Early Chordate Origins of the Vertebrate Second Heart Field

Abstract

Building the Heart The multichambered heart of birds and mammals develops through addition of second heart field (SHF)–derived precursor cells to a primary heart tube. Stolfi et al. (p. 565 ) show that, in the simple chordate Ciona intestinalis , the heart and atrial siphon muscle (ASM) precursors arise from common progenitors following asymmetric cell divisions and that the transcription factor COE (Collier/Olf1/EBF) is involved in this fate choice. The ASM precursors express molecular markers of the vertebrate pharyngeal mesoderm that gives rise to the SHF and lower jaw muscles, suggesting that the origins of both can be traced back to the last common ancestor of tunicates and vertebrates.