Yuichiro Hara

Optimizing and benchmarking de novo transcriptome sequencing: from library preparation to assembly evaluation

BackgroundRNA-seq enables gene expression profiling in selected spatiotemporal windows and yields massive sequence information with relatively low cost and time investment, even for non-model species. However, there remains a large room for optimizing its workflow, in order to take full advantage of continuously developing sequencing capacity.MethodTranscriptome sequencing for three embryonic stages of Madagascar ground gecko (Paroedura picta) was performed with the Illumina platform. The output reads were assembled de novo for reconstructing transcript sequences. In order to evaluate the completeness of transcriptome assemblies, we prepared a reference gene set consisting of vertebrate one-to-one orthologs.ResultTo take advantage of increased read length of >150 nt, we demonstrated shortened RNA fragmentation time, which resulted in a dramatic shift of insert size distribution. To evaluate products of multiple de novo assembly runs incorporating reads with different RNA sources, read lengths, and insert sizes, we introduce a new reference gene set, core vertebrate genes (CVG), consisting of 233 genes that are shared as one-to-one orthologs by all vertebrate genomes examined (29 species)., The completeness assessment performed by the computational pipelines CEGMA and BUSCO referring to CVG, demonstrated higher accuracy and resolution than with the gene set previously established for this purpose. As a result of the assessment with CVG, we have derived the most comprehensive transcript sequence set of the Madagascar ground gecko by means of assembling individual libraries followed by clustering the assembled sequences based on their overall similarities.ConclusionOur results provide several insights into optimizing de novo RNA-seq workflow, including the coordination between library insert size and read length, which manifested in improved connectivity of assemblies. The approach and assembly assessment with CVG demonstrated here would be applicable to transcriptome analysis of other species as well as whole genome analyses.

gVolante for standardizing completeness assessment of genome and transcriptome assemblies

Motivation Along with the increasing accessibility to comprehensive sequence information, such as whole genomes and transcriptomes, the demand for assessing their quality has been multiplied. To this end, metrics based on sequence lengths, such as N50, have become a standard, but they only evaluate one aspect of assembly quality. Conversely, analyzing the coverage of pre‐selected reference protein‐coding genes provides essential content‐based quality assessment, but the currently available pipelines for this purpose, CEGMA and BUSCO, do not have a user‐friendly interface to serve as a uniform environment for assembly completeness assessment. Results Here, we introduce a brand‐new web server, gVolante, which provides an online tool for (i) on‐demand completeness assessment of sequence sets by means of the previously developed pipelines CEGMA and BUSCO and (ii) browsing pre‐computed completeness scores for publicly available data in its database section. Completeness assessments performed on gVolante report scores based on not just the coverage of reference genes but also on sequence lengths (e.g. N50 scaffold length), allowing quality control in multiple aspects. Using gVolante, one can compare the quality of original assemblies between their multiple versions (obtained through program choice and parameter tweaking, for example) and evaluate them in comparison to the scores of public resources found in the database section. Availability and implementation gVoalte is freely available at https://gvolante.riken.jp/. Contact shigehiro.kuraku@riken.jp

Diversification of non-visual photopigment parapinopsin in spectral sensitivity for diverse pineal functions.

BackgroundRecent genome projects of various animals have uncovered an unexpectedly large number of opsin genes, which encode protein moieties of photoreceptor molecules, in most animals. In visual systems, the biological meanings of this diversification are clear; multiple types of visual opsins with different spectral sensitivities are responsible for color vision. However, the significance of the diversification of non-visual opsins remains uncertain, in spite of the importance of understanding the molecular mechanism and evolution of varied non-visual photoreceptions.ResultsHere, we investigated the diversification of the pineal photopigment parapinopsin, which serves as the UV-sensitive photopigment for the pineal wavelength discrimination in the lamprey, linking it with other pineal photoreception. Spectroscopic analyses of the recombinant pigments of the two teleost parapinopsins PP1 and PP2 revealed that PP1 is a UV-sensitive pigment, similar to lamprey parapinopsin, but PP2 is a blue-sensitive pigment, with an absorption maximum at 460–480 nm, showing the diversification of non-visual pigment with respect to spectral sensitivity. We also found that PP1 and PP2 exhibit mutually exclusive expressions in the pineal organs of three teleost species. By using transgenic zebrafish in which these parapinopsin-expressing cells are labeled, we found that PP1-expressing cells basically possess neuronal processes, which is consistent with their involvement in wavelength discrimination. Interestingly, however, PP2-expressing cells rarely possess neuronal processes, raising the possibility that PP2 could be involved in non-neural responses rather than neural responses. Furthermore, we found that PP2-expressing cells contain serotonin and aanat2, the key enzyme involved in melatonin synthesis from serotonin, whereas PP1-expressing cells do not contain either, suggesting that blue-sensitive PP2 is instead involved in light-regulation of melatonin secretion.ConclusionsIn this paper, we have clearly shown the different molecular properties of duplicated non-visual opsins by demonstrating the diversification of parapinopsin with respect to spectral sensitivity. Moreover, we have shown a plausible link between the diversification and its physiological impact by discovering a strong candidate for the underlying pigment in light-regulated melatonin secretion in zebrafish; the diversification could generate a new contribution of parapinopsin to pineal photoreception. Current findings could also provide an opportunity to understand the “color” preference of non-visual photoreception.

Incorporating tree‐thinking and evolutionary time scale into developmental biology

Phylogenetic approaches are indispensable in any comparative molecular study involving multiple species. These approaches are in increasing demand as the amount and availability of DNA sequence information continues to increase exponentially, even for organisms that were previously not extensively studied. Without the sound application of phylogenetic concepts and knowledge, one can be misled when attempting to infer ancestral character states as well as the timing and order of evolutionary events, both of which are frequently exerted in evolutionary developmental biology. The ignorance of phylogenetic approaches can also impact non‐evolutionary studies and cause misidentification of the target gene or protein to be examined in functional characterization. This review aims to promote tree‐thinking in evolutionary conjecture and stress the importance of a sense of time scale in cross‐species comparisons, in order to enhance the understanding of phylogenetics in all biological fields including developmental biology. To this end, molecular phylogenies of several developmental regulatory genes, including those denoted as “cryptic pan‐vertebrate genes”, are introduced as examples.

Gene expression profiling of granule cells and Purkinje cells in the zebrafish cerebellum

The structure of the neural circuitry of the cerebellum, which functions in some types of motor learning and coordination, is generally conserved among vertebrates. However, some cerebellar features are species specific. It is not clear which genes are involved in forming these conserved and species‐specific structures and functions. This study uses zebrafish transgenic larvae expressing fluorescent proteins in granule cells, Purkinje cells, or other cerebellar neurons and glial cells to isolate each type of cerebellar cells by fluorescence‐activated cell sorting and to profile their gene expressions by RNA sequencing and in situ hybridization. We identify genes that are upregulated in granule cells or Purkinje cells, including many genes that are also expressed in mammalian cerebella. Comparison of the transcriptomes in granule cells and Purkinje cells in zebrafish larvae reveals that more developmental genes are expressed in granule cells, whereas more neuronal‐function genes are expressed in Purkinje cells. We show that some genes that are upregulated in granule cells or Purkinje cells are also expressed in the cerebellum‐like structures. Our data provide a platform for understanding the development and function of the cerebellar neural circuits in zebrafish and the evolution of cerebellar circuits in vertebrates. J. Comp. Neurol. 525:1558–1585, 2017.

CTCF binding landscape in jawless fish with reference to Hox cluster evolution

The nuclear protein CCCTC-binding factor (CTCF) contributes as an insulator to chromatin organization in animal genomes. Currently, our knowledge of its binding property is confined mainly to mammals. In this study, we identified CTCF homologs in extant jawless fishes and performed ChIP-seq for the CTCF protein in the Arctic lamprey. Our phylogenetic analysis suggests that the lamprey lineage experienced gene duplication that gave rise to its unique paralog, designated CTCF2, which is independent from the previously recognized duplication between CTCF and CTCFL. The ChIP-seq analysis detected comparable numbers of CTCF binding sites between lamprey, chicken, and human, and revealed that the lamprey CTCF protein binds to the two-part motif, consisting of core and upstream motifs previously reported for mammals. These findings suggest that this mode of CTCF binding was established in the last common ancestor of extant vertebrates (more than 500 million years ago). We analyzed CTCF binding inside Hox clusters, which revealed a reinforcement of CTCF binding in the region spanning Hox1-4 genes that is unique to lamprey. Our study provides not only biological insights into the antiquity of CTCF-based epigenomic regulation known in mammals but also a technical basis for comparative epigenomic studies encompassing the whole taxon Vertebrata.

Madagascar ground gecko genome analysis characterizes asymmetric fates of duplicated genes

BackgroundConventionally, comparison among amniotes – birds, mammals, and reptiles – has often been approached through analyses of mammals and, for comparison, birds. However, birds are morphologically and physiologically derived and, moreover, some parts of their genomes are recognized as difficult to sequence and/or assemble and are thus missing in genome assemblies. Therefore, sequencing the genomes of reptiles would aid comparative studies on amniotes by providing more comprehensive coverage to help understand the molecular mechanisms underpinning evolutionary changes.ResultsHerein, we present the whole genome sequences of the Madagascar ground gecko (Paroedura picta), a promising study system especially in developmental biology, and used it to identify changes in gene repertoire across amniotes. The genome-wide analysis of the Madagascar ground gecko allowed us to reconstruct a comprehensive set of gene phylogenies comprising 13,043 ortholog groups from diverse amniotes. Our study revealed 469 genes retained by some reptiles but absent from available genome-wide sequence data of both mammals and birds. Importantly, these genes, herein collectively designated as ‘elusive’ genes, exhibited high nucleotide substitution rates and uneven intra-genomic distribution. Furthermore, the genomic regions flanking these elusive genes exhibited distinct characteristics that tended to be associated with increased gene density, repeat element density, and GC content.ConclusionThis highly continuous and nearly complete genome assembly of the Madagascar ground gecko will facilitate the use of this species as an experimental animal in diverse fields of biology. Gene repertoire comparisons across amniotes further demonstrated that the fate of a duplicated gene can be affected by the intrinsic properties of its genomic location, which can persist for hundreds of millions of years.

Selective Deposition of SiO2 on Ion Conductive Area of Soda-lime Glass Surface.

Selective deposition of SiO2 nanoparticles was demonstrated on a soda-lime glass surface with a periodic sodium deficient pattern formed using the electrical nanoimprint. Positively charged SiO2 particles generated using corona discharge in a cyclic siloxane vapor, were selectively deposited depending on the sodium pattern. For such phenomena to occur, the sodium ion migration to the cathode side was indispensable to the electrical charge compensation on the glass surface. Therefore, the deposition proceeded preferentially outside the alkali-deficient area. Periodic SiO2 structures with 424 nm and 180 nm heights were obtained using one-dimensional (6 μm period) and two-dimensional (500 nm period) imprinted patterns.

Shark genomes provide insights into elasmobranch evolution and the origin of vertebrates

Modern cartilaginous fishes are divided into elasmobranchs (sharks, rays and skates) and chimaeras, and the lack of established whole-genome sequences for the former has prevented our understanding of early vertebrate evolution and the unique phenotypes of elasmobranchs. Here we present de novo whole-genome assemblies of brownbanded bamboo shark and cloudy catshark and an improved assembly of the whale shark genome. These relatively large genomes (3.8–6.7 Gbp) contain sparse distributions of coding genes and regulatory elements and exhibit reduced molecular evolutionary rates. Our thorough genome annotation revealed Hox C genes previously hypothesized to have been lost, as well as distinct gene repertories of opsins and olfactory receptors that would be associated with adaptation to unique underwater niches. We also show the early establishment of the genetic machinery governing mammalian homoeostasis and reproduction at the jawed vertebrate ancestor. This study, supported by genomic, transcriptomic and epigenomic resources, provides a foundation for the comprehensive, molecular exploration of phenotypes unique to sharks and insights into the evolutionary origins of vertebrates.Genomic resources for cartilaginous fishes are scarce. Here, the authors sequence the genome of three sharks and provide insights on the molecular basis of adaptation to underwater lifestyle and the evolutionary origins of vertebrates.