Two models for communicating signals from the node to the left lateral plate. A cartoon representation (not to scale) of a section through the left side of the embryo, including the left side of the node (as represented in Figure 2) and tissues lateral to the node. The cells of the node are shown in blue, the endoderm in green, the ectoderm in red, paraxial mesoderm in yellow and lateral plate mesoderm in purple. Viotti and colleagues'  and Saund and colleagues' work  argues that calcium signaling, via gap junctions, carries signals from the node leftwards through the endoderm. Oki and colleagues' analyses  argue that Nodal protein itself travels leftwards through an extracellular, but intraembryonic, route and directly activates the Nodal locus in the lateral plate.