Fig. 3. cPouV expression during chick embryo development. (A-J) Whole-mount in situ hybridisation to cPouV transcripts. Transcripts are detected in the area pellucida and area opaca of the epiblast in pre-streak embryos (A, stage XI; B, stage XIII), and in the hypoblast in a salt-and-pepper manner (B'). At stage XIV (C), the expression is very strong in the area pellucida of the epiblast, especially where the streak is forming (C'). Transcripts are expressed in the ingressing mesoderm at stages 2-3 (D,D'). As the primitive streak elongates and the embryo grows, expression is still detected in the ectoderm and mesoderm (E, stage 3+; F,F', stage 4+; G, stage 5). At stage 7 (H) and 8 (I), cPouV mRNA is detected in the forming neural tube and in the underlying mesoderm, but is absent from the endoderm (data not shown). At stage 9 (J), cPouV mRNA is expressed in neural tissue (nt) and presumptive migrating germ cells (gc). B',C',D',F' are transverse sections of the embryos in B,C,D,F, respectively. ao, area opaca; ep, epiblast; gc, germ cells; hy, hypoblast; m, mesoderm; np, neural plate; nt, neural tube; ps, primitive streak.