Aïssani B, Bernardi G
Laboratoire de Génétique Moléculaire, Institut Jacques Monod, Paris, France.
Gene. 1991 Oct 15;106(2):173-83. doi: 10.1016/0378-1119(91)90197-j.
We have investigated the distribution of unmethylated CpG islands in vertebrate genomes fractionated according to their base composition. Genomes from warm-blooded vertebrates (man, mouse and chicken) are characterized by abundant CpG islands, whose frequency increases in DNA fractions of increasing % of guanine + cytosine; % G + C (GC), in parallel with the distribution of genes and CpG doublets. Small, yet significant, differences in the distribution of CpG islands were found in the three genomes. In contrast, genomes from cold-blooded vertebrates (two reptiles, one amphibian, and two fishes) were characterized by an extreme scarcity or absence of CpG islands (detected in these experiments as HpaII tiny fragments or HTF). CpG islands associated with homologous genes from cold- and warm-blooded vertebrates were then compared by analyzing CpG frequencies, GC levels, HpaII sites, rare-cutter sites and G/C boxes (GGGGCGGGGC and closely related motifs) in sequences available in gene banks. Small, yet significant, differences were again detected among the CpG islands associated with homologous genes from warm-blooded vertebrates, in that CpG islands associated with mouse or rat genes often showed low CpG and/or GC levels, as well as low numbers of HpaII sites, rare-cutter sites and G/C boxes, compared to homologous human genes; more rarely, CpG islands were just absent. As far as cold-blooded vertebrates were concerned, a number of genes showed CpG islands, which exhibited a much lower frequency of CpG doublets than that found in CpG islands of warm-blooded vertebrates, but still approached the statistically expected frequency; none of the other features of CpG islands associated with genes from warm-blooded vertebrates were present. Other genes did not show any associated CpG islands, unlike their homologues from warm-blooded vertebrates.
我们研究了根据碱基组成进行分级分离的脊椎动物基因组中未甲基化的CpG岛的分布情况。温血脊椎动物（人类、小鼠和鸡）的基因组以丰富的CpG岛为特征，其频率在鸟嘌呤+胞嘧啶（%G + C，即GC）含量增加的DNA组分中升高，这与基因和CpG双联的分布情况平行。在这三个基因组中发现了CpG岛分布的微小但显著的差异。相比之下，冷血脊椎动物（两种爬行动物、一种两栖动物和两种鱼类）的基因组特征是CpG岛极度稀少或不存在（在这些实验中被检测为HpaII微小片段或HTF）。然后，通过分析基因库中可用序列的CpG频率、GC水平、HpaII位点、稀有切割酶位点和G/C盒（GGGGCGGGGC及密切相关的基序），比较了冷血和温血脊椎动物同源基因相关的CpG岛。在温血脊椎动物同源基因相关的CpG岛之间再次检测到微小但显著的差异，即与小鼠或大鼠基因相关的CpG岛，与同源人类基因相比，通常显示出较低的CpG和/或GC水平，以及较少的HpaII位点、稀有切割酶位点和G/C盒；更罕见的情况是，CpG岛完全不存在。就冷血脊椎动物而言，一些基因显示出CpG岛，其CpG双联的频率比温血脊椎动物的CpG岛中发现的频率低得多，但仍接近统计预期频率；与温血脊椎动物基因相关的CpG岛的其他特征均不存在。其他基因未显示任何相关的CpG岛，这与它们来自温血脊椎动物的同源基因不同。
