Abstract
Loss of tooth or enamel is widespread in multiple mammal lineages. Although several studies have been reported, the evolutionary mechanisms of tooth/enamel loss are still unclear. Most previous studies have found that some tooth-related genes have been inactivated in toothless and/or enamel-less mammals, such as ENAM, ODAM, C4orf26, AMBN, AMTN, DSPP, etc. Here, we conducted evolutionary analyses on ACPT playing a key role in amelogenesis, to interrogate the mechanisms. We obtained the ACPT sequences from 116 species, including edentulous and enamel-less mammals. The results shows that variant ORF-disrupting mutations were detected in ACPT coding region among nine edentulous baleen whales and three enamel-less taxa (pygmy sperm whale, aardvark, nine-banded armadillo). Furtherly, selective pressure uncovered that the selective constraints have been relaxed among all toothless and enamel-less lineages. Moreover, our results support the hypothesis that mineralized teeth were lost or degenerated in the common ancestor of crown Mysticeti through two shared single-base sites deletion in exon 4 and 5 of ACPT among all living baleen whales. DN/dS values on transitional branches were used to estimate ACPT inactivation records. In the case of aardvark, inactivation of ACPT was estimated at ~23.60–28.32 Ma, which is earlier than oldest aardvark fossil record (Orycteropus minutus, ~19 Ma), suggesting that ACPT inactivation may result in degeneration or loss of enamel. Conversely, the inactivation time of ACPT estimated in armadillo (~10.18–11.30 Ma) is later than oldest fossil record, suggesting that inactivation of ACPT may result from degeneration or loss of enamel in these mammals. Our findings suggested that different mechanisms of degeneration of tooth/enamel might exist among toothless and enamel-less lineages during evolution. Our study further considered that ACPT is a novel gene for studying tooth evolution.
Highlights
Dental innovations have been regarded as the great success of mammalian evolution and adaptation (Ungar, 2010)
Premature stop codons were found in B. acutorostrata and B. bonaerensis, frameshift indels were found in baleen whales
ACPT is a novel candidate gene for studying mammalian tooth loss and enamel loss The well-conserved gene structure in extant species indicates that this organization and arrangement might be present in the last common mammalian ancestor, which represented the vital function for organisms (Madsen, 2009)
Summary
Dental innovations (such as differentiated dentitions and the evolution of tri-bosphenic molar) have been regarded as the great success of mammalian evolution and adaptation (Ungar, 2010). In spite of their importance for animal survival, teeth have been lost independently in multiple mammalian lineages, such as baleen whales and pangolins. Some lineages have lost their outer enamel of teeth, such as pygmy. How to cite this article Mu Y, Huang X, Liu R, Gai Y, Liang N, Yin D, Shan L, Xu S, Yang G. ACPT gene is inactivated in mammalian lineages that lack enamel or teeth. Tooth loss and/or enamel loss is one of the most important field for mammalian tooth evolution
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