Molecular blueprints for spinal circuit modules controlling locomotor speed
The flexibility of motor actions is ingrained in the diversity of neurons and how they are organized into functional circuit modules, yet our knowledge of the molecular underpinning of motor circuit modularity remains limited. Locomotion is a motor behavior characterized by sudden changes in speed and strength enabled by the coordinated recruitment of different motoneuron subtypes. Here we use adult zebrafish to link the molecular diversity of motoneurons and the rhythm-generating V2a interneurons with their modular circuit organization that is responsible for changes in locomotor speed. We show that the molecular diversity of motoneurons and V2a interneurons reflects their functional segregation into slow, intermediate or fast subtypes. Furthermore, we reveal shared molecular signatures between V2a interneurons and motoneurons of the three speed circuit modules. Overall, by characterizing how the molecular diversity of motoneurons and V2a interneurons relates to their function, connectivity and behavior, our study provides important insights not only into the molecular mechanisms for neuronal and circuit diversity for locomotor flexibility but also for charting circuits for motor actions in general. Overall design: To determine whether the functional subtypes of motoneurons and V2a (Chx10+) interneurons are molecularly distinct, we performed single-cell RNA sequencing respectively on adult islet1a:GFP and chx10:GFP transgenic zebrafish using SmartSeq2.