LOCALIZATION OF DEOXYRIBONUCLEASE-I GENE TRANSCRIPTS AND PROTEIN IN RAT-TISSUES AND ITS CORRELATION WITH APOPTOTIC CELL ELIMINATION

The expression and distribution of deoxyribonuclease I (DNase I) in ra t parotid gland, kidney, small intestine and keratinized epithelium wa s further analysed at the level of its mRNA by in situ hybridization a nd correlated to immunohistochemical results using polyclonal anti-DNa se I antibodies. High amounts of DNase I-specific mRNA and immunoreact ivity were detected in the parotid gland, kidney and small intestine i n agreement with previous immunohistochemical results. In the parotid gland, both the DNase I-specific mRNA and antigenicity were detected w ithin the secretory cells. In the kidney, DNase I gene transcripts wer e localized in distal tubules and the collecting duct system. In this organ an identical localization of DNase I antigenicity was obtained. In the small intestine only the enterocytes covering the villi were sh own to express DNase I-specific mRNA; the highest level being detected within the enterocytes along the lower third of the villi. In contras t, the highest level of immunoreactivity was found in enterocytes cove ring the middle and upper thirds of the villi. Within the stratified e pithelium of the tongue, DNase I gene transcription and protein expres sion started in lower parts of the stratum spinosum and reached into t he stratum granulosum. However, the gradient of DNase I gene transcrip t expression appeared to be shifted to lower layers of the stratum spi nosum when compared to DNase I immunoreactivity. No DNase I expression was found in the keratinocytes of the basal cell layer. The results o btained for the small intestine and stratified epithelium allowed a te mporal analysis of the time course of DNase I expression at the level of mRNA and protein: DNase I-specific mRNA peaked before protein biosy nthesis. In contrast, apoptotic elimination of the terminally differen tiated entero- and keratinocytes was shown to occur only at the upperm ost villar tips or underneath the keratinized layer, as demonstrated b y in situ end-labelling of free 3'-OH ends of cleaved DNA.