Figure 4

Ino-POU2 -expression during development of I. notoides . Cartoons highlight Ino-POU2-expression as black checkered domains (see Figure 1 for color-code of ganglia). Dorsal (d)-ventral (v), anterior (a)-posterior (p), and left (l)-right (r) axes indicate the orientation. (A) During stage 19 Ino-POU2 is expressed in the gills close to the mantle (m). (B) Stage 20 embryos exhibit expression in the gills (arrowheads), the posterior mantle, the palliovisceral (pvg), the pedal (pg), and the optic ganglia (og) (posteroventral view). (C) Stage 21 individuals globally express Ino-POU2 including the palliovisceral and pedal ganglia, however not in the cerebral ganglia (cg) or the funnel (upper and lower left inset). Ino-POU2 is expressed in the eyes (e) during stage 22 (lower right inset) (yolk sac removed in images). (D) During stage 24, Ino-POU2 is expressed in the anterior (asm), middle (msm), and posterior subesophageal masses (psm). Slight expression was observed in the lobes of the supraesophageal mass (arrowhead) (sagittal vibratome section). The staining in the statocyst is unspecific. (E) During stage 25, Ino-POU2 is expressed in the brain including the supraesophageal mass (spm). (F) Close-up of Ino-POU2 expression in the supraesophageal mass during stage 26. Expression domains comprise the anterior (ab) and posterior basal lobes (pb), the superior frontal lobe (sf), and the optic lobes (o) (sagittal vibratome section). (G) The expression domains of later embryos resemble the ones of stage 26 individuals (sagittal vibratome section). During stage 27 Ino-POU2 is expressed in the vertical lobe complex (arrowhead) of the supraesophageal mass. Ino-POU2 is expressed in the superior buccal (sb) and inferior buccal lobes (ib) as well as the inferior frontal lobes (if). (H) Ino-POU2 expression during stage 27. Asterisks mark the statocysts. Abbreviations: a, arm; f, funnel; iy, internal yolk; mo, mouth; y, yolk. Scale bars: A-E: 150 μm, F-H: 200 μm.