage 4+ (F), and are confined anteriorly in a crescent region in the epiblast (G, stage 5+). At stage 6 (H), expression is restricted to the neural plate and the neural tube (I, stage 7; J, stage 8). cNanog is also expressed in scattered cells in the germinal crescent from stage 4 (arrowhead in I and H'). B' is a longitudinal section of the embryo in B, anterior at the right; C',E',H' are transverse sections of embryos in C,E,H, respectively. ep, epiblast; gd, gonad; ms, mesonephros; np, neural plate; nt, neural tube; ps, primitive streak.