Construction and characterization of the BAC library for common carp Cyprinus carpio L. and establishment of microsynteny with zebrafish Danio rerio

BAC-FISH Based Physical Map of Endangered Catfish Clarias magur for Chromosome Cataloguing and Gene Isolation through Positional Cloning

Construction of a physical chromosome map of a species is important for positional cloning, targeted marker development, fine mapping of genes, selection of candidate genes for molecular breeding, as well as understanding the genome organization. The genomic libraries in the form of bacterial artificial chromosome (BAC) clones are also a very useful resource for physical mapping and identification and isolation of full-length genes and the related cis acting elements. Some BAC-FISH based studies reported in the past were gene based physical chromosome maps of Clarias magur (magur) to understand the genome organization of the species and to establish the relationships with other species in respect to genes' organization and evolution in the past. In the present study, we generated end sequences of the BAC clones and analyzed those end sequences within the scaffolds of the draft genome of magur to identify and map the genes bioinformatically for each clone. A total of 36 clones mostly possessing genes were identified and used in probe construction and their subsequent hybridization on the metaphase chromosomes of magur. This study successfully mapped all 36 specific clones on 16 chromosome pairs, out of 25 pairs of magur chromosomes. These clones are now recognized as chromosome-specific makers, which are an aid in individual chromosome identification and fine assembly of the genome sequence, and will ultimately help in developing anchored genes' map on the chromosomes of C. magur for understanding their organization, inheritance of important fishery traits and evolution of magur with respect to channel catfish, zebrafish and other species.

The neuropeptide Y receptor gene repository, phylogeny and comparative expression in allotetraploid common carp

NPY-family receptors belong to G protein-coupled receptors (GPCR), which lays a physiological foundation for the transmembrane transport of an endogenous appetite-stimulating factor neuropeptide Y and related peptides. In this study, we investigated the npyr genes in ten representative species, and twelve npyr genes were identified from allotetraploid C. carpio, the npyr gene number of C. carpio was twice the number of its subgenome B progenitor-like diploid Poropuntius huangchuchieni. Phylogenetic analysis showed that all npyr genes were divided into three subgroups, and they underwent strong purifying selection according to selection pressure analysis. Subsequently, synteny analysis showed that most npyr genes were evenly distributed on the homologous chromosomes of two subgenomes in allotetraploid C. carpio, in which npy1r and npy2r were tandem duplicated, respectively. In addition, the global expression of npyr genes during embryonic development in allotetraploid C. carpio suggested the potential function of npyr genes in immunity and reproduction. In adult tissues, npyr genes were mainly distributed in the brain, gonad, and skin, which displayed a similar expression pattern between the C. carpio B subgenome and P. huangchuchieni. In general, our research could provide reference information for future exploration of the NPY receptors and neuroendocrine system of allotetraploid C. carpio and vertebrates.

Genome-wide mining of gpx gene family provides new insights into cadmium stress responses in common carp (Cyprinus carpio)

Glutathione peroxidase (Gpx) is an important member of antioxidant enzymes, which can play a vital role in metabolizing reactive oxygen species (ROS) and in maintaining cell homeostasis. In order to study the evolutionary dynamics of gpx gene family in allotetraploid fish species, we identified a total of 14 gpx genes in common carp Cyprinus carpio, while 9 gpx genes were discovered in the diploid progenitor-like species Poropuntius huangchuchieni. Comparative genomic analysis and phylogenetic analysis revealed that the common carp gpx genes had significant expansion and were divided into five distinct subclades. Exon-intron distribution patterns and conserved motif analysis revealed highly conserved evolutionary patterns. Transcript profiles suggested that different gpx genes had specific patterns of regulation during early embryonic development. In adult tissues, gpx genes had a relatively broad expression distribution, most of which were highly expressed in the gills, intestines, and gonads. RT-qPCR studies showed that most gpx genes were downregulated during the initial cd²⁺ treatment stage. Dietary supplementation of Bacillus coagulans at different concentrations (Group 2 of 1.0 × 10⁷ cfu/g, Group 3 of 1.0 × 10⁸ cfu/g, and Group 4 of 1.0 × 10⁹ cfu/g) induced different regulatory responses of gpx subclades. This result suggested that the appropriate concentration of B. coagulans can improve gpx gene expression when exposed to heavy metal cadmium treatment, which may play a vital role in the resistance to oxidative stress and immune responses. This study has expanded our understanding of the functional evolution of the gpx gene family in common carp.

Improved protocols for BAC insert DNA isolation, BAC end sequencing and FISH for construction of BAC based physical map of genes on the chromosomes

Bacterial artificial chromosome (BAC) library is an important genomic resource useful in targeted marker development, positional cloning, physical mapping and a substrate for genome sequencing for better understanding the genome organization of a species. The present manuscript elucidates the improvement in protocols for economical and efficient BAC insert DNA isolation, BAC end sequencing and FISH for physical localization on the metaphase chromosome complements. BAC clones of Clarias magur, maintained in 384-well plate format in our laboratory, were used in this study. The protocols gave consistent and efficient results. We use routinely these protocols for BAC insert DNA extraction, generating end sequence data of the clone and constructing DNA probes to hybridize on the metaphase spreads of C. magur using FISH for physical their localization.

The allotetraploid origin and asymmetrical genome evolution of the common carp Cyprinus carpio

Common carp (Cyprinus carpio) is an allotetraploid species derived from recent whole genome duplication and provides a model to study polyploid genome evolution in vertebrates. Here, we generate three chromosome-level reference genomes of C. carpio and compare to related diploid Cyprinid genomes. We identify a Barbinae lineage as potential diploid progenitor of C. carpio and then divide the allotetraploid genome into two subgenomes marked by a distinct genome similarity to the diploid progenitor. We estimate that the two diploid progenitors diverged around 23 Mya and merged around 12.4 Mya based on the divergence rates of homoeologous genes and transposable elements in two subgenomes. No extensive gene losses are observed in either subgenome. Instead, we find gene expression bias across surveyed tissues such that subgenome B is more dominant in homoeologous expression. CG methylation in promoter regions may play an important role in altering gene expression in allotetraploid C. carpio.

The common carp is derived from recent whole genome duplication and represents a model for polyploid genome evolution, rare in vertebrates. Here, the authors generate and analyse chromosome-level reference genomes for common carp, and describe subgenome gene expression changes.

Genome-Scale Association Study of Abnormal Scale Pattern in Yellow River Carp Identified Previously Known Causative Gene in European Mirror Carp

Common carp (Cyprinus carpio) is one of the most widely studied fish species due to its great economic value and strong environmental adaptability. Scattered scale, a typical phenotype of the mirror carp that is derived from Europe, has never been observed in the Yellow River carp previously. We recently identified approximately one fourth of the F1 progenies displaying scattered scale in a full-sib Yellow River carp family in our breeding program, despite both parents that showed wild type with normal scale patterns. This family provides us unique materials to investigate the genetic basis underlying the abnormal scale mutant in Yellow River carp population. Genome-wide association study (GWAS) and association mapping were performed based on genome-wide single nucleotide polymorphisms (SNP) genotyped with common carp 250 K SNP genotyping array in 82 samples of the Yellow River carp family. We identified a 1.4 Mb genome region that was significantly associated with abnormal scattered scale patterns. We further identified a deletion mutation in fibroblast growth factor receptor 1 a1 (fgfr1a1) gene within this genome region. Amplification and sequencing analysis of this gene revealed a 311-bp deletion in intron 10 and exon 11, which proved that fgfr1a1 could be the causal gene responsible for abnormal scattered scale in the Yellow River carp family. Since similar fragment mutation with 306-bp and 310-bp deletions had been previously reported as causal mutation of scattered scale patterns in the mirror carp, we speculate that either the deletion mutation was introduced from Europe-derived mirror carp or the deletion independently occurred in the mutation hotspot in fgfr1a1 gene. The results provided insights into the genetic basis of scale pattern mutant in Yellow River carp population, which would help us to eliminate the recessive allele of the abnormal scale patterns in Yellow River carp population by molecular marker-assisted breeding.

Genome-Wide Association Study for Muscle Fat Content and Abdominal Fat Traits in Common Carp (Cyprinus carpio)

Muscle fat content is an important phenotypic trait in fish, as it affects the nutritional, technical and sensory qualities of flesh. To identify loci and candidate genes associated with muscle fat content and abdominal fat traits, we performed a genome-wide association study (GWAS) using the common carp 250 K SNP assay in a common carp F₂ resource population. A total of 18 loci surpassing the genome-wide suggestive significance level were detected for 4 traits: fat content in dorsal muscle (MFdo), fat content in abdominal muscle (MFab), abdominal fat weight (AbFW), and AbFW as a percentage of eviscerated weight (AbFP). Among them, one SNP (carp089419) affecting both AbFW and AbFP reached the genome-wide significance level. Ten of those loci were harbored in or near known genes. Furthermore, relative expressions of 5 genes related to MFdo were compared using dorsal muscle samples with high and low phenotypic values. The results showed that 4 genes were differentially expressed between the high and low phenotypic groups. These genes are, therefore, prospective candidate genes for muscle fat content: ankyrin repeat domain 10a (ankrd10a), tetratricopeptide repeat, ankyrin repeat and coiled-coil containing 2 (tanc2), and four jointed box 1 (fjx1) and choline kinase alpha (chka). These results offer valuable insights into the complex genetic basis of fat metabolism and deposition.

Genome Wide Identification, Phylogeny, and Expression of Aquaporin Genes in Common Carp (Cyprinus carpio)

Background

Aquaporins (Aqps) are integral membrane proteins that facilitate the transport of water and small solutes across cell membranes. Among vertebrate species, Aqps are highly conserved in both gene structure and amino acid sequence. These proteins are vital for maintaining water homeostasis in living organisms, especially for aquatic animals such as teleost fish. Studies on teleost Aqps are mainly limited to several model species with diploid genomes. Common carp, which has a tetraploidized genome, is one of the most common aquaculture species being adapted to a wide range of aquatic environments. The complete common carp genome has recently been released, providing us the possibility for gene evolution of aqp gene family after whole genome duplication.

Results

In this study, we identified a total of 37 aqp genes from common carp genome. Phylogenetic analysis revealed that most of aqps are highly conserved. Comparative analysis was performed across five typical vertebrate genomes. We found that almost all of the aqp genes in common carp were duplicated in the evolution of the gene family. We postulated that the expansion of the aqp gene family in common carp was the result of an additional whole genome duplication event and that the aqp gene family in other teleosts has been lost in their evolution history with the reason that the functions of genes are redundant and conservation. Expression patterns were assessed in various tissues, including brain, heart, spleen, liver, intestine, gill, muscle, and skin, which demonstrated the comprehensive expression profiles of aqp genes in the tetraploidized genome. Significant gene expression divergences have been observed, revealing substantial expression divergences or functional divergences in those duplicated aqp genes post the latest WGD event.

Conclusions

To some extent, the gene families are also considered as a unique source for evolutionary studies. Moreover, the whole set of common carp aqp gene family provides an essential genomic resource for future biochemical, toxicological, physiological, and evolutionary studies in common carp.

Quantitative trait loci for morphometric traits in multiple families of common carp (Cyprinus carpio)

Quantitative trait locus (QTL) mapping is frequently used to understand the genetic architecture of quantitative traits. Herein, we performed a genome scan for QTL affecting the morphometric characters in eight full-sib families containing 522 individuals using different statistical methods (Sib-pair and half-sib model). A total of 194 QTLs were detected in 25 different regions on 10 linkage groups (LGs). Among them, 37 QTLs on five LGs (eight, 13, 24, 40 and 45) were significant (5% genome-wide level), while the remaining 40 (1% chromosome-wide level) and 117 (5% chromosome-wide level) indicated suggestive effect on those traits. Heritabilities for most morphometric traits were moderate to high, ranging from 0.21 to 0.66, with generally strong phenotypic and genetic correlations between the traits. A large number of QTLs for morphometric traits were co-located, consistent with their high correlations, and may reflect pleiotropic effect on the same genes. Biological pathways were mapped for possible candidate genes on QTL regions. One significantly enriched pathway was identified on LG45, which had a P-value of 0.04 and corresponded to the "regulation of actin cytoskeleton pathway". The results are expected to be useful in marker-assisted selection (MAS) and provide valuable information for the study of gene pathway for morphometric and growth traits of the common carp.

BAC-pool sequencing and analysis confirms growth-associated QTLs in the Asian seabass genome

The Asian seabass is an important marine food fish that has been cultured for several decades in Asia Pacific. However, the lack of a high quality reference genome has hampered efforts to improve its selective breeding. A 3D BAC pool set generated in this study was screened using 22 SSR markers located on linkage group 2 which contains a growth-related QTL region. Seventy-two clones corresponding to 22 FPC contigs were sequenced by Illumina MiSeq technology. We co-assembled the MiSeq-derived scaffolds from each FPC contig with error-corrected PacBio reads, resulting in 187 sequences covering 9.7 Mb. Eleven genes annotated within this region were found to be potentially associated with growth and their tissue-specific expression was investigated. Correlation analysis demonstrated that SNPs in ctsb, skp1 and ppp2ca can be potentially used as markers for selecting fast-growing fingerlings. Conserved syntenies between seabass LG2 and five other teleosts were identified. This study i) provided a 10 Mb targeted genome assembly; ii) demonstrated NGS of BAC pools as a potential approach for mining candidates underlying QTLs of this species; iii) detected eleven genes potentially responsible for growth in the QTL region; and iv) identified useful SNP markers for selective breeding programs of Asian seabass.

Genomic Basis of Adaptive Evolution: The Survival of Amur Ide (Leuciscus waleckii) in an Extremely Alkaline Environment

The Amur ide (Leuciscus waleckii) is a cyprinid fish that is widely distributed in Northeast Asia. The Lake Dali Nur population inhabits one of the most extreme aquatic environments on Earth, with an alkalinity up to 50 mmol/L (pH 9.6), thus providing an exceptional model with which to characterize the mechanisms of genomic evolution underlying adaptation to extreme environments. Here, we developed the reference genome assembly for L. waleckii from Lake Dali Nur. Intriguingly, we identified unusual expanded long terminal repeats (LTRs) with higher nucleotide substitution rates than in many other teleosts, suggesting their more recent insertion into the L. waleckii genome. We also identified expansions in genes encoding egg coat proteins and natriuretic peptide receptors, possibly underlying the adaptation to extreme environmental stress. We further sequenced the genomes of 10 additional individuals from freshwater and 18 from Lake Dali Nur populations, and we detected a total of 7.6 million SNPs from both populations. In a genome scan and comparison of these two populations, we identified a set of genomic regions under selective sweeps that harbor genes involved in ion homoeostasis, acid-base regulation, unfolded protein response, reactive oxygen species elimination, and urea excretion. Our findings provide comprehensive insight into the genomic mechanisms of teleost fish that underlie their adaptation to extreme alkaline environments.

Construction and characterization of a bacterial artificial chromosome library for mandarin fish Siniperca chuatsi (Basilewsky)

Siniperca chuatsi (Basilewsky), a demersal piscivore, is an endemic freshwater fish species in China. For the purpose of genomics research, we have constructed the first bacterial artificial chromosome (BAC) library for S. chuatsi. The BAC library comprised a total of 84,480 clones with an average insert size of 124.6 kb and less than 2.5% empty clones, corresponding to a 10.5-fold coverage of the S. chuatsi genome. The probability of isolating genes of interest was more than 99%. To validate the library, we screened 220 superpools and found that 1-19 were positive for six SSR markers, while none was positive for two mitochondrial gene markers. Therefore, the S. chuatsi BAC library will provide useful genomics resources and tools for cloning, functional genomics research and identification of economically important genes in this species.

An ultra-high density linkage map and QTL mapping for sex and growth-related traits of common carp (Cyprinus carpio)

High density genetic linkage maps are essential for QTL fine mapping, comparative genomics and high quality genome sequence assembly. In this study, we constructed a high-density and high-resolution genetic linkage map with 28,194 SNP markers on 14,146 distinct loci for common carp based on high-throughput genotyping with the carp 250 K single nucleotide polymorphism (SNP) array in a mapping family. The genetic length of the consensus map was 10,595.94 cM with an average locus interval of 0.75 cM and an average marker interval of 0.38 cM. Comparative genomic analysis revealed high level of conserved syntenies between common carp and the closely related model species zebrafish and medaka. The genome scaffolds were anchored to the high-density linkage map, spanning 1,357 Mb of common carp reference genome. QTL mapping and association analysis identified 22 QTLs for growth-related traits and 7 QTLs for sex dimorphism. Candidate genes underlying growth-related traits were identified, including important regulators such as KISS2, IGF1, SMTLB, NPFFR1 and CPE. Candidate genes associated with sex dimorphism were also identified including 3KSR and DMRT2b. The high-density and high-resolution genetic linkage map provides an important tool for QTL fine mapping and positional cloning of economically important traits, and improving common carp genome assembly.

QTL variations for growth-related traits in eight distinct families of common carp (Cyprinus carpio)

BACKGROUND

Comparing QTL analyses of multiple pair-mating families can provide a better understanding of important allelic variations and distributions. However, most QTL mapping studies in common carp have been based on analyses of individual families. In order to improve our understanding of heredity and variation of QTLs in different families and identify important QTLs, we performed QTL analysis of growth-related traits in multiple segregating families.

RESULTS

We completed a genome scan for QTLs that affect body weight (BW), total length (TL), and body thickness (BT) of 522 individuals from eight full-sib families using 250 microsatellites evenly distributed across 50 chromosomes. Sib-pair and half-sib model mapping identified 165 QTLs on 30 linkage groups. Among them, 10 (genome-wide P <0.01 or P < 0.05) and 28 (chromosome-wide P < 0.01) QTLs exhibited significant evidence of linkage, while the remaining 127 exhibited a suggestive effect on the above three traits at a chromosome-wide (P < 0.05) level. Multiple QTLs obtained from different families affect BW, TL, and BT and locate at close or identical positions. It suggests that same genetic factors may control variability in these traits. Furthermore, the results of the comparative QTL analysis of multiple families showed that one QTL was common in four of the eight families, nine QTLs were detected in three of the eight families, and 26 QTLs were found common to two of the eight families. These common QTLs are valuable candidates in marker-assisted selection.

CONCLUSION

A large number of QTLs were detected in the common carp genome and associated with growth-related traits. Some of the QTLs of different growth-related traits were identified at similar chromosomal regions, suggesting a role for pleiotropy and/or tight linkage and demonstrating a common genetic basis of growth trait variations. The results have set up an example for comparing QTLs in common carp and provided insights into variations in the identified QTLs affecting body growth. Discovery of these common QTLs between families and growth-related traits represents an important step towards understanding of quantitative genetic variation in common carp.

Construction of the BAC Library of Small Abalone (Haliotis diversicolor) for Gene Screening and Genome Characterization

The small abalone (Haliotis diversicolor) is one of the most important aquaculture species in East Asia. To facilitate gene cloning and characterization, genome analysis, and genetic breeding of it, we constructed a large-insert bacterial artificial chromosome (BAC) library, which is an important genetic tool for advanced genetics and genomics research. The small abalone BAC library includes 92,610 clones with an average insert size of 120 Kb, equivalent to approximately 7.6× of the small abalone genome. We set up three-dimensional pools and super pools of 18,432 BAC clones for target gene screening using PCR method. To assess the approach, we screened 12 target genes in these 18,432 BAC clones and identified 16 positive BAC clones. Eight positive BAC clones were then sequenced and assembled with the next generation sequencing platform. The assembled contigs representing these 8 BAC clones spanned 928 Kb of the small abalone genome, providing the first batch of genome sequences for genome evaluation and characterization. The average GC content of small abalone genome was estimated as 40.33%. A total of 21 protein-coding genes, including 7 target genes, were annotated into the 8 BACs, which proved the feasibility of PCR screening approach with three-dimensional pools in small abalone BAC library. One hundred fifty microsatellite loci were also identified from the sequences for marker development in the future. The BAC library and clone pools provided valuable resources and tools for genetic breeding and conservation of H. diversicolor.

Phylogeny and Evolution of Multiple Common Carp (Cyprinus carpio L.) Populations Clarified by Phylogenetic Analysis Based on Complete Mitochondrial Genomes

Common carp (Cyprinus carpio L.) is one of the oldest, most widely farmed commercially important freshwater fish in the world. However, many undetermined phylogenetic relationships and origins of common carp lineages remain, which are obstacles to conservation and genetic breeding of this species. Phylogenetic analyses based on molecular tools are helpful to distinguish the origin of species, understand and clarify their evolutionary history, and provide a genetic basis for selective breeding. In this study, we demonstrated a method to extract complete mitochondrial genome sequences from whole-genome resequencing data using the Illumina platform. The complete mitochondrial genome sequences of 26 individuals representing nine strains were obtained and subjected to a phylogenetic analysis. We reconstructed the phylogenetic topologies of the nine strains and analyzed the haplotypes. Results from both analyses suggested that the genome sequences belonged to two distinct subspecies from Europe and East Asia. We also estimated the time of divergence of the nine strains, which was up to 100 KYA. The phylogenetic results clarified the breeding history of Songpu mirror carp and suggest that this species may be hybrid of paternal European mirror carp and maternal Xingguo red carp. The results also support a previous hypothesis that koi may have originated from or have close ancestry with Oujiang color carp in China.

Diversification of the duplicated Rab1a genes in a hypoxia-tolerant fish, common carp (Cyprinus carpio)

Common carp is a widely cultivated fish with longer than 2,000 years domestication history, due to its strong environmental adaptabilities, especially hypoxia tolerance. The common carp genome has experienced a very recent whole genome duplication (WGD) event. Among a large number of highly similar duplicated genes, a pair of Ras-associated binding-GTPase 1a (Rab1a) genes were found fast diverging. Four analogous Rab1a genes were identified in the common carp genome. Comparisons of gene structures and sequences indicated Rab1a-1 and Rab1a-2 was a pair of fast diverging duplicates, while Rab1a-3 and Rab1a-4 was a pair of less diverged duplicates. All putative Rab1a proteins shared conserved GTPase domain, which enabled the proteins serve as molecular switches for vesicular trafficking. Rab1a-1 and Rab1a-2 proteins varied in their C-terminal sequences, which were generally considered to encode the membrane localization signals. Differential expression patterns were observed between Rab1a-1 and Rab1a-2 genes. In blood, muscle, spleen, and heart, the mRNA level of Rab1a-1 was higher than that of Rab1a-2. In liver and intestine, the mRNA level of Rab1a-2 was higher. Expression of Rab1a-1 and Rab1a-2 showed distinct hypoxia responses. Under severe hypoxia, Rab1a-1 expression was down-regulated in blood, while Rab1a-2 expression was up-regulated in liver. Compared with the less diverged Rab1a-3/4 gene pair, common carp Rab1a-1/2 gene pair exhibited strong characteristics of sub-functionalization, which might contribute to a sophisticated and efficient Ras-dependent regulating network for the hypoxia-tolerant fish.

Development and evaluation of the first high-throughput SNP array for common carp (Cyprinus carpio)

Background

A large number of single nucleotide polymorphisms (SNPs) have been identified in common carp (Cyprinus carpio) but, as yet, no high-throughput genotyping platform is available for this species. C. carpio is an important aquaculture species that accounts for nearly 14% of freshwater aquaculture production worldwide. We have developed an array for C. carpio with 250,000 SNPs and evaluated its performance using samples from various strains of C. carpio.

Results

The SNPs used on the array were selected from two resources: the transcribed sequences from RNA-seq data of four strains of C. carpio, and the genome re-sequencing data of five strains of C. carpio. The 250,000 SNPs on the resulting array are distributed evenly across the reference C.carpio genome with an average spacing of 6.6 kb. To evaluate the SNP array, 1,072 C. carpio samples were collected and tested. Of the 250,000 SNPs on the array, 185,150 (74.06%) were found to be polymorphic sites. Genotyping accuracy was checked using genotyping data from a group of full-siblings and their parents, and over 99.8% of the qualified SNPs were found to be reliable. Analysis of the linkage disequilibrium on all samples and on three domestic C.carpio strains revealed that the latter had the longer haplotype blocks. We also evaluated our SNP array on 80 samples from eight species related to C. carpio, with from 53,526 to 71,984 polymorphic SNPs. An identity by state analysis divided all the samples into three clusters; most of the C. carpio strains formed the largest cluster.

Conclusions

The Carp SNP array described here is the first high-throughput genotyping platform for C. carpio. Our evaluation of this array indicates that it will be valuable for farmed carp and for genetic and population biology studies in C. carpio and related species.

A consensus linkage map provides insights on genome character and evolution in common carp (Cyprinus carpio L.)

Common carp (Cyprinus carpio L.) is cultured worldwide and is a major contributor to the world's aquaculture production. The common carp has a complex tetraploidized genome, which may historically experience additional whole genome duplication than most other Cyprinids. Fine maps for female and male carp were constructed using a mapping panel containing one F1 family with 190 progeny. A total of 1,025 polymorphic markers were used to construct genetic maps. For the female map, 559 microsatellite markers in 50 linkage groups cover 3,468 cM of the genome. For the male map, 383 markers in 49 linkage groups cover 1,811 cM of the genome. The consensus map was constructed by integrating the new map with two published linkage maps, containing 732 markers and spanning 3,278 cM in 50 linkage groups. The number of consensus linkage groups corresponds to the number of common carp chromosomes. A significant difference on sex recombinant rate was observed that the ratio of female and male recombination rates was 4.2:1. Comparative analysis was performed between linkage map of common carp and genome of zebrafish (Danio rerio), which revealed clear 2:1 relationship of common carp linkage groups and zebrafish chromosomes. The results provided evidence that common carp did experienced a specific whole genome duplication event comparing with most other Cyprinids. The consensus linkage map provides an important tool for genetic and genome study of common carp and facilitates genetic selection and breeding for common carp industry.

A dense genetic linkage map for common carp and its integration with a BAC-based physical map

Background

Common carp (Cyprinus carpio) is one of the most important aquaculture species with an annual global production of 3.4 million metric tons. It is also an important ornamental species as well as an important model species for aquaculture research. To improve the economically important traits of this fish, a number of genomic resources and genetic tools have been developed, including several genetic maps and a bacterial artificial chromosome (BAC)-based physical map. However, integrated genetic and physical maps are not available to study quantitative trait loci (QTL) and assist with fine mapping, positional cloning and whole genome sequencing and assembly. The objective of this study was to integrate the currently available BAC-based physical and genetic maps.

Results

The genetic map was updated with 592 novel markers, including 312 BAC-anchored microsatellites and 130 SNP markers, and contained 1,209 genetic markers on 50 linkage groups, spanning 3,565.9 cM in the common carp genome. An integrated genetic and physical map of the common carp genome was then constructed, which was composed of 463 physical map contigs and 88 single BACs. Combined lengths of the contigs and single BACs covered a physical length of 498.75 Mb, or around 30% of the common carp genome. Comparative analysis between common carp and zebrafish genomes was performed based on the integrated map, providing more insights into the common carp specific whole genome duplication and segmental rearrangements in the genome.

Conclusion

We integrated a BAC-based physical map to a genetic linkage map of common carp by anchoring BAC-associated genetic markers. The density of the genetic linkage map was significantly increased. The integrated map provides a tool for both genetic and genomic studies of common carp, which will help us to understand the genomic architecture of common carp and facilitate fine mapping and positional cloning of economically important traits for genetic improvement and modification.

A consensus linkage map of common carp (Cyprinus carpio L.) to compare the distribution and variation of QTLs associated with growth traits

The ability to detect and identify quantitative trait loci (QTLs) in a single population is often limited. Analyzing multiple populations in QTL analysis improves the power of detecting QTLs and provides a better understanding of their functional allelic variation and distribution. In this study, a consensus map of the common carp was constructed, based on four populations, to compare the distribution and variation of QTLs. The consensus map spans 2371.6 cM across the 42 linkage groups and comprises 257 microsatellites and 421 SNPs, with a mean marker interval of 3.7 cM/marker. Sixty-seven QTLs affecting four growth traits from the four populations were mapped to the consensus map. Only one QTL was common to three populations, and nine QTLs were detected in two populations. However, no QTL was common to all four populations. The results of the QTL comparison suggest that the QTLs are responsible for the phenotypic variability observed for these traits in a broad array of common carp germplasms. The study also reveals the different genetic performances between major and minor genes in different populations.

Genome-Wide SNP Discovery from Transcriptome of Four Common Carp Strains

Background

Single nucleotide polymorphisms (SNPs) have been used as genetic marker for genome-wide association studies in many species. Gene-associated SNPs could offer sufficient coverage in trait related research and further more could themselves be causative SNPs for traits. Common carp (Cyprinus carpio) is one of the most important aquaculture species in the world accounting for nearly 14% of freshwater aquaculture production. There are various strains of common carp with different economic traits, however, the genetic mechanism underlying the different traits have not been elucidated yet. In this project, we identified a large number of gene-associated SNPs from four strains of common carp using next-generation sequencing.

Results

Transcriptome sequencing of four strains of common carp (mirror carp, purse red carp, Xingguo red carp, Yellow River carp) was performed with Solexa HiSeq2000 platform. De novo assembled transcriptome was used as reference for alignments, and SNP calling was done through BWA and SAMtools. A total of 712,042 Intra-strain SNPs were discovered in four strains, of which 483,276 SNPs for mirror carp, 486,629 SNPs for purse red carp, 478,028 SNPs for Xingguo red carp and 488,281 SNPs for Yellow River carp were discovered, respectively. Besides, 53,893 inter-SNPs were identified. Strain-specific SNPs of four strains were 53,938, 53,866, 48,701, 40,131 in mirror carp, purse red carp, Xingguo red carp and Yellow River carp, respectively. GO and KEGG pathway analysis were done to reveal strain-specific genes affected by strain-specific non-synonymous SNPs. Validation of selected SNPs revealed that 48% percent of SNPs (12 of 25) were tested to be true SNPs.

Conclusions

Transcriptome analysis of common carp using RNA-Seq is a cost-effective way of generating numerous reads for SNP discovery. After validation of identified SNPs, these data will provide a solid base for SNP array designing and genome-wide association studies.

High throughput mining and characterization of microsatellites from common carp genome

In order to supply sufficient microsatellite loci for high-density linkage mapping, whole genome shotgun (WGS) sequences of the common carp (Cyprinus carpio) were assembled and surveyed for microsatellite identification. A total of 79,014 microsatellites were collected which were harbored in 68,827 distinct contig sequences. These microsatellites were characterized in the common carp genome. Information of all microsatellites, including previously published BAC-based microsatellites, was then stored in a MySQL database, and a web-based database interface (http://genomics.cafs.ac.cn/ssrdb) was built for public access and download. A total of 3,110 microsatellites, including 1,845 from WGS and 1,265 from BAC end sequences (BES), were tested and genotyped on a mapping family with 192 individuals. A total of 963 microsatellites markers were validated with polymorphism in the mapping family. They will soon be used for high-density linkage mapping with a vast number of polymorphic SNP markers.

Characterization of common carp transcriptome: sequencing, de novo assembly, annotation and comparative genomics

BACKGROUND

Common carp (Cyprinus carpio) is one of the most important aquaculture species of Cyprinidae with an annual global production of 3.4 million tons, accounting for nearly 14% of the freshwater aquaculture production in the world. Due to the economical and ecological importance of common carp, genomic data are eagerly needed for genetic improvement purpose. However, there is still no sufficient transcriptome data available. The objective of the project is to sequence transcriptome deeply and provide well-assembled transcriptome sequences to common carp research community.

RESULT

Transcriptome sequencing of common carp was performed using Roche 454 platform. A total of 1,418,591 clean ESTs were collected and assembled into 36,811 cDNA contigs, with average length of 888 bp and N50 length of 1,002 bp. Annotation was performed and a total of 19,165 unique proteins were identified from assembled contigs. Gene ontology and KEGG analysis were performed and classified all contigs into functional categories for understanding gene functions and regulation pathways. Open Reading Frames (ORFs) were detected from 29,869 (81.1%) contigs with an average ORF length of 763 bp. From these contigs, 9,625 full-length cDNAs were identified with sequence length from 201 bp to 9,956 bp. Comparative analysis revealed that 27,693(75.2%) contigs have significant similarity to zebrafish Refseq proteins, and 24,371(66.2%), 24,501(66.5%) and 25,025(70.0%) to teraodon, medaka and three-spined stickleback refseq proteins. A total of 2,064 microsatellites were initially identified from 1,730 contigs, and 1,639 unique sequences had sufficient flanking sequences on both sides for primer design.

CONCLUSION

The transcriptome of common carp had been deep sequenced, de novo assembled and characterized, providing the valuable resource for better understanding of common carp genome. The transcriptome data will facilitate future functional studies on common carp genome, and gradually apply in breeding programs of common carp, as well as closely related other Cyprinids.

Generation of the first BAC-based physical map of the common carp genome

Background

Common carp (Cyprinus carpio), a member of Cyprinidae, is the third most important aquaculture species in the world with an annual global production of 3.4 million metric tons, accounting for nearly 14% of the all freshwater aquaculture production in the world. Apparently genomic resources are needed for this species in order to study its performance and production traits. In spite of much progress, no physical maps have been available for common carp. The objective of this project was to generate a BAC-based physical map using fluorescent restriction fingerprinting.

Result

The first generation of common carp physical map was constructed using four- color High Information Content Fingerprinting (HICF). A total of 72,158 BAC clones were analyzed that generated 67,493 valid fingerprints (5.5 × genome coverage). These BAC clones were assembled into 3,696 contigs with the average length of 476 kb and a N50 length of 688 kb, representing approximately 1.76 Gb of the common carp genome. The largest contig contained 171 BAC clones with the physical length of 3.12 Mb. There are 761 contigs longer than the N50, and these contigs should be the most useful resource for future integrations with linkage map and whole genome sequence assembly. The common carp physical map is available at http://genomics.cafs.ac.cn/fpc/WebAGCoL/Carp/WebFPC/.

Conclusion

The reported common carp physical map is the first physical map of the common carp genome. It should be a valuable genome resource facilitating whole genome sequence assembly and characterization of position-based genes important for aquaculture traits.

A genetic linkage map and comparative genome analysis of common carp (Cyprinus carpio L.) using microsatellites and SNPs

A genetic linkage map is a powerful research tool for mapping traits of interest and is essential to understanding genome evolution. The aim of this study is to provide an expanded genetic linkage map of common carp to effectively carry out quantitative trait loci analysis and conduct comparative mapping analysis between lineages. Here, we constructed a genetic linkage map of common carp (Cyprinus carpio L.) using microsatellite and single-nucleotide polymorphism (SNP) markers in a 159 sibling family. A total of 246 microsatellites and 306 SNP polymorphic markers were genotyped in this family. Linkage analysis using JoinMap 4.0 organized 427 markers (186 microsatellites and 241 SNPs) to 50 linkage groups, ranging in size from 1.4 to 130.1 cM. Each group contained 2-30 markers. The linkage map covered a genetic distance of 2,039.2 cM and the average interval for markers within the linkage groups was approximately 6.4 cM. In addition, comparative genome analysis within five model teleost fish revealed a high percentage (74.7%) of conserved loci corresponding to zebrafish chromosomes. In most cases, each zebrafish chromosome comprised two common carp linkage groups. The comparative analysis also revealed independent chromosome rearrangements in common carp and zebrafish. The linkage map will be of great assistance in mapping genes of interest and serve as a reference to approach comparative mapping and enable further insights into the comprehensive investigations of genome evolution of common carp.

Molecular characterization of CART, AgRP, and MC4R genes and their expression with fasting and re-feeding in common carp (Cyprinus carpio)

Cocaine and amphetamine-regulated transcript (CART), agouti-related proteins (AgRP) and Melanocortin 4 Receptor (MC4R) involves in the control of appetite. The genes were cloned and characterized, and their regulation was studied in common carp. The CARTI and CARTII genes encode 117- and 120-amino acids, respectively. The AgRP-1 and AgRP-2 genes encode 128- and 136-amino acids, respectively. CARTI was principally expressed in the brain, eye and ovary, while CARTII was highly expressed in the brain. AgRP-1 was strongly expressed in the brain, intestine, testis and eye, while AgRP-2 was highly expressed only in the gill and eye. The MC4R gene, encoding 326-amino acids, was mainly expressed in the brain testis, pituitary and eye. Phylogenetic analysis had been conducted which implied that both CARTI/CARTII and AgRP-1/AgRP-2 might derived from gene duplication events during genome evolution of common carp. CART, AgRP and MC4R gene expression in brain were decreased after fasting treatment and increased sharply after refeeding comparing with normal fed controls, which suggested that CART, AgRP and MC4R are involved in appetite regulation in common carp.

Genomic insight into the common carp (Cyprinus carpio) genome by sequencing analysis of BAC-end sequences

Background

Common carp is one of the most important aquaculture teleost fish in the world. Common carp and other closely related Cyprinidae species provide over 30% aquaculture production in the world. However, common carp genomic resources are still relatively underdeveloped. BAC end sequences (BES) are important resources for genome research on BAC-anchored genetic marker development, linkage map and physical map integration, and whole genome sequence assembling and scaffolding.

Result

To develop such valuable resources in common carp (Cyprinus carpio), a total of 40,224 BAC clones were sequenced on both ends, generating 65,720 clean BES with an average read length of 647 bp after sequence processing, representing 42,522,168 bp or 2.5% of common carp genome. The first survey of common carp genome was conducted with various bioinformatics tools. The common carp genome contains over 17.3% of repetitive elements with GC content of 36.8% and 518 transposon ORFs. To identify and develop BAC-anchored microsatellite markers, a total of 13,581 microsatellites were detected from 10,355 BES. The coding region of 7,127 genes were recognized from 9,443 BES on 7,453 BACs, with 1,990 BACs have genes on both ends. To evaluate the similarity to the genome of closely related zebrafish, BES of common carp were aligned against zebrafish genome. A total of 39,335 BES of common carp have conserved homologs on zebrafish genome which demonstrated the high similarity between zebrafish and common carp genomes, indicating the feasibility of comparative mapping between zebrafish and common carp once we have physical map of common carp.

Conclusion

BAC end sequences are great resources for the first genome wide survey of common carp. The repetitive DNA was estimated to be approximate 28% of common carp genome, indicating the higher complexity of the genome. Comparative analysis had mapped around 40,000 BES to zebrafish genome and established over 3,100 microsyntenies, covering over 50% of the zebrafish genome. BES of common carp are tremendous tools for comparative mapping between the two closely related species, zebrafish and common carp, which should facilitate both structural and functional genome analysis in common carp.