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RUNX2 tandem repeats and the evolution of facial length in placental mammals
BioMed Central (2012)
  • Jason M Kamilar, University of Massachusetts Amherst
  • Marie A. Pointer
  • Vera Warmuth, University of Cambridge
  • Stephen GB Chester, Yale University
  • Frédéric Delsuc, Universite Montpellier
  • Nicholas I Mundy, University of Cambridge
  • Robert J. Asher, University of Cambridge
  • Brenda J. Bradley, Yale University
Background: When simple sequence repeats are integrated into functional genes, they can potentially act as
evolutionary ‘tuning knobs’, supplying abundant genetic variation with minimal risk of pleiotropic deleterious
effects. The genetic basis of variation in facial shape and length represents a possible example of this phenomenon. Runt-related transcription factor 2 (RUNX2), which is involved in osteoblast differentiation, contains a functionally important tandem repeat of glutamine and alanine amino acids. The ratio of glutamines to alanines (the QA ratio) in this protein seemingly influences the regulation of bone development. Notably, in domestic breeds of dog, and in carnivorans in general, the ratio of glutamines to alanines is strongly correlated with facial length.
In this study we examine whether this correlation holds true across placental mammals, particularly those mammals for which facial length is highly variable and related to adaptive behavior and lifestyle (e.g., primates, afrotherians, xenarthrans). We obtained relative facial length measurements and RUNX2 sequences for 41 mammalian species representing 12 orders. Using both a phylogenetic generalized least squares model and a
recently-developed Bayesian comparative method, we tested for a correlation between genetic and morphometric
data while controlling for phylogeny, evolutionary rates, and divergence times. Non-carnivoran taxa generally had
substantially lower glutamine-alanine ratios than carnivorans (primates and xenarthrans with means of 1.34 and
1.25, respectively, compared to a mean of 3.1 for carnivorans), and we found no correlation between RUNX2
sequence and face length across placental mammals.
Results of our diverse comparative phylogenetic analyses indicate that QA ratio does not consistently correlate with face length across the 41 mammalian taxa considered. Thus, although RUNX2 might function as a ‘tuning knob’ modifying face length in carnivorans, this relationship is not conserved across mammals in general.
  • Mammalian Evolution,
  • Prognathism,
  • Molecular evolution,
  • Primates,
  • Afrotheria,
  • Xenarthra,
  • Morphology
Publication Date
Summer June 28, 2012
Citation Information
Jason M Kamilar, Marie A. Pointer, Vera Warmuth, Stephen GB Chester, et al.. "RUNX2 tandem repeats and the evolution of facial length in placental mammals" BioMed Central (2012) p. 1 - 11
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Creative Commons License
This work is licensed under a Creative Commons CC_BY International License.