To address the consequences of precocious ETS signaling for proprioceptive afferent differentiation, we next expressed EWS-Pea3 in DRG neurons as soon as they became post-mitotic. We used a binary mouse genetic system based on Cre-recombinase-mediated excision of a transcriptional stop cassette flanked by loxP sites. Targeting cassettes were integrated into the Tau locus to generate two strains of mice conditionally expressing either EWS-Pea3 or a membrane-targeted green fluorescent protein (mGFP) to trace axonal projections of DRG neurons (Figure S3; [25]). Embryos positive for either Isl1Cre/+ and TauEWS-Pea3/+ or Isl1Cre/+ and TaumGFP/+ alleles showed efficient activation of the silent Tau allele in 95% or more of all DRG neurons, including proprioceptive afferents, at all segmental levels (Figure S3).