SNPmasker: automatic masking of SNPs and repeats across eukaryotic genomes

SNPmasker is a comprehensive web interface for masking large eukaryotic genomes. The program is designed to mask SNPs from recent dbSNP database and to mask the repeats with two alternative programs. In addition to the SNP masking, we also offer population-specific substitution of SNP alleles in genomic sequence according to SNP frequencies in HapMap Phase II data. The input to SNPmasker can be defined in chromosomal coordinates or inserted as a sequence. The sequences masked by our web server are most useful as a preliminary step for different primer and probe design tasks. The service is available at and is free for all users

GENOMEMASKER package for designing unique genomic PCR primers

BACKGROUND: The design of oligonucleotides and PCR primers for studying large genomes is complicated by the redundancy of sequences. The eukaryotic genomes are particularly difficult to study due to abundant repeats. The speed of most existing primer evaluation programs is not sufficient for large-scale experiments. RESULTS: In order to improve the efficiency and success rate of automatic primer/oligo design, we created a novel method which allows rapid masking of repeats in large sequence files, for example in eukaryotic genomes. It also allows the detection of all alternative binding sites of PCR primers and the prediction of PCR products. The new method was implemented in a collection of efficient programs, the GENOMEMASKER package. The performance of the programs was compared to other similar programs. We also modified the PRIMER3 program, to be able to design primers from lowercase-masked sequences. CONCLUSION: The GENOMEMASKER package is able to mask the entire human genome for non-unique primers within 6 hours and find locations of all binding sites for 10 000 designed primer pairs within 10 minutes. Additionally, it predicts all alternative PCR products from large genomes for given primer pairs

Genome-wide histone modification profiling of inner cell mass and trophectoderm of bovine blastocysts by RAT-ChIP

Chromatin immunoprecipitation coupled with next-generation sequencing (ChIP-seq) has revolutionized our understanding of chromatin-related biological processes. The method, however, requires thousands of cells and has therefore limited applications in situations where cell numbers are limited. Here we describe a novel method called Restriction Assisted Tagmentation Chromatin Immunoprecipitation (RAT-ChIP) that enables global histone modification profiling from as few as 100 cells. The method is simple, cost-effective and takes a single day to complete. We demonstrate the sensitivity of the method by deriving the first genome-wide maps of histone H3K4me3 and H3K27me3 modifications of inner cell mass and trophectoderm of bovine blastocyst stage embryos.Peer reviewe

Predicting failure rate of PCR in large genomes

We have developed statistical models for estimating the failure rate of polymerase chain reaction (PCR) primers using 236 primer sequence-related factors. The model involved 1314 primer pairs and is based on more than 80 000 PCR experiments. We found that the most important factor in determining PCR failure is the number of predicted primer-binding sites in the genomic DNA. We also compared different ways of defining primer-binding sites (fixed length word versus thermodynamic model; exact match versus matches including 1–2 mismatches). We found that the most efficient prediction of PCR failure rates can be achieved using a combination of four factors (number of primer-binding sites counted in different ways plus GC% of the primer) combined into single statistical model GM1. According to our estimations from experimental data, the GM1 model can reduce the average failure rate of PCR primers nearly 3-fold (from 17% to 6%). The GM1 model can easily be implemented in software to premask genome sequences for potentially failing PCR primers, thus improving large-scale PCR-primer design

Genome and low-iron response of an oceanic diatom adapted to chronic iron limitation

ABSTRACT: BACKGROUND: Biogeochemical elemental cycling is driven by primary production of biomass via phototrophic phytoplankton growth, with 40% of marine productivity being assigned to diatoms. Phytoplankton growth is widely limited by the availability of iron, an essential component of the photosynthetic apparatus. The oceanic diatom Thalassiosira oceanica shows a remarkable tolerance to low-iron conditions and was chosen as a model for deciphering the cellular response upon shortage of this essential micronutrient. RESULTS: The combined efforts in genomics, transcriptomics and proteomics reveal an unexpected metabolic flexibility in response to iron availability for T. oceanica CCMP1005. The complex response comprises cellular retrenchment as well as remodeling of bioenergetic pathways, where the abundance of iron-rich photosynthetic proteins is lowered, whereas iron-rich mitochondrial proteins are preserved. As a consequence of iron deprivation, the photosynthetic machinery undergoes a remodeling to adjust the light energy utilization with the overall decrease in photosynthetic electron transfer complexes. CONCLUSIONS: Beneficial adaptations to low-iron environments include strategies to lower the cellular iron requirements and to enhance iron uptake. A novel contribution enhancing iron economy of phototrophic growth is observed with the iron-regulated substitution of three metal-containing fructose-bisphosphate aldolases involved in metabolic conversion of carbohydrates for enzymes that do not contain metals. Further, our data identify candidate components of a high-affinity iron-uptake system, with several of the involved genes and domains originating from duplication events. A high genomic plasticity, as seen from the fraction of genes acquired through horizontal gene transfer, provides the platform for these complex adaptations to a low-iron world

AIRE activated tissue specific genes have histone modifications associated with inactive chromatin

The Autoimmune Regulator (AIRE) protein is expressed in thymic medullary epithelial cells, where it promotes the ectopic expression of tissue-restricted antigens needed for efficient negative selection of developing thymocytes. Mutations in AIRE cause APECED syndrome, which is characterized by a breakdown of self-tolerance. The molecular mechanism by which AIRE increases the expression of a variety of different genes remains unknown. Here, we studied AIRE-regulated genes using whole genome expression analysis and chromatin immunoprecipitation. We show that AIRE preferentially activates genes that are tissue-specific and characterized by low levels of initial expression in stably transfected HEK293 cell model and mouse thymic medullary epithelial cells. In addition, the AIRE-regulated genes lack active chromatin marks, such as histone H3 trimethylation (H3K4me3) and acetylation (AcH3), on their promoters. We also show that during activation by AIRE, the target genes acquire histone H3 modifications associated with transcription and RNA polymerase II. In conclusion, our data show that AIRE is able to promote ectopic gene expression from chromatin associated with histone modifications characteristic to inactive genes