Fig. 2

smpx embryonic expression pattern analyzed by in-situ hybridization. (A) At first smpx signal appears at 4-somite stage at the level of the Kupffer's vesicle (white arrowhead, frontal view), as also shown in the inset (lateral view). (B–D) From 10 to 24 hpf the gene is abundantly expressed in each somite. (B′) Cross-section of a 10 somites embryo showing smpx mRNA labeling the most adaxial cells next to the notochord. (D) The 24 hpf stage marks the onset of smpx expression in the developing heart (white arrowhead); smpx now labels both fast (white asterisk) and slow (black arrowhead) muscle fibers, as shown by the cross-section in the inset. (E–G) While smpx expression decreases in the trunk, the signal at 36, 48, and 72 hpf persists in the heart (black arrowhead), labeling both ventricle and atrium (K) and is now visible in the forming ear (white arrow), specifically in the territories corresponding to the anterior (I,I′) and posterior (J,J′) maculae. (G,H) Larvae at 72 hpf; besides heart and ear, smpx is also expressed in the muscles of the branchial arches (bracket), of the eye (white arrowheads) and of the pectoral fins (black arrowhead).B,C,D,E,F,G: Lateral views, anterior to the left. H: Dorsal view, anterior up. n, notochord; nt, neural tube; am, anterior macula; pm, posterior macula; v, ventricle; a, atrium. Scale bars = 200 μm in A,B; 20 μm in B’; 150 μm in C; 500 μm in D,E,F,G; 25 μm in I,J; 10 μm in I′,J′,K.