Opazo Juan C, Zavala Kattina, Krall Paola, Arias Rodrigo A
Instituto de Ciencias Ambientales y Evolutivas, Universidad Austral de Chile , Valdivia , Chile.
Unidad de Nefrología, Universidad Austral de Chile , Valdivia , Chile.
PeerJ. 2017 Jan 26;5:e2901. doi: 10.7717/peerj.2901. eCollection 2017.
Understanding the processes that give rise to genomic variability in extant species is an active area of research within evolutionary biology. With the availability of whole genome sequences, it is possible to quantify different forms of variability such as variation in gene copy number, which has been described as an important source of genetic variability and in consequence of phenotypic variability. Most of the research on this topic has been focused on understanding the biological significance of gene duplication, and less attention has been given to the evolutionary role of gene loss. Gremlin 2 is a member of the DAN gene family and plays a significant role in tooth development by blocking the ligand-signaling pathway of BMP2 and BMP4. The goal of this study was to investigate the evolutionary history of gremlin 2 in cetartiodactyl mammals, a group that possesses highly divergent teeth morphology. Results from our analyses indicate that gremlin 2 has experienced a mixture of gene loss, gene duplication, and rate acceleration. Although the last common ancestor of cetartiodactyls possessed a single gene copy, pigs and camels are the only cetartiodactyl groups that have retained gremlin 2. According to the phyletic distribution of this gene and synteny analyses, we propose that gremlin 2 was lost in the common ancestor of ruminants and cetaceans between 56.3 and 63.5 million years ago as a product of a chromosomal rearrangement. Our analyses also indicate that the rate of evolution of gremlin 2 has been accelerated in the two groups that have retained this gene. Additionally, the lack of this gene could explain the high diversity of teeth among cetartiodactyl mammals; specifically, the presence of this gene could act as a biological constraint. Thus, our results support the notions that gene loss is a way to increase phenotypic diversity and that gremlin 2 is a dispensable gene, at least in cetartiodactyl mammals.
了解现存物种基因组变异产生的过程是进化生物学中一个活跃的研究领域。随着全基因组序列的可得性，可以量化不同形式的变异，如基因拷贝数变异，它被认为是遗传变异的一个重要来源，进而也是表型变异的来源。关于这个主题的大多数研究都集中在理解基因复制的生物学意义上，而对基因丢失的进化作用关注较少。Gremlin 2是DAN基因家族的成员，通过阻断BMP2和BMP4的配体信号通路在牙齿发育中发挥重要作用。本研究的目的是调查鲸偶蹄目哺乳动物中gremlin 2的进化历史，该类群具有高度不同的牙齿形态。我们的分析结果表明，gremlin 2经历了基因丢失、基因复制和速率加速的混合过程。虽然鲸偶蹄目的最后一个共同祖先拥有一个单一的基因拷贝，但猪和骆驼是仅有的保留了gremlin 2的鲸偶蹄目类群。根据该基因的系统发育分布和共线性分析，我们提出gremlin 2在5630万至6350万年前作为染色体重排的产物在反刍动物和鲸类的共同祖先中丢失。我们的分析还表明，gremlin 2在保留该基因的两个类群中的进化速率加快。此外，该基因的缺失可以解释鲸偶蹄目哺乳动物牙齿的高度多样性；具体来说，该基因的存在可能起到生物学限制的作用。因此，我们的结果支持了基因丢失是增加表型多样性的一种方式以及gremlin 2是一个可有可无的基因的观点，至少在鲸偶蹄目哺乳动物中是这样。
