Teaching transposon classification as a means to crowd source the curation of repeat annotation - a tardigrade perspective.

BACKGROUND: The advancement of sequencing technologies results in the rapid release of hundreds of new genome assemblies a year providing unprecedented resources for the study of genome evolution. Within this context, the significance of in-depth analyses of repetitive elements, transposable elements (TEs) in particular, is increasingly recognized in understanding genome evolution. Despite the plethora of available bioinformatic tools for identifying and annotating TEs, the phylogenetic distance of the target species from a curated and classified database of repetitive element sequences constrains any automated annotation effort. Moreover, manual curation of raw repeat libraries is deemed essential due to the frequent incompleteness of automatically generated consensus sequences. RESULTS: Here, we present an example of a crowd-sourcing effort aimed at curating and annotating TE libraries of two non-model species built around a collaborative, peer-reviewed teaching process. Manual curation and classification are time-consuming processes that offer limited short-term academic rewards and are typically confined to a few research groups where methods are taught through hands-on experience. Crowd-sourcing efforts could therefore offer a significant opportunity to bridge the gap between learning the methods of curation effectively and empowering the scientific community with high-quality, reusable repeat libraries. CONCLUSIONS: The collaborative manual curation of TEs from two tardigrade species, for which there were no TE libraries available, resulted in the successful characterization of hundreds of new and diverse TEs in a reasonable time frame. Our crowd-sourcing setting can be used as a teaching reference guide for similar projects: A hidden treasure awaits discovery within non-model organisms.

Comparative Venomics of the Cryptic Cone Snail Species Virroconus ebraeus and Virroconus judaeus.

The venom duct transcriptomes and proteomes of the cryptic cone snail species Virroconus ebraeus and Virroconus judaeus were obtained and compared. The most abundant and shared conotoxin precursor superfamilies in both species were M, O1, and O2. Additionally, three new putative conotoxin precursor superfamilies (Virro01-03) with cysteine pattern types VI/VII and XVI were identified. The most expressed conotoxin precursor superfamilies were SF-mi2 and M in V. ebraeus, and Cerm03 and M in V. judaeus. Up to 16 conotoxin precursor superfamilies and hormones were differentially expressed between both species, and clustered into two distinct sets, which could represent adaptations of each species to different diets. Finally, we predicted, with machine learning algorithms, the 3D structure model of selected venom proteins including the differentially expressed Cerm03 and SF-mi2, an insulin type 3, a Gastridium geographus GVIA-like conotoxin, and an ortholog to the Pionoconus magus ω-conotoxin MVIIA (Ziconotide).

Chromosome-level genome of the venomous snail Kalloconus canariensis: a valuable model for venomics and comparative genomics.

BACKGROUND: Genomes are powerful resources to understand the evolutionary mechanisms underpinning the origin and diversification of the venoms of cone snails (Conidae: Caenogastropoda) and could aid in the development of novel drugs. FINDINGS: Here, we used PacBio continuous long reads and Omni-C data to assemble the chromosome-level genome of Kalloconus canariensis, a vermivorous cone endemic to the Canary Islands. The final genome size was 2.87 Gb, with a N50 of 79.75 Mb and 91% of the reads located into the 35 largest scaffolds. Up to 55.80% of the genome was annotated as repetitive regions, being class I of transposable elements (16.65%) predominant. The annotation estimated 34,287 gene models. Comparative analysis of this genome with the 2 cone snail genomes released to date (Dendroconus betulinus and Lautoconus ventricosus) revealed similar genome sizes and organization, although chromosome sizes tended to be shorter in K. canariensis. Phylogenetic relationships within subclass Caenogastropoda were recovered with strong statistical support. The family Conidae was recovered as a clade, with K. canariensis plus L. ventricosus sister to D. betulinus. CONCLUSIONS: Despite the great diversity of cone snails (>900 species) and their venoms (hundreds of peptides per species), only 2 recently reported genomes are available for the group. The high-quality chromosome-level assembly of K. canariensis will be a valuable reference for studying the origin and evolution of conotoxin genes as well as whole-genome duplication events during gastropod evolution.

The genome of the venomous snail Lautoconus ventricosus sheds light on the origin of conotoxin diversity.

BACKGROUND: Venoms are deadly weapons to subdue prey or deter predators that have evolved independently in many animal lineages. The genomes of venomous animals are essential to understand the evolutionary mechanisms involved in the origin and diversification of venoms. RESULTS: Here, we report the chromosome-level genome of the venomous Mediterranean cone snail, Lautoconus ventricosus (Caenogastropoda: Conidae). The total size of the assembly is 3.59 Gb; it has high contiguity (N50 = 93.53 Mb) and 86.6 Mb of the genome assembled into the 35 largest scaffolds or pseudochromosomes. On the basis of venom gland transcriptomes, we annotated 262 complete genes encoding conotoxin precursors, hormones, and other venom-related proteins. These genes were scattered in the different pseudochromosomes and located within repetitive regions. The genes encoding conotoxin precursors were normally structured into 3 exons, which did not necessarily coincide with the 3 structural domains of the corresponding proteins. Additionally, we found evidence in the L. ventricosus genome for a past whole-genome duplication event by means of conserved gene synteny with the Pomacea canaliculata genome, the only one available at the chromosome level within Caenogastropoda. The whole-genome duplication event was further confirmed by the presence of a duplicated hox gene cluster. Key genes for gastropod biology including those encoding proteins related to development, shell formation, and sex were located in the genome. CONCLUSIONS: The new high-quality L. ventricosus genome should become a reference for assembling and analyzing new gastropod genomes and will contribute to future evolutionary genomic studies among venomous animals.

Correction to: Historical biogeography reveals new independent evolutionary lineages in the Pantosteus plebeius-nebuliferus speciesgroup (Actinopterygii: Catostomidae).

Following publication of the original article.

Historical biogeography reveals new independent evolutionary lineages in the Pantosteus plebeius-nebuliferus species-group (Actinopterygii: Catostomidae).

BACKGROUND: The Pantosteus plebeius-nebuliferus species-group is a group of freshwater fishes distributed in endo- and exorheic drainage basins in the Mexican Sierra Madre Occidental mountain range system and central North Mexico. The geological history of this region is considered an important factor in explaining the evolutionary history of low vagility animals like freshwaters fishes. The aim of this study was to examine the phylogenetic relationships and describe the evolutionary history of the species-group. We hypothesized that the genetic structure and distribution of the main clades of Pantosteus plebeius-nebuliferus are associated with the geological history of Northern Mexico. To this end, we obtained DNA sequences of mitochondrial and nuclear genes and performed phylogenetic and phylogeographic analyses. Divergence time estimation and ancestral area reconstruction were also carried out to propose a biogeographical hypothesis, and species boundaries within the species-group were also tested. RESULTS: We identified four clades within the Pantosteus plebeius-nebuliferus species-group in both markers. Divergence ranged from 5.9% to 9.2% for cytb and 0.1% to 0.9% for GHI. We observed significant genetic structure and no shared haplotypes between clades. We estimated that the clades diverged during the last 5.1 Myr, with a biogeographic scenario suggesting eight vicariant and four dispersal events through the historic range of the species-group. We found that the best species-delimitation model is when four species are assumed, which correspond to the main clades. We identified nine evolutionary significance units (ESUs), pertinent to the conservation of the group, each representing populations present in distinct drainage basins. CONCLUSIONS: The evolutionary history of the Pantosteus plebeius-nebuliferus species-group is characterized by vicariant post-dispersal processes, linked to geological changes in the Sierra Madre Occidental and central Northern Mexico since the Pliocene. This is congruent with biogeographic patterns described for other co-distributed fish species. We propose a new phylogenetic hypothesis for the species-group, clarifying the taxonomy of this evolutionarily complex group. Our results suggest that the species-group consists of at least four clades with independent evolutionary histories, two of which may represent new undescribed species. Our identification of ESUs provides a basis upon which conservation measures can be developed for the species-group.

Structural, dynamical, and electronic transport properties of modified DNA duplexes containing size-expanded nucleobases.

Among the distinct strategies proposed to expand the genetic alphabet, size-expanded nucleobases are promising for the development of modified DNA duplexes with improved biotechnological properties. In particular, duplexes built up by replacing canonical bases with the corresponding benzo-fused counterparts could be valuable as molecular nanowires. In this context, this study reports the results of classical molecular dynamics simulations carried out to examine the structural and dynamical features of size-expanded DNAs, including both hybrid duplexes containing mixed pairs of natural and benzo-fused bases (xDNA) and pure size-expanded (xxDNA) duplexes. Furthermore, the electronic structure of both natural and size-expanded duplexes is examined by means of density functional computations. The results confirm that the structural and flexibility properties of the canonical DNA are globally little affected by the presence of benzo-fused bases. The most relevant differences are found in the enhanced size of the grooves, and the reduction in the twist. However, the analysis also reveals subtle structural effects related to the nature and sequence of benzo-fused bases in the duplex. On the other hand, electronic structure calculations performed for xxDNAs confirm the reduction in the HOMO-LUMO gap predicted from the analysis of the natural bases and their size-expanded counterparts, which suggests that pure size-expanded DNAs can be good conductors. A more complex situation is found for xDNAs, where fluctuations in the electrostatic interaction between base pairs exerts a decisive influence on the modulation of the energy gap.

Binding affinities of oligonucleotides and PNAs containing phenoxazine and G-clamp cytosine analogues are unusually sequence-dependent.

Melting temperatures of DNA duplexes containing the phenoxazine (P) and G-clamp (X) cytosine analogues exhibited a strong and unusual dependence on the nucleoside flanking the modified nucleobase, and the same trend was observed in PNA-DNA duplexes incorporating X in the PNA chain. Molecular dynamics simulations of the DNA duplexes show that generalized stacking (including secondary interactions of the ammonium group of X) and hydrogen bonding are good descriptors of the different duplex stabilities.

Benzoderivatives of nucleic acid bases as modified DNA building blocks.

The tautomeric properties of benzoderivatives of the canonical nucleic acid bases have been studied by using different computational approaches. Attention has been paid to the impact of the benzene group in altering the tautomeric preferences of the canonical bases both in the gas phase and in aqueous solution. To this end, relative solvation free energies of the tautomers determined from Self-Consistent Reaction Field continuum calculations and Monte Carlo-Free Energy Perturbation are combined with gas-phase tautomerization free energies determined from quantum mechanical calculations. The results provide a detailed picture of the tautomeric preferences of the benzoderivatives of nucleic acid bases. This information is used to examine the recognition properties of the preferred tautomers of the benzo-fused derivatives, paying particular attention to the ability to form Watson-Crick hydrogen-bonding and stacking interactions as well as to the hydrophobic nature of the modified bases. The implications of present results on the potential use of benzo-fused bases as potential building blocks in modified DNA duplexes are examined.

Exploring the Essential Dynamics of B-DNA.

The essential dynamics of different normal and chemically modified DNA duplexes pertaining to the B family have been extensively explored from molecular dynamics simulations using powerful data mining techniques. Some of them, which are presented here for the first time, might become standard, powerful tools to characterize the dynamical behavior of complex biomolecular structures such as nucleic acids. Their potential impact is illustrated by examining the extended trajectories sampled for the set of DNA duplexes considered in this study, which allows us to discuss the degree of conservation of the natural flexibility pattern of the different DNAs, which in specific cases contain severe chemical modifications.

Unique tautomeric properties of isoguanine.

The tautomeric properties of isoguanine (also named 2-oxoadenine or 2-hydroxyadenine) have been studied in the gas phase, in different pure solvents, and in the DNA environment using state of the art theoretical methods. Our results show that isoguanine constitutes an unique example of how tautomerism can be modulated by the environment. Compared to the tautomeric preference in the gas phase, both polar solvents and the DNA microenvironment dramatically change the intrinsic tautomeric properties of isoguanine. Tautomers which are important in physiological conditions are less than 1/10(5) of the total population of isoguanine in the gas phase. The impact of the present findings in the understanding of spontaneous mutations and in the design of new nucleobases with multiple recognition properties is discussed.