抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

High-throughput mRNA sequencing (RNA-Seq) promises simultaneous transcript discovery and abundance estimation. However, this would require algorithms that are not restricted by prior gene annotations and that account for alternative transcription and splicing. Here we introduce such algorithms in an open-source software program called Cufflinks. To test Cufflinks, we sequenced and analyzed >430 million paired 75-bp RNA-Seq reads from a mouse myoblast cell line over a differentiation time series. We detected 13,692 known transcripts and 3,724 previously unannotated ones, 62% of which are supported by independent expression data or by homologous genes in other species. Over the time series, 330 genes showed complete switches in the dominant transcription start site (TSS) or splice isoform, and we observed more subtle shifts in 1,304 other genes. These results suggest that Cufflinks can illuminate the substantial regulatory flexibility and complexity in even this well-studied model of muscle development and that it can improve transcriptome-based genome annotation.

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Transcript assembly and quantification by RNA-Seq reveals unannotated transcripts and isoform switching during cell differentiation

Statistical method for testing the neutral mutation hypothesis by DNA polymorphism.

So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

Human biochemical genetics

We created a visualization tool called Circos to facilitate the identification and analysis of similarities and differences arising from comparisons of genomes. Our tool is effective in displaying variation in genome structure and, generally, any other kind of positional relationships between genomic intervals. Such data are routinely produced by sequence alignments, hybridization arrays, genome mapping, and genotyping studies. Circos uses a circular ideogram layout to facilitate the display of relationships between pairs of positions by the use of ribbons, which encode the position, size, and orientation of related genomic elements. Circos is capable of displaying data as scatter, line, and histogram plots, heat maps, tiles, connectors, and text. Bitmap or vector images can be created from GFF-style data inputs and hierarchical configuration files, which can be easily generated by automated tools, making Circos suitable for rapid deployment in data analysis and reporting pipelines.

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Circos: An information aesthetic for comparative genomics

The forest tree speaes generally display very high level of genetic diversity (Miiller-Starck et al. 1992) and therefore an accurate analysis of the entity and distribution of their genetic resources requires the screening of many popuiations and many individuals within populations. Hence the choice of appropriate genetic markers assumes great importance in order to reduce costs and to save time. In particular genetic markers should be highly polymorphic and inherited in a Mendelian codominant manner. Microsatellites, or simple sequence repeats (SSR), that are tandem repeats of six base pairs or less (Litt Q Luty 1989; Weber Q May 1989), have these characteristics and therefore Seem to be suitable genetic markers for population genetic studies aIso in forest tree species. The length variation of the tandem repeats can easily be scored following amplification of the SSR-containing fragments by the polymerase chain reaction using unique flanking primers. In plants the possibility to screen highly polymorphic microsatellite regions also in the chloroplast genome, which shows lower mutation rates than the nuclear genome and is usually uniparentally inherited, might increase the knowledge about the biology of these organisms. In particular chloroplast microsatellites may be very useful for studying cytoplasmic diversity, cytonuclear interactions and monitoring gene flow. Powell ef al. (1995a,b) recently demonstrated the utility of the analysis of the length variation of chloroplast microsatellites. In particular they analysed (Powell et d. 1995b) a mononudeotide microsatellite located in the intergenic region between the trnK and psbA genes for assaying genetic variation in pine species. It was shown that the primers worked in aU the species tested and that the amplified fragment showed high levels of polymorphism due to size variations between and within species. Sequencing of the fragments confirmed that the size dif-

A set of primers for the amplification of 20 chloroplast microsatellites in Pinaceae

The phytohormone abscisic acid (ABA) plays important regulatory roles in many plant developmental processes including seed dormancy, germination, growth, and stomatal movements. These physiological responses to ABA are in large part brought about by changes in gene expression. To study genome-wide ABA-responsive gene expression we applied massively parallel signature sequencing (MPSS) to samples from Arabidopsis thaliana wildtype (WT) and abi1-1 mutant seedlings. We identified 1354 genes that are either up- or downregulated following ABA treatment of WT seedlings. Among these ABA-responsive genes, many encode signal transduction components. In addition, we identified novel ABA-responsive gene families including those encoding ribosomal proteins and proteins involved in regulated proteolysis. In the ABA-insensitive mutant abi1-1, ABA regulation of about 84.5% and 6.9% of the identified genes was impaired or strongly diminished, respectively; however, 8.6% of the genes remained appropriately regulated. Compared to other methods of gene expression analysis, the high sensitivity and specificity of MPSS allowed us to identify a large number of ABA-responsive genes in WT Arabidopsis thaliana. The database given in our supplementary material (http://jcs.biologists.org/supplemental) provides researchers with the opportunity to rapidly assess whether genes of interest may be regulated by ABA. Regulation of the majority of the genes by ABA was impaired in the ABA-insensitive mutant abi1-1. However, a subset of genes continued to be appropriately regulated by ABA, which suggests the presence of at least two ABA signaling pathways, only one of which is blocked in abi1-1.

/pdf/genome-wide-gene-expression-profiling-in-arabidopsis-2cblurp2x0.pdf

Genome-wide gene expression profiling in Arabidopsis thaliana reveals new targets of abscisic acid and largely impaired gene regulation in the abi1-1 mutant.

Allelic chromosomal regions totaling more than 2.8 Mb and located on maize (Zea mays) chromosomes 1L, 2S, 7L, and 9S have been sequenced and compared over distances of 100 to 350 kb between the two maize inbred lines Mo17 and B73. The alleles contain extended regions of nonhomology. On average, more than 50% of the compared sequence is noncolinear, mainly because of the insertion of large numbers of long terminal repeat (LTR)-retrotransposons. Only 27 LTR-retroelements are shared between alleles, whereas 62 are allele specific. The insertion of LTR-retrotransposons into the maize genome is statistically more recent for nonshared than shared ones. Most surprisingly, more than one-third of the genes (27/72) are absent in one of the inbreds at the loci examined. Such nonshared genes usually appear to be truncated and form clusters in which they are oriented in the same direction. However, the nonshared genome segments are gene-poor, relative to regions shared by both inbreds, with up to 12-fold difference in gene density. By contrast, miniature inverted terminal repeats (MITEs) occur at a similar frequency in the shared and nonshared fractions. Many times, MITES are present in an identical position in both LTRs of a retroelement, indicating that their insertion occurred before the replication of the retroelement in question. Maize ESTs and/or maize massively parallel signature sequencing tags were identified for the majority of the nonshared genes or homologs of them. In contrast with shared genes, which are usually conserved in gene order and location relative to rice (Oryza sativa), nonshared genes violate the maize colinearity with rice. Based on this, insertion by a yet unknown mechanism, rather than deletion events, seems to be the origin of the nonshared genes. The intergenic space between conserved genes is enlarged up to sixfold in maize compared with rice. Frequently, retroelement insertions create a different sequence environment adjacent to conserved genes.

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Evolution of DNA Sequence Nonhomologies among Maize Inbreds

This chapter presents description and comparison of different DNA marker systems. DNA markers are being applied to a wide variety of problems central to plant genome analysis. Each marker system is characterized by a unique combination of advantages and disadvantages and the choice of a marker system is dictated to a significant extent by the application. Factors to consider in choosing a marker system include the amount of available plant material, the quality of the DNA, and the availability of public collections of DNA markers for the species being examined. Restriction fragment length polymorphism (RFLP) markers are generally codominant, allowing detection and characterization of multiple alleles at a given RELP locus among individuals in a population. Several types of polymorphism can be detected, including single base substitutions, insertions, and deletions. One clear disadvantage to using RFLP markers is the large amount of high-quality genomic DNA required from each individual. It is suggested that once the mapping parents have been chosen and low-copy RFLP probes obtained, those probes that detect useful polymorphisms in the segregating population must be identified. The polymerase chain reaction analysis and identification of polymorphisms are also elaborated.

4 – Generating and Using DNA Markers in Plants

We investigated the effects of human selection for yellow endosperm color, representing increased carotenoid content, on two maize genes, the Y1 phytoene synthase and PSY2, a putative second phytoene synthase. Multiple polymorphic sites were identified at Y1 and PSY2 in 75 white and yellow maize inbred lines. Many polymorphic sites showed strong association with the endosperm color phenotype at Y1, but no detectable association was found at PSY2. Nucleotide diversity was equivalent for whites and yellows at PSY2 but was 19-fold less in yellows than in whites at Y1, consistent with the white ancestral state of the gene. The strong sequence haplotype conservation within yellows at Y1 and a significant, negative Tajima's D both verified positive selection for yellow endosperm. We propose that two independent gain-of-function events associated with insertions into the promoter of the Y1 gene and upregulation of expression in endosperm have been incorporated into yellow maize.

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Michele Morgante

Papers

A set of primers for the amplification of 20 chloroplast microsatellites in Pinaceae

Genome-wide gene expression profiling in Arabidopsis thaliana reveals new targets of abscisic acid and largely impaired gene regulation in the abi1-1 mutant.

Evolution of DNA Sequence Nonhomologies among Maize Inbreds

4 – Generating and Using DNA Markers in Plants

Contrasting effects of selection on sequence diversity and linkage disequilibrium at two phytoene synthase loci.