Comparison of c‐jun, junB, and junD mRNA expression and protein in the rat dorsal root ganglia following sciatic nerve transection

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Abstract
The present study was designed to compare the expression of the Jun family of protooncogenes following nerve injury. Adult rats were anesthetized and the sciatic nerve transected. Dorsal root ganglia (DRG) at 1, 2, 3, and 7 days after nerve transection were collected, their total RNA extracted, and Northern blots performed using 32P‐labeled oligonucleotide probes. The constitutive expression of c‐jun mRNA was very low in DRG. Induction of c jun mRNA was observed by day 1 after nerve transection, with a sixfold peak at 3 stays and a twofold induction still present by day 7. The constitutive expression of junB mRNA was also low in the DRG, and sciatic nerve transection produced only a modest induction (1.7fold by day 3) in the DRG ipsilateral to the nerve cut. junD mRNA was constitutively expressed at high levels in the DRG, and its level of expression did not change after sciatic nerve transection. Immunocytochemistry studies demonstrated a pattern of c‐Jun, JunB, and JunD immunoreactivity (IR) associated with the cell nuclei of DRG neurons. c‐Jun IR was found at very low levels in the undamaged contralateral DRG neurons, but sciatic nerve transection dramatically increased the number of c‐Jun‐immunoreactive neurons. Dot blot immunoblotting assay confirmed that the DRG ipsilateral to the sciatic nerve cut contained a higher level of c‐Jun protein than the contralateral control DRG. Similar to c‐Jun IR, JunB IR was minimal in the undamaged contralateral DRAG. However, the DRG ipsilateral to the nerve transection did not show an increase in the number of immunoreactive neurons. JunD protein was expressed at high levels in the contralateral DRG, and this level of expression persisted after sciatic nerve transection in the ipsilateral DRG. DNA gel retardation assay experiments with an AP‐1 consensus sequence showed a single DNA‐protein complex. This complex was increased in ipsilateral as compared with contralateral DRG extracts. The amount of DNA protein complex was reduced byc‐Jun protein antiserum but was not altered when treated with a Fos antibody. We conclude that cjun, junB and junD mRNAs and proteins are differentially regulated in the DRG after sciatic nerve transection.