IN-SITU HYBRIDIZATION STUDY OF CYTOKERATIN-4, CYTOKERATIN-13, CYTOKERATIN-16 AND CYTOKERATIN-19 MESSENGER-RNAS IN HUMAN DEVELOPING JUNCTIONAL EPITHELIUM

Cytokeratins (CKs) are now considered to be reliable markers for follo wing the development and differentiation of epithelial tissue. We have investigated the pathway of differentiation in human developing junct ional epithelium using monoclonal antibodies and two-dimensional gel e lectrophoresis of microdissected tissue to identify CK 19, CK 16, CK 1 4, CK 13, CK 6, CK 5, CK 4 in the junctional epithelium (JE) over part ially erupted human teeth. The CK profile was similar to that of devel oping oral epithelia, suggesting that the junctional epithelium in tee th during eruption is of odontogenic origin. The present study used in situ hybridization to determine the distribution of the mRNAs of CKs 19, 16, 13 and 4 in human developing junctional epithelium and to exam ine the correlation between mRNAs and their encoded proteins. CK 19 mR NA was abundant in the basal cell layers of the primary junctional epi thelium (PJE) but less concentrated in the suprabasal layers. CK16, 13 and 4 mRNAs were abundant in the basal cell layers of the PJE. The pa rabasal cell layers reacted intensely to the cRNA probe complementary to CK16 mRNA, as were the reactions in the suprabasal cell layers of t he PJE for the CK 13 and 4 probes. Our results demonstrate that the PJ E express the genes encoding far CKs 16 and 4 that have been revealed previously only by electrophoresis. They therefore confirm that the PJ E is a well-differentiated stratified epithelium with a complex unique phenotype that produces CKs specific for basal cells (CK 19), CKs ass ociated with hyperproliferation (CK 16), and finally those associated with stratification (CKs 4 and 13). Only synthesis of CK 19 protein an d mRNA are strictly parallel. CKs 4 and 13 mRNAs are present in basal and suprasal cells, while their encoded proteins were not, except for CK 13 in suprabasal cell layers of PJE, where the amount of its mRNAs was coincident with the expression of the protein.