In June of 2017 a group of dental researchers met at the NIDCR to discuss the future of enamel research and concluded, in a summary statement, that in the field of enamel research, a lack of models to study enamel formation and disease has hampered recent progress. The group concluded that more appropriate ameloblast- like cell lines, investment in organoid and chip technology and novel animal models could be used to advance the field. With respect to animal models, I believe enamel researchers suffer from not having enamel organ- specific Cre recombinase mutant mouse. For the past 2 decades enamel researchers have used the Krt14-Cre (keratin 14-Cre recombinase) mutant to study enamel-specific activities by cross breeding with various loxP mouse lines. The significant disadvantage of using the Krt14-Cre mouse for enamel research is that Krt14 is expressed in multiple tissues including skin, bronchial epithelia, tongue, trachea, salivary glands, and many more organs, and because of this many of the developed loxP mouse lines are not appropriate to study amelogenesis. For example, mRNA expression levels of the anion exchanger protein (Slc4a2/AE2), or the cystic fibrosis transmembrane conductance regulator (Cftr), increases ~ 6-fold and 3-fold respectively in the enamel organ during maturation stage (compared to secretory stage), and beyond tooth formation both genes are widely expressed in lung and pancreas and are critical to their development. Both Slc4a2-null and Cftr-null mice have severe enamel pathologies. To use the Krt14-Cre mutant mouse to study the role of either AE2fl/fl or Cftrfl/fl would have significant limitations because these animals would predictably suffer from multiple organ failures at a young age. I propose to develop two animal models with a knockin of Cre recombinase into the ameloblastin (Ambn) and odontogenic ameloblast-associated (Odam) gene loci such that Cre expression is limited to secretory ameloblasts and maturation ameloblasts respectively. The UG3 stage of this grant will be devoted to the development of these two animal models; Ambn-Cre and Odam-Cre, and the UH3 phase will validate these two animals as unique in vivo models to study amelogenesis. At the completion of this project data from these animals will be published, and both lines deposited in an appropriate facility such as the Mutamt Mouse Resource and Research Centers (MMRRC).
Enamel researchers have identified a need to develop new and novel animal models to expand our understanding of enamel development and disease. Having access to enamel organ-specific Cre recombinase mouse lines would be an invaluable addition to the tools currently available to researchers focused on various developmental pathways active during amelogenesis. We propose the development of two knockin mutant mouse lines, those being Ambn-Cre and Odam-Cre where expression is limited to secretory ameloblasts and maturation ameloblasts respectively.