We investigated by RT PCR whether PROG activated expression of transcription factors : Egr 1 ( Krox 24 ) Egr 2 ( Krox 20 ) , Egr 3 , c jun , jun B , jun D , c Fos , Fos B , Fra 1 , Fra 2 , CREB , ATF 4 , SCIP and Sox 10 in cultured Schwann cells . ^^^