Distal cis-regulatory elements are required for tissue-specific expression of enamelin (Enam)

Enamel formation is orchestrated by the sequential expression of genes encoding enamel matrix proteins; however, the mechanisms sustaining the spatio-temporal order of gene transcription during amelogenesis are poorly understood. The aim of this study was to characterize the cis-regulatory sequences necessary for normal expression of enamelin (Enam). Several enamelin transcription regulatory regions, showing high sequence homology among species, were identified. DNA constructs containing 5.2 or 3.9 kb regions upstream of the enamelin translation initiation site were linked to a LacZ reporter and used to generate transgenic mice. Only the 5.2-Enam-LacZ construct was sufficient to recapitulate the endogenous pattern of enamelin tooth-specific expression. The 3.9-Enam-LacZ transgenic lines showed no expression in dental cells, but ectopic beta-galactosidase activity was detected in osteoblasts. Potential transcription factor-binding sites were identified that may be important in controlling enamelin basal promoter activity and in conferring enamelin tissue-specific expression. Our study provides new insights into regulatory mechanisms governing enamelin expression.