CP27 transgenic strategies reveal dental lamina expression and enamel phenotypes

CP27 is a unique gene product expressed during early embryogenesis and tooth formation. In recent studies, we have shown that CP27 affects viability, proliferation, attachment and gene expression in vitro and is necessary for cell survival and differentiation during tooth morphogenesis in organ culture. Objective: To define CP27 expression in tooth development and to determine the effect of CP27 on enamel formation. Methods: In order to determine CP27 expression patterns, antisense probes for CP27 in situ hybridization from full-length CP27 cDNA were generated and mRNA localization patterns were analyzed on paraffin sections of E10-3dpn tooth organs. Expression patterns were verified using (i) a CP27 promoter-driven beta-galactosidase (b-gal) transgenic mouse and (ii) a heterozygous knock-in model replacing CP27 exon 1 with b-gal were generated and whole-mount lacZ stainings were performed and analyzed. Finally, a K14-driven, CP27 overexpressing mouse was created to probe the effect of CP27 overexpression in epithelial tissues. Results: In situ hybridization established strong CP27 expression in dental papilla cells and odontoblasts, in the outer and inner enamel epithelium, in the dental follicle, and in developing alveolar bone. Specific labeling of the ƒ"-gal reporter gene driven by our cp27 promoter was detected in both the incisor and molar tooth organs. In CP27-lacZ knock-in mice, CP27 signals were detected as early as mouse embryonic stage E9 in the dental lamina and in developing tooth organs thereafter. K14-CP27 overexpressing mice featured 56 percent reduction in enamel thickness, wide cracks in the enamel layer, and densely packed, parallel enamel crystals without prismatic organization. Conclusion: CP27 is expressed throughout tooth development starting as early as E9. Enamel defects in CP27 overexpressing mice suggest a role for CP27 during enamel formation. Funding by NIH grant DE13095 is gratefully acknowledged.