Drosophila IgSF proteins DIP-α and Dpr10 mediate stereotyped leg motor neuron axon branching

Coordinated animal movements fundamentally rely on the precise organization of neural circuits, particularly the accurate targeting and branching of motor neurons (MNs). These MNs project axons from the central nervous system to form highly specific terminal patterns on target muscles. Understanding the molecular mechanisms that guide this stereotyped axon branching is crucial for comprehending neural development and function. Current knowledge gaps exist in identifying the specific trans-synaptic adhesion molecules that orchestrate this intricate process, especially in the context of terminal axon arborization rather than initial pathfinding.

Researchers investigated the molecular mechanisms underlying stereotyped terminal axon branching in the Drosophila leg neuromuscular system. They focused on the role of interacting transmembrane Ig superfamily (IgSF) proteins, DIP-α (expressed in MNs) and Dpr10 (expressed in target muscles). The study utilized live imaging techniques to observe the dynamic establishment of precise terminal branching patterns. They analyzed the requirement for the DIP-α/Dpr10 interaction at different stages of development and assessed its impact on various leg MNs, correlating findings with the morphological complexity of the neurons and their muscle targets.

The study revealed that the stereotyped terminal branching of a specific subset of leg motor neurons in Drosophila is indeed mediated by the interaction between IgSF proteins DIP-α and Dpr10. This interaction is highly localized and temporally specific: it is required only after motor neuron axons have successfully reached the immediate vicinity of their muscle targets, suggesting a role in fine-tuning rather than initial guidance. Live imaging observations provided dynamic insights into this process. > Precise terminal branching patterns are gradually established through DIP-α/Dpr10-dependent interactions occurring between fine axon filopodia and the developing muscle targets. Furthermore, the degree to which different leg motor neurons depend on the DIP-α and Dpr10 interaction was found to vary. This differential dependence directly correlated with the morphological complexity of the individual motor neurons and their respective muscle targets, indicating a nuanced and context-dependent role for these adhesion proteins in shaping neural architecture.