Author response: Glial and neuronal Semaphorin signaling instruct the development of a functional myotopic map for Drosophila walking

Abstract

Motoneurons developmentally acquire appropriate cellular architectures that ensure connections with postsynaptic muscles and presynaptic neurons. In Drosophila, leg motoneurons are organized as a myotopic map, where their dendritic domains represent the muscle field. Here, we investigate mechanisms underlying development of aspects of this myotopic map, required for walking. A behavioral screen identified roles for Semaphorins (Sema) and Plexins (Plex) in walking behavior. Deciphering this phenotype, we show that PlexA/Sema1a mediates motoneuron axon branching in ways that differ in the proximal femur and distal tibia, based on motoneuronal birth order. Importantly, we show a novel role for glia in positioning dendrites of specific motoneurons; PlexB/Sema2a is required for dendritic positioning of late-born motoneurons but not early-born motoneurons. These findings indicate that communication within motoneurons and between glia and motoneurons, mediated by the combined action of different Plexin/Semaphorin signaling systems, are required for the formation of a functional myotopic map.

Misregulation of Drosophila Sidestep Leads to Uncontrolled Wiring of the Adult Neuromuscular System and Severe Locomotion Defects

“…Largely unknown are also the guidance factors that establish the adult neuromuscular pattern. Amongst classical axon guidance molecules, only Semaphorins and their receptors, plexins have been functionally examined in the imago (Syed et al, 2016). Downregulation of Semaphorin-1a or Plexin-A in leg motor neurons using transgenic RNA interference (RNAi) led to defasciculation defects in the leg nerve and axonal stalls at the level of femur muscles.…”

“…Downregulation of Semaphorin-1a or Plexin-A in leg motor neurons using transgenic RNA interference (RNAi) led to defasciculation defects in the leg nerve and axonal stalls at the level of femur muscles. These flies showed irregular footprint patterns and leg dragging phenotypes on carbon soot-coated glass slides, suggesting that these genes are required for the establishment of functional motor circuits (Syed et al, 2016).…”