Diagram of axial patterning genes in early amphioxus development of amphioxus. In the late blastula, Nodal/Vg1 signaling, presumably opposed by Lefty marks the future dorsal side (D) of the embryo, while FoxQ2 marks the anterior ectoderm. At the onset of gastrulation, dorsal Nodal/Vg1 signaling becomes opposed by BMP signaling in the mesendoderm. BMP signaling is modulated by several dorsally and anteriorly expressed genes. Wnt8 is expressed throughout the future mesendoderm, most strongly in the rim of the forming blastopore, which will be the posterior pole of the embryo. By the early gastrula, additional modulators of Nodal/Vg1 and BMP signaling, Evx, a marker of ventral ectoderm, and the neuroectoderm marker Sox1/2/3 are first expressed. A= anterior pole, An = animal pole, P= posterior pole, V= ventral.