Proprioception is governed by highly diverse and versatile sensory neuron types

Proprioceptive neurons (PNs) are essential for the proper execution of all our movements by providing muscle sensory feedback to the central motor network. Here, using deep single cell RNAseq of adult PNs coupled with advanced virus- and genetic tracings, we have molecularly identified the 3 main types of PNs (Ia, Ib and II) and unexpectedly found that they segregate into 8 subgroups. Our data further reveal a highly sophisticated organization of PNs into discrete sensory input channels with distinct spatial distribution, innervation patterns and molecular profiles, that together contribute to the sensory monitoring of complex motor behavior. Moreover, while Ib- and II-PN subtypes are specified around birth, Ia-PN subtypes diversify later along with increased motor activity and show versatility in the adult following exercise training, suggesting adaptive proprioceptive function. Exploring the molecular heterogeneity of mouse proprioceptors at different developmental stages (E16.5, P5 and P54)