Formation of the Heart and Progenitor Cells

Abstract

An early model of heart formation suggested that the heart is sequentially formed through the anatomical compartmentalization of the cardiac primordium along the anteroposterior axis, from the outflow tract to the atrium. However, this model has drastically changed since the proposal 20 years ago of the secondary heart field, where cardiac progenitor cells exist on the medial side of the cardiac primordia. Recently, transcriptome analyses of single cells have shown that the fate of each anatomically segmented region may be determined in a different spatial and temporal order depending on the timing of mesoderm formation, thereby prompting further refinement of the model. Cell fate is determined by mesodermal cell migration to the anterior part of the embryo to form the cardiac primordium, including designated cardiac regions, along the mediolateral axis. The heart is formed when a portion of the cardiac primordium changes morphologically and remains as a pool of cardiac progenitor cells supplying the inflow and outflow tracts. The behavior of cells from the progenitor pool during heart formation is now better understood. This review evaluates recent findings and provides an updated model of heart formation.