Comparative analysis of Prtg expression at the end of gastrulation. A: Schematic representation of a mouse embryo at the headfold (7.95 days postcoitum [dpc]) stage, showing the two regions (1 and 2) from which RNA was extracted to build the subtracted libraries. B-D: In situ hybridization (ISH) on mouse embryos at the headfold stage with probes corresponding to the most frequently found genes from the posterior library: Prtg, a novel gene, represented by clone P1-50 (B and C for antisense and sense probe, respectively) and Hoxa1 (D). E: Double ISH with Prtg (blue) and Hoxa1 (red). In the medial neural plate, Hoxa1 and Prtg were coexpressed in the same anteroposterior (AP) domain giving rise to a brown staining. Laterally, cells expressing Prtg (blue cells) were present anterior to the Hoxa1 domain, near the borders of the neural plate. F-H: ISH on mouse embryos at the 7.75 dpc (F), 7.95 dpc (G), and 8 dpc (H) stages, with a Prtg probe. I-K: ISH on mouse embryos at the 7.25 dpc (I), 7.95 dpc (J), and 8 dpc (K) stages, with a Punc probe. L-N: ISH on chick embryos at stages 4 (L), 7 (M), and 8 (N), with a chick Prtg probe. O-Q: ISH on zebrafish embryos at the 100% epiboly (O), 1 s (P), and 4 s (Q) stages, with a zebrafish prtga probe. All embryos are oriented with anterior to the left. In B-E, G, H, J, and K, mouse embryos have been cut posterior to the node. n, node; nf, neural fold; ps, primitive streak; r, rhombomere; s1, somite 1; r3/r4 indicates the prospective boundary between rhombomeres 3 and 4 of the hindbrain.

Comparison of murine and chicken Prtg expression patterns. A-I: In situ hybridization (ISH) performed on mouse embryos with an antisense Prtg probe. A,B,C, and E show lateral views, D and F dorsal views, and G, H and I sections performed on a 20 s embryo as indicated in C. J-L: ISH performed on chick embryos with a chick Prtg probe. J and K show sections, and L shows a lateral view. The embryonic stages are indicated on each panel, in somite number and according to Hamburger and Hamilton classification. ba1, first branchial arch; cnp, caudal neural plate; dm, dermomyotome; mb, midbrain; nt, neural tube; op, otic pit; r, rhombomere; rp, roof plate; s, somite; sc, spinal cord; sld, sub-lip domain; tel, telencephalon.

Expression patterns of the zebrafish prtga and prtgb genes. A-T: In situ hybridization (ISH) performed on zebrafish embryos with antisense prtga (A-L) or prtgb (M-T) probes. The embryonic stages are indicated on each panel, in somites (s) or hours postfertilization (hpf). B and H show dorsal views of whole embryos, A, C, E, G, M, N, P and R, lateral views of whole embryos; D and O, dorsal views of flat-mounted embryos; F, a lateral view of a flat-mounted embryo; I-L, Q, S, and T, sections at levels indicated in G, P and R. Cb, cerebellum; d, diencephalon; fb, forebrain; fp, floor plate; hb, hindbrain; le, lens; lm, lateral mesoderm; mb, midbrain; ml, mantle layer; nt, neural tube; rp, roof plate; sc, spinal cord; tec, tectum; teg, tegmentum.

Unillustrated author statements