To explore the function of genes expressed in adult mouse nociceptive neurons, we generated heterozygous knock-in mice expressing the tamoxifen-inducible Cre recombinase construct CreERT2 downstream of the Na(V)1.8 promoter. CreERT2 encodes a Cre recombinase (Cre) fused to a mutant estrogen ligand-binding domain (ERT2) that requires the presence of tamoxifen for activity. We have previously shown that heterozygous Na(V)1.8-Cre mice will delete loxP flanked genes specifically in nociceptive sensory neurons from embryonic day 14. We therefore used the same strategy of homologous recombination and mouse generation, substituting the Cre cassette with CreERT2. No functional Cre recombinase activity was found in CreERT2 mice crossed with reporter mice in the absence of tamoxifen. We found that, as with Na(V)1.8-Cre mice, functional Cre recombinase was present in nociceptive sensory neurons after tamoxifen induction in vivo. However, the percentage of dorsal root ganglion (DRG) neurons expressing functional Cre activity was much reduced (<10% of the number found in the Na(V)1.8-Cre mouse). We also examined Cre recombinase activity in sensory neurons in culture. After treatment with 1 muM tamoxifen for 48 h, 15% of DRG neurons showed Cre activity. Na(V)1.8-CreERT2 animals may thus be useful for single cell studies of the functional consequences of gene ablation in culture, but are unlikely to be useful for behavioral studies.
Copyright 2006 Wiley-Liss, Inc.