Schematic representation of the <i>Drosophila</i> dorsal vessel’s cellular composition and organization.

<p>Top, presents <i>Drosophila</i> DV at embryonic stage 15 while cardiac progenitors are migrating towards the dorsal midline. Bottom is an schematic representation of the embryonic heart proper at stage 17 when the DV lumen has formed. Aortic portion (right) is oriented anteriorly and the beating (heart) portion (left), posteriorly. Based on the expressed marker TFs, different cell types are colored. CBs are divided into Tin-(green) or Svp-expressing SMCs (light green) subtypes. SMCs of the last three posterior segments of DV make the future ostial cells (inflow valves). CBs are surrounded by pericardial cells (PCs; blue) on their ventrolateral side. PCs are divided into Tin-positive (blue) or Tin-negative PCs (not pictured). Bottom right, is a schematic representation of cross-section view of the DV lumen at stage 17. CBs on the opposite sides assume a crescent-like shape by contacting each other at the two dorsal and ventral apical sides, avoiding contact at the luminal domains, therefore making a hollow space in between. Unc-5 and NetB have been proposed to play a role in the formation of the hollow space between each CB on each row and its counterpart on the opposite row [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0148526#pone.0148526.ref009" target="_blank">9</a>].