Fig. 2

unc45b mRNA expression occurs long before muscle myosin expression, and correlates spatially and temporally with NMM. In situ hybridization of zebrafish embryos at the tailbud (A, E, I, M), 2 somite (B, F, J, N), 5 somite (C, G, K, O) and 10 somite (D, H, L, P) stages of development. In situ probes were generated against myh10 (A–D), unc45b (E–H). smyhc1 (I–L) and myhc4 (M–P). Non-muscle myosin (myh10) expression was detectable at the tailbud stage (A) in the bud itself, spreading throughout the neural tube by the 2-somite stage (B). Expression was also detectable in adaxial cells (arrows) and the lateral paraxial mesoderm (arrowheads), growing more pronounced from the 5-somite stage onwards (C, D). Expression of myh10 was not limited to the differentiating somites, extending throughout the presomitic mesoderm as well. Unc45b expression was detectable in presomitic adaxial mesoderm at the tailbud stage (E), extending to the tail from the 2-somite stage (arrow in F) onwards. Expression of unc45b in the lateral paraxial mesoderm was detected initially in differentiating somite cells only (arrowhead in F). However, from the 5-somite stage onwards (G, H), unc45b was detectable throughout all paraxial mesoderm (arrowheads) in both differentiating somites and caudal presomitic mesoderm (G2, H2, white arrowheads). By contrast, the earliest slow-muscle myosin (smyhc1) was not significantly expressed until the 5-somite stage (K), and was restricted to adaxial cells as expected (arrowheads in J–L). Expression extended into the first few presomites (white arrowheads in K and L) but not to the caudal-most presomitic tissue. Likewise, fast-muscle myosin (myhc4) was not detectable at all before the 5-somite stage, and was also restricted initially to adaxial cells (arrowheads in O and P), extending into the first few presomites (white arrowhead in O), but not to the caudal-most tissue (white arrowhead in P2). Prime labels indicate lateral views of the same embryo. Arrowhead positions are the same between dorsal and lateral views.