The minimum free energy of G-quadruplex-forming sequences of the MSX1 intron is associated with relative molar and premolar size in eutherians

The mammalian dentition is an important model for studying morphological diversity and evolutionary processes. The main characteristics contributing to this fact are its organization into interrelated modules and its self-regulated development by activating and inhibiting molecules. A previous study from our group showed that the minimum free energy of an intronic G-quadruplex (G4)-forming RNA sequence of Pax9 was correlated with the diversity of molar patterns in mammals. In this work, a similar approach was used to search for possible associations between the minimum free energy of RNA sequences in the MSX1 and the relative size of molars and premolars in eutherian mammals. A region (named hereby Int1Seq) located at the beginning of the first intron presented a significant correlation between its minimum free energies and molar and premolar relative sizes. This region presented high sequence diversity, and in many species, it had the ability to form a stable G-quadruplex (G4). Besides the correlation analyses, when Int1Seq minimum free energies were used as a proxy of the activator molecules, it also increased the correlation between molar proportions in the inhibitory molar cascade model, as well as in the molar-module-component and premolar-molar-module models. Our results indicate this region, located in the MSX1 intronic sequences, is involved in the patterning of posterior teeth and reinforces the role of G4 sequences in the diversification of mammalian dentition. Graphic abstract: The exon-intron structure of the human MSX1 gene with emphasis on the position and relationship between the minimum free energies of the Int1Seq secondary structure and molar ratios for Saimiri sciureus, Mus musculus, Homo sapiens, and Bos taurus*. *The images of the dental arches are for illustrative purposes only and do not represent the skulls of the specimens used for measurements in this study. (Figure presented.)