Fig. 2

Expression of Nodal and BMP genes in Heliocidaris erythrogramma from gastrula to rudiment formation (24–40 hpf). Orientation of larvae is with anterior to the top and posterior, the blastopore, to the base. The left coelom is either on the left, or the view is of the larval left side with the left coelom in frontal view. a–d. Nodal was initially expressed in the right ectoderm extending approximately half way around the gastrula (a). This expression was reduced until only weak expression was detected along the right side and along the ciliated band of the 40 hpf larva (d). e–h. Lefty was also expressed in the right ectoderm extending halfway around the gastrula (e), (e insert, posterior view). Lefty was expressed in cells along the right ectoderm in a domain that was less extensive than Nodal, being reduced to a small domain at 40 hpf (f–h). i–l. BMP2/4 was expressed in the posterior half of the gastrula ectoderm (i) and at 32 hpf BMP2/4 was expressed in the presumptive vestibular ectoderm on the left side (j). A left-lateral view at 36 hpf (k) shows expression in the hydrocoele lobes with expression no longer detectable in the ectoderm. Left-lateral view of a 40 hpf larva (l) shows BMP2/4 expression in five clusters of cells at the bases of the primary podia. m–p Chordin was expressed in the left ectoderm in the 24 hpf gastrula (m) and at 32 hpf (n) extends halfway around the larva. This is followed by weak (36 hpf, o) expression of Chordin in posterior portion of the vestibule and then no evidence of expression in the 40 hpf larva (p). Ar, archenteron; H, hydrocoele; Lc, left coelom; Pp, primary podia; Cb, ciliated band; V, vestibule. Scale bar: 200 μm