Cain James A, Montibus Bertille, Oakey Rebecca J
Department of Medical and Molecular Genetics, King's College London, Guy's Hospital, London, United Kingdom.
Front Cell Dev Biol. 2022 Feb 11;10:832348. doi: 10.3389/fcell.2022.832348. eCollection 2022.
The mammalian genome is depleted in CG dinucleotides, except at protected regions where they cluster as CpG islands (CGIs). CGIs are gene regulatory hubs and serve as transcription initiation sites and are as expected, associated with gene promoters. Advances in genomic annotations demonstrate that a quarter of CGIs are found within genes. Such intragenic regions are repressive environments, so it is surprising that CGIs reside here and even more surprising that some resist repression and are transcriptionally active within a gene. Hence, intragenic CGI positioning within genes is not arbitrary and is instead, selected for. As a wealth of recent studies demonstrate, intragenic CGIs are embedded within genes and consequently, influence 'host' gene mRNA isoform length and expand transcriptome diversity.
哺乳动物基因组中CG二核苷酸含量较低，除了在受保护区域，这些区域以CpG岛（CGIs）的形式聚集。CGIs是基因调控中心，作为转录起始位点，正如预期的那样，与基因启动子相关。基因组注释的进展表明，四分之一的CGIs存在于基因内部。这种基因内区域是抑制性环境，因此令人惊讶的是CGIs存在于此，更令人惊讶的是一些CGIs能够抵抗抑制并在基因内具有转录活性。因此，基因内CGIs在基因中的定位并非随意，而是经过选择的。正如最近大量研究所表明的，基因内CGIs嵌入在基因中，因此会影响“宿主”基因mRNA异构体的长度并扩展转录组多样性。
