Enrichment profiles of Ser-5 phosphorylated RNA polymerase II (PolII S5p) in mouse female ES cells

Many animal species employ a chromosome-based mechanism of sex determination, which has led to coordinate evolution of dosage compensation systems. Dosage compensation not only corrects the imbalance in the number of X-chromosomes between the sexes, but is also hypothesized to correct dosage imbalance within cells due to mono-allelic X expression and bi-allelic autosomal expression, by upregulating X-linked genes (termed ‘Ohno’s hypothesis’). It is unknown whether any epigenetic mark or protein is involved in X upregulation in mammals. Ser-5 phosphorylated RNA polymerase II (PolII S5p) is required for transcription initiation. Chromatin immunoprecipitation combined with DNA tiling array analysis (ChIP-chip) of PolII S5p in mouse female ES cells with two active X chromosomes demonstrated a greater enrichment of RNA polymerase II on X-linked genes relative to autosomal genes, suggesting that enhanced transcription initiation may play a role in X upregulation. Comparison of RNA PolII S5p enrichment on the X versus autosomes in mouse

诸多动物物种采用基于染色体的性别决定机制，这推动了剂量补偿（dosage compensation）系统的协同演化。剂量补偿不仅可纠正两性间X染色体数量的失衡，同时也被假说认为能够通过上调X连锁基因，纠正因单等位基因X染色体表达与双等位基因常染色体表达所导致的细胞内剂量失衡，该假说被称为"大野假说（Ohno’s hypothesis）"。目前尚不清楚哺乳动物的X染色体上调是否涉及任何表观遗传标记或蛋白质。Ser-5磷酸化RNA聚合酶II（PolII S5p）是转录起始所必需的。对拥有两条活性X染色体的小鼠雌性胚胎干细胞（ES细胞）开展Ser-5磷酸化RNA聚合酶II的染色质免疫沉淀-芯片（ChIP-chip）分析结果显示，相较于常染色体基因，X连锁基因上的RNA聚合酶富集程度更高，这提示增强的转录起始可能在X染色体上调中发挥作用。针对小鼠X染色体与常染色体上RNA聚合酶II S5p富集程度的比较。