Structural and functional analysis of a 0.5-Mb chicken region orthologous to the imprinted mammalian Ascl2/Mash2-Igf2-H19 region.
Structural and functional analysis of a 0.5-Mb chicken region orthologous to the imprinted mammalian Ascl2/Mash2-Igf2-H19 region.
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DOI：
10.1101/gr.2609605
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发表时间：
2005
期刊：
影响因子：
7
通讯作者：
T. Yokomine;H. Shirohzu;Wahyu Purbowasito;A. Toyoda;H. Iwama;K. Ikeo;T. Hori;S. Mizuno;M. Tsudzuki;Y. Matsuda;M. Hattori;Y. Sakaki;H. Sasaki
中科院分区：
文献类型：
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作者：
T. Yokomine;H. Shirohzu;Wahyu Purbowasito;A. Toyoda;H. Iwama;K. Ikeo;T. Hori;S. Mizuno;M. Tsudzuki;Y. Matsuda;M. Hattori;Y. Sakaki;H. Sasaki
先前的研究表明，Igf 2和Mpr/Igf 2 r在真兽目哺乳动物和有袋类动物中有印记，但在单孔目动物或鸟类中没有。igf 2存在于真兽目动物的一个大的印迹簇中，其印迹受长程机制调控。作为了解印迹簇如何进化的一步，我们已经确定了一个490 kb的鸡序列，其中包含哺乳动物Ascl 2/Mash 2，Ins 2和Igf 2的直系同源物。我们发现该区域的大部分基因在鸡和哺乳动物之间是保守的，保持相同的转录极性和外显子-内含子结构。然而，H19，一个印记的非编码转录本，是不存在的鸡序列。鸡的ASCL 2/CASH 4和INS，直系同源的印记哺乳动物基因，表现出双等位基因表达，进一步支持的概念，印记进化后的分歧哺乳动物和鸟类。H19印迹中心和许多在哺乳动物中发现的局部调控元件在鸡中没有发现。此外，在小鼠中的两个印迹亚结构域之间鉴定的大片段串联重复序列和逆转录元件在鸡中未发现。我们的研究结果表明，印迹基因集群之前出现的印迹和印迹相关的元素可能进化后，哺乳动物和鸟类的分歧。
Previous studies revealed that Igf2 and Mpr/Igf2r are imprinted in eutherian mammals and marsupials but not in monotremes or birds. Igf2 lies in a large imprinted cluster in eutherians, and its imprinting is regulated by long-range mechanisms. As a step to understand how the imprinted cluster evolved, we have determined a 490-kb chicken sequence containing the orthologs of mammalian Ascl2/Mash2, Ins2 and Igf2. We found that most of the genes in this region are conserved between chickens and mammals, maintaining the same transcriptional polarities and exon-intron structures. However, H19, an imprinted noncoding transcript, was absent from the chicken sequence. Chicken ASCL2/CASH4 and INS, the orthologs of the imprinted mammalian genes, showed biallelic expression, further supporting the notion that imprinting evolved after the divergence of mammals and birds. The H19 imprinting center and many of the local regulatory elements identified in mammals were not found in chickens. Also, a large segment of tandem repeats and retroelements identified between the two imprinted subdomains in mice was not found in chickens. Our findings show that the imprinted genes were clustered before the emergence of imprinting and that the elements associated with imprinting probably evolved after the divergence of mammals and birds.