Repeats and EST analysis for new organisms

MeShClust v3.0: high-quality clustering of DNA sequences using the mean shift algorithm and alignment-free identity scores

Background

Tools for accurately clustering biological sequences are among the most important tools in computational biology. Two pioneering tools for clustering sequences are CD-HIT and UCLUST, both of which are fast and consume reasonable amounts of memory; however, there is a big room for improvement in terms of cluster quality. Motivated by this opportunity for improving cluster quality, we applied the mean shift algorithm in MeShClust v1.0. The mean shift algorithm is an instance of unsupervised learning. Its strong theoretical foundation guarantees the convergence to the true cluster centers. Our implementation of the mean shift algorithm in MeShClust v1.0 was a step forward. In this work, we scale up the algorithm by adapting an out-of-core strategy while utilizing alignment-free identity scores in a new tool: MeShClust v3.0.

Results

We evaluated CD-HIT, MeShClust v1.0, MeShClust v3.0, and UCLUST on 22 synthetic sets and five real sets. These data sets were designed or selected for testing the tools in terms of scalability and different similarity levels among sequences comprising clusters. On the synthetic data sets, MeShClust v3.0 outperformed the related tools on all sets in terms of cluster quality. On two real data sets obtained from human microbiome and maize transposons, MeShClust v3.0 outperformed the related tools by wide margins, achieving 55%–300% improvement in cluster quality. On another set that includes degenerate viral sequences, MeShClust v3.0 came third. On two bacterial sets, MeShClust v3.0 was the only applicable tool because of the long sequences in these sets. MeShClust v3.0 requires more time and memory than the related tools; almost all personal computers at the time of this writing can accommodate such requirements. MeShClust v3.0 can estimate an important parameter that controls cluster membership with high accuracy.

Conclusions

These results demonstrate the high quality of clusters produced by MeShClust v3.0 and its ability to apply the mean shift algorithm to large data sets and long sequences. Because clustering tools are utilized in many studies, providing high-quality clusters will help with deriving accurate biological knowledge.

Supplementary Information

The online version contains supplementary material available at (10.1186/s12864-022-08619-0).

Bioinformatics Resources for Plant Abiotic Stress Responses: State of the Art and Opportunities in the Fast Evolving -Omics Era

Abiotic stresses are among the principal limiting factors for productivity in agriculture. In the current era of continuous climate changes, the understanding of the molecular aspects involved in abiotic stress response in plants is a priority. The rise of -omics approaches provides key strategies to promote effective research in the field, facilitating the investigations from reference models to an increasing number of species, tolerant and sensitive genotypes. Integrated multilevel approaches, based on molecular investigations at genomics, transcriptomics, proteomics and metabolomics levels, are now feasible, expanding the opportunities to clarify key molecular aspects involved in responses to abiotic stresses. To this aim, bioinformatics has become fundamental for data production, mining and integration, and necessary for extracting valuable information and for comparative efforts, paving the way to the modeling of the involved processes. We provide here an overview of bioinformatics resources for research on plant abiotic stresses, describing collections from -omics efforts in the field, ranging from raw data to complete databases or platforms, highlighting opportunities and still open challenges in abiotic stress research based on -omics technologies.

Construction of a cDNA library from female adult of Toxocara canis, and analysis of EST and immune-related genes expressions

Toxocara canis is a widespread intestinal nematode parasite of dogs, which can also cause disease in humans. We employed an expressed sequence tag (EST) strategy in order to study gene-expression including development, digestion and reproduction of T. canis. ESTs provided a rapid way to identify genes, particularly in organisms for which we have very little molecular information. In this study, a cDNA library was constructed from a female adult of T. canis and 215 high-quality ESTs from 5'-ends of the cDNA clones representing 79 unigenes were obtained. The titer of the primary cDNA library was 1.83×10(6)pfu/mL with a recombination rate of 99.33%. Most of the sequences ranged from 300 to 900bp with an average length of 656bp. Cluster analysis of these ESTs allowed identification of 79 unique sequences containing 28 contigs and 51 singletons. BLASTX searches revealed that 18 unigenes (22.78% of the total) or 70 ESTs (32.56% of the total) were novel genes that had no significant matches to any protein sequences in the public databases. The rest of the 61 unigenes (77.22% of the total) or 145 ESTs (67.44% of the total) were closely matched to the known genes or sequences deposited in the public databases. These genes were classified into seven groups based on their known or putative biological functions. We also confirmed the gene expression patterns of several immune-related genes using RT-PCR examination. This work will provide a valuable resource for the further investigations in the stage-, sex- and tissue-specific gene transcription or expression.

Identification of repetitive elements in the genome of Oreochromis niloticus: tilapia repeat masker

The large-scale bacterial artificial chromosome-end sequencing project of Nile tilapia (Oreochromis niloticus) has generated extensive sequence data that allowed the examination of the repeat content in this fish genome and building of a repeat library specific for this species. This library was established based on Tilapiini repeat sequences from GenBank, sequences orthologous to the repeat library of zebrafish in Repbase, and novel repeats detected by genome analysis using MIRA assembler. We estimate that repeats constitute about 14% of the tilapia genome and also give estimates for the occurrence of the different repeats based on the Basic Local Alignment Search Tool searches within the database of known tilapia sequences. The frequent occurrence of novel repeats in the tilapia genome indicates the importance of using the species-specific repeat masker prior to sequence analyses. A web tool based on the RepeatMasker software was designed to assist tilapia genomics.

Generation and analysis of expressed sequence tags from a cDNA library of Moniezia expansa

The Moniezia expansa is a parasite of sheep that causes diarrhea and fleshless leading to stockbreeding losses. A genomic resource for large-scale molecular studies in this parasite is lacking. To study the gene expression including development, digestion and reproduction organs of M. expansa, a cDNA library had been constructed and expressed sequence tags (ESTs) had been analyzed, which were helpful for the development of a powerful microarray platform which are used to analyze gene expression in this species. cDNAs are useful resources in annotating genes and providing functional analysis of genes. In this study, a cDNA library from adult cestode of M. expansa was created and 2642 ESTs from 5'-ends of the cDNA clones representing 1081 unigenes were obtained. Cluster analysis of these ESTs allowed identification of 1081 unique sequences containing 351 contigs and 730 singletons. BLASTX searches identified 780 significant (E-value<10(-5)) hits and further Gene Ontology (GO) analysis was used to annotate these genes. All the EST sequences were deposited under dbEST in GenBank (GenBank: FE905224-FE905315, FE942104-FE942773, FE969189-FE969190, FF677548-FF677734, FF848124-FF848253). Although we only obtained 1081 unigenes, the set of ESTs identified represents a significant proportion of the M. expansa and provides molecular resource for the development of microarrays for gene expression studies concerning development, metabolism and reproduction.