Asynchronous activation of 10 muscle-specific protein (MSP) genes during zebrafish somitogenesis

In the present study, 10 zebrafish cDNA clones coding for muscle-specific p roteins (MSPs) were characterized and most of them encode fast skeletal mus cle isoforms. They are skeletal muscle alpha-actin (acta1), fast skeletal m uscle atropomyosin (tpma), fast skeletal muscle troponin C (tnnc), fast ske letal muscle troponin T (tnnt), fast skeletal muscle myosin heavy chain (my hz1), fast skeletal muscle myosin light chain 2 (mylz2), fast skeletal musc le myosin light chain 3 (mylz3), muscle creatine kinase (ckm), parvalbumin (pvalb), and desmin (desm). Using these cDNA probes, their expression patte rns in developing embryos and adults were compared by Northern blot hybridi zation and whole-mount in situ hybridization. All of the 10 genes are expre ssed in both embryos and adult fish, and the expression is highly abundant in skeletal muscle. Among them, acta1, tpma, tnnc, tnnt, myhz1, mylz2, mylz 3 and pvalb, are expressed specifically in fast skeletal muscle while ckm a nd desm are expressed in both fast and slow skeletal muscles. In addition, tpma, ckm, and desm are also expressed in the heart. Ontogenetically, the o nset of expression of these MSP genes in zebrafish skeletal muscle varies a nd the expression occurs rostral-caudally in developing somites. Shortly af ter the expression of myoD, desm is the first to be activated at similar to 9 hpf, followed by tpma (similar to 10 hpf), tnnc (similar to 12 hpf), act a1 (similar to 12 hpf), ckm (similar to 14 hpf), myhz1 (similar to 14 hpf), mylz2 (similar to 16 hpf), mylz3 (similar to 16.5 hpf), tnnt (similar to 1 6.5 hpf), and pvalb (similar to 16.5 hpf). At later stages (after 48 hpf), these MSP genes are also expressed in fin buds and head muscles including e ye, jaw, and gill muscles. Thus, our experiment demonstrated the order of e xpression of the 10 MSP genes, which may reflect the sequence of muscle fil ament assembly. In spite of the asynchrony in activation of these MSP genes , the timing of expression for each individual MSP gene appears to be synch ronous to somite development as each somite has an identical timetable to e xpress the set of MSP genes. (C) 2000 Wiley-Liss, Inc.