Figure 7.

Expression patterns of Pdu-Hes2 and their schematic representations in Platynereis larvae and during posterior elongation (PE). Whole-mount in situ hybridization (WMISH) for the different stages indicated on each panel is shown. Pdu-Hes2 is first expressed in two lateral ectodermal patches at 24 h post fertilization (hpf) and expands broadly in the 12 chaetal sacs, and in few cells of the brain at 48 hpf. At 72 hpf its expression is restricted to the dorsal segment addition zone (SAZ) located between the third segment and the pygidium (expressions in the silk glands, indicated by an asterisk, are an artifact). During PE, Pdu-Hes2 is expressed very early, in the future chaetal sacs of each segment, in a ring-like shape, corresponding to the follicular cells of the follicles (that compose the chaetal sacs) with the deeper seating cells, the chaetoblasts, not stained. When chaetae protrude, the expression is in a larger spot at the basis of chaetae. Panels are ventral views (anterior is up) for the larvae and during PE.