A Phylogenetic Assembly and Positive Selection Analysis of the DMP1 Gene in Aves, Testudines and Crocodilia

The DMP1 gene codes for proteins that play a role in the calcification of hard tissues, including dentin, in vertebrates. Deleterious mutations in the gene can cause genetic disorders such as rickets in humans. The gene function, however, has only been investigated widely within mammalian lineages, and has not been thoroughly researched within sauropsids (reptiles and birds). Birds are edentulous (toothless) and have a unique bone structure that allows a majority of species to withstand the rigors of flight. In contrast, their closest living relatives, the crocodilians, are polydontous and possess dense skeletons as an adaptation to their semi-aquatic lifestyle. In the present study, we attempt to identify DMP1 gene sites that have been positivity selected for within 185 extant taxa: Crocodilians (crocodiles, alligators, and gharials), Testudines (turtles and tortoises), and Aves (birds). Given the unique bone characteristics of these three groups, we explored the evolutionary history of the DMP1 gene. Individual sites analyses for Aves, Crocodilia, Testudines, Palaeognathae, and Galloanserae, yielded significant positive selection sites for Aves: 39, Crocodilia:1, Testudines:1, and Palaeognathae:2. No positively selected sites were found on the branches leading to penguins or the kakapo, while there were seven positively selected sites identified on the branch leading to Pleurodira. Five distinct DMP1 isoforms and 24 conserved motifs were identified in Crocodilia, Testudines, and Aves