Cell morphology in amphioxus nerve cord may reflect the time course of cell differentiation.

Amphioxus embryos elongate following neurulation, and this lengthens the developing nerve cord. Most neurons and support cells remain attached at their apices to the neuroepithelium, and the apices themselves become correspondingly longer. In consequence, apex length can be used in some instances as a measure of whether a given cell last divided before elongation or after, and approximately when. The data indicate that most floorplate, ependymoglial and infundibular cells are generated comparatively early, before most neurons. Among the neurons, the segmentally arranged DC (dorsal compartment) motoneurons appear to be among the first to develop, which accords with molecular data on the time course of neural development, using neurogenin and islet as markers.