Department of Computational Biology, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-15 Kashiwanoha, Kashiwa City, Chiba 277-0882, Japan.
Gene. 2012 Sep 1;505(2):324-32. doi: 10.1016/j.gene.2012.05.047. Epub 2012 Jun 12.
Coelacanths are known as "living fossils" because their morphology has changed very little from that in the fossil record. To elucidate why coelacanths have evolved so slowly is thus of primary importance in evolutionary biology. In the present study, we determined the entire sequence of the HOX cluster of the Tanzanian coelacanth (Latimeria chalumnae) and compared it with that of the Indonesian coelacanth (L. menadoensis), which was available in the literature. The most intriguing result was the extremely small genetic divergence between the two coelacanths. The synonymous divergence of the HOX coding region between the two coelacanths was estimated to be 0.07%, which is ~11-fold smaller than that of human-chimp. When we applied the estimated divergence time of the two coelacanths of 6 million years ago (MYA) and 30 MYA, which were proposed in independent mitochondrial DNA analyses, the synonymous substitution rate of the coelacanth HOX cluster was estimated to be ~11-fold and 56-fold smaller than that of human-chimp, respectively. Thus, the present study implies that the reduction of the nucleotide substitution rate in coelacanth HOX genes may account for the conservation of coelacanth morphology during evolution.
腔棘鱼被称为“活化石”，因为它们的形态与化石记录中的形态几乎没有变化。因此，阐明腔棘鱼为何进化如此缓慢，在进化生物学中至关重要。在本研究中，我们测定了坦桑尼亚腔棘鱼（Latimeria chalumnae）HOX 簇的全长序列，并与文献中提供的印度尼西亚腔棘鱼（L. menadoensis）进行了比较。最有趣的结果是两种腔棘鱼之间存在极小的遗传差异。这两种腔棘鱼的 HOX 编码区同义分歧估计为 0.07%，比人类-黑猩猩小约 11 倍。当我们应用独立的线粒体 DNA 分析提出的两种腔棘鱼 600 万年前（MYA）和 3000 万年前的估计分歧时间时，腔棘鱼 HOX 簇的同义替代率分别估计比人类-黑猩猩小约 11 倍和 56 倍。因此，本研究表明，腔棘鱼 HOX 基因中核苷酸替换率的降低可能导致腔棘鱼在进化过程中形态的保守。
