iTRAQ proteomic analysis of salinity acclimation proteins in the gill of tropical marbled eel (Anguilla marmorata)

Protein expression patterns and metal metabolites in a protogynous hermaphrodite fish, the ricefield eel (Monopterus albus)

BACKGROUND

The ricefield eel Monopterus albus undergoes a natural sex change from female to male during its life cycle, and previous studies have shown the potential mechanisms of this transition at the transcriptional and protein levels. However, the changes in protein levels have not been fully explored, especially in the intersexual stage.

RESULTS

In the present study, the protein expression patterns in the gonadal tissues from five different periods, the ovary (OV), early intersexual stage gonad (IE), middle intersexual stage gonad (IM), late intersexual stage gonad (IL), and testis (TE), were determined by untargeted proteomics sequencing. A total of 5125 proteins and 394 differentially expressed proteins (DEPs) were detected in the gonadal tissues. Of the 394 DEPs, there were 136 between the OV and IE groups, 20 between the IM and IE groups, 179 between the IL and IM groups, and 59 between the TE and IL groups. Three candidate proteins, insulin-like growth factor 2 mRNA-binding protein 3 isoform X1 (Igf2bp3), triosephosphate isomerase (Tpi), and Cu-Zn superoxide dismutase isoform X1 [(Cu-Zn) Sod1], were validated by western blotting to verify the reliability of the data. Furthermore, metal metabolite-related proteins were enriched in the IL vs. IM groups and TE vs. IL groups, which had close relationships with sex change, including Cu2+-, Ca2+-, Zn2+- and Fe2+/Fe3+-related proteins. Analysis of the combined transcriptome data revealed consistent protein/mRNA expression trends for two metal metabolite-related proteins/genes [LOC109953912 and calcium Binding Protein 39 Like (cab39l)]. Notably, we detected significantly higher levels of Cu2+ during the sex change process, suggesting that Cu2+ is a male-related metal metabolite that may have an important function in male reproductive development.

CONCLUSIONS

In summary, we analyzed the protein profiles of ricefield eel gonadal tissues in five sexual stages (OV, IE, IM, IL, and TE) and verified the plausibility of the data. After preforming the functional enrichment of metal metabolite-related DEPs, we detected the contents of the metal metabolites Zn2+, Cu2+, Ca2+, and Fe2+/Fe3+ at these five stages and screened for (Cu-Zn) Sod1 and Mmp-9 as possible key proteins in the sex reversal process.

Comprehensive transcriptomics and proteomics analysis of Carassius auratus gills in response to Aeromonas hydrophila

As one of the mucosal barriers, fish gills represent the first line of defense against pathogen infection. However, the exact mechanism of gill mucosal immune response to bacterial infection still needs further investigation in fish. Here, to investigate pathological changes and molecular mechanisms of the mucosal immune response in the gills of crucian carp (Carassius auratus) challenged by Aeromonas hydrophila, the transcriptomics and proteomics were performed by using multi-omics analyses of RNA-seq coupled with iTRAQ techniques. The results demonstrated gill immune response were mostly related to the activation of complement and coagulation cascades, antigen processing and presentation, phagosome, NOD-like receptor (NLR) and nuclear factor κB (NFκB) signaling pathway. Selected 21 immune-related DEGs (ie., Clam, nfyal, snrpf, acin1b, psme, sf3b5, rbm8a, rbm25, prpf18, g3bp2, snrpd3l, tecrem-2, cfl-A, C7, lysC, ddx5, hsp90, α-2M, C9, C3 and slc4a1a) were verified for their immune roles in the A. hydrophila infection via using qRT-PCR assay. Meanwhile, some complement (C3, C7, C9, CFD, DF and FH) and antigen presenting (HSP90, MHC Ⅱ, CALR, CANX and PSME) proteins were significantly participated in the process of defense against infections in gill tissues, and protein-protein interaction (PPI) network displayed the immune signaling pathways and interactions among these DEPs. The correlation analysis indicated that the iTRAQ and qRT-PCR results was significantly correlated (Pearson's correlation coefficient = 0.70, p < 0.01). To our knowledge, the transcriptomics and proteomics of gills firstly identified by multi-omics analyses contribute to understanding on the molecular mechanisms of local mucosal immunity in cyprinid species.

Gill Transcriptome Analysis Revealed the Difference in Gene Expression Between Freshwater and Seawater Acclimated Guppy (Poecilia reticulata)

Guppy (Poecilia reticulata) can adapt to a wide range of salinity changes. To investigate the gene expression changes in the guppy exposed to seawater, we characterized its gill transcriptome using RNA sequencing. Experimental fish were exposed to salinity increase from 0 to 30‰ within 4 days, while control fish were cultured in freshwater (0‰ salinity). Seven days after salinity exposure, the gills were sampled and the mortality within 2 weeks was recorded. No significant difference in the cumulative mortality at the second week was found between the two groups. Transcriptomic analysis identified 3477 differentially expressed genes (DEGs), including 1067 upregulated and 2410 downregulated genes. These DEGs were enriched in several biological processes, including ion transport, ion homeostasis, ATP biosynthetic process, metabolic process, and immune system process. Oxidative phosphorylation was the most activated pathway. DEGs involved in the pathway "endoplasmic reticulum (ER)-mediated phagocytosis," "starch and sucrose metabolism," and "steroid biosynthesis" were mainly downregulated; chemokines and interleukins involved in "cytokine-cytokine receptor interaction" were differentially expressed. The present results suggested that oxidative phosphorylation had essential roles in osmoregulation in the gills of seawater acclimated guppy, during which the decline in the expression of genes encoding V-ATPases and calreticulin had a negative effect on the phagocytosis and immune response. Besides, several metabolic processes including "starch and sucrose metabolism" and "steroid biosynthesis" were affected. This study elucidates transcriptomic changes in osmotic regulation, metabolism, and immunity in seawater acclimated guppy.

Investigating Diadromy in Fishes and Its Loss in an -Omics Era

Diadromy, the predictable movements of individuals between marine and freshwater environments, is biogeographically and phylogenetically widespread across fishes. Thus, despite the high energetic and potential fitness costs involved in moving between distinct environments, diadromy appears to be an effective life history strategy. Yet, the origin and molecular mechanisms that underpin this migratory behavior are not fully understood. In this review, we aim first to summarize what is known about diadromy in fishes; this includes the phylogenetic relationship among diadromous species, a description of the main hypotheses regarding its origin, and a discussion of the presence of non-migratory populations within diadromous species. Second, we discuss how recent research based on -omics approaches (chiefly genomics, transcriptomics, and epigenomics) is beginning to provide answers to questions on the genetic bases and origin(s) of diadromy. Finally, we suggest future directions for -omics research that can help tackle questions on the evolution of diadromy.

Skin proteome profiling of tongue sole (Cynoglossus semilaevis) challenged with Vibrio vulnificus

Vibrio vulnificus is a major pathogen of cultured Cynoglossus semilaevis and results in skin ulceration and haemorrhage, but the proteomic mechanism of skin immunity against V. vulnificus remains unclear. In this study, we investigated the histopathology and skin immune response in C. semilaevis with V. vulnificus infection at the protein levels, the differential proteomic profiling of its skin was examined by using iTRAQ and LC-MS/MS analyses. A total of 951 proteins were identified in skin, in which 134 and 102 DEPs were screened at 12 and 36 hpi, respectively. Selected eleven immune-related DEPs (pvβ, Hsp71, MLC1, F2, α2ML, HCII, C3, C5, C8β, C9 and CD59) were verified for their immune roles in the V. vulnificus infection via using qRT-PCR assay. KEGG enrichment analysis revealed that most of the identified immune proteins were significantly associated with complement and coagulation cascades, antigen processing and presentation, salivary secretion and phagosome pathways. To our knowledge, this study is the first to describe the proteome response of C. semilaevis skin against V. vulnificus infection. The outcome of this study contributed to provide a new perspective for understanding the molecular mechanism of local skin mucosal immunity, and facilitating the development of novel mucosal vaccination strategies in fish.

Gill transcriptomes reveal expression changes of genes related with immune and ion transport under salinity stress in silvery pomfret (Pampus argenteus)

Salinity is a major ecological factor in the marine environment, and extremely important for the survival, development, and growth of fish. In this study, gill transcriptomes were examined by high-throughput sequencing at three different salinities (12 ppt as low salinity, 22 ppt as control salinity, and 32 ppt as high salinity) in an importantly economical fish silvery pomfret. A total of 187 genes were differentially expressed, including 111 up-regulated and 76 down-regulated transcripts in low-salinity treatment group and 107 genes differentially expressed, including 74 up-regulated and 33 down-regulated transcripts in high-salinity treatment group compared with the control group, respectively. Some pathways including NOD-like receptor signaling pathway, cytokine-cytokine receptor interaction, Toll-like receptor pathway, cardiac muscle contraction, and vascular smooth muscle contraction were significantly enriched. qPCR analysis further confirmed that mRNA expression levels of immune (HSP90A, IL-1β, TNFα, TLR2, IP-10, MIG, CCL19, and IL-11) and ion transport-related genes (WNK2, NPY2R, CFTR, and SLC4A2) significantly changed under salinity stress. Low salinity stress caused more intensive expression changes of immune-related genes than high salinity. These results imply that salinity stress may affect immune function in addition to regulating osmotic pressure in silvery pomfret.

Does silvering or 11-ketotestosterone affect osmoregulatory ability in the New Zealand short-finned eel (Anguilla australis)?

Silvering has been associated with advancing osmoregulatory ability. Given the demonstrated role of 11-ketotestosterone (11KT) in mediating many of the silvering-related changes, we investigated the role of 11KT in driving this advanced osmoregulatory ability in the New Zealand short-finned eel (Anguilla australis). Yellow (non-migratory) eels with or without 11KT implants and blank-implanted silver (migratory) eels, either held in freshwater or subjected to seawater challenge, were sampled to determine serum [Na⁺] and [Cl^-], pituitary prolactin mRNA levels, gill Na⁺/K⁺-ATPase activity and gill mRNA levels for Na⁺/K⁺-ATPase-α1 subunit and for Na⁺/K⁺/2Cl^- co-transporter-1α-subunit. Developmental stage and 11KT treatment advanced the eels' osmoregulatory ability. Thus, serum [Na⁺] and [Cl^-] were affected by developmental stage and 11KT treatment upon seawater challenge. However, seawater challenge, not 11KT treatment or developmental stage, produced the strongest and the most consistent effects on A. australis osmoregulatory processes, inducing significant effects in all the relevant parameters we measured. In light of our results and in view of the eel's marine ancestry, we contend that A. australis, or freshwater eels in general, are highly tolerant and able to adapt quickly to changing salinities even at the yellow stage, which may preclude a critical need for an advanced osmoregulatory ability at silvering.

Physiological mechanism of osmoregulatory adaptation in anguillid eels

In recent years, the production of eel larvae has dramatic declines due to reductions in spawning stocks, overfishing, growth habitat destruction and access reductions, and pollution. Therefore, it is particularly important and urgent for artificial production of glass eels. However, the technique of artificial hatching and rearing larvae is still immature, which has long been regarded as an extremely difficult task. One of the huge gaps is artificial condition which is far from the natural condition to develop their capability of osmoregulation. Thus, understanding their osmoregulatory mechanisms will help to improve the breed and adapt to the changes in the environment. In this paper, we give a general review for a study progress of osmoregulatory mechanisms in eels from five aspects including tissues and organs, ion transporters, hormones, proteins, and high throughput sequencing methods.

Toxic responses of Perna viridis hepatopancreas exposed to DDT, benzo(a)pyrene and their mixture uncovered by iTRAQ-based proteomics and NMR-based metabolomics

Dichlorodiphenyltrichloroethane (DDT) and benzo(a)pyrene (BaP) are environmental estrogens (EEs) that are ubiquitous in the marine environment. In the present study, we integrated isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomic and nuclear magnetic resonance (NMR)-based metabolomic approaches to explore the toxic responses of green mussel hepatopancreas exposed to DDT (10μg/L), BaP (10μg/L) and their mixture. The metabolic responses indicated that BaP primarily disturbed energy metabolism and osmotic regulation in the hepatopancreas of the male green mussel P. viridis. Both DDT and the mixture of DDT and BaP perturbed the energy metabolism and osmotic regulation in P. viridis. The proteomic responses revealed that BaP affected the proteins involved in energy metabolism, material transformation, cytoskeleton, stress responses, reproduction and development in green mussels. DDT exposure could change the proteins involved in primary metabolism, stress responses, cytoskeleton and signal transduction. However, the mixture of DDT and BaP altered proteins associated with material and energy metabolism, stress responses, signal transduction, reproduction and development, cytoskeleton and apoptosis. This study showed that iTRAQ-based proteomic and NMR-based metabolomic approaches could effectively elucidate the essential molecular mechanism of disturbances in hepatopancreas function of green mussels exposed to environmental estrogens.