Fig. 3
Expression of downstream targets of Nodal and BMP in the left and right coeloms during rudiment formation. Orientation of larvae is with anterior to the top and posterior, the blastopore, to the base and the left coelom on the left. a–d Pitx2. The gastrula (a) shows Pitx2 expressed in the right side of the anterior archenteron where the right coelom is beginning to form and in the right posterior ectoderm. In the 32 hpf larva (b), Pitx2 was expressed in the right coelom and right lateral ectoderm (arrow) and at 36 hpf (c) was expressed throughout the right coelom (insert) extending to where the anterior coelom meets the right coelom. In the 40 hpf (d) Pitx2 was expressed in the right coelom and right ectoderm (arrow), with expression extending between the ciliated band and the lipid rich apical end of the larva. e–h. Six1/2. In the 24 hpf gastrula (e), Six1/2 was expressed in anterior half of the archenteron. At 32 hpf (f) Six1/2 was expressed in the anterior coelom at the head of the archenteron and in the anterior (top arrow) and posterior (bottom arrow) walls of the proximal left coelom. In the 36 hpf larva (g), Six1/2 was expressed in the anterior coelom and hydrocoele underlying the vestibular ectoderm. The 40 hpf larva (h), shows Six1/2 expression in the anterior coelom and hydrocoele. Expression is restricted to the central hydrocoele and does not extend into the lobes of the forming podia. i–l. In the 24 hpf gastrula (i), Eya was expressed in the mid region of the archenteron. In the 32 hpf larva (j), Eya was expressed at the head of the archenteron on the left side extending into the posterior wall of the proximal left coelom (arrow), as well as in the anterior coelom and the anterior wall of the proximal left coelom. In the 36 hpf larva (k), Eya was expressed in the anterior coelom and proximal hydrocoele. A lateral and frontal view of the adult rudiment in the 40 hpf larva (l) shows Eya expression in the anterior coelom, the hydrocoele and extending into the podia. Ar, archenteron; Lc, left coelom; Rc, right coelom; Ac, anterior coelom; Pp, primary podia; Ve, vestibular ectoderm; H, hydrocoele; V, vestibule. Scale bar: 200 μm