Cardiac trabeculation in vertebrates: Convergent evolution or evolutionary adaptations associated with heart complexity?

One of the most important processes during early heart development is the formation of trabecular myocardium. Cardiac trabeculation is the process by which the ventricular chambers develop a complex sponge-like myocardium essential for optimal cardiac function to provide efficient oxygenation and nourishment to the developing embryo. Indeed, its importance is highlighted by the fact that defects in trabecular formation lead to embryonic lethality and congenital heart disease. In the last decades, our understanding of cardiac trabeculation in different vertebrate models has advanced significantly. However, instead of reinforcing cardiac trabeculation as a highly evolutionarily conserved process across vertebrates, these studies have identified significant differences in the way the process occurs and how it is regulated in different vertebrate species. In this review, we assembled the current knowledge on cardiac trabeculation in different vertebrate species and examined if trabecular myocardium development can be achieved through different morphogenetic processes across vertebrates or if these differences are associated with evolutionary adaptations required to develop more complex vertebrate hearts.