Dongpo Xu

Testes transcriptome profiles of the anadromous fish Coilia nasus during the onset of spermatogenesis

RNA-Seq technology has been widely applied to transcriptomics, genomics and functional gene study. Here, we performed de novo transcriptome sequencing to produce 23,842,172 clean reads representing a total of 4,815,798,404 (4.8 Gb) nucleotides from comprehensive transcript dataset for testis of Coilia nasus. Over 20 million Illumina reads were assembled into 194,636 unigenes, and 42,642 annotated genes were predicted by Blastx and ESTScan, respectively. Applying Blast analysis and functional annotation (e.g., GO, COG, SwissProt and KEGG) using the assembled gene models from catalogs of other species, we have sampled an extensive and diverse expressed gene catalog for C. nasus representing a large proportion of the genes involved in the onset of spermatogenesis. The results will provide a general clue to the potential spermatogenesis molecular mechanisms for this species.

Ovary transcriptome profiling of Coilia nasus during spawning migration stages by Illumina sequencing

Coilia nasus is an anadromous kind of small to moderate size fish species, and limited transcriptomics research has been performed. In the present study, we performed Illumina sequencing to produce a 22,996,612 clean reads representing with a total of 4,599,079,601 (4.5Gb) nucleotides comprehensive transcript dataset for ovary of C. nasus. Over 20 million total reads were assembled into 63,141 unigenes, and 27,027 annotated genes were predicted by Blastx and ESTScan, respectively. Applying Blast analysis and functional annotation (e.g., GO, COG, Swissprot and KEGG), we have sampled an extensive and diverse expressed gene catalog for C. nasus representing a large proportion of the genes expressed in the ovary development process. This approach will assist in the discovery and annotation of novel genes that play key roles in anadromous fish spawning migration process.

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.

Developmental Expression of HSP60 and HSP10 in the Coilia nasus Testis during Upstream Spawning Migration

Heat shock protein 60 (HSP60) and heat shock protein 10 (HSP10) are important chaperones, which have been proven to have essential roles in mediating the correct folding of nuclear encoded proteins imported to mitochondria. Mitochondria are known as the power house of the cell, with which it produces energy and respires aerobically. In this regard, the obtained HSP60 and HSP10 have typical characteristics of the HSP60/10 family signature. Their mRNA transcripts detected were highest during the developmental phase (in April), while the lowest levels were found in the resting phase (after spawning in late July). Additionally, the strongest immunolabeling positive signals were found in the primary spermatocyte, with lower positive staining in secondary sperm cells, and a weak or absent level in the mature sperm. At the electron microscopic level, immunogold particles were localized in the mitochondrial matrix. Data indicated that HSP10 and HSP60 were inducible and functional in the Coilia nasus testis development and migration process, suggesting their essential roles in this process. The results also indicated that HSP60 may be one indicator of properly working mitochondrial import and refolding in the fish testis. This study also provides an expanded perspective on the role of heat shock protein families in spawning migration biology.

Molecular Characteristic, Protein Distribution and Potential Regulation of HSP90AA1 in the Anadromous Fish Coilia nasus

Heat shock proteins play essential roles in basic cellular events. Spawning migration is a complex process, with significant structural and biochemical changes taking place in the adult gonad. To date, the molecular mechanisms underlying migration reproductive biology remain undetermined. In this regard, a full length HSP90AA1 comprising 2608 nucleotides from the anadromous fish Coilia nasus was characterized, encoding 742 amino acid (aa) residues with potential phosphorylation sites. HSP90AA1 mRNA transcripts were detected in all organs, especially in the gonad. Furthermore, the greatest transcript levels were found during the developmental phase, while the lowest levels were found during the resting phase. In addition, the strongest immunolabeling positive signal was found in the primary spermatocyte and oocyte, with lower positive staining in secondary germ cells, and a weak or absent level in the mature sperm and oocyte. Interestingly, HSP90AA1 was mainly located in the cytoplasm of germ cells. These results are important for understanding the molecular mechanism of anadromous migration reproductive biology. In combination with data from other fish species, the result of this present study may facilitate further investigations on the spawning migration mechanism.

Changes of gonadotropin-releasing hormone receptor 2 during the anadromous spawning migration in Coilia nasus

BackgroundAn increase in the activity of the pituitary-gonad axis (PG-axis) and gonad development are essential for the onset of spawning migration in teleosts. In the fish Coilia nasus, gonad development and spawning migration up the Yangtze River occurs by the end of each summer. We hypothesized that gonadotropin releasing hormones receptor 2 (GnRH-R2), which together produce a signal that interacts with the PG-axis, may help to regulate spawning migration processes.ResultsIn this regard, we (1) characterized the gonadosomatic index (GSI) in the anadromous fish C. nasus; (2) analyzed the GnRH-R2 mRNA expression levels in ovary and brain, and concentrations in the serum; and (3) identified the GnRH-R2 protein distribution in the brain and ovaries. We found strong relationships between all of these indices.ConclusionsThe results indicate that GnRH-R2 could act together to promote spawning during the anadromous migration. There is some evidence that the GnRH-R2 gene expression levels and protein distributions change in association with the migratory behavior.

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.

Diversity of Intestinal Microbiota in Coilia ectenes from Lake Taihu, China

Abstract To investigate the community structure and species composition of intestinal microbiota in Coilia ectenes, sixty-seven samples were collected from Lake Taihu in China. The intestinal microbiota of the C. ectenes were identified by the V4 of the 16S ribosomal RNA gene using high-throughput sequencing. Furthermore, the water quality of different sampling sites was also evaluated. A total of 53 phyla and 730 classified genera were found in all the samples. The eight dominant phyla Planctomycetes, Firmicutes, Proteobacteria, Bacteroidetes, Cyanobacteria, Crenarchaeota, Actinobacteria, and Verrucomicrobia were included. The intestinal microbiota compositions of the C. ectenes obtained from the same location presented more similar profiles, and the intestinal microbiota compositions of the C. ectenes from different geographical locations showed considerable differences. The operational taxonomic units (OTUs) abundance of the intestinal microbiota was significantly correlated with both the concentrations of total nitrogen and chlorophyll-a of the aquatic environment (p<0.05). Geographical location was an important determinant for the fish’s intestinal microbiota composition. The intestinal microbiota of C. ectenes would be affected by the concentrations of total nitrogen and chlorophyll-a in the water. These findings achieve a basic understanding of fish’s gut microbiota, and are helpful for the protection of fish resources in Lake Taihu and provided the cornerstone to sustainable utlization of C. ectenes.

Complete mitochondrial genome of Lateolabrax maculatus.

Abstract In this study, we sequence the complete mitochondrial genome of Lateolabrax maculatus. This mitochondrial genome is 16,597 bp in length, encoding 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs and a non-coding control region as found in other vertebrates, with the gene synteny identical to those of typical vertebrates. Control region (D-Loop), of 929 bp in length, is located between tRNAPro and tRNAPhe. The overall base composition of the heavy strand shows T 25.9%, C 29.5%, A 27.3% and G 17.3%, with an AT bias of 53.2%.