Figure 2.

Staging system for cardiac development. We developed a numerical staging system to describe different phases of early cardiac development in a fine-grained manner. Stages 0 to 2 correspond to progressively more developed cardiac crescents (CC), whereas stage 3 represents a transition toward the linear heart tube (LHT) stage. Images are maximum-intensity projections of whole mount immunofluorescence showing the expression of NKX2-5, a marker of cardiac progenitors, highlighting changes in cardiac morphology during these stages. The table shows other staging systems for comparison, including two other recent systems specific to the heart. (FD) Foregut diverticulum, (ML) midline, (HF) headfold.