Smad4 is required for the development of cardiac and skeletal muscle in zebrafish

• Smad4 was expressed at all developmental stages of zebrafish.
• Knockdown of smad4 in embryos resulted in defects in the heart and the trunk structure.
• Knockdown of smad4 in embryos downregulated the expression of two heart-chamber markers.
• Knockdown of smad4 in embryos increased the expression of myogenic regulatory factors.
• Knockdown of smad4 in embryos resulted in an obvious increase of cell apoptosis.

Transforming growth factor-beta (TGF-beta) regulates cellular functions and plays key roles in development and carcinogenesis. Smad4 is the central intracellular mediator of TGF-beta signaling and plays crucial roles in tissue regeneration, cell differentiation, embryonic development, regulation of the immune system and tumor progression. To clarify the role of smad4 in development, we examined both the pattern of smad4 expression in zebrafish embryos and the effect of smad4 suppression on embryonic development using smad4-specific antisense morpholino-oligonucleotides. We show that smad4 is expressed in zebrafish embryos at all developmental stages examined and that embryonic knockdown of smad4 results in pericardial edema, decreased heartbeat and defects in the trunk structure. Additionally, these phenotypes were associated with abnormal expression of the two heart-chamber markers, cmlc2 and vmhc, as well as abnormal expression of three makers of myogenic terminal differentiation, mylz2, smyhc1 and mck. Furthermore, a notable increase in apoptosis was apparent in the smad4 knockdown embryos, while no obvious reduction in cell proliferation was observed. Collectively, these data suggest that smad4 plays an important role in heart and skeletal muscle development.