François M. Lambert, Didier Le Ray et al. dans eLife

Functional limb muscle innervation prior to cholinergic transmitter specification during early metamorphosis in Xenopus.
Lambert FM^*, Cardoit L, Courty E, Bougerol M, Thoby-Brisson M, Simmers J, Tostivint H, Le Ray D^*.
eLife 2018;7:e30693 doi: 10.7554/eLife.30693

François M. Lambert and Didier Le Ray are CR CNRS in the team “Organization and Adaptability of Motor Systems” (Team leader: Muriel Thoby-Brisson) at the Institut de Neurosciences Cognitives et Intégratives d’Aquitaine (INCIA)

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In vertebrates functional motoneurons are defined as differentiated neurons belonging to a motor network, activating muscle fibers and using acetylcholine as neurotransmitter.

Motoneurons and muscles develop simultaneously in the majority of species, and their development during embryogenesis follows quite stereotyped rules. In the frog Xenopus however, the appendicular neuromuscular system emerges during pre-metamorphosis, and limb motoneurons must reach their developing target muscles through a larval neuromuscular system, composed of already fully functional cholinergic neurons and muscles. In this study, researchers from the team “Organization and Adaptability of Motor Systems” at the Institut de Neurosciences Cognitives et Intégratives d’Aquitaine (UMR 5287) in collaboration with a team from the Muséum National d’Histoire Naturelle (UMR 7221, Paris) hypothesized that the axial myotomes and their innervation constitute a potential interfering environment for the newly developing appendicular neuromuscular system, and that consequently, the latter may have to follow particular developmental rules adapted to this unusual context. (Picture: left François M. Lambert and right Didier Le Ray) 

Combining various techniques of neuroanatomy, immunohistology, cell biology, electrophysiology and dynamic imaging, the authors demonstrate that during a brief pre-metamorphic period, the emerging limb motoneurons transiently express a non-cholinergic transmitter phenotype that involves glutamate, while exhibiting all other characteristics of typical vertebrate motoneurons. Congruously, pre-metamorphosis hindlimb muscles transiently expressed glutamate receptors instead of nicotinic receptor. This study demonstrates a novel context-dependent re-specification of neurotransmitter phenotype during neuromuscular system development.

Didier Le Ray / Francois M Lambert / INCIA / mailto: