Biology subjects

Sakamoto, T.

Publications and source records attributed to Sakamoto, T..

At least 55 records · Page 3Linked to original sources

bioRxiv2022

Charge neutralization and β-elimination cleavage mechanism of family 42 L-rhamnose-α-1,4-D-glucuronate lyase revealed using neutron crystallography

Gum arabic (GA) is widely used as an emulsion stabilizer and edible coating, and consists of a complex carbohydrate moiety with a rhamnosyl-glucuronate group capping the non-reducing ends. Enzymes that can specifically cleave the glycosidic chains of GA and modify their properties are valuable tools for structural analysis and industrial application. Cryogenic X-ray crystal structure of GA-specific L-rhamnose--1,4-D-glucuronate lyase from Fusarium oxysporum (FoRham1), belonging to the polysaccharide lyase (PL) family 42, has been previously reported. To determine the specific reaction mechanism based on its hydrogen-containing enzyme structure, we performed joint X-ray/neutron crystallography of FoRham1. Large crystals were grown in the presence of L-rhamnose (a reaction product), and neutron and X-ray diffraction datasets were collected at room temperature up to 1.80 and 1.25 [A] resolutions, respectively. The active site contained L-rhamnose and acetate, the latter being a partial analog of glucuronate. Incomplete H/D exchange between Arg166 and acetate suggested that a strong salt-bridge interaction was maintained. Doubly deuteronated His105 and deuteronated Tyr150 supported this interaction. The unusually hydrogen-rich environment functions as a charge neutralizer for glucuronate and stabilizes the oxyanion intermediate. The NE2 atom of His85 was deprotonated and formed a hydrogen bond with the deuterated O1 hydroxy of L-rhamnose, indicating the function of His85 as the base/acid catalyst for bond cleavage via {beta}-elimination. Asp83 functions as a pivot between the two catalytic histidine residues by bridging them, and this His-His-Asp structural motif is conserved in the three PL families. Significance StatementAlthough hydrogen transfer plays an important role in enzymatic reactions, hydrogen atoms are generally invisible in macromolecular X-ray crystallography. In the reaction of polysaccharide lyases, substrate activation by negative charge stabilization of uronic acid and base/acid-catalyzed {beta}-elimination reaction have been postulated. Here, we report the neutron crystallography of polysaccharide lyase. Joint X-ray/neutron crystallography of L-rhamnose--1,4-D-glucuronate lyase from Fusarium oxysporum (FoRham1) complexed with L-rhamnose was performed, and the hydrogen and deuterium atoms were visualized at a high resolution. FoRham1 catalyzes the specific cleavage of the cap structure of gum arabic, which is useful for various applications in the food, cosmetic, and pharmaceutical industries. A detailed catalytic mechanism for FoRham1 was proposed based on the key structural features of its active site.

biophysics↗

bioRxiv2022

Sunscreen redox status in a multicellular cyanobacterium visualized by Raman scattering spectral microscope

UV radiation, desiccation, and starvation induce some cyanobacteria to produce a UVA-absorbing pigment, scytonemin, at extracellular sheaths. Although the accumulation of scytonemin is recognizable as dark sheaths through optical microscopes, it has been nontrivial to identify its redox status and obtain its subcellular distribution in response to physiological conditions. Here, we show that a spontaneous Raman scattering spectral microscopy based on an excitation-laser-line-scanning method unveil 3D subcellular distributions of non-UV-induced scytonemins with distinct redox statuses in a filamentous cyanobacterium with a single nitrogen-fixing cell at the basal end. Cellular differentiations and scytonemin redox conditions were simultaneously visualized with an excitation wavelength at 1064 nm that is virtually free from the optical screening by the dark sheaths. The molecular imaging results give insights into not only secretion mechanisms of the sunscreen pigment but also interdependence between photosynthesis, nitrogen fixation, and redox homeostasis in one of the simplest forms of multicellular organisms.

microbiology↗

bioRxiv2022

Chromosome-level genome assembly of Rorippa aquatica revealed its allotetraploid origin and mechanisms of heterophylly upon submergence

The ability to respond to environmental variability is essential for living systems, especially to sessile organisms such as plants. The amphibious plant Rorippa aquatica exhibits a drastic type of phenotypic plasticity known as heterophylly, a phenomenon where leaf form is altered in response to the surrounding environment. Although heterophylly has been studied in various plant species, its molecular mechanism has not been fully elucidated. To establish the genetic basis and analyze the evolutionary processes responsible for heterophylly, we assembled the chromosome-level genome of R. aquatica by combining data from Illumina short-read sequencing, PacBio long-read sequencing, and High-throughput Chromosome Conformation Capture (Hi-C) sequencing technologies. Fine-scale comparative chromosome painting and chromosomal genomics revealed that allopolyploidization and subsequent post-polyploid descending dysploidy occurred during R. aquatica speciation. The genomic information above was the basis for the transcriptome analyses to examine the mechanisms involved in heterophylly, especially in response to the submerged condition, which uncovered that the ethylene and blue light signaling pathways participate in regulating heterophylly under submerged conditions. The assembled R. aquatica reference genome provides novel insights into the molecular mechanisms and evolution of heterophylly.

plant biology↗

bioRxiv2022

Systematic functional annotation workflow for insects

Next generation sequencing has revolutionized entomological study, rendering it possible to analyze the genomes and transcriptomes of non-model insects. However, use of this technology is often limited to obtaining nucleotide sequences of target or related genes, with many of the acquired sequences remaining unused because other available sequences are not sufficiently annotated. To address this issue, we have developed a functional annotation workflow for transcriptome-sequenced insects to determine transcript descriptions, which represents a significant improvement over the previous method (functional annotation pipeline for insects). The developed workflow attempts to annotate not only the protein sequences obtained from transcriptome analysis but also the ncRNA sequences obtained simultaneously. In addition, the workflow integrates the expression level information obtained from transcriptome sequencing for application as functional annotation information. Using the workflow, functional annotation was performed on the sequences obtained from transcriptome sequencing of stick insect (Entoria okinawaensis) and silkworm (Bombyx mori), yielding richer functional annotation information than that obtained in our previous study. The improved workflow allows more comprehensive exploitation of transcriptome data and is applicable to other insects because the workflow has been openly developed on GitHub. Simple SummaryThe function of all genes encoded in the genome should be studied for genome editing. The genome editing technology can speeds up insect research for functional analysis of genes. Our knowledge about the functional information of genes is still incomplete currently while genome sequencing of an organism can be completed. The functional information has been annotated based solely on the information that has been obtained from the result of previous biological research. However, this information will be important in determining the target genes for genome editing. In particular, it is very important that this information is in machine-readable form because computer programs mainly parse this information for the understanding of biological systems. In this paper, we describe a workflow-based method for annotating gene functions in insects that make use of transcribed sequence information as well as reference genome and protein sequence databases. Using the developed workflow, we annotated functional information of Japanese stick insect and silkworm, including gene expression as well as sequence analysis. The functional annotation information obtained by the workflow will greatly expand the possibilities of entomological research using genome editing.

bioinformatics↗

bioRxiv2022

Collaborative workflow between pathologists and deep learning for evaluation of tumor cellularity in lung adenocarcinoma

Owing to the high demand for molecular testing, the reporting of tumor cellularity in cancer samples has become a mandatory task for pathologists. However, the pathological estimation of tumor cellularity is often inaccurate. We developed a collaborative workflow between pathologists and artificial intelligence (AI) models to evaluate tumor cellularity in lung cancer samples and prospectively applied it to routine practice. We also developed a quantitative model that we validated and tested on retrospectively analyzed cases and ran the model prospectively in a collaborative workflow where pathologists could access the AI results and apply adjustments (Adjusted-Score). The Adjusted-Scores were validated by comparing them with the ground truth established by manual annotation of hematoxylin-eosin slides with reference to immunostains with thyroid transcription factor-1 and napsin A. For training, validation, retrospective testing, and prospective application of the model, we used 40, 10, 50, and 151 whole slide images, respectively. The sensitivity and specificity of tumor segmentation were 97% and 87%, and the accuracy of nuclei recognition was 99%. Pathologists altered the initial scores in 87% of the cases after referring to the AI results and found that the scores became more precise after collaborating with AI. For validation of Adjusted-Score, we found the Adjusted-Score was significantly closer to the ground truth than non-AI-aided estimates (p<0.05). Thus, an AI-based model was successfully implemented into the routine practice of pathological investigations. The proposed model for tumor cell counting efficiently supported the pathologists to improve the prediction of tumor cellularity for genetic tests.

pathology↗

bioRxiv2021

Auxin-driven ecophysiological diversification of leaves in domesticated tomato

Heterobaric leaves have bundle sheath extensions (BSEs) that compartmentalise the parenchyma, whereas homobaric leaves do not. The presence of BSEs affects leaf hydraulics and photosynthetic rate. The tomato (Solanum lycopersicum) obscuravenosa (obv) mutant lacks BSEs. Here we identify the obv gene and the causative mutation, a non-synonymous amino acid change that disrupts a C2H2 zinc finger motif in a putative transcription factor. This mutation exists as a rare polymorphism in the natural range of wild tomatoes, but has increased in frequency in domesticated tomatoes, suggesting that the latter diversified into heterobaric and homobaric leaf types. The obv mutant displays reduced vein density, leaf hydraulic conductance and photosynthetic assimilation rate. We show that these and other effects on plant development, including changes in leaf insertion angle, leaf margin serration, minor vein density and fruit shape, are controlled by OBV via changes in auxin signalling. Loss of function of the transcriptional regulator AUXIN RESPONSE FACTOR (ARF4) also results in defective BSE development, revealing an additional component of a novel genetic module controlling aspects of leaf development important for ecological adaptation and subject to breeding selection. One sentence summarydistribution of tomato heterobaric and homobaric leaves is controlled by a single-nucleotide polymorphism in an auxin-related transcription factor

plant biology↗

bioRxiv2021

Immunoelectron microscopic characterization of vasopressin neurons in macaques by use of formaldehyde-fixed tissues stored for several years

Translational research often requires the testing of experimental therapies in primates, but research in non-human primates is now stringently controlled by law around the world. Tissues fixed in formaldehyde without glutaraldehyde have been thought to be inappropriate for use in electron microscopic analysis, particularly those of the brain. Here we report the immunoelectron microscopic characterization of arginine vasopressin (AVP)-producing neurons in macaque hypothalamo-pituitary axis tissues fixed with 4% formaldehyde and stored at -25{degrees}C for several years. The size difference of dense-cored vesicles between magnocellular and parvocellular AVP neurons was detectable in their cell bodies and perivascular nerve endings located, respectively, in the posterior pituitary and median eminence. Furthermore, glutamate and the vesicular glutamate transporter 2 were colocalized with AVP in perivascular nerve endings of both the posterior pituitary and the external layer of the median eminence, suggesting that both magnocellular and parvocellular AVP neurons are glutamatergic in primates. Both ultrastructure and immunoreactivity can therefore be sufficiently preserved in macaque brain tissues stored long-term for light microscopy. Taken together, these results suggest that this methodology could be applied to the human post-mortem brain and be very useful in translational research.

neuroscience↗

bioRxiv2021

Deceleration of cell cycle underpins a switch from proliferative- to terminal division in plant stomatal lineage

Differentiation of specialized cell types from self-renewing progenitors requires precise cell cycle control. Plant stomata are generated through asymmetric divisions of a stem-cell-like precursor meristemoid followed by the single symmetric division that creates an adjustable pore surrounded by paired guard cells. The stomatal-lineage-specific transcription factor MUTE terminates the asymmetric divisions and triggers differentiation. However, the role of cell cycle machinery in this transition remains unknown. Through time-lapse imaging, we discover that the symmetric division is slower than the asymmetric division. We identify a plant-specific cyclin-dependent kinase inhibitor, SIAMESE-RELATED4 (SMR4), as a molecular brake that decelerates cell cycle during this transition. SMR4 is directly induced by MUTE and transiently accumulates in differentiating meristemoids. SMR4 physically and functionally associates with CYCD3;1 and extends G1-phase of asymmetric divisions. By contrast, SMR4 fails to interact with CYCD5;1, a MUTE-induced G1 cyclin, and permits the symmetric division. Our work unravels a molecular framework of the proliferation-to-differentiation switch within the stomatal lineage and suggests that a timely proliferative cell cycle is critical for the stomatal fate specification.

plant biology↗

bioRxiv2021

Binding mechanism underlying FIH-1 suppression caused by the N-terminal disordered region of Mint3

Mint3 is known to enhance aerobic ATP production, known as the Warburg effect, by binding to FIH-1. Since this effect is considered to be beneficial for cancer cells, the interaction is a promising target for cancer therapy. However, previous research has suggested that the interacting region of Mint3 with FIH-1 is intrinsically disordered, which makes investigation of this interaction challenging. Therefore, we adopted a physicochemical approach that combined thermodynamic studies with structural analyses in solution, to clarify the binding mechanism. First, using a combination of CD, NMR, and hydrogen/deuterium exchange mass spectrometry (HDX-MS), we confirmed that the N-terminal half, which is the interacting part of Mint3, is mostly disordered. Next, using isothermal titration calorimetry (ITC), we revealed that the interaction of Mint3 and FIH-1 produces an enormous change in enthalpy and entropy. The profile is consistent with the model that the flexibility of disordered Mint3 is drastically reduced upon binding to FIH-1. Moreover, we performed a series of ITC experiments with several types of truncated Mint3s, an effective approach since the interacting part of Mint3 is disordered, and identified 78-88 as a novel core site for binding to FIH-1. The truncation study of Mint3 also revealed the thermodynamic contribution of each part to the interaction, where one contributes to the affinity ({Delta}G), while the other only affects enthalpy ({Delta}H), by forming non-covalent bonds. This insight can serve as a foothold for further investigation of IDRs and drug development for cancer therapy.

biochemistry↗

bioRxiv2020

TaxOnTree: a tool that generates trees annotated with taxonomic information

Phylogenetic analysis is a widely used approach for analyzing and illustrating gene/protein/species evolution and is being benefited by the increasing number of species with their DNA/genome sequenced. Generating a phylogenetic tree with sequences from hundreds of species can be considered a routine task. However, tree visualization has been challenged to organize and bring by accessible means relevant information, e.g. taxonomy, about the sampled genes/proteins. Here we present TaxOnTree, a computational tool that incorporates and allows a quick accession of the taxonomic information of samples in a phylogenetic tree. TaxOnTree takes as input a single phylogenetic tree in Newick format containing gene/protein identifiers from NCBI or Uniprot databases in their leaves but TaxOnTree also allows users to have as input a protein identifier, a single protein in FASTA, a list of protein accessions, or a(n) (un)aligned multi-FASTA file. Non-tree inputs are submitted to a phylogenetic reconstruction pipeline implemented into TaxOnTree. The tree provided by the user or generated by the pipeline is converted to Nexus format and then automatically annotated with the taxonomic information of each sample comprising the tree. The taxonomic information is retrieved by web requests from NCBI or Uniprot servers or from a local MySQL database and annotated as tags in the tree nodes. The final tree archive is in Nexus format and should be opened with FigTree software which allows visual inspection, by branch coloring or tip/node labeling, of the taxonomic information incorporated in the tree. TaxOnTree provides prompt inspection of the taxonomic distribution of orthologs and paralogs. It can be used for manual curation of taxonomic/phylogenetic scenarios and coupled to any tool that links homologous sequences to a seed sequence. TaxOnTree provides computational support to help users to inspect phylogenetic trees with a taxonomic view, even without being taxonomy experts. TaxOnTree is available at http://bioinfo.icb.ufmg.br/taxontree.

bioinformatics↗

bioRxiv2020

Establishment of a new sex-determining allele driven by sexually antagonistic selection

Some species undergo frequent turnovers of sex-determining locus, rather than having stable diverged sex chromosomes. In such species, how often turnover occurs is a fundamental evolutionary question. We model the process with considering a linked locus under sexually antagonistic selection. The entire process of a turnover may be divided into two phases, which are referred to as the stochastic and deterministic phases. The stochastic phase is when a new sex-determining allele just arises and is still rare and random genetic drift plays an important role. In the deterministic phase, the new allele further increases in frequency by positive selection. The theoretical results currently available are for the deterministic phase, which demonstrated that a turnover of a newly arisen sex determining locus could benefit from selection at a linked locus under sexually antagonistic selection, by assuming that sexually antagonistic selection works in a form of balancing selection. In this work, we provide a comprehensive theoretical description of the entire process from the stochastic phase to the deterministic phase. In addition to balancing selection, we explore several other modes of selection on the linked locus. Our theory allows us make a quantitative argument on the rate of turnover and the effect of the mode of selection at the linked locus. We also performed simulations to explore the pattern of polymorphism around the new sex determining locus. We find that the pattern of polymorphism is informative to infer how selection worked through the turnover process.

evolutionary biology↗

bioRxiv2020

Characterization and analysis of the transcriptome in Arapaima gigas using multi-tissue RNA-sequencing

Arapaima gigas is a giant bony tongue air-breathing fish, and a promising species for aquaculture due to its particular features. However, there is still a lack of information on its biology and few transcriptome studies are available. Our aim was to characterize the transcriptome of arapaima in order to shed light on molecular networks contributing to its unique traits. Through RNA-sequencing, we generated a transcriptome from eight tissues (brain, pituitary, heart, muscle, kidney, lung, ovary, and testis) collected from arapaima adults specimens. Using a genome-guided strategy associated with homologous protein evidence, 57,706 transcripts were assembled, which aligned to 23,353 high confidence protein-coding genes. The analysis revealed a global view of expression patterns, as well as it allowed us to identify tissue-specific gene clusters, transcription factors within the clusters, and to compare expression patterns between male and female. These analyses has generated tissue-specific and sex-biased transcriptome profiles, which will be helpful to understand its molecular biology, evolution, and also guide future functional studies of the arapaima.

genomics↗

bioRxiv2020

Curing genetic skin disease through altered replication stress response

Revertant mosaicism, or natural gene therapy, refers to the spontaneous in vivo reversion of an inherited mutation in a somatic cell1. Only [~]50 human genetic disorders exhibit revertant mosaicism, implicating a distinctive role played by mutant proteins in somatic correction of a pathogenic germline mutation2. However, the process by which mutant proteins induce somatic genetic reversion in these diseases remains unknown. Here we show that heterozygous pathogenic CARD14 mutations causing autoinflammatory skin diseases, including psoriasis and pityriasis rubra pilaris, are repaired mainly via homologous recombination. Rather than altering the DNA damage response to exogenous stimuli such as X-irradiation or etoposide treatment, mutant CARD14 increased DNA double-strand breaks under conditions of replication stress. Furthermore, mutant CARD14 suppressed new origin firings without promoting crossover events in the replication stress state. Together, these results suggest that mutant CARD14 alters the replication stress response and preferentially drives break-induced replication (BIR), which is generally suppressed in eukaryotes3. Our results highlight the involvement of BIR in reversion events, thus revealing a previously undescribed role of BIR that could potentially be exploited to develop therapeutics for currently intractable genetic diseases.

molecular biology↗

bioRxiv2020

Taxallnomy: Closing gaps in the NCBI Taxonomy

NCBI Taxonomy is the main taxonomic source for several bioinformatics tools and databases since all organisms with sequence accessions deposited on INSDC are organized in its hierarchical structure. Despite the extensive use and application of this data source, taking advantage of its taxonomic tree could be challenging because (1) some taxonomic ranks are missing in some lineages and (2) some nodes in the tree do not have a taxonomic rank assigned (referred to as "no rank"). To address this issue, we developed an algorithm that takes the tree structure from NCBI Taxonomy and generates a hierarchically complete taxonomic tree. The procedures performed by the algorithm consist of attempting to assign a taxonomic rank to "no rank" nodes and of creating/deleting nodes throughout the tree. The algorithm also creates a name for the new nodes by borrowing the names from its ranked child or, if there is no child, from its ranked parent node. The new hierarchical structure was named taxallnomy and it contains 33 hierarchical levels corresponding to the 33 taxonomic ranks currently used in the NCBI Taxonomy database. From taxallnomy, users can obtain the complete taxonomic lineage with 33 nodes of all taxa available in the NCBI Taxonomy database. Taxallnomy is applicable to several bioinformatics analyses that depend on NCBI Taxonomy data. In this work, we demonstrate its applicability by embedding taxonomic information of a specified rank into a phylogenetic tree; and by making metagenomics profiles. Taxallnomy algorithm was written in PERL and all its resources are available at bioinfo.icb.ufmg.br/taxallnomy. Database URL: http://bioinfo.icb.ufmg.br/taxallnomy

bioinformatics↗

bioRxiv2020

Revisiting the gastrin-releasing peptide/bombesin system: A reverse-evolutionary study considering Xenopus

Gastrin-releasing peptide (GRP), first isolated from the porcine stomach, is a neuropeptide that modulates the autonomic system in mammals and has previously been considered to be the mammalian equivalent of bombesin, a fourteen amino acid peptide first isolated from the skin of the European fire-bellied toad, Bombina bombina. Bombesin-like peptides and the related neuromedin B (NMB) have since been identified in mammals. However, the orthologous relationships among GRP/NMB/bombesin and their receptors in vertebrates are still not well understood. Our studies have focused on the GRP system that is widely conserved among vertebrates. We have used phylogenetic analysis and reverse transcription-PCR, quantitative PCR, immunohistochemistry, and Western blotting experiments to examine the expression of both GRP and its receptor (GRPR) in a clawed frog (Xenopus tropicalis) and to understand the derivation of GRP system in the ancestor of mammals. We demonstrate, by phylogenetic and synteny analyses, that GRP is not a mammalian counterpart of bombesin and also that, whereas the GRP system is widely conserved among vertebrates, the NMB/bombesin system has diversified in certain lineages, in particular in frog species. In Xenopus, we found the expression of the mRNA for both GRP and GRPR in the brain and stomach. In addition, our quantitative PCR analysis shows that, in Xenopus, the expression of GRP mRNA is highest in the brain, whereas expression of GRPR mRNA is highest in the spinal cord. Our immunohistochemical analysis shows that GRP-immunoreactive cell bodies and fibers are distributed in several telencephalic, diencephalic, and rhombencephalic regions and spinal cord of Xenopus. Our Western blotting analysis also indicates the presence of GRPR protein in the brain and spinal cord of Xenopus. We conclude that GRP peptides and their receptors have evolved to play multiple roles in both the gut and brain of amphibians as one of the gut-brain peptide systems. Author SummaryBombesin is a putative antibacterial peptide isolated from the skin of the frog, Bombina bombina. Two related (bombesin-like) peptides, gastrin-releasing peptide (GRP) and neuromedin B (NMB) have been found in mammals. The history of GRP/bombesin discovery has caused little attention to be paid to the evolutionary relationship of GRP/bombesin and their receptors in vertebrates. We have classified the peptides and their receptors from the phylogenetic viewpoint using a newly established genetic database and bioinformatics. We demonstrate, by phylogenetic and synteny analyses, that GRP is not a mammalian counterpart of bombesin and also that, whereas the GRP system is widely conserved among vertebrates, the NMB/bombesin system has diversified in certain lineages, in particular in frogs. Gene expression analyses combined with immunohistochemistry and Western blotting experiments indicate that GRP peptides and their receptors have evolved from ancestral (GRP) homologues to play multiple roles in both the gut and the brain as one of the gut-brain peptide systems of vertebrates, which is distinct from the frog bombesin lineage.

evolutionary biology↗

bioRxiv2020

RADSex: a computational workflow to study sex determination using Restriction Site-Associated DNA Sequencing data

The study of sex determination and sex chromosome organisation in non-model species has long been technically challenging, but new sequencing methodologies are now enabling precise and high-throughput identification of sex-specific genomic sequences. In particular, Restriction Site-Associated DNA Sequencing (RAD-Seq) is being extensively applied to explore sex determination systems in many plant and animal species. However, software designed to specifically search for sex-biased markers using RAD-Seq data is lacking. Here, we present RADSex, a computational analysis workflow designed to study the genetic basis of sex determination using RAD-Seq data. RADSex is simple to use, requires few computational resources, makes no prior assumptions about type of sex-determination system or structure of the sex locus, and offers convenient visualization through a dedicated R package. To demonstrate the functionality of RADSex, we re-analyzed a published dataset of Japanese medaka, Oryzias latipes, where we uncovered a previously unknown Y chromosome polymorphism. We then used RADSex to analyze new RAD-Seq datasets from 15 fish species spanning multiple systematic orders. We identified the sex determination system and sex-specific markers in six of these species, five of which had no known sex-markers prior to this study. We show that RADSex greatly facilitates the study of sex determination systems in non-model species and outperforms the commonly used RAD-Seq analysis software STACKS. RADSex in speed, resource usage, ease of application, and visualization options. Furthermore, our analysis of new datasets from 15 species provides new insights on sex determination in fish.

bioinformatics↗

bioRxiv2020

Assessing the sex-related genomic composition difference using a K-mer-based approach: a case of study in Arapaima gigas (Pirarucu).

Arapaima gigas is one of the largest freshwater bony fish in the world, in which adults could weigh 200 kilograms and measure 3 meters in length. Due to its large size and its low-fat meat, Arapaima gigas has quickly become a species of special interest in fish-farming. One challenge faced during their production is the lack of an efficient sexing methodology, since their sexual maturation occurs late (around the third to the fifth year) and the genetic mechanisms linked to their sex determination system are not known yet. For a more sustainable management, it is of paramount importance to seek an effective and non-invasive method to differentiate sexually juvenile individuals of Arapaima gigas. For this, the establishment of genetic markers associated with sexual differentiation would be an advantageous tool. In this study, we proposed a k-mer based approach to identify genome features with sex-determining properties. For this purpose, we used genomic data from four adult representatives of Arapaima gigas, two males and two females, and counted the k-mers comprising them. As result, we found k-mers from repetitive regions with high difference and disproportion in the count among individuals of the opposite sex. These differences in the k-mer-based genomic composition indicate the existence of genetic factors involved in the sexing of individuals in Arapaima gigas.

genomics↗

bioRxiv2019

Establishment Process of a Magic Trait Allele subject to Both Divergent Selection and Assortative Mating

Sexual selection and divergent selection are among the major driving forces of reproductive isolation, which could eventually result in speciation. A magic trait is defined such that a single trait is subject to both divergent selection and sexual selection through phenotype-based assortative mating. We are here interested in the evolutionary behavior of alleles in a genetic locus responsible for a magic trait. We assume that, in a pair of homogeneous subpopulations, a mutant allele arises at the magic trait locus, and theoretically obtain the probability that the new allele establishes in the population. We also consider the trajectory of allele frequency along the establishment. Divergent selection simply favors the new allele to fix where it is beneficial, whereas assortative mating works against rare alleles. It is theoretically demonstrated that the fate of the new allele is determined by the relative contributions of the two selective forces, divergent selection and assortative mating, when the allele is rare so that the two selective forces counteract. We also show that random genetic drift also plays an important role. The theoretical results would contribute to improve our understanding of how natural selection initiates speciation.

evolutionary biology↗