Fig. 2

Expression of the four pSF genes from 6 to 8 hpf. Panels a-c are schematic diagrams showing the development of the shell field during this period (dorsal views). The shaded areas indicate the central region with surface elaborations (Fig. 1), and the dashed lines indicate the territory of the shell field roughly estimated based on the wedge-shaped peripheral cells (Fig. 1) and the expression of pSF genes shown in panels d-o. Panels d-o are dorsal views, anterior to the top; and panels d’-o’ are posterior views, dorsal to the top. The pSF gene expression spanned relatively wide ranges at 6 hpf, which aggregated to the dorsal side in the subsequent development (indicated by red arrows in d-o and d’-o’). At the same time, their dorsal expression moved posteriorly (indicated by green arrows in d-o). The white crosses in m-o and m’-o’ indicate the Engrailed expression in the cells that do not contribute to shell field development. For clarity, Engrailed expression domains at 6 hpf are indicated by numbers (1 and 2 in m and m’) given that the signals were distributed on dorsal and ventral sides and it was relatively difficult to discriminate them in different panels