Modular co-option of cardiopharyngeal genes during non-embryonic myogenesis

ABSTRACT Background In chordates cardiac and body muscles arise from different embryonic origins. Myogenesis can in addition be triggered in adult organisms, during asexual development or regeneration. In the non-vertebrate ascidians, muscles originate from embryonic precursors regulated by a conserved set of genes that orchestrate cell behavior and dynamics during development. In colonial ascidians, besides embryogenesis and metamorphosis, an adult can propagate asexually via blastogenesis, skipping embryo and larval stages, and form anew the adult body, including the complete body musculature. Results To investigate the cellular origin and mechanisms that trigger non-embryonic myogenesis, we followed the expression of ascidian myogenic genes during Botryllus schlosseri blastogenesis, and reconstructed the dynamics of muscle precursors. Based on the expression dynamics of Tbx1/10, Ebf, Mrf, Myh3 for body wall and of FoxF, Tbx1/10, Nk4, Myh2 for heart development we show that the embryonic factors regulating myogenesis are only partially co-opted in blastogenesis, and propose that the cellular precursors contributing to heart or body muscles have different origins. Conclusions Regardless of the developmental pathway, non-embryonic myogenesis shares a similar molecular and anatomical setup as embryonic myogenesis, but implements co-option and loss of molecular modules.