Comparison of orthologous neuroectodermal gene expression domains among the deuterostomes. (A-E) Indirectly developing echinoderms. (F) Directly developing hemichordate. (G) Generalized vertebrate. Sea stars (Figures 1A-1C) and sea urchins (Figures 1D and 1E) are viewed laterally; animal pole is up and oral side is right. Figures 1F and 1G are dorsal views; anterior is up. Genes are listed beside their cognate expression domains. Vertical bars in Figures 1A, 1B, 1F and 1G approximate domain boundaries. The orange to yellow gradient in Figures 1A, 1F and 1G reflects a general conservation of anterior (animal)-most axial patterning among the three phyla. (A) Nested, concentric expression domains pattern the animal-vegetal (AV) axis of blastulae; asterisks denote previously reported expression [18, 19]. (B) Concentric domains of zic, foxq2, rx and six3 persist in gastrulae (orange to peach gradient); additional oral (for example, foxg, foxd and gbx; light orange) and aboral (for example, lhx2; purple) domains are evident. Genes (left) are broadly expressed. (C) Expression in larval animal pole domain (orange to peach) and/or ciliary bands (gold). (D) Sea urchin animal pole (orange and light orange), ciliary band (gold), aboral ectoderm (turquoise) and oral ectoderm (foxg; gray) are molecularly distinct territories in blastulae. (E) Expression is maintained in gastrulae animal pole (orange) and ciliary band (gold). (D and E) Pink circles represent skeletogenic mesoderm. See references [20, 22, 23, 41–49]. (F) Orthologs expressed in hemichordate anterior, middle and posterior body segments show corresponding expression in the vertebrate forebrain, midbrain and hindbrain, respectively; data are summarized from Lowe et al. . (G) Expression in generalized vertebrate centralized nervous system. F, forebrain; M, midbrain; R1-R8, rhombomeres of hindbrain. zic ; pea3 ; hnf-6/onecut ; and tbr ; foxj1 ; hox genes . See references  and [26–32]. Echinoderm gene names (quotations) are substituted for simplicity in Figures 1F and 1G.