Germline-specific dgcr8 knockout in zebrafish using a BACK approach

Zebrafish is an important model to study developmental biology and human diseases. However, an effective approach to achieve spatial and temporal gene knockout in zebrafish has not been well established. In this study, we have developed a new approach, namely bacterial artificial chromosome-rescue-based knockout (BACK), to achieve conditional gene knockout in zebrafish using the Cre/loxP system. We have successfully deleted the DiGeorge syndrome critical region gene 8 (dgcr8) in zebrafish germ line and demonstrated that the maternal-zygotic dgcr8 (MZdgcr8) embryos exhibit MZdicer-like phenotypes with morphological defects which could be rescued by miR-430, indicating that canonical microRNAs play critical role in early development. Our findings establish that Cre/loxP-mediated tissue-specific gene knockout could be achieved using this BACK strategy and that canonical microRNAs play important roles in early embryonic development in zebrafish.     

IFT54 regulates IFT20 stability but is not essential for tubulin transport during ciliogenesis

Intraflagellar transport (IFT) is required for ciliogenesis by ferrying ciliary components using IFT complexes as cargo adaptors. IFT54 is a component of the IFT-B complex and is also associated with cytoplasmic microtubules (MTs). Loss of IFT54 impairs cilia assembly as well as cytoplasmic MT dynamics. The N-terminal calponin homology (CH) domain of IFT54 interacts with tubulins/MTs and has been proposed to transport tubulin during ciliogenesis, whereas the C-terminal coiled-coil (CC) domain binds IFT20. However, the precise function of these domains in vivo is not well understood. We showed that in Chlamydomonas, loss of IFT54 completely blocks ciliogenesis but does not affect spindle formation and proper cell cycle progression, even though IFT54 interacts with mitotic MTs. Interestingly, IFT54 lacking the CH domain allows proper flagellar assembly. The CH domain is required for the association of IFT54 with the axoneme but not with mitotic MTs, and also regulates the flagellar import of IFT54 but not IFT81 and IFT46. The C-terminal CC domain is essential for IFT54 to bind IFT20, and for its recruitment to the basal body and incorporation into IFT complexes. Complete loss of IFT54 or the CC domain destabilizes IFT20. ift54 mutant cells expressing the CC domain alone rescue the stability of IFT20 and form stunted flagella with accumulation of both IFT-A component IFT43 and IFT-B component IFT46, indicating that IFT54 also functions in IFT turn-around at the flagellar tip.     

Genome-wide association studies of 14 agronomic traits in rice landraces

Uncovering the genetic basis of agronomic traits in crop landraces that have adapted to various agro-climatic conditions is important to world food security. Here we have identified ～ 3.6 million SNPs by sequencing 517 rice landraces and constructed a high-density haplotype map of the rice genome using a novel data-imputation method. We performed genome-wide association studies (GWAS) for 14 agronomic traits in the population of Oryza sativa indica subspecies. The loci identified through GWAS explained ～ 36% of the phenotypic variance, on average. The peak signals at six loci were tied closely to previously identified genes. This study provides a fundamental resource for rice genetics research and breeding, and demonstrates that an approach integrating second-generation genome sequencing and GWAS can be used as a powerful complementary strategy to classical biparental cross-mapping for dissecting complex traits in rice.     

Genome-wide association study of flowering time and grain yield traits in a worldwide collection of rice germplasm

A high-density haplotype map recently enabled a genome-wide association study (GWAS) in a population of indica subspecies of Chinese rice landraces. Here we extend this methodology to a larger and more diverse sample of 950 worldwide rice varieties, including the Oryza sativa indica and Oryza sativa japonica subspecies, to perform an additional GWAS. We identified a total of 32 new loci associated with flowering time and with ten grain-related traits, indicating that the larger sample increased the power to detect trait-associated variants using GWAS. To characterize various alleles and complex genetic variation, we developed an analytical framework for haplotype-based de novo assembly of the low-coverage sequencing data in rice. We identified candidate genes for 18 associated loci through detailed annotation. This study shows that the integrated approach of sequence-based GWAS and functional genome annotation has the potential to match complex traits to their causal polymorphisms in rice.     

The genome of the extremophile crucifer Thellungiella parvula

Thellungiella parvula is related to Arabidopsis thaliana and is endemic to saline, resource-poor habitats, making it a model for the evolution of plant adaptation to extreme environments. Here we present the draft genome for this extremophile species. Exclusively by next generation sequencing, we obtained the de novo assembled genome in 1,496 gap-free contigs, closely approximating the estimated genome size of 140 Mb. We anchored these contigs to seven pseudo chromosomes without the use of maps. We show that short reads can be assembled to a near-complete chromosome level for a eukaryotic species lacking prior genetic information. The sequence identifies a number of tandem duplications that, by the nature of the duplicated genes, suggest a possible basis for T. parvula's extremophile lifestyle. Our results provide essential background for developing genomically influenced testable hypotheses for the evolution of environmental stress tolerance.     

基于非等量采样的伪码同步技术研究

针对数字通信系统中伪随机噪声(pseudo-random noise, PN)码同步技术的同步精度受限于采样间隔的问题,结合可变群时延的高精度同步思想,利用采样点位置偏移量的变化,推导出了非等量采样(non-commensurate sampling, NCS)下的PN码相关函数解析表达式,提出了基于精度因子的NCS率选取准则,通过精度因子可快速判断出NCS后PN码的同步精度下限。在此基础上,分析了码序列周期、接收机前端滤波器等附加因素对PN码同步精度的影响。对NCS率选取准则的研究,为优化数字通信系统设计提供了理论指导,达到以低硬件消耗实现高精度同步的目的。     

Differential space-time modulation in rapidly fading channels

Previously proposed differential modulation schemes for time-varying channels may not achieve the full transmit diversity and the maximum Doppler diversity simultaneously. Based on an existing basis expansion model, a new differential space-time code, which wisely combines interleaver/de-interleaver with traditonal space-time transmitting technique to overcome such limitation, .is presented. Two noncoherent differential decoders, named decision-feedback differential detector （DF-DD） and Viterbi-algorithmbased multiple-symbol-detection differential detector （ MSD-DD）, are also derived. We show that our design may recover data symbols with full antenna diversity and the maximum Doppler diversity at high signal-to-noise ratio. System performance is evaluated with simulations.     

Estimation and Inference in Semi-Functional Partially Linear Measurement Error Models

Journal of Systems Science and Complexity - This article studies the estimation and statistical inference problems of semi-functional partially linear regression models when the covariates in the...     

头盘微小间隙动态浮动理论研究

本文对微小浮动间隙的磁头浮动块的动态浮动性能进行了仿真计算。在考虑头盘碰撞的基础上,分析了磁头浮动块对冲击的响应。分析结果表明:在微小浮动间隙的头盘系统中,盘片表面粗糙度和外界干扰冲击对浮动块的浮动性能影响较大。新的动态浮动理论中,必须包含头盘磁撞的研究。