Fig. 1. An intersectional genetic labeling strategy for proprioceptive muscle afferents.

a Schematic rendering of the groups Ia, II and Ib proprioceptor subtypes labeled in mice carrying a PV:Cre, Rx3:FlpO, and the double stop Ai65:tdTomato allele (PVRx3:tdT). In sensory neurons that co-express PV and Rx3, the dual activity of Cre and FlpO recombinases will allow expression of the tdTomato reporter. b Expression of Runx3, PV, and tdTomato in DRG at p2 indicates efficient induction of the tdTomato reporter in PV⁺Rx3⁺ sensory neurons, but not in PV⁺Rx3^off (arrowhead in ii) or PV^offRx3⁺ (arrow in ii) neurons (i and ii are independent images). c Efficiency of tdTomato reporter induction in T10, L2, and L5 DRG in p2 PVRx3:tdT mice. Mean percentage ± S.E.M. of tdT⁺PV⁺Rx3⁺ neurons (of all PV⁺Rx3⁺) per ganglia for T10: 98.0 ± 1.3%, for L2: 94.4 ± 2.5%, for L5: 94.8 ± 1.9%; n = 6 DRG per segmental level. Number of sections per T10 DRG: 7, 6, 6, 7, 7, 8; Number of sections per L2 DRG: 7, 3, 6, 5, 8, 7; Number of sections per L5 DRG: 9, 8, 10, 6, 7, 10. d tdTomato expression in vGlut1⁺ muscle spindle (MS) and Golgi tendon organ (GTO) afferent terminals in p10 EDL muscle of PVRx3:tdT animals. Diagram depicts muscle with red boxes showing areas in images below. Expression of tdTomato in Merkel cell afferents present in hind paw glabrous skin (e) and in SubstanceP(SubP)^off sensory neurons that appear to innervate the nail of forepaw digits (f) of adult (≥p56) PVRx3:tdT mice. Diagram depicts foot paw with red boxes showing areas in images below. In e, Merkel cells are indicated by expression of Troma1. i, ii show higher magnifications of boxed areas in e, f; ii shows tdTomato expression. Similar data obtained from at least three (b, d, e) biological replicates. In boxplot (c), boxes indicate medians and 25th/75th percentiles, and whiskers extend to the furthest point <1.5 standard deviations from the mean. Scale 20 (b) or 50 (d–f) μm.