Fig. 4

Expression in vestibular ectoderm and pentameral structures. 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 face view. a–c Gsc. At 24 hpf Gsc (a) was expressed in the posterior half of the gastrula ectoderm, extending halfway around as seen in the posterior view (insert). In the 32 hpf larva (b), Gsc was expressed on the left in the presumptive vestibular ectoderm. In the 36 and 40 hpf larvae (c) Gsc was expressed in the vestibular ectoderm. d–g Dlx. In the gastrula (24 hpf d), Dlx was expressed in the posterior ectoderm extending anteriorly to the head/tip/anterior of the archenteron. Expression extends halfway around the gastrula (insert). In the 32 hpf larva (e) Dlx expression was restricted to the vestibular ectoderm. At 36 hpf (f) expression was strong throughout the vestibular ectoderm with particularly strong staining around the rim of the vestibule (and insert). Additional expression was evident in the right and posterior ectoderm (arrows). In a lateral and frontal view of the adult rudiment in the 40 hpf larva (g), Dlx expression was in the ectoderm of the vestibule roof (insert shows a second plane of focus through vestibule) and in interambulacral regions of the vestibule floor ectoderm, as well as in the right ectoderm (arrow). h–k Tbx2/3. In the gastrula (h), Tbx2/3 was expressed in the posterior ectoderm, close to the margins of the blastopore (insert, posterior view). In the 32 hpf larva (i), Tbx2/3 was expressed in the vestibular ectoderm and at 36 hpf (j) was expressed in the hydrocoele lobes at the bases of the forming podia. A frontal and lateral view of the adult rudiment in the 40 hpf larva (k) shows Tbx2/3 expression in the hydrocoele at the bases of the primary podia. l–d Msx. In gastrulae (l), Msx was expressed broadly in posterior ectoderm with stronger expression on the left side as also in the 32 hpf larva (m). In a left side view (two focal planes) of a 36 hpf larva (n) Msx was expressed in the rim of the vestibule, particularly in the posterior portion and in the hydrocoele lobes with strongest expression at the base of the lobes. In the left side view of a 40 hpf larva (o), Msx expression was evident in the posterior rim of the vestibule wall and in the hydrocoele at the bases of the primary podia (arrow in insert). Ar, archenteron; Lc, left coelom; Ve, vestibular ectoderm; V, vestibule; Pp, primary podia; Scale bar: 200 μm