Figure 2

Whole mount in situ hybridization (WMISH) of sea urchin regulatory genes whose orthologs are known myogenic factors. Sum1/MyoD1, MyoD2, MyoR, Maf, Myocardin, Mef2, Twist and Tbx6 expression was localized using WMISH at the gastrula (44 to 48 h; A-H), prism (60 to 65 h; A’-H’), and pluteus larva stage (72 to 80 h; A”-H”). All embryos are viewed along the animal top/vegetal down axis with the exceptions of panel A, which is shown in a vegetal view with the oral side on the bottom, B’, C’, D’ and H are viewed in a lateral view with the oral side on the left (B’) or right (C’, D’ and H’). Domains of expression other than the tip of the archenteron and the coelomic pouches are indicated as follows: black arrow, primary mesenchyme cells (PMC); black arrowhead, the cardiac sphincter; white arrowhead, the apical organ; black asterisk, the blastopore.