Pao Xu

The Sinocyclocheilus cavefish genome provides insights into cave adaptation

BackgroundAn emerging cavefish model, the cyprinid genus Sinocyclocheilus, is endemic to the massive southwestern karst area adjacent to the Qinghai-Tibetan Plateau of China. In order to understand whether orogeny influenced the evolution of these species, and how genomes change under isolation, especially in subterranean habitats, we performed whole-genome sequencing and comparative analyses of three species in this genus, S. grahami, S. rhinocerous and S. anshuiensis. These species are surface-dwelling, semi-cave-dwelling and cave-restricted, respectively.ResultsThe assembled genome sizes of S. grahami, S. rhinocerous and S. anshuiensis are 1.75 Gb, 1.73 Gb and 1.68 Gb, respectively. Divergence time and population history analyses of these species reveal that their speciation and population dynamics are correlated with the different stages of uplifting of the Qinghai-Tibetan Plateau. We carried out comparative analyses of these genomes and found that many genetic changes, such as gene loss (e.g. opsin genes), pseudogenes (e.g. crystallin genes), mutations (e.g. melanogenesis-related genes), deletions (e.g. scale-related genes) and down-regulation (e.g. circadian rhythm pathway genes), are possibly associated with the regressive features (such as eye degeneration, albinism, rudimentary scales and lack of circadian rhythms), and that some gene expansion (e.g. taste-related transcription factor gene) may point to the constructive features (such as enhanced taste buds) which evolved in these cave fishes.ConclusionAs the first report on cavefish genomes among distinct species in Sinocyclocheilus, our work provides not only insights into genetic mechanisms of cave adaptation, but also represents a fundamental resource for a better understanding of cavefish biology.

The Asian arowana (Scleropages formosus) genome provides new insights into the evolution of an early lineage of teleosts

The Asian arowana (Scleropages formosus), one of the world’s most expensive cultivated ornamental fishes, is an endangered species. It represents an ancient lineage of teleosts: the Osteoglossomorpha. Here, we provide a high-quality chromosome-level reference genome of a female golden-variety arowana using a combination of deep shotgun sequencing and high-resolution linkage mapping. In addition, we have also generated two draft genome assemblies for the red and green varieties. Phylogenomic analysis supports a sister group relationship between Osteoglossomorpha (bonytongues) and Elopomorpha (eels and relatives), with the two clades together forming a sister group of Clupeocephala which includes all the remaining teleosts. The arowana genome retains the full complement of eight Hox clusters unlike the African butterfly fish (Pantodon buchholzi), another bonytongue fish, which possess only five Hox clusters. Differential gene expression among three varieties provides insights into the genetic basis of colour variation. A potential heterogametic sex chromosome is identified in the female arowana karyotype, suggesting that the sex is determined by a ZW/ZZ sex chromosomal system. The high-quality reference genome of the golden arowana and the draft assemblies of the red and green varieties are valuable resources for understanding the biology, adaptation and behaviour of Asian arowanas.

Draft genome of the protandrous Chinese black porgy, Acanthopagrus schlegelii

Abstract Background As one of the most popular and valuable commercial marine fishes in China and East Asian countries, the Chinese black porgy (Acanthopagrus schlegelii), also known as the blackhead seabream, has some attractive characteristics such as fast growth rate, good meat quality, resistance to diseases, and excellent adaptability to various environments. Furthermore, the black porgy is a good model for investigating sex changes in fish due to its protandrous hermaphroditism. Here, we obtained a high-quality genome assembly of this interesting teleost species and performed a genomic survey on potential genes associated with the sex-change phenomenon. Findings We generated 175.4 gigabases (Gb) of clean sequence reads using a whole-genome shotgun sequencing strategy. The final genome assembly is approximately 688.1 megabases (Mb), accounting for 93% of the estimated genome size (739.6 Mb). The achieved scaffold N50 is 7.6 Mb, reaching a relatively high level among sequenced fish species. We identified 19 465 protein-coding genes, which had an average transcript length of 17.3 kb. By performing a comparative genomic analysis, we found 3 types of genes potentially associated with sex change, which are useful for studying the genetic basis of the protandrous hermaphroditism. Conclusions We provide a draft genome assembly of the Chinese black porgy and discuss the potential genetic mechanisms of sex change. These data are also an important resource for studying the biology and for facilitating breeding of this economically important fish.

Effects of exposure to Streptococcus iniae on microRNA expression in the head kidney of genetically improved farmed tilapia (Oreochromis niloticus).

BackgroundGenetically improved farmed tilapia (GIFT, Oreochromis niloticus) are susceptible to infection by Streptococcus iniae when maintained in modern intensive culture systems. GIFT are commercially important fishes that are cultured widely in southern China. The role of microRNAs (miRNAs) in the regulatory response of GIFT to S. iniae infection has been underestimated and has not yet been well studied. Head kidney has an important immune function in teleost fishes. The main aim of this study was to determine the possible function of miRNAs in head kidney of S. iniae-infected GIFT. MiRNAs are small, non-coding RNAs that regulate gene expression by binding to the 3’-untranslated regions of their target mRNAs. MiRNAs are known to regulate immune-regulated signaling and inflammatory response pathways.ResultsHigh-throughput deep sequencing of two libraries (control group [CO] and infected group [IN]) of RNA extracted from GIFT head kidney tissues generated 12,089,630 (CO) and 12,624,975 (IN) clean reads. Bioinformatics analysis identified 1736 and 1729 conserved miRNAs and 164 and 165 novel miRNAs in the CO and IN libraries, respectively. Three miRNAs (miR-310-3p, miR-92, and miR-127) were found to be up-regulated and four miRNAs (miR-92d-3p, miR-375-5p, miR-146-3p, and miR-694) were found to be down-regulated in the S. iniae-infected GIFT. The expressions of these miRNAs were verified by quantitative real-time PCR. RNAhybrid and TargetScan were used to identify complementary miRNA and mRNA target sites, and the Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases were used to annotate and predict potential downstream regulation of biological pathways. Seven target genes, which encode immune-related proteins (complement C3, cytidine deaminase, regulator of G-protein Rgs22, mitogen-activated protein kinase Mapk1, metabotropic glutamate receptorm GluR8, calcium-sensing receptor CaSR, and microtubule-associated protein Map1S) were predicted to play crucial roles in the GIFT response to S. iniae infection.ConclusionsS. iniae outbreaks have hindered the development of the tilapia industry in China. Understanding the miRNA transcriptome of S. iniae-infected GIFT is important for exploring the immune responses regulated by miRNAs as well as for studying novel regulated networks to prevent and treat S. iniae infections in the future.

Inhibition of miR-92d-3p enhances inflammation responses in genetically improved farmed tilapia (GIFT, Oreochromis niloticus) with Streptococcus iniae infection by modulating complement C3

Abstract MicroRNAs (miRNAs) are small, non‐coding RNAs that regulate target gene expression by binding to the 3′‐untranslated regions (3′‐UTRs) of their target mRNAs. The miR‐92 family is an important miRNA family, which was discovered to be related to regulation of tumor proliferation, apoptosis, invasion, and metastasis. Inhibition of miR‐92d‐3p was found previously in head kidney of genetically improved farmed tilapia (GIFT, Oreochromis niloticus) exposed to Streptococcus iniae infection. In this study, we found that miR‐92d‐3p regulated complement C3 mRNA levels by binding to its 3′‐UTR by 3′‐UTR luciferase reporter assay, and reduced miR‐92d‐3p expression resulted in increased C3 mRNA levels. We detected a negative relationship between the expression levels of miR‐92d‐3p and C3 in GIFT injected with miRNA antagomir. We performed in vivo functional analysis by miR‐92d‐3p silencing. Inhibition of miR‐92d‐3p levels in GIFT head kidney caused a significant increase in C3 expression, which consequently increased the white blood cell counts and interleukin‐1&bgr;, tumor necrosis factor‐&agr;, and interferon‐&ggr; mRNA levels, all of which may help to activate the inflammatory response in GIFT post‐infection with S. iniae. Our findings indicate that miR‐92d‐3p regulated C3 levels by binding with the C3 mRNA 3′‐UTR, and this interaction affected S. iniae infection induction and the immune response in GIFT. We concluded that miR‐92d‐3p plays an important role in modulating the inflammatory response in GIFT head kidney. Our findings may contribute to understanding the mechanisms of miRNA‐mediated gene regulation in tilapia in response to S. iniae infection. HighlightsmiR‐92d‐3p regulated GIFT C3 by directly targeting C3 3′UTR.miR‐92d‐3p level was conversely related to C3 level under S. iniae infection.miR‐92d‐3p silencing up‐regulated C3 mRNA expression.miR‐92d‐3p loss activated inflammatory response and WBC counts.

A chromosome-level genome assembly of the Asian arowana, Scleropages formosus

Asian arowana (Scleropages formosus), an ancient teleost belonging to the Order Osteoglossomorpha, has been a valuable ornamental fish with some varieties. However, its biological studies and breeding germplasm have been remarkably limited by the lack of a reference genome. To solve these problems, here we report high-quality genome sequences of three common varieties of Asian arowana (the golden, red and green arowana). We firstly generated a chromosome-level genome assembly of the golden arowana, on basis of the genetic linkage map constructed with the restriction site-associated DNA sequencing (RAD-seq). In addition, we obtained draft genome assemblies of the red and green varieties. Finally, we annotated 22,016, 21,256 and 21,524 protein-coding genes in the genome assemblies of golden, red and green varieties respectively. Our data were deposited in publicly accessible repositories to promote biological research and molecular breeding of Asian arowana.

Draft genome of the lined seahorse, Hippocampus erectus

Abstract Background: The lined seahorse, Hippocampus erectus, is an Atlantic species and mainly inhabits shallow sea beds or coral reefs. It has become very popular in China for its wide use in traditional Chinese medicine. In order to improve the aquaculture yield of this valuable fish species, we are trying to develop genomic resources for assistant selection in genetic breeding. Here, we provide whole genome sequencing, assembly, and gene annotation of the lined seahorse, which can enrich genome resource and further application for its molecular breeding. Findings: A total of 174.6 Gb (Gigabase) raw DNA sequences were generated by the Illumina Hiseq2500 platform. The final assembly of the lined seahorse genome is around 458 Mb, representing 94% of the estimated genome size (489 Mb by k-mer analysis). The contig N50 and scaffold N50 reached 14.57 kb and 1.97 Mb, respectively. Quality of the assembled genome was assessed by BUSCO with prediction of 85% of the known vertebrate genes and evaluated using the de novo assembled RNA-seq transcripts to prove a high mapping ratio (more than 99% transcripts could be mapped to the assembly). Using homology-based, de novo and transcriptome-based prediction methods, we predicted 20 788 protein-coding genes in the generated assembly, which is less than our previously reported gene number (23 458) of the tiger tail seahorse (H. comes). Conclusion: We report a draft genome of the lined seahorse. These generated genomic data are going to enrich genome resource of this economically important fish, and also provide insights into the genetic mechanisms of its iconic morphology and male pregnancy behavior.

Whole genome sequencing of Chinese clearhead icefish, Protosalanx hyalocranius

Abstract Background: Chinese clearhead icefish, Protosalanx hyalocranius, is a representative icefish species with economic importance and special appearance. Due to its great economic value in China, the fish was introduced into Lake Dianchi and several other lakes from the Lake Taihu half a century ago. Similar to the Sinocyclocheilus cavefish, the clearhead icefish has certain cavefish-like traits, such as transparent body and nearly scaleless skin. Here, we provide the whole genome sequence of this surface-dwelling fish and generated a draft genome assembly, aiming at exploring molecular mechanisms for the biological interests. Findings: A total of 252.1 Gb of raw reads were sequenced. Subsequently, a novel draft genome assembly was generated, with the scaffold N50 reaching 1.163 Mb. The genome completeness was estimated to be 98.39 % by using the CEGMA evaluation. Finally, we annotated 19 884 protein-coding genes and observed that repeat sequences account for 24.43 % of the genome assembly. Conclusion: We report the first draft genome of the Chinese clearhead icefish. The genome assembly will provide a solid foundation for further molecular breeding and germplasm resource protection in Chinese clearhead icefish, as well as other icefishes. It is also a valuable genetic resource for revealing the molecular mechanisms for the cavefish-like characters.

Assessing the genetic diversity of the critically endangered Chinese sturgeon Acipenser sinensis using mitochondrial markers and genome-wide single-nucleotide polymorphisms from RAD-seq

As a living fossil, the endangered Chinese sturgeon (Acipenser sinensis) has been considered a national treasure in China. Here, the famous Gezhouba Dam and Three Gorges Dam on the Yangtze River were built in 1988 and 2006, for economic purposes. The natural population of Chinese sturgeon has declined since then, as these dams block its migratory route to the original spawning grounds in the middle reaches of the Yangtze River. In 2013 and 2014, there was an absence of spawning where it typically happened near the Gezhouba Dam. Nevertheless, from April to June in 2015, over 1,000 larvae with different body lengths (10–35 cm) were detected along the Shanghai Yangtze Estuary; but only little is currently known about the population genetic structure of the Chinese sturgeon. Herein, we inferred population genetic parameters from 462 available Chinese sturgeon specimens based on a 421-bp fragment of the mitochondrial DNA (mtDNA) D-loop region and 1,481,620 SNPs (single-nucleotide polymorphisms) generated by restriction site-associated DNA sequencing (RAD-seq). For the D-loop dataset, 15 haplotypes were determined. Randomly picked 23 individuals, representing the 15 D-loop haplotype groups, were subsequently used for further RAD-seq validation. The average nucleotide diversity calculated from the mtDNA and RAD datasets was 0.0086 and 0.000478, respectively. The overall effective female population size was calculated to be 1,255 to 2,607, and the long-term effective population size was estimated to range from 11,950 to 119,500. We observed that the genetic variability and the effective female population size of the current population in the Yangtze River are severely low, which are similar to the data reported over 10 years ago. The deduced relatively small effective population of female fish, limiting the genetic connectivity among Chinese sturgeon, should be considered a serious threat to this endangered species.

China is initiating the Aquatic 10-100-1,000 Genomics Program

1Chinese Academy of Fishery Sciences, Beijing 100141, China; 2BGI Research Center for Aquatic Genomics, Chinese Academy of Fishery Sciences, Shenzhen 518083, China; 3Freshwater Fisheries Research Center, Chinese Academy of Fishery Sciences, Wuxi 214081, China; 4BGI Shenzhen Academy of Marine Sciences, BGI Fisheries, BGI, Shenzhen 518083, China; 5Pearl River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou 510380, China; 6Marine Research Center, College of Life Sciences and Oceanography, Shenzhen University, Shenzhen 518060, China