The growth cones of identified motoneurons in embryonic zebrafish select appropriate pathways in the absence of specific cellular interactions.

Developing motoneurons in zebrafish embryos follow a stereotyped sequence of axonal outgrowth and accurately project their axons to cell-specific target muscles. During axonal pathfinding, an identified motoneuron pioneers the peripheral motor pathway. Growth cones of later motoneurons interact with the pioneer via contact, coupling, and axonal fasciculation. In spite of these interactions, ablation of the pioneer motoneuron does not affect the ability of other identified motoneurons to select the pathways that lead to appropriate target muscles. We conclude that interactions between these cells during pathfinding are not required for accurate pathway selection.