Paucity of genes on the Drosophila X chromosome showing male-biased expression

Sex chromosomes are primary determinants of sexual dimorphism in many organisms. These chromosomes are thought to arise via the divergence of an ancestral autosome pair and are almost certainly influenced by differing selection in males and females. Exploring how sex chromosomes differ from autosomes is highly amenable to genomic analysis. We examined global gene expression in Drosophila melanogaster and report a dramatic underrepresentation of X-chromosome genes showing high relative expression in males. Using comparative genomics, we find that these same X-chromosome genes are exceptionally poorly conserved in the mosquito Anopheles gambiae. These data indicate that the X chromosome is a disfavored location for genes selectively expressed in males.     

非编码RNA Xist调节X染色体失活的分子机制

非编码KNAXist介导的X染色体失活是表观遗传研究的一个典范,该系统能使一整条染色体变为异染状态。从Xist与X染色体计数、失活的选择、失活的起始和失活的维持等方面综述了其分子机制。     

Regulation of X-chromosome counting by Tsix and Xite sequences

In mammals, X-inactivation establishes X-chromosome dosage parity between males and females. How X-chromosome counting regulates this process remains elusive, because neither the hypothesized inactivation "blocking factor" nor the required cis-elements have been defined. Here, a mouse knockout and transgenic analysis identified DNA sequences within the noncoding Tsix and Xite genes as numerators. Homozygous deficiency of Tsix resulted in "chaotic choice" and a variable number of inactive X's, whereas overdosage of Tsix/Xite inhibited X-inactivation. Thus, counting was affected by specific Tsix/Xite mutations, suggesting that counting is genetically separable from but molecularly coupled to choice. The mutations affect XX and XY cells differently, demonstrating that counting and choice are regulated not by one "blocking factor," but by both a "blocking" and a "competence" factor.     

An X chromosome gene, WTX, is commonly inactivated in Wilms tumor

Wilms tumor is a pediatric kidney cancer associated with inactivation of the WT1 tumor-suppressor gene in 5 to 10% of cases. Using a high-resolution screen for DNA copy-number alterations in Wilms tumor, we identified somatic deletions targeting a previously uncharacterized gene on the X chromosome. This gene, which we call WTX, is inactivated in approximately one-third of Wilms tumors (15 of 51 tumors). Tumors with mutations in WTX lack WT1 mutations, and both genes share a restricted temporal and spatial expression pattern in normal renal precursors. In contrast to biallelic inactivation of autosomal tumor-suppressor genes, WTX is inactivated by a monoallelic "single-hit" event targeting the single X chromosome in tumors from males and the active X chromosome in tumors from females.     

Clonal analysis of human colorectal tumors

The clonal composition of human colorectal tumors was studied by means of restriction fragment length polymorphisms (RFLPs). First, X-linked RFLPs were used to examine the pattern of X chromosome inactivation in colorectal tumors of females. All 50 tumors examined showed monoclonal patterns of X chromosome inactivation; these tumors included 20 carcinomas as well as 30 adenomas of either familial or spontaneous type. Second, RFLPs of autosomes were used as clonal markers to detect the somatic loss or gain of specific chromosomal sequences in colorectal tumors. Among other changes, it was found that somatic loss of chromosome 17p sequences occurred in over 75 percent of the carcinomas examined, but such loss was rare in adenomas. These data support a monoclonal origin for colorectal neoplasms, and suggest that a gene on the short arm of chromosome 17 may be associated with progression from the benign to the malignant state.     

Autosomal dominant mutations affecting X inactivation choice in the mouse

X chromosome inactivation is the silencing mechanism eutherian mammals use to equalize the expression of X-linked genes between males and females early in embryonic development. In the mouse, genetic control of inactivation requires elements within the X inactivation center (Xic) on the X chromosome that influence the choice of which X chromosome is to be inactivated in individual cells. It has long been posited that unidentified autosomal factors are essential to the process. We have used chemical mutagenesis in the mouse to identify specific factors involved in X inactivation and report two genetically distinct autosomal mutations with dominant effects on X chromosome choice early in embryogenesis.     

Role of histone H3 lysine 27 methylation in X inactivation

The Polycomb group (PcG) protein Eed is implicated in regulation of imprinted X-chromosome inactivation in extraembryonic cells but not of random X inactivation in embryonic cells. The Drosophila homolog of the Eed-Ezh2 PcG protein complex achieves gene silencing through methylation of histone H3 on lysine 27 (H3-K27), which suggests a role for H3-K27 methylation in imprinted X inactivation. Here we demonstrate that transient recruitment of the Eed-Ezh2 complex to the inactive X chromosome (Xi) occurs during initiation of X inactivation in both extraembryonic and embryonic cells and is accompanied by H3-K27 methylation. Recruitment of the complex and methylation on the Xi depend on Xist RNA but are independent of its silencing function. Together, our results suggest a role for Eed-Ezh2-mediated H3-K27 methylation during initiation of both imprinted and random X inactivation and demonstrate that H3-K27 methylation is not sufficient for silencing of the Xi.     

Molecular analysis of a constitutional X-autosome translocation in a female with muscular dystrophy

The gene responsible for Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) maps to the X chromosome short arm, band Xp21. In a few females with DMD or BMD, the Xp21 region is disrupted by an X-autosome translocation. Accumulating evidence suggests that the exchange has physically disrupted the DMD/BMD locus to cause the disease. One affected female with a t(X;21)(p21;p12) translocation was studied in detail. The exchange points from both translocation chromosomes were cloned, restriction-mapped, and sequenced. The translocation is reciprocal, but not conservative. A small amount of DNA is missing from the translocated chromosomes; 71 to 72 base pairs from the X chromosome and 16 to 23 base pairs from the 28S ribosomal gene on chromosome 21.     

逆转座子LINE-1在基因组中的调控作用

近年来研究发现真核生物基因组中的许多重复序列以及基因的内含子参与基因表达的调控。在这些重复序列中,有一种广泛分布于基因组中的逆转座子LINE-1,目前发现其对细胞的增殖与分化以及肿瘤的发生起着非常重要的作用,具体表现为影响基因的转录及整个基因组的稳定性、参与X染色体失活及基因组进化等。在正常细胞的分化调控中,基因的激活与沉默具有时间与空间的特异性,实现其“预定”的、有序的、不可逆转的分化过程。主要阐述了逆转座子LINE-1的结构特征和其在基因组中的调控作用及这些作用影响基因表达从而调节生物体的生命活动。研究LINE-1的调控机制对认识细胞的时空调控以及癌症的发生与发展具有重要的价值。     

Mosaic histocompatibility of skin grafts from female mice

The histoincompatibility determined by one or more genes on the X chromosome of the mouse effects a complete rejection of skin of the (C57BL/6 female symbol x BALB/c male symbol) F(1) hybrid male grafted onto the reciprocal type F(1) hybrid male, but only an incomplete rejection of either reciprocal type F(1) hybrid female skin, grafted onto the same type of male host. The resulting mosaic survival pattern of the female graft is interpreted as support for the Lyon hypothesis of X-chromosome inactivation.     

淅川乌骨鸡全基因组转座子的鉴定与分析

【目的】 通过分析淅川乌骨鸡全基因组重测序数据,获取淅川乌骨鸡转座子的基本信息和特征分布,探究转座子相关基因参与的通路。不仅对研究淅川乌骨鸡转座子的生物学功能具有重要的意义,而且为探索基因组扩增、基因组功能及进化研究提供重要基础数据。 【方法】 对淅川乌骨鸡血液DNA进行全基因组重测序,采用双末端短序列比对基因组,运用RepeatModeler、TEclass、RepeatMasker等使用流程对转座子进行鉴定、构建、校正、分类和注释,获得淅川乌骨鸡整个基因组所有的转座子,对转座子的特征、分布及和基因的关系等方面进行分析。并对转座子插入的所有基因进行GO和KEGG数据库富集,分别结合GO和KEGG注释结果对功能进行描述。 【结果】 经鉴定、分类和注释,淅川乌骨鸡共鉴定到370 252个转座子序列,分为19个超家族,主要为CR1、TcMar-Mariner、ERVL、ERV1等超家族,进一步说明淅川乌骨鸡转座子类型主要是逆转录转座子;转座子的数目和染色体长度有关,染色体越长,转座子数目越多。在基因组中转座子和基因的密度成反比,基因密集的区域中转座子密度较低;基因组内转座子的插入并非随机的,LTR/ERVL、LTR/ERV1、DNA/PIF-Harbinger、DNA/Hat-Charlie、RC/Helitron等转座子倾向于插入基因外部。GO富集分析表明,在生物过程条目中鉴定出的转座子富集相对较多的是细胞过程、单生物过程、代谢过程、生物调节、刺激反应等;分子功能条目中鉴定出的转座子富集相对较多的是结合、催化活性等;细胞组分条目中鉴定出的转座子富集相对较多的是细胞部分、细胞器、膜等。KEGG富集分析表明,鉴定出的转座子主要在甘油酯代谢、PPAR信号通路、PI3K-Akt信号通路、胰岛素抵抗、Jak-STAT信号通路等通路。着重关注了与淅川乌骨鸡特性相关的通路,如和色素沉积有关的酪氨酸代谢、和肉品质有关的脂代谢、脂肪酸的合成、PI3K-Akt信号通路等。 【结论】 转座子含量与基因组大小,具有一定的正相关性,而且淅川乌骨鸡转座子在基因组的分布存在一定偏好性。转座子相关基因在色素相关通路中富集,其可能与淅川乌骨鸡的种质特性有关,具体的调控机制还有待进一步研究。     

Duchenne muscular dystrophy involving translocation of the dmd gene next to ribosomal RNA genes

Duchenne muscular dystrophy (DMD) is a severe X-linked disorder leading to early death of affected males. Females with the disease are rare, but seven are known to be affected because of a chromosomal rearrangement involving a site at or near the dmd gene on the X chromosome. One of the seven has a translocation between the X and chromosome 21. The translocation-derived chromosomes from this patient have been isolated, and the translocation is shown to have split the block of genes encoding ribosomal RNA on the short arm of chromosome 21. Thus ribosomal RNA gene probes may be used to identify a junction fragment from the translocation site, allowing access to cloned segments of the X at or near the dmd gene and presenting a new approach to the study of this disease.     

Identification of a coordinate regulator of interleukins 4, 13, and 5 by cross-species sequence comparisons

Long-range regulatory elements are difficult to discover experimentally; however, they tend to be conserved among mammals, suggesting that cross-species sequence comparisons should identify them. To search for regulatory sequences, we examined about 1 megabase of orthologous human and mouse sequences for conserved noncoding elements with greater than or equal to 70% identity over at least 100 base pairs. Ninety noncoding sequences meeting these criteria were discovered, and the analysis of 15 of these elements found that about 70% were conserved across mammals. Characterization of the largest element in yeast artificial chromosome transgenic mice revealed it to be a coordinate regulator of three genes, interleukin-4, interleukin-13, and interleukin-5, spread over 120 kilobases.     

Transient homologous chromosome pairing marks the onset of X inactivation

Mammalian X inactivation turns off one female X chromosome to enact dosage compensation between XX and XY individuals. X inactivation is known to be regulated in cis by Xite, Tsix, and Xist, but in principle the two Xs must also be regulated in trans to ensure mutually exclusive silencing. Here, we demonstrate that interchromosomal pairing mediates this communication. Pairing occurs transiently at the onset of X inactivation and is specific to the X-inactivation center. Deleting Xite and Tsix perturbs pairing and counting/choice, whereas their autosomal insertion induces de novo X-autosome pairing. Ectopic X-autosome interactions inhibit endogenous X-X pairing and block the initiation of X-chromosome inactivation. Thus, Tsix and Xite function both in cis and in trans. We propose that Tsix and Xite regulate counting and mutually exclusive choice through X-X pairing.     

水稻分离群体中半矮秆和致死性黄苗突变体的形成机理研究

[目的]鉴定sdwrky和lysrcc1突变体的Ds插入突变基因,初步分析sdwrky和lysrcc1突变体形成的分子机理。[方法]采用TAIL-PCR技术,分别从sdwrky突变体和lysrcc1突变体克隆Ds侧翼基因序列,并进行序列分析。[结果]Ds分别插入sdwrky突变体4号染色体Os04g0597300（sdwrky）基因和lysrcc1突变体3号染色体Os03g0599600（lysrcc1）基因,导致sdwrky和lysrcc1基因突变。[结论]sdwrky基因编码包含WRKY结构域的蛋白质（SDWRKY）,推测SDWRKY与OsWRKY24具相似功能,作为糊粉层细胞内ABA和GA信号传导途径中共同的抑制因子,调控水稻种子萌发及幼苗生长,Sdwrky基因突变导致形成sdwrky突变体。lysrcc1基因编码包含RCC1结构域的蛋白质（LYSRCC1）,LYSRCC1可能作为RanGEF参与核质运输,影响叶绿体合成的某一环节,lysrcc1基因隐性突变导致形成ylrcc1突变体。     

Epigenetic dynamics of imprinted X inactivation during early mouse development

The initiation of X-chromosome inactivation is thought to be tightly correlated with early differentiation events during mouse development. Here, we show that although initially active, the paternal X chromosome undergoes imprinted inactivation from the cleavage stages, well before cellular differentiation. A reversal of the inactive state, with a loss of epigenetic marks such as histone modifications and polycomb proteins, subsequently occurs in cells of the inner cell mass (ICM), which give rise to the embryo-proper in which random X inactivation is known to occur. This reveals the remarkable plasticity of the X-inactivation process during preimplantation development and underlines the importance of the ICM in global reprogramming of epigenetic marks in the early embryo.     

Genetics. Reprogramming X inactivation

Inactivation of one of the two X chromosomes occurs in all cells of female adult mice so that genes are expressed from only one X chromosome. In a Perspective, Clerc and Avner describe an elegant series of experiments in mouse embryos cloned from adult and embryonic female cell nuclei (Eggan et al.) that reveal how the inactivation state of the X chromosomes is reprogrammed.     

Recruitment and spreading of the C. elegans dosage compensation complex along X chromosomes

To achieve X-chromosome dosage compensation, organisms must distinguish X chromosomes from autosomes. We identified multiple, cis-acting regions that recruit the Caenorhabditis elegans dosage compensation complex (DCC) through a search for regions of X that bind the complex when detached from X. The DCC normally assembles along the entire X chromosome, but not all detached regions recruit the complex, despite having genes known to be dosage compensated on the native X. Thus, the DCC binds first to recruitment sites, then spreads to neighboring X regions to accomplish chromosome-wide gene repression. From a large chromosomal domain, we defined a 793-base pair fragment that functions in vivo as an X-recognition element to recruit the DCC.     

Transgenic animals

The ability to introduce foreign genes into the germ line and the successful expression of the inserted gene in the organism have allowed the genetic manipulation of animals on an unprecedented scale. The information gained from the use of the transgenic technology is relevant to almost any aspect of modern biology including developmental gene regulation, the action of oncogenes, the immune system, and mammalian development. Because specific mutations can be introduced into transgenic mice, it becomes feasible to generate precise animal models for human genetic diseases and to begin a systematic genetic dissection of the mammalian genome.     

信号肽对鸡Igλ轻链绿色荧光蛋白重组分子在COS7细胞上分泌表达的影响

分别将鸡Igλ轻链信号肽、小鼠纤溶酶原信号肽与pEGFP-C1载体的绿色荧光蛋白N端融合,产生带有信号肽的中间载体pEGFP-SPc和pEGFP-SPm。对鸡Igλ轻链基因的定向克隆,构建了带有纯化标签的鸡Igλ轻链绿色荧光蛋白真核表达载体pEGFP-SPc-λ和pEGFP-SPm-λ。转染COS7细胞后,荧光显微镜观察及Western blotting检测融合蛋白的分泌表达,结果显示,鸡Igλ轻链信号肽能引导鸡Igλ轻链绿色荧光蛋白融合分子的分泌表达;而小鼠纤溶酶原信号肽不具备引导该重组蛋白分泌表达的功能。表明信号肽在蛋白分泌表达中的关键作用,重组蛋白的分泌表达要选择合适的信号肽。