(D–F and J–L) Analysis of sensory afferent projections (green) into the skin (D and J) or muscle (E and K; red, α-Bungarotoxin, BTX) of wild-type (D–F) and TauEWS-Pea3/+ Isl1Cre/+ (J–L) embryos at E16.5 by Cre-recombinase-mediated activation of mGFP (D, E, J, and K) expression from the Tau locus. (F and L) show Egr3 expression in intrafusal muscle fibers using in situ hybridization (consecutive sections to [E and K] are shown).