Fig. S2

Cdkn1c mRNA accumulation in slow and fast muscle development.

Wholemount in situ mRNA hybridization for zebrafish cdkn1c in dorsal (A,B,L; anterior to top) or lateral (G,M; anterior to top, dorsal to right) flatmount or transverse cryosections at the levels indicated by dashed lines (C–F, H–K, N–R; dorsal to top). Bar: 100 μm (A). At 5 som, Cdkn1c mRNA is detected in adaxial cells, the base of the notochord and the overlying neural plate. (B–F). By 15 som, expression continues in basal notochord, adaxial cells and differentiated slow muscle, commences in fast muscle precursors in rostral somites and in ventrolateral regions near the tailbud and becomes regionalized in ventral and lateral spinal chord. (G–K). At 25 som, expression becomes widespread in rostral somites, persists in neural tube, adaxial cells and posterior notochord and is high in cloacal region. (L–R). By 24 hpf, cdkn1c mRNA has complex neural expression reminiscent of differentiating neurons, is abundant in fast and slow muscle, persists in cloaca but is declining in posterior notochord. (S–V). Cdkn1c (S,T) and mylz2 myosin (U,V) mRNA in head muscle anlagen at 48 hpf in ventral (S,U) or lateral (T,V) view, anterior up, dorsal to right. Note hyoid muscle anlagen (arrow) and bilateral precursors overlying the differentiated fibres (arrowheads). (T). Cdkn1c mRNA in fin muscle masses at 48 hpf. ad adaxial cells, cl cloaca, dc diencephalon, fm fast muscle precursors, hb hindbrain, m mouth, nc notochord, np neural plate, nt neural tube, pn posterior notochord, sm slow muscle, ss superficial somite, tc telencephalon, tm tegmentum, y yolk.