Newton Axel H, Feigin Charles Y, Pask Andrew J
The School of BioSciences, The University of Melbourne, Victoria, 3010, Australia.
BMC Evol Biol. 2017 May 4;17(1):110. doi: 10.1186/s12862-017-0955-6.
Runt-related transcription factor 2 (RUNX2) is a transcription factor essential for skeletal development. Variation within the RUNX2 polyglutamine / polyalanine (QA) repeat is correlated with facial length within orders of placental mammals and is suggested to be a major driver of craniofacial diversity. However, it is not known if this correlation exists outside of the placental mammals.
Here we examined the correlation between the RUNX2 QA repeat ratio and facial length in the naturally evolving sister group to the placental mammals, the marsupials. Marsupials have a diverse range of facial lengths similar to that seen in placental mammals. Despite their diversity there was almost no variation seen in the RUNX2 QA repeat across individuals spanning the entire marsupial infraclass. The extreme conservation of the marsupial RUNX2 QA repeat indicates it is under strong purifying selection. Despite this, we observed an unexpectedly high level of repeat purity.
Unlike within orders of placental mammals, RUNX2 repeat variation cannot drive craniofacial diversity in marsupials. We propose conservation of the marsupial RUNX2 QA repeat is driven by the constraint of accelerated ossification of the anterior skeleton to facilitate life in the pouch. Thus, marsupials must utilize alternate pathways to placental mammals to drive craniofacial evolution.
runt相关转录因子2（RUNX2）是骨骼发育所必需的转录因子。RUNX2多聚谷氨酰胺/多聚丙氨酸（QA）重复序列内的变异与胎盘哺乳动物目内的面部长度相关，并且被认为是颅面多样性的主要驱动因素。然而，尚不清楚这种相关性是否存在于胎盘哺乳动物之外。
在这里，我们研究了胎盘哺乳动物的自然进化姐妹类群有袋动物中RUNX2 QA重复序列比率与面部长度之间的相关性。有袋动物的面部长度范围多样，类似于胎盘哺乳动物。尽管它们具有多样性，但在整个有袋动物亚纲的个体中，RUNX2 QA重复序列几乎没有变化。有袋动物RUNX2 QA重复序列的极端保守性表明它受到强烈的纯化选择。尽管如此，我们观察到重复序列的纯度出乎意料地高。
与胎盘哺乳动物目不同，RUNX2重复序列变异不能驱动有袋动物的颅面多样性。我们认为有袋动物RUNX2 QA重复序列的保守性是由前骨骼加速骨化的限制所驱动的，以促进育儿袋中的生活。因此，有袋动物必须利用与胎盘哺乳动物不同的途径来驱动颅面进化。
