Binding of DCC by netrin-1 to mediate axon guidance independent of adenosine A2B receptor activation

Netrins stimulate and orient axon growth through a mechanism requiring receptors of the DCC family. It has been unclear, however, whether DCC proteins are involved directly in signaling or are mere accessory proteins in a receptor complex. Further, although netrins bind cells expressing DCC, direct binding to DCC has not been demonstrated. Here we show that netrin-1 binds DCC and that the DCC cytoplasmic domain fused to a heterologous receptor ectodomain can mediate guidance through a mechanism involving derepression of cytoplasmic domain multimerization. Activation of the adenosine A2B receptor, proposed to contribute to netrin effects on axons, is not required for rat commissural axon outgrowth or Xenopus spinal axon attraction to netrin-1. Thus, DCC plays a central role in netrin signaling of axon growth and guidance independent of A2B receptor activation.     

The evolution of sex chromosomes

Structurally distinct sex chromosomes (X and Y) are the most familiar mode of genetic sex determination and have evolved independently in many different taxa. The evolutionary paths by which their characteristic properties may have evolved are reviewed. These properties include the failure of X and Y to recombine through much or all of their length, the genetic inertness of much of the Y chromosome, dosage compensation of the activity of X chromosomal loci, and the accumulation of repeated DNA sequences on the Y chromosome.     

The Xist RNA gene evolved in eutherians by pseudogenization of a protein-coding gene

The Xist noncoding RNA is the key initiator of the process of X chromosome inactivation in eutherian mammals, but its precise function and origin remain unknown. Although Xist is well conserved among eutherians, until now, no homolog has been identified in other mammals. We show here that Xist evolved, at least partly, from a protein-coding gene and that the loss of protein-coding function of the proto-Xist coincides with the four flanking protein genes becoming pseudogenes. This event occurred after the divergence between eutherians and marsupials, which suggests that mechanisms of dosage compensation have evolved independently in both lineages.     

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.     

Intersection of the RNA interference and X-inactivation pathways

In mammals, dosage compensation is achieved by X-chromosome inactivation (XCI) in the female. The noncoding Xist gene initiates silencing of the X chromosome, whereas its antisense partner Tsix blocks silencing. The complementarity of Xist and Tsix RNAs has long suggested a role for RNA interference (RNAi). Here, we report that murine Xist and Tsix form duplexes in vivo. During XCI, the duplexes are processed to small RNAs (sRNAs), most likely on the active X (Xa) in a Dicer-dependent manner. Deleting Dicer compromises sRNA production and derepresses Xist. Furthermore, without Dicer, Xist RNA cannot accumulate and histone 3 lysine 27 trimethylation is blocked on the inactive X (Xi). The defects are partially rescued by truncating Tsix. Thus, XCI and RNAi intersect, down-regulating Xist on Xa and spreading silencing on Xi.     

Christmas factor: dosage compensation and the production of blood coagulation factor IX

The amount of factor IX (Christmas factor) for different genotypic classes was determined by means of a variant of the thromboplastin generation test. The mean value for females heterozygous for the Christmas gene was about half the mean values for normal males and for normal homozygous females; means for the latter two groups were about equal. This dosage compensation is interpreted as evidence in support of Lyon's hypothesis, according to which one X chromosome is inactive in mammalian females.     

A functional dosage compensation complex required for male killing in Drosophila

Bacteria that selectively kill males ("male-killers") were first characterized more than 50 years ago in Drosophila and have proved to be common in insects. However, the mechanism by which sex specificity of virulence is achieved has remained unknown. We tested the ability of Spiroplasma poulsonii to kill Drosophila melanogaster males carrying mutations in genes that encode the dosage compensation complex. The bacterium failed to kill males lacking any of the five protein components of the complex.     

Function of an axonal chemoattractant modulated by metalloprotease activity

The axonal chemoattractant netrin-1 guides spinal commissural axons by activating its receptor DCC (Deleted in Colorectal Cancer). We have found that chemical inhibitors of metalloproteases potentiate netrin-mediated axon outgrowth in vitro. We have also found that DCC is a substrate for metalloprotease-dependent ectodomain shedding, and that the inhibitors block proteolytic processing of DCC and cause an increase in DCC protein levels on axons within spinal cord explants. Thus, potentiation of netrin activity by inhibitors may result from stabilization of DCC on the axons, and proteolytic activity may regulate axon migration by controlling the number of functional extracellular axon guidance receptors.     

A general mechanism for network-dosage compensation in gene circuits

Coping with variations in network dosage is crucial for maintaining optimal function in gene networks. We explored how network structure facilitates network-level dosage compensation. By using the yeast galactose network as a model, we combinatorially deleted one of the two copies of its four regulatory genes and found that network activity was robust to the change in network dosage. A mathematical analysis revealed that a two-component genetic circuit with elements of opposite regulatory activity (activator and inhibitor) constitutes a minimal requirement for network-dosage invariance. Specific interaction topologies and a one-to-one interaction stoichiometry between the activating and inhibiting agents were additional essential elements facilitating dosage invariance. This mechanism of network-dosage invariance could represent a general design for gene network structure in cells.     

Scheme of Weather-Based Indemnity Indices for Insuring Against Freeze Damage to Citrus Orchards in Zhejiang, China

We design a weather-based indemnity index for the insurance against freeze damage to citrus orchards so as to provide technological support for the development of policy-based agriculture. The indices are prepared by separating a relative meteorological yield from the yield that is dependent on tree age, high-yield and low-yield years, and environmental factors, and then using a risk assessment scheme to determine the percentage yield reduction due to the meteorological hazard. We thus develop a set of indices associated with cold temperature damage with which to construct more severe weather indices in conjunction with the yield percentage decrease. We then combine the insured regional citrus yield index with the insured meteorological counterpart to obtain a weather-based indemnity index for the varying degree of freeze damage to crops. When the freeze damage index （FDI） is greater than -7.0℃ for the coastal belt of Zhejiang Province, China, or greater than -9.0℃ for other regions of Zhejiang, weather-based indemnity index （WBII） is zero, meaning there is no compensation; when the FDI is from -7.0 to -7.9℃ for the coastal belt or from -9.0 to -9.9℃ for other regions, the WBII is 1 with 50% compensation; when the FDI is from -8.0 to -8.9℃ for the coastal belt or from -10.0 to -10.9℃ for other regions, the WBII is 2 with 70% compensation; and when the FDI is less than -9.0℃ for the coastal belt or less than -11.0℃ for other regions, the WBII is 3 with 90% compensation. The weather indemnity indices of insured orchards are developed in the interest of owners, thereby eliminating adverse selection and moral hazard issues and providing timely recompense from the insurer, and resolving the problem of high indemnity cost in agricultural insurance.     

Inhibition of netrin-mediated axon attraction by a receptor protein tyrosine phosphatase

During axon guidance, the ventral guidance of the Caenorhabditis elegans anterior ventral microtubule axon is controlled by two cues, the UNC-6/netrin attractant recognized by the UNC-40/DCC receptor and the SLT-1/slit repellent recognized by the SAX-3/robo receptor. We show here that loss-of-function mutations in clr-1 enhance netrin-dependent attraction, suppressing ventral guidance defects in slt-1 mutants. clr-1 encodes a transmembrane receptor protein tyrosine phosphatase (RPTP) that functions in AVM to inhibit signaling through the DCC family receptor UNC-40 and its effector, UNC-34/enabled. The known effects of other RPTPs in axon guidance could result from modulation of guidance receptors like UNC-40/DCC.     

复合型生态补偿机制构建研究——以河源市为例

目前生态补偿机制设计中往往仅考虑某一类生态服务功能,无法完全补偿区域外溢性生态服务的外部成本。针对此问题,从区域外溢生态服务复合性出发,选择河源市这一同时提供水源涵养、固碳、防洪抗灾等复合型生态地位的地区为案例,深入分析复合型生态补偿机制构建的要点,包括复合型生态补偿额度核算、复合型生态补偿主客体及责任确定以及对应的复合型生态补偿方式。     

我国耕地保护补偿机制问题与建议

为更好地促进耕地保护补偿机制发挥,采用文献研读法、经验总结法、实地调研法及定性描述法对国内各地耕地保护补偿实践效果梳理分析,总结该制度目前存在的问题及提出政策建议。研究表明:资金筹措压力大、标准难确定及配套机制较薄弱是当前耕地保护补偿机制实践与发展所面临的主要瓶颈。拓展资金筹措渠道是确保耕地保护补偿持续稳定实施的重要基础,建立分区性多类型补偿标准测算体系并尝试选点试行有助于补偿方案更加客观公平,针对性多样化的补偿方式不仅扩宽耕地保护补偿思路,同时也缓解当前经济补偿造成的财政压力,而科学合理的规划设计、规范透明的资金监管与健全完善的耕地数量、质量动态监测是保障耕地保护补偿机制有效可行的必备条件。     

X-linked 6-phosphogluconate dehydrogenase in drosophila: subunit associations

6-Phosphogluconate dehydrogenase (PGD) subunits have been dissociated and reassociated in vitro. The intermediate PGD of the heterozygous phenotype is reproduced by reassociation in vitro of subunits derived from the two types of PGD from homozygous flies. This result has a bearingon gene action in the diploid organism and on the mechanism of dosage compensation in Drosophila melanogaster.     

并联式曲线送料平台机构误差补偿方法的研究

并联式曲线送料平台是用于实现细木工带锯机曲线切割的自动进给平台,由于该机构运动支链多,机构误差大,难以实现平台末端位姿的精确进给。为了实现并联式曲线送料平台的末端位姿误差补偿,本文从连杆运动学位姿建模出发,利用机构运动学逆解的分析方法,得到各关节参数与送料平台位姿参数关系方程,再运用尺寸矢量链法建立机构误差、机构参数与动平台位姿误差的误差正解数学模型,分离得到与动平台位姿参数有关的误差传递矩阵,最终得到由各轴驱动来补偿平台机构误差的方法。运用该方法对并联式曲线送料平台误差实例进行计算分析,结合MATLAB计算得到送料平台各轴随加工曲线变化的误差补偿实际值,数值导入到各轴进给补偿程序中对曲线送料平台试验机进行实验验证。结果表明:并联式曲线送料平台机构误差补偿方法有效地减小了末端执行机构的位姿误差。未补偿前并联式曲线送料平台工件运动曲线X轴、Y轴方向最大误差为3 mm,绕Z轴最大旋转误差为3°;补偿后工件运动曲线X轴、Y轴方向最大误差在1 mm以内,绕Z轴最大旋转误差在1°以内。说明本方法能够显著提高并联式曲线送料平台的精度,有效地补偿并联式曲线送料平台的机构误差。      

Optimal design of culling compensation policy under the African swine fever — Based on simulations of typical pig farms in China

This paper aims to optimize the culling compensation policy from a micro perspective through scenario simulation. Based on an investigation of 273 pig farms in eight regions, four typical pig farms were constructed according to farm size and breeding mode, representing the swine producers in China. Besides, a decision objective function of pig farms facing suspected African swine fever (ASF) outbreaks was constructed. This study used a mathematical programming model to design and simulate scenarios based on compensation standards and local implementation levels, aiming to incentivize pig farms to report epidemics. The results show that the optimal decisions on epidemic reports differed among typical farms and by herd daily age. The results suggest the following adjustments for optimizing culling compensation policies: (1) to set culling compensation standards based on the market value and (2) to maintain a high level of epidemic surveillance capability in the animal husbandry and veterinary sector.     

烟草赤星病菌致病力测定方法的研究

用烟草赤星病菌(Alternaria alternata)和其它植物来源的分离物(Alternaria sp.)共39个菌株分别接种烟草品种G80和G140的幼苗,并用其中24个菌株接种此二品种的离体叶片。结果表明,不同菌株对离体叶片的穿透生长能力与致病力以及对幼苗的致病力(病叶率与病情指数),明显地表现为从低到高的组群关系。其中,烟草赤星病菌5个菌株,TBA6、TBA8、TBA12、TBA19和TBA28,为表现一致的高致病力,而TBA20和TBA27表现一致的低致病力。比较发现,病菌对离体叶片的致病力(等级)与其对幼苗的致病力,在烟草赤星病菌的24个菌株间以及在两个烟草品种间的趋势相一致,而病菌对离体叶的穿透生长能力与其对幼苗的致病力之间无一致趋势。讨论认为,离体叶片法用于测定病菌的致病力不失为一种准确快速而又易于控制的方法。