Figure 5.

Models of valve sculpting. (A) Histological images showing how the leaflet sculpts from a bulky cushion at E11.5, to a well-defined leaflet by E14.5. (B) The leaflet elongation model proposes that under the influence of factors secreted by the thickened valve endocardium, the leaflet actively elongates to acquire its sculpted form. (C) In the second model a process of cell death removes cushion tissue at the boundary with the outflow wall and in this way excavates the sinus, leading to freeing of the leaflet. (D) In the final model, the endocardium bends into the cushion tissue and in so doing creates the sinus, again freeing the leaflet. Experimental evidence is minimal for each of the three models and further work is needed to determine which, if any, are accurate.