Nakabayashi Kazuhiko, Bentley Louise, Hitchins Megan P, Mitsuya Kohzoh, Meguro Makiko, Minagawa Sachi, Bamforth John S, Stanier Philip, Preece Michael, Weksberg Rosanna, Oshimura Mitsuo, Moore Gudrun E, Scherer Stephen W
Department of Genetics, The Hospital for Sick Children, and Department of Molecular and Medical Genetics, University of Toronto, Toronto, ON, Canada.
Hum Mol Genet. 2002 Jul 15;11(15):1743-56. doi: 10.1093/hmg/11.15.1743.
Imprinted gene(s) on human chromosome 7 are thought to be involved in Russell-Silver syndrome (RSS), based on the fact that approximately 10% of patients have maternal uniparental disomy of chromosome 7. However, involvement of the known imprinted genes (GRB10 at 7p12, PEG10 at 7q21.3 and MEST at 7q32) in RSS has yet to be established. To screen for new imprinted genes, we are initially using somatic cell hybrids containing a paternal or maternal human chromosome 7. Transcripts located between D7S530 and D7S649 (a 1.5 Mb interval encompassing MEST ) were subjected to RT-PCR analysis using somatic cell hybrids. One transcript named MESTIT1 (for MEST intronic transcript 1) reproducibly showed paternal-specific expression. Upon further analysis, we found MESTIT1 to be (1) paternally (and not maternally) expressed in all fetal tissues and fibroblasts examined, (2) to be located in an intron of one of the two isoforms of MEST but transcribed in the opposite direction, (3) to be composed of at least two exons without any significant open reading frame, and (4) to exist as a 4.2 kb transcript in many fetal and adult tissues. We could also identify two isoforms of the mouse Mest gene as observed in humans, but it is still unknown if a murine ortholog of MESTIT1 exists. We also examined the imprinting status of MEST isoforms as a first step in assessing whether MESTIT1 might influence the allelic expression pattern of the sense transcript. MEST isoform 1 was determined to be exclusively expressed from the paternal allele in all fetal tissues and cell lines examined, whereas MEST isoform 2 was only preferentially expressed from the paternal allele in a tissue/cell-type-specific manner. Our results suggest that MESTIT1 is a paternally expressed non-coding RNA that may be involved in the regulation of MEST expression during development. MESTIT1 (also known as PEG1-AS) is now the third independent transcript (with MEST and COPG2IT1) identified at human chromosome 7q32 demonstrating paternal chromosome-specific expression.
基于约10%的罗素-西尔弗综合征（RSS）患者存在7号染色体母源单亲二倍体这一事实，人们认为人类7号染色体上的印记基因与该综合征有关。然而，已知的印记基因（7p12处的GRB10、7q21.3处的PEG10和7q32处的MEST）是否参与RSS尚未确定。为了筛选新的印记基因，我们最初使用了含有父源或母源人类7号染色体的体细胞杂种。利用体细胞杂种，对位于D7S530和D7S649之间（一个包含MEST的1.5 Mb区间）的转录本进行逆转录聚合酶链反应（RT-PCR）分析。一个名为MESTIT1（MEST内含子转录本1）的转录本可重复性地显示出父源特异性表达。进一步分析发现，MESTIT1具有以下特点：（1）在所有检测的胎儿组织和成纤维细胞中均为父源（而非母源）表达；（2）位于MEST两种异构体之一的内含子中，但转录方向相反；（3）由至少两个外显子组成，无任何明显的开放阅读框；（4）在许多胎儿和成人组织中以4.2 kb转录本的形式存在。我们还能鉴定出与人类中观察到的类似的小鼠Mest基因的两种异构体，但MESTIT1的小鼠直系同源基因是否存在仍不清楚。作为评估MESTIT1是否可能影响正义转录本等位基因表达模式的第一步，我们还检测了MEST异构体的印记状态。在所有检测的胎儿组织和细胞系中，MEST异构体1被确定仅从父源等位基因表达，而MEST异构体2仅以组织/细胞类型特异性的方式优先从父源等位基因表达。我们的结果表明，MESTIT1是一种父源表达的非编码RNA，可能参与发育过程中MEST表达的调控。MESTIT1（也称为PEG1-AS）现在是在人类7号染色体q32处鉴定出的第三个独立转录本（与MEST和COPG2IT1一起），显示出父源染色体特异性表达。
