The Study of Sensorimotor Circuit Assembly in Embryos and Larvae.

In animals, movement is generated by the activity of motor circuits housed in the vertebrate spinal cord or the arthropod nerve cord. How motor circuits form is a fundamental question, with wide-ranging impacts on the fields of development, neurobiology, medicine, evolution, and beyond. Until recently, studying circuit assembly had been experimentally difficult, with a paucity of suitable models. Due to the introduction of novel neuroscience tools (calcium imaging, optogenetics, connectomics), embryos and larvae can be used as models to study motor circuit assembly. Here, we briefly review the knowledge relevant to motor circuit assembly in larvae. We discuss the larval body and its movements, larval neurons and circuits in the motor system, and how the generation of neural diversity starting from stem cells relates to circuit formation. The long-term goal of research in this field is to identify developmental rules, determine when the rules apply, generate an integrated understanding of motor circuit development, and uncover molecular mechanisms driving the assembly process. Motor circuits are an ancient part of the nervous system, and so far, the developmental programs guiding motor circuit assembly appear to be largely conserved across phyla. Thus, as methods improve in other systems, findings in will provide foundational concepts that will inspire hypotheses in those systems.