Lee Jeannie T
Howard Hughes Medical Institute, Department of Molecular Biology, Massachusetts General Hospital, Department of Genetics, Harvard Medical School, Boston, MA 02114, USA.
Philos Trans R Soc Lond B Biol Sci. 2003 Aug 29;358(1436):1417-23; discussion 1423. doi: 10.1098/rstb.2003.1328.
Long known to be riddled with repetitive elements and regarded as 'junk', intergenic regions in the mammalian genome now appear to be more than incidental spacers between coding sequences. Here, I review the example of Xite, an intergenic region at the X-inactivation centre which was recently shown to regulate the X-chromosome choice decision. Xite contains a series of DNaseI-hypersensitive sites and harbours two intergenic transcription start sites. These intergenic transcription elements act at the onset of X-chromosome inactivation (XCI) to bias the selection of the active X. It has been proposed that Xite acts in cis on Tsix by promoting its persistence during XCI. Xite has also been proposed to be a candidate for the X-controlling element, a naturally occurring modifier of XCI ratios in mice and possibly also in humans. It seems likely that intergenic transcription will turn out to be a widespread phenomenon in mammals and that, more importantly, it will emerge as a significant regulatory mechanism for the expression of coding sequences.
长期以来，哺乳动物基因组中的基因间区域被认为充满了重复元件，并被视为“垃圾”，但现在它们似乎不仅仅是编码序列之间的偶然间隔区。在此，我将回顾Xite的例子，它是X染色体失活中心的一个基因间区域，最近被证明可调控X染色体的选择决定。Xite包含一系列对DNaseI敏感的位点，并含有两个基因间转录起始位点。这些基因间转录元件在X染色体失活（XCI）开始时起作用，以偏向活性X染色体的选择。有人提出，Xite通过在XCI期间促进Tsix的持续存在而顺式作用于Tsix。Xite也被认为是X控制元件的候选者，X控制元件是小鼠乃至人类中XCI比例的一种天然修饰因子。基因间转录似乎很可能是哺乳动物中的一种普遍现象，更重要的是，它将成为编码序列表达的一种重要调控机制。
