Transcriptome analysis of the growth performance of hybrid mandarin fish after food conversion

Transcriptome and DNA methylation analyses provide insight into the heterosis of growth-related traits in hybrid yellow croaker

BACKGROUND

Interspecific hybrid combinations of Larimichthys crocea × Larimichthys polyactis exhibit heterosis in terms of growth traits; however, the molecular regulatory mechanism underlying this phenomenon remains unclear. DNA methylation plays a pivotal role in regulating gene expression and is involved in growth and development processes. In this study, we comprehensively investigated intricate regulatory processes by integrating transcriptome and methylome datasets from brain, liver, and muscle tissues.

RESULTS

We analyzed a total of 72 sequence datasets, including transcriptome and genome-wide DNA methylome data, from 36 tissue samples using LC, LP, LPC and LCP. We elucidated the distinct expression patterns of these four populations and examined their interactions with DNA methylation. Our findings revealed diverse DNA methylation profiles and demonstrated a greater number of hypo-DMRs in hybrid yellow croakers than in their parental lines. The majority (86 ~ 92%) of these DMRs were observed within the CG context. Moreover, we found that most DMRs were located within promoter regions as well as exons and introns. A total of 1288 DMEGs were identified through correlation analysis between DNA methylation and transcriptional activity. Functional enrichment analysis revealed that most of the DMEGs were significantly enriched in pathways related to the protein export pathway, proteasome, terpenoid backbone biosynthesis, ubiquitin-mediated proteolysis, autophagy-other pathway. Furthermore, we screened candidate growth-related genes, such as stat2, capn2, akt1, mTOR, and mef2aa. Among these, the expression levels of capn2, mTOR, and akt1 exhibited a positive correlation with DNA methylation levels, whereas the expression levels of stat2 and mef2aa showed a negative correlation. These findings suggest that alterations in DNA methylation patterns may promote growth advantages in hybrid yellow croaker by modulating the expression of these genes.

CONCLUSIONS

Epigenetic changes exert distinct influences on genes related to growth heterosis. The presented data establish a foundation for comprehending the epigenetic and transcriptomic alterations underlying the growth of hybrid yellow croaker, thereby providing preliminary insights into the molecular mechanisms of growth heterosis. These findings have significant implications for breeding programs aimed at enhancing yellow croaker production.

Characterization of Myf6 and association with growth traits in swimming crab (Portunus trituberculatus)

BACKGROUND

Myogenic factor 6 (Myf6) plays an important role in muscle growth and differentiation. In aquatic animals and livestock, Myf6 contributes to improving meat quality and strengthening the accumulation of muscle flavor substances. However, studies on Myf6 gene polymorphisms in crustaceans have not been reported.

RESULTS

In the current study, we characterized the Myf6 gene for Portunus trituberculatus to better understand its biological function. The full-length cDNA of Myf6 was 4,101 bp, with a 915 bp open reading frame encoding 304 amino acids. In addition, Myf6 included a conservative bHLH domain. Homology analysis showed that Myf6 shared the highest identity with Penaeus vannamei. Expression pattern analysis of Myf6 in fast- and slow-growing groups revealed that the expression level of the latter was significantly higher than that of the former (P < 0.05). qPCR studies revealed that Myf6 was expressed in various tissues with the highest level in muscle. Nineteen single nucleotide polymorphisms (SNPs) of Myf6 were identified and five of them were significantly associated with growth-related traits of P. trituberculatus (P < 0.05), including full carapace width, carapace length, body height, and body weight. The AG and GG genotypes of g.1,187,834 A > G exhibited superior growth-related traits than the AA genotype. In the combined genotypes of g.1,187,324 C > T and g.1,187,834 A > G, the average body weight of diplotype D5 (CT-GG) was higher than that of diplotype D1 (CC-AA), D2 (CC-AG), and D3 (CC-GG) in a cultivated population. A haploblock was generated by three significant SNPs (g.1187834 A > G, g.1188616 A > G, and g.1189024 C > A), containing four haplotypes (AAA, AAC, AGC, and GGC), among which GGC haplotype exhibited superior growth traits (full carapace width and body weight) than the AAA haplotype.

CONCLUSIONS

To our knowledge, this is the first report on Myf6 in crustaceans. The results of this study would contribute to elucidating multiple functions of the Myf6 gene in crustaceans and exploring the potential as a candidate gene in selective breeding programs of P. trituberculatus.

Growth Superiority and Genetic Characterization of the Hybrid from Female Ussuri Catfish (Pseudobagrus ussuriensis) and Male Longsnout Catfish (Leiocassis longirostris)

Crossbreeding is a traditional breeding technique and has been performed successfully in many fish species. However, distant hybridization between different genera is hard to be successful because of reproductive isolation. In this study, diploid hybrids (PL) were successfully derived from the hybridization of Ussuri catfish (Pseudobagrus ussuriensis, PU, ♀, 2n = 52) and longsnout catfish (Leiocassis longirostris, LL, ♂, 2n = 52). And the morphological data, external frame parameters, chromosomal karyotypes, DNA content measurement, mitochondrial DNA control region, and species-specific marker identification were applied to investigate the traits and genetic characterization of the PL hybrid offspring and their parents. Both quantifiable traits and shape frame parameters of the PL hybrid offspring were revealed to be intermediate between those of their parents; however, cluster analysis showed that their external morphology was more in favor of the maternal PU. The growth comparisons showed that the hybrids had significant growth advantages over maternal PU. Based on karyotype patterns, DNA contents and mitochondrial DNA, the hybrid origin and maternal inheritance of hybrid offspring were further confirmed. According to the sequence variations identified from the genome sequences of the two catfish species, one species-specific marker was developed to distinguish the PL hybrid offspring and their parents. Therefore, this study provides a successful case for intergeneric hybridization and hybrid superiority, and the PL hybrid shows promise for commercial application, pending further studies into its husbandry, health, and welfare with larger populations of fish.

New evidence for gut-muscle axis: Lactic acid bacteria-induced gut microbiota regulates duck meat flavor

The interaction between gut microbiota and muscles through the gut-muscle axis has received increasing attention. This study attempted to address existing research gaps by investigating the effects of gut microbiota on meat flavor. Specifically, lactic acid bacteria were administered to ducks, and the results of e-nose and e-tongue showed significantly enhanced meat flavor in the treatment group. Further analyses using GC-MS revealed an increase in 6 characteristic volatile flavor compounds, including pentanal, hexanal, heptanal, 1-octen-3-ol, 2,3-octanedione, and 2-pentylfuran. Linoleic acid was identified as the key fatty acid that influences meat flavor. Metagenomic and transcriptomic results further confirmed that cecal microbiota affects the duck meat flavor by regulating the metabolic pathways of fatty acids and amino acids, especially ACACB was related to fatty acid biosynthesis and ACAT2, ALDH1A1 with fatty acid degradation. This study sheds light on a novel approach to improving the flavor of animal-derived food.

Effect of different feeding regimens on physiological indicators, intestinal transcriptome, and bacterial flora of mandarin fish (Siniperca chuatsi)

Mandarin fish (Siniperca chuatsi) represents a typical carnivorous freshwater economic fish in China. Recently, the study of their feeding behavior to acclimate formulated diets has become a research focus. This study evaluated the effects of various diets on the body composition, nutritional content, digestive enzyme activity, gene expression, and gut microbiota of mandarin fish. Firstly, no significant differences were found in the muscle's basic nutritional components (moisture, crude protein, crude fat, and crude ash), as well as in the fatty acid and amino acid content, between the live feed group (LFSC) and the compound feed group (CFSC). However, mandarin fish in the LFSC group exhibited significantly higher lipase activity in the liver and intestine compared to the CFSC group, while amylase activity in the intestine showed an opposite pattern. Additionally, intestinal transcriptome analysis revealed 6238 differentially expressed genes and identified several differentially expressed clock genes associated with diet type. Furthermore, gut microbiota analysis indicated that different feeding regimens influenced microbial composition, revealing correlations between bacterial genera and intestinal gene expression levels. These findings provided novel insights into the gut microbiota and transcriptomic responses of mandarin fish to different dietary types.

Identification of Single-Nucleotide Polymorphisms in Differentially Expressed Genes Favoring Soybean Meal Tolerance in Higher-Growth Zebrafish (Danio rerio)

Genetic variability within the same fish species could confer soybean meal (SBM) tolerance in some individuals, thus favoring growth. This study investigates the single-nucleotide polymorphisms (SNPs) in differentially expressed genes (DEGs) favoring SBM tolerance in higher-growth zebrafish (Danio rerio). In a previous work, nineteen families of zebrafish were fed a fish meal diet (100FM control diet) or SBM-based diets supplemented with saponin (50SBM + 2SPN-experimental diet), from juvenile to adult stages. Individuals were selected from families with a genotype-by-environment interaction higher (170 ± 18 mg) or lower (76 ± 10 mg) weight gain on 50SBM + 2SPN in relation to 100FM. Intestinal transcriptomic analysis using RNA-seq revealed six hundred and sixty-five differentially expressed genes in higher-growth fish fed 50SBM + 2SPN diet. In this work, using these results, 47 SNPs in DEGs were selected. These SNPs were genotyped by Sequenom in 340 zebrafish that were fed with a 50SBM + 2SPN diet or with 100FM diet. Marker-trait analysis revealed 4 SNPs associated with growth in 3 immunity-related genes (aif1l, arid3c, and cst14b.2) in response to the 50SBM + 2SPN diet (p-value < 0.05). Two SNPs belonging to aif1l y arid3c produce a positive (+19 mg) and negative (-26 mg) effect on fish growth, respectively. These SNPs can be used as markers to improve the early selection of tolerant fish to SBM diet or other plant-based diets. These genes can be used as biomarkers to identify SNPs in commercial fish, thus contributing to the aquaculture sustainability.

Transcriptome analysis of large yellow croaker (Larimichthys crocea) at different growth rates

The unsynchronized growth of the large yellow croaker (Larimichthys crocea), which impacts growth efficiency, poses a challenge for aquaculture practitioners. In our study, juvenile stocks of large yellow croaker were sorted by size after being cultured in offshore cages for 4 months. Subsequently, individuals from both the fast-growing (FG) and slow-growing (SG) groups were sampled for analysis. High-throughput RNA-Seq was employed to identify genes and pathways that are differentially expressed during varying growth rates, which could suggest potential physiological mechanisms that influence growth rate. Our transcriptome analysis identified 382 differentially expressed genes (DEGs), comprising 145 upregulated and 237 downregulated genes in comparison to the SG group. GO and KEGG enrichment analyses indicated that these DEGs are predominantly involved in signal transduction and biochemical metabolic pathways. Quantitative PCR (qPCR) results demonstrated that cat, fasn, idh1, pgd, fgf19, igf2, and fads2 exhibited higher expression levels, whereas gadd45b and gadd45g showed lower expression compared to the slow-growing group. In conclusion, the differential growth rates of large yellow croaker are intricately associated with cellular proliferation, metabolic rates of the organism, and immune regulation. These findings offer novel insights into the molecular mechanisms and regulatory aspects of growth in large yellow croaker and enhance our understanding of growth-related genes.

First neurotranscriptome of adults Tambaquis (Colossoma macropomum) with characterization and differential expression between males and females

The Tambaqui is one of the most representative Amazon fish species, being highly exploited in fisheries, aquaculture and as a research model. Nonetheless, data about functional genome are still required to evaluate reproductive and nutrition parameters as well as resistance to pathogens. The of next-generation sequencing has allows assessing the transcriptional processes in non-model species by providing comprehensive gene collections to be used as a database in further genomic applications and increased performance of captive populations. In this study, we relied on RNAseq approach to generate the first transcriptome of the telencephalon from adult males and females of Colossoma macropomum, resulting in a reference dataset for future functional studies. We retrieved 896,238 transcripts, including the identification of 267,785 contigs and 203,790 genes. From this total, 91 transcripts were differentially expressed, being 63 and 28 of them positively regulated for females and males, respectively. The functional annotation resulted in a library of 40 candidate genes for females and 20 for males. The functional enrichment classes comprised reproductive processes (GO:0,048,609; GO:0,003,006; GO:0,044,703; GO:0,032,504; GO:0,019,953) being related to sex differentiation (e.g., SAFB) and immune response (e.g., SLC2A6, AHNAK, NLRC3, NLRP3 and IgC MHC I alpha3), thus indicating that the genes in the neurotranscriptome of Tambaqui participate in sex differentiation and homeostasis of captive specimens. These data are useful to design the selection of genes related to sex determination and animal welfare in raising systems of Tambaqui.

Multiple Tissues Transcriptome of Zig-Zag Eel (Mastacembelus armatus) with Different Growth Rates

In order to explore the main regulatory genes and related pathways of growth traits, transcriptome sequencing was first performed on the brain, liver, and muscle tissues of 3-month-old M. armatus with different growth rates. By comparative transcriptome analysis of fast-growing and slow-growing groups of M. armatus, a total of 2887 DEGs were screened, of which 59 up-regulated genes and 105 down-regulated genes were detected in the brain, 146 up-regulated genes and 202 down-regulated genes were detected in the liver, and 529 up-regulated genes and 1846 down-regulated genes were detected in muscle, including insulin-like growth factor binding protein 1a (IGFBP1A), insulin-like growth factor binding protein 1b (IGFBP1B), myosin, light chain 1 (MYL1), and myoglobin (MB). Through Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, we identified a total of 288 significantly enriched GO entries and 68 significantly enriched KEGG pathways related to growth, such as skeletal muscle tissue development, insulin-like growth factor binding, and the mitotic cell cycle. These key genes and signaling pathways may play a key role in regulating the growth of M. armatus. Digging into the regulatory mechanisms of these key genes will provide a theoretical basis for further exploration of the molecular mechanisms related to the growth and development of M. armatus, and help to breed new varieties of M. armatus with rapid growth.

Transcriptomic sequencing analysis of key long noncoding RNAs and mRNAs expression profiles in postoperative recurrence of hepatocellular carcinoma

BACKGROUND

Recurrence is the main cause of death in hepatocellular carcinoma (HCC) patients after liver resection.

OBJECTIVE

The long non-coding RNAs (lncRNAs) have been reported participated in progression and prognosis of HCC, however, the vital role of lncRNA in postoperative recurrence of HCC has rarely been systematically identified.

METHODS

RNA-sequencing (RNA-seq) was performed between orthotopic model of HCC and hepatoma postoperative recurrent model to comprehensively analyze the integrated transcriptome expression profiles of lncRNA and mRNA. Quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) was then conducted to quantify the expression levels of DElncRNAs and their target mRNAs.

RESULTS

In our study, 211 lncRNAs (P-value < 0.05) and 1125 mRNAs (P-adjust < 0.05) were significantly differentially expressed (DE) between two groups. Moreover, gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses showed that DElncRNAs and DEmRNAs were mainly enriched in lipid metabolism, including Arachidonic acid metabolism, PPAR signaling pathway, Steroid hormone biosynthesis, Linoleic acid metabolism, Inflammatory mediator regulation of TRP channels, and Fatty acid degradation. Furthermore, we constructed lncRNA-mRNA interaction networks and protein-protein interaction (PPI) network, and verified by qRT-PCR, suggesting that increased DEIncRNAs (XLOC_063499 and XLOC_042016) may prevent HCC recurrence after surgery by upregulating on targeted cytochrome P450 (CYP) family genes in the lipid metabolism pathway, such as cyp3a16, cyp3a44, cyp2c39, cyp2c40 and cyp2c68.

CONCLUSION

Overall, Our findings provided new insights for further investigation of biological function in lncRNA related HCC recurrence.

Identification of hub genes in digestive system of mandarin fish (Siniperca chuatsi) fed with artificial diet by weighted gene co-expression network analysis

Mandarin fish (Siniperca chuatsi) is a carnivorous freshwater fish and an economically important species. The digestive system (liver, stomach, intestine, pyloric caecum, esophagus, and gallbladder) is an important site for studying fish domestication. In our previous study, we found that mandarin fish undergoes adaptive changes in histological morphology and gene expression levels of the digestive system when subjected to artificial diet domestication. However, we are not clear which hub genes are highly associated with domestication. In this study, we performed WGCNA on the transcriptomes of 17 tissues and 9 developmental stages and combined differentially expressed genes analysis in the digestive system to identify the hub genes that may play important functions in the adaptation of mandarin fish to bait conversion. A total of 31,657 genes in 26 samples were classified into 23 color modules via WGCNA. The modules midnightblue, darkred, lightyellow, and darkgreen highly associated with the liver, stomach, esophagus, and gallbladder were extracted, respectively. Tan module was highly related to both intestine and pyloric caecum. The hub genes in liver were cp, vtgc, c1in, c9, lect2, and klkb1. The hub genes in stomach were ghrl, atp4a, gjb3, muc5ac, duox2, and chia2. The hub genes in esophagus were mybpc1, myl2, and tpm3. The hub genes in gallbladder were dyst, npy2r, slc13a1, and slc39a4. The hub genes in the intestine and pyloric caecum were slc15a1, cdhr5, btn3a1, anpep, slc34a2, cdhr2, and ace2. Through pathway analysis, modules highly related to the digestive system were mainly enriched in digestion and absorption, metabolism, and immune-related pathways. After domestication, the hub genes vtgc and lect2 were significantly upregulated in the liver. Chia2 was significantly downregulated in the stomach. Slc15a1, anpep, and slc34a2 were significantly upregulated in the intestine. This study identified the hub genes that may play an important role in the adaptation of the digestive system to artificial diet, which provided novel evidence and ideas for further research on the domestication of mandarin fish from molecular level.

Identification of differentially expressed genes and SNPs linked to harvest body weight of genetically improved rohu carp, Labeo rohita

In most of the aquaculture selection programs, harvest body weight has been a preferred performance trait for improvement. Molecular interplay of genes linked to higher body weight is not elucidated in major carp species. The genetically improved rohu carp with 18% average genetic gain per generation with respect to harvest body weight is a promising candidate for studying genes' underlying performance traits. In the present study, muscle transcriptome sequencing of two groups of individuals, with significant difference in breeding value, belonging to the tenth generation of rohu carp was performed using the Illumina HiSeq 2000 platform. A total of 178 million paired-end raw reads were generated to give rise to 173 million reads after quality control and trimming. The genome-guided transcriptome assembly and differential gene expression produced 11,86,119 transcripts and 451 upregulated and 181 downregulated differentially expressed genes (DEGs) between high-breeding value and low-breeding value (HB & LB) groups, respectively. Similarly, 39,158 high-quality coding SNPs were identified with the Ts/Tv ratio of 1.23. Out of a total of 17 qPCR-validated transcripts, eight were associated with cellular growth and proliferation and harbored 13 SNPs. The gene expression pattern was observed to be positively correlated with RNA-seq data for genes such as myogenic factor 6, titin isoform X11, IGF-1 like, acetyl-CoA, and thyroid receptor hormone beta. A total of 26 miRNA target interactions were also identified to be associated with significant DETs (p-value < 0.05). Genes such as Myo6, IGF-1-like, and acetyl-CoA linked to higher harvest body weight may serve as candidate genes in marker-assisted breeding and SNP array construction for genome-wide association studies and genomic selection.

Full-length transcriptome from different life stages of cobia (Rachycentron canadum, Rachycentridae)

Cobia (Rachycentron canadum, Rachycentridae) is one of the prospective species for mariculture. The transcriptome-based study on cobia was hampered by an inadequate reference genome and a lack of full-length cDNAs. We used a long-read based sequencing technology (PacBio Sequel II Iso-Seq3 SMRT) to obtain complete transcriptome sequences from larvae, juveniles, and various tissues of adult cobia, and a single SMRTcell generated 99 gigabytes of data and 51,205,946,694 bases. A total of 8609435, 7441673 and 9140164 subreads were generated from the larval, juvenile, and adult sample pools, with mean sub-read lengths of 2109.9, 1988.2 and 1996.2 bp, respectively. All samples were combined to increase transcript recovery and clustered into 35661 high-quality reads. This is the first report on a full-length transcriptome from R. canadum. Our results illustrate a significant increase in the identified amount of cobia LncRNAs and alternatively spliced transcripts, which will help improve genome annotation. Furthermore, this information will be beneficial for nutrigenomics and functional studies on cobia and other commercially important mariculture species.

Transcriptome analysis and gene expression analysis related to salinity-alkalinity and low temperature adaptation of Triplophysa yarkandensis

T. yarkandensis is a common species of Triplophysa, and it is distributed in Shule river of Hexi Corridor, of Gansu province in China. In order to enrich gene database resources and explore the environment adaptation of T. yarkandensis, fifteen tissues were collected from three adult T. yarkandensis for transcriptome sequencing and de novo assembly. Nine major international gene annotation databases (NR, COG, egg_NOG, TrEMBL, Pfam, KOG, Swiss prot, KEGG and Gene Ontology) were utilized to annotate unigenes. A detailed study was conducted to explore the gene expression and the differentially expressed genes among five tissues (brain, heart, kidney, liver and spleen). In addition, the current study showed that candidate genes involved in salinity-alkalinity and low temperature adaptation were differentially expressed in tissues of T. yarkandensis. Precisely, mapk1, abcc1, gpx1, gpx4, cat and aqp1 genes participated in the regulation process of salinity-alkalinity adaptation, and elovl4, acaca, fasn, acaa2, acox1 and acox3 genes were involved in fatty acid metabolism and closely associated with low temperature adaptation. On the one hand, it was found that the expression of these genes varied among different tissues, and the important pathways involved in these genes were mapped. Furthermore, we analyzed mapk1 and acox1 genes in depth to obtain the predicted gene structure and important amino acid sites. The transcriptome information in this study will be conducive to provide further understanding for the molecular level research and exploration of the environmental adaptation of T. yarkandensis.

Screening of Genes Related to Sex Determination and Differentiation in Mandarin Fish (Siniperca chuatsi)

Mandarin fish has an XX/XY sex-determination system. The female mandarin fish is typically larger than the male. Sex identification and the discovery of genes related to sex determination in mandarin fish have important theoretical significance in the elucidation of the regulation and evolutionary mechanism of animal reproductive development. In this study, the chromosome-level genome of a female mandarin fish was assembled, and we found that LG24 of the genome was an X chromosome. A total of 61 genes on the X chromosome showed sex-biased expression. Only six gonadal genes (LG24G00426, LG24G003280, LG24G003300, LG24G003730, LG24G004200, and LG24G004770) were expressed in the testes, and the expression of the other gene LG24G003870 isoform 1 in the ovaries was significantly higher than that in the testes (p < 0.01). Five (except LG24G003280 and LG24G003300) of the seven aforementioned genes were expressed at the embryonic development stage, suggesting their involvement in early sex determination. The expression of LG24G004770 (encoding HS6ST 3-B-like) was also significantly higher in female muscles than in male muscles (p < 0.01), indicating other functions related to female growth. ZP3 encoded by LG24G003870 isoform 1 increased the C-terminal transmembrane domain, compared with that encoded by other fish zp3 isoforms, indicating their different functions in sex determination or differentiation. This study provides a foundation for the identification of sex-determining genes in mandarin fish.

Dynamic transcriptome analysis of the muscles in high-fat diet-induced obese zebrafish (Danio rerio) under 5-HT treatment

Peripheral 5-hydroxytryptamine (5-HT, also called serotonin) is reportedly a potential therapeutic target in obesity-related metabolic diseases due to its regulatory role in energy homeostasis in mammals. However, information on the detailed effect of peripheral 5-HT on the energy metabolism in fishes, especially the lipid metabolism, and the underlying mechanism remains elusive. In this study, a diet-induced obesity model was developed in the zebrafish (Danio rerio), a prototypical animal model for metabolic disorders. The zebrafish were fed a high-fat diet for 8 weeks and were simultaneously injected with PBS, 0.1 mM and 10 mM 5-HT, intraperitoneally. The body weight was significantly lower in the zebrafish injected with 0.1 mM 5-HT (P < 0.05), however, there was no change in body length (P > 0.05) at the end of the 8-week treatment. The muscle tissues from the zebrafish treated with PBS and 5-HT were collected for transcriptomic analysis and the RNA-seq revealed 1134, 3713, and 2535 genes were screened out compared to the muscular DEGs among three groups. The enrichment analysis revealed DEGs to be significantly associated with multiple metabolic pathways, including ribosome, oxidative phosphorylation, proteasome, PPAR signaling pathway, and ferroptosis. Additionally, the qRT-PCR validated 12 DEGs out of which 10 genes exhibited consistent trends. Taken together, this data provided useful information on the transcriptional characteristics of the muscle tissue in the obese zebrafish exposed to 5-HT, offering important insights into the regulatory effect of peripheral 5-HT in teleosts, as well as novel approaches for preventing and treating obesity-related metabolic dysfunction.

Assembly-free rapid differential gene expression analysis in non-model organisms using DNA-protein alignment

BACKGROUND

RNA-seq is being increasingly adopted for gene expression studies in a panoply of non-model organisms, with applications spanning the fields of agriculture, aquaculture, ecology, and environment. For organisms that lack a well-annotated reference genome or transcriptome, a conventional RNA-seq data analysis workflow requires constructing a de-novo transcriptome assembly and annotating it against a high-confidence protein database. The assembly serves as a reference for read mapping, and the annotation is necessary for functional analysis of genes found to be differentially expressed. However, assembly is computationally expensive. It is also prone to errors that impact expression analysis, especially since sequencing depth is typically much lower for expression studies than for transcript discovery.

RESULTS

We propose a shortcut, in which we obtain counts for differential expression analysis by directly aligning RNA-seq reads to the high-confidence proteome that would have been otherwise used for annotation. By avoiding assembly, we drastically cut down computational costs - the running time on a typical dataset improves from the order of tens of hours to under half an hour, and the memory requirement is reduced from the order of tens of Gbytes to tens of Mbytes. We show through experiments on simulated and real data that our pipeline not only reduces computational costs, but has higher sensitivity and precision than a typical assembly-based pipeline. A Snakemake implementation of our workflow is available at: https://bitbucket.org/project_samar/samar .

CONCLUSIONS

The flip side of RNA-seq becoming accessible to even modestly resourced labs has been that the time, labor, and infrastructure cost of bioinformatics analysis has become a bottleneck. Assembly is one such resource-hungry process, and we show here that it can be avoided for quick and easy, yet more sensitive and precise, differential gene expression analysis in non-model organisms.

The first transcriptome sequencing and data analysis of the Javan mahseer (Tor tambra)

The Javan mahseer (Tor tambra) is one of the most valuable freshwater fish found in Tor species. To date, other than mitogenomic data (BioProject: PRJNA422829), genomic and transcriptomic resources for this species are still lacking which is crucial to understand the molecular mechanisms associated with important traits such as growth, immune response, reproduction and sex determination. For the first time, we sequenced the transcriptome from a whole juvenile fish using Illumina NovaSEQ6000 generating raw paired-end reads. De novo transcriptome assembly generated a draft transcriptome (BUSCO5 completeness of 91.2% [Actinopterygii_odb10 database]) consisting of 259,403 putative transcripts with a total and N50 length of 333,881,215 bp and 2283 bp, respectively. A total count of 77,503 non-redundant protein coding sequences were predicted from the transcripts and used for functional annotation. We mapped the predicted proteins to 304 known KEGG pathways with signal transduction cluster having the highest representation followed by immune system and endocrine system. In addition, transcripts exhibiting significant similarity to previously published growth-and immune-related genes were identified which will facilitate future molecular breeding of Tor tambra.