MECP2 mutations in Rett syndrome adversely affect lymphocyte growth, but do not affect imprinted gene expression in blood or brain
MECP2 mutations in Rett syndrome adversely affect lymphocyte growth, but do not affect imprinted gene expression in blood or brain
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DOI：
10.1007/s00439-002-0724-4
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发表时间：
2002-06-01
期刊：
影响因子：
5.3
通讯作者：
LaSalle, JM
中科院分区：
文献类型：
--
作者：
Balmer, D;Arredondo, J;LaSalle, JM
Rett综合征（RTT）是一种X连锁显性神经发育障碍，由编码甲基CpG结合蛋白2（MeCP 2）的MECP 2突变引起。由于女性体细胞是嵌合体以表达突变型MECP 2，我们对来自四名具有MECP 2突变的RTT患者的T淋巴细胞进行单细胞克隆以分离表达突变型MECP 2的细胞。表达Muc的克隆以比野生型克隆显著更低的频率（P < 0.0001）存在。这些结果表明，虽然MECP 2不是淋巴细胞生长所必需的，但MECP 2突变的表达通过降低对促有丝分裂刺激的应答而导致培养的克隆T细胞的生长不利。突变体MECP 2在正常的转录和蛋白质水平上表达，并且对乙酰化组蛋白或甲基结合蛋白3（MBD 3）水平没有表现出显著影响。由于预测MeCP 2沉默甲基化基因的转录，我们假设MeCP 2可能是沉默印记或甲基化基因表达所需的。通过RT-PCR和RFLP分析检测了三个不同印记基因（SNRPN，IPW和IGF 2）的等位基因表达，并证明所有RTT克隆的正常单等位基因表达。我们还检查了五个印迹基因（SNRPN，IPW，NECDIN，H19和IGF 2）在RTT脑样品中的表达，并观察到排他性的单等位基因表达。在MECP 2突变体表达T细胞中，IFNG的表达水平也是正常的，IFNG是一种在T细胞中差异表达的非印迹但甲基化的基因，LINE-1逆转录转座子假设被MeCP 2沉默。组蛋白去乙酰化酶抑制剂曲古抑菌素A没有改变SNRPN的表达，但在MECP 2-muconase表达克隆中逆转IFNG的沉默。总之，我们的研究结果不支持MeCP 2或HDAC在沉默几个印记基因中的重要作用。
Rett syndrome (RTT) is an X-linked dominant neurodevelopmental disorder caused by mutations in MECP2, encoding methyl-CpG-binding protein 2 (MeCP2). As female somatic cells are mosaic for expression of mutant MECP2, we performed single cell cloning of T lymphocytes from four RTT patients with MECP2 mutations to isolate cells expressing mutant MECP2. Mutant-expressing clones were present at a significantly lower frequency (P < 0.0001) than wild-type clones. These results demonstrate that although MECP2 is not essential for lymphocyte growth, expression of the MECP2 mutation causes a growth disadvantage in cultured clonal T cells by reducing the response to mitogenic stimulation. Mutant MECP2 was expressed at normal transcript and protein levels, and exhibited no significant effect on acetylated histones or methyl-binding protein 3 (MBD3) levels. Since MeCP2 was predicted to silence transcription of methylated genes, we hypothesized that MeCP2 may be required for silencing imprinted or methylated gene expression. The allelic expression of three different imprinted genes (SNRPN, IPW and IGF2) was examined by RT-PCR and RFLP analysis, and demonstrated normal monoallelic expression of all RTT clones. We also examined the expression of five imprinted genes (SNRPN, IPW, NECDIN, H19 and IGF2) in RTT brain samples and observed exclusive monoallelic expression. Expression levels were also normal in MECP2 mutant-expressing T cells for IFNG, a non-imprinted, but methylated gene differentially expressed in T cells, and LINE-1 retrotransposons hypothesized to be silenced by MeCP2. The histone deacetylase inhibitor Trichostatin A did not alter SNRPN expression, but did reverse silencing of IFNG in a MECP2-mutant-expressing clone. In conclusion, our results do not support an essential role for either MeCP2 or HDAC in the silencing of several imprinted genes.