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 rat parotid gland, kidney, small intestine and keratinized epithelium was further analysed at the level of its mRNA by in situ hybridization and correlated to immunohistochemical results using polyclonal anti-DNase I antibodies. High amounts of DNase I-specific mRNA and immunoreactivity were detected in the parotid gland, kidney and small intestine in agreement with previous immunohistochemical results. In the parotid gland, both the DNase I-specific mRNA and antigenicity were detected within the secretory cells. In the kidney, DNase I gene transcripts were 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 shown to express DNase I-specific mRNA; the highest level being detected within the enterocytes along the lower third of the villi. In contrast, the highest level of immunoreactivity was found in enterocytes covering the middle and upper thirds of the villi. Within the stratified epithelium of the tongue, DNase I gene transcription and protein expression started in lower parts of the stratum spinosum and reached into the stratum granulosum. However, the gradient of DNase I gene transcript expression appeared to be shifted to lower layers of the stratum spinosum when compared to DNase I immunoreactivity. No Dnase I expression was found in the keratinocytes of the basal cell layer. The results obtained for the small intestine and stratified epithelium allowed a temporal analysis of the time course of DNase I expression at the level of mRNA and protein: DNase I-specific mRNA peaked before protein biosynthesis. In contrast, apoptotic elimination of the terminally differentiated entero- and keratinocytes was shown to occur only at the uppermost villar tips or underneath the keratinized layer, as demonstrated by in situ end-labelling of free 3′-OH ends of cleaved DNA.