Department of Biology, University of Konstanz, 78457 Konstanz, Germany.
Development and Neurobiology Program, Jacques Monod Institute, 75013 Paris, France.
Evodevo. 2010 Nov 3;1(1):11. doi: 10.1186/2041-9139-1-11.
The modern coelacanth (Latimeria) is the extant taxon of a basal sarcopterygian lineage and sister group to tetrapods. Apart from certain apomorphic traits, its morphology is characterized by a high degree of retention of ancestral vertebrate structures and little morphological change. An insight into the molecular evolution that may explain the unchanged character of Latimeria morphology requires the analysis of the expression patterns of developmental regulator genes and their cis-regulatory modules (CRMs).
We describe the comparative and functional analysis of the sonic hedgehog (shh) genomic region of Latimeria menadoensis. Several putative enhancers in the Latimeria shh locus have been identified by comparisons to sarcopterygian and actinopterygian extant species. Specific sequence conservation with all known actinopterygian enhancer elements has been detected. However, these elements are selectively missing in more recently diverged actinopterygian and sarcopterygian species. The functionality of the putative Latimeria enhancers was confirmed by reporter gene expression analysis in transient transgenic zebrafish and chick embryos.
Latimeria shh CRMs represent the ancestral set of enhancers that have emerged before the split of lobe-finned and ray-finned fishes. In contrast to lineage-specific losses and differentiations in more derived lineages, Latimeria shh enhancers reveal low levels of sequence diversification. High overall sequence conservation of shh conserved noncoding elements (CNE) is consistent with the general trend of high levels of conservation of noncoding DNA in the slowly evolving Latimeria genome.
现代腔棘鱼（Latimeria）是基干肉鳍鱼的现存分类群，是四足动物的姐妹群。除了某些特化特征外，其形态特征还表现出高度保留祖先脊椎动物结构和很少形态变化。要深入了解可能解释腔棘鱼形态不变的分子进化，需要分析发育调节基因及其顺式调控模块（CRMs）的表达模式。
我们描述了拉蒂迈鱼（Latimeria menadoensis） sonic hedgehog（shh）基因组区域的比较和功能分析。通过与肉鳍鱼和硬骨鱼现存物种的比较，在拉蒂迈鱼 shh 基因座中鉴定出了几个推定的增强子。已经检测到与所有已知硬骨鱼增强子元件的特定序列保守性。然而，这些元件在最近分化的硬骨鱼和肉鳍鱼物种中选择性缺失。通过瞬时转基因斑马鱼和鸡胚的报告基因表达分析，证实了推定的拉蒂迈鱼增强子的功能。
拉蒂迈鱼 shh CRMs 代表了在有颌类和无颌类鱼类分化之前出现的祖先增强子集。与衍生谱系中的谱系特异性缺失和分化相反，拉蒂迈鱼 shh 增强子显示出较低的序列多样化水平。shh 保守非编码元件（CNE）的总体序列高度保守与缓慢进化的拉蒂迈鱼基因组中非编码 DNA 高水平保守的总体趋势一致。
