Department of Zoology, University of Cambridge, Cambridge, CB2 3EJ, UK.
BMC Evol Biol. 2012 Jun 28;12:103. doi: 10.1186/1471-2148-12-103.
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.
当简单序列重复整合到功能基因中时，它们可能充当进化的“调谐旋钮”，提供丰富的遗传变异，而几乎没有多效有害影响的风险。面部形状和长度的遗传变异就是这种现象的一个可能例子。 runt 相关转录因子 2（RUNX2）参与成骨细胞分化，包含一个具有功能重要的谷氨酰胺和丙氨酸氨基酸串联重复。该蛋白中的谷氨酰胺与丙氨酸的比例（QA 比）似乎影响着骨骼发育的调节。值得注意的是，在犬科的家养品种中，以及在所有食肉目中，谷氨酰胺与丙氨酸的比率与面部长度强烈相关。
在这项研究中，我们研究了这种相关性是否适用于胎盘哺乳动物，特别是那些面部长度变化较大且与适应行为和生活方式相关的哺乳动物（例如灵长类动物、非洲有蹄类动物、异关节类动物）。我们获得了 41 种哺乳动物的相对面部长度测量值和 RUNX2 序列，代表了 12 个目。我们使用了一种基于进化的广义最小二乘法模型和一种新开发的贝叶斯比较方法，在控制了进化率和分歧时间的情况下，检验了遗传和形态数据之间的相关性。非食肉目动物的谷氨酰胺-丙氨酸比率普遍明显低于食肉目动物（灵长类动物和异关节类动物的平均值分别为 1.34 和 1.25，而食肉目动物的平均值为 3.1），我们在胎盘哺乳动物中没有发现 RUNX2 序列与面部长度之间的相关性。
我们对多种比较进化分析的结果表明，QA 比在 41 种被考虑的哺乳动物中与面部长度不一致相关。因此，尽管 RUNX2 可能在食肉目中作为一种调节面部长度的“调谐旋钮”发挥作用，但这种关系在一般哺乳动物中并不保守。
