Persistent organic pollutants in Antarctic notothenioid fish and invertebrates associated with trophic levels.
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ABSTRACT:
SUBMITTER: Ko FC
PROVIDER: S-EPMC5894976 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Climate changes can promote disease outbreaks, but their nature and potential impacts in remote areas have received little attention. In a hot spot of biodiversity on the West Antarctic Peninsula, which faces among the fastest changing climates on Earth, we captured specimens of two notothenioid fish species affected by large skin tumors at an incidence never before observed in the Southern Ocean. Molecular and histopathological analyses revealed that X-cell parasitic alveolates, members of a genus we call Notoxcellia, are the etiological agent of these tumors. Parasite-specific molecular probes showed that xenomas remained within the skin but largely outgrew host cells in the dermis. We further observed that tumors induced neovascularization in underlying tissue and detrimentally affected host growth and condition. Although many knowledge gaps persist about X-cell disease, including its mode of transmission and life cycle, these findings reveal potentially active biotic threats to vulnerable Antarctic ecosystems.
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Project description:Numerous novel adaptations characterise the radiation of notothenioids, the dominant fish group in the freezing seas of the Southern Ocean. To improve understanding of the evolution of this iconic fish group, here we generate and analyse new genome assemblies for 24 species covering all major subgroups of the radiation, including five long-read assemblies. We present a new estimate for the onset of the radiation at 10.7 million years ago, based on a time-calibrated phylogeny derived from genome-wide sequence data. We identify a two-fold variation in genome size, driven by expansion of multiple transposable element families, and use the long-read data to reconstruct two evolutionarily important, highly repetitive gene family loci. First, we present the most complete reconstruction to date of the antifreeze glycoprotein gene family, whose emergence enabled survival in sub-zero temperatures, showing the expansion of the antifreeze gene locus from the ancestral to the derived state. Second, we trace the loss of haemoglobin genes in icefishes, the only vertebrates lacking functional haemoglobins, through complete reconstruction of the two haemoglobin gene clusters across notothenioid families. Both the haemoglobin and antifreeze genomic loci are characterised by multiple transposon expansions that may have driven the evolutionary history of these genes.
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Project description:The antifreeze glycoprotein-fortified Antarctic notothenioid fishes comprise the predominant fish suborder in the isolated frigid Southern Ocean. Their ecological success undoubtedly entailed evolutionary acquisition of a full suite of cold-stable functions besides antifreeze protection. Prior studies of adaptive changes in these teleost fishes generally examined a single genotype or phenotype. We report here the genome-wide investigations of transcriptional and genomic changes associated with Antarctic notothenioid cold adaptation. We sequenced and characterized 33,560 ESTs from four tissues of the Antarctic notothenioid Dissostichus mawsoni and derived 3,114 nonredundant protein gene families and their expression profiles. Through comparative analyses of same-tissue transcriptome profiles of D. mawsoni and temperate/tropical teleost fishes, we identified 177 notothenioid protein families that were expressed many fold over the latter, indicating cold-related up-regulation. These up-regulated gene families operate in protein biosynthesis, protein folding and degradation, lipid metabolism, antioxidation, antiapoptosis, innate immunity, choriongenesis, and others, all of recognizable functional importance in mitigating stresses in freezing temperatures during notothenioid life histories. We further examined the genomic and evolutionary bases for this expressional up-regulation by comparative genomic hybridization of DNA from four pairs of Antarctic and basal non-Antarctic notothenioids to 10,700 D. mawsoni cDNA probes and discovered significant to astounding (3- to >300-fold, P < 0.05) Antarctic-specific duplications of 118 protein-coding genes, many of which correspond to the up-regulated gene families. Results of our integrative tripartite study strongly suggest that evolution under constant cold has resulted in dramatic genomic expansions of specific protein gene families, augmenting gene expression and gene functions contributing to physiological fitness of Antarctic notothenioids in freezing polar conditions.
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Project description:Antarctic notothenioid fishes and several northern cods are phylogenetically distant (in different orders and superorders), yet produce near-identical antifreeze glycoproteins (AFGPs) to survive in their respective freezing environments. AFGPs in both fishes are made as a family of discretely sized polymers composed of a simple glycotripeptide monomeric repeat. Characterizations of the AFGP genes from notothenioids and the Arctic cod show that their AFGPs are both encoded by a family of polyprotein genes, with each gene encoding multiple AFGP molecules linked in tandem by small cleavable spacers. Despite these apparent similarities, detailed analyses of the AFGP gene sequences and substructures provide strong evidence that AFGPs in these two polar fishes in fact evolved independently. First, although Antarctic notothenioid AFGP genes have been shown to originate from a pancreatic trypsinogen, Arctic cod AFGP genes share no sequence identity with the trypsinogen gene, indicating trypsinogen is not the progenitor. Second, the AFGP genes of the two fish have different intron-exon organizations and different spacer sequences and, thus, different processing of the polyprotein precursors, consistent with separate genomic origins. Third, the repetitive AFGP tripeptide (Thr-Ala/Pro-Ala) coding sequences are drastically different in the two groups of genes, suggesting that they arose from duplications of two distinct, short ancestral sequences with a different permutation of three codons for the same tripeptide. The molecular evidence for separate ancestry is supported by morphological, paleontological, and paleoclimatic evidence, which collectively indicate that these two polar fishes evolved their respective AFGPs separately and thus arrived at the same AFGPs through convergent evolution.
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Project description:Hepcidin is a small peptide composed of signal peptide, propeptide, and the bioactive mature peptide from N terminal to C terminal. Mature hepcidin is an antibacterial peptide and iron regulator with eight highly conserved cysteines forming four intramolecular disulfide bonds, giving it a β sheet hairpin-like structure. Hepcidin homologs are found in a variety of vertebrates, especially fish, and their diversity may be associated with different habitats and different levels of pathogens. Dissostichus mawsoni, an Antarctic notothenioid fish that lives in the coldest water unlike most places of the world, with at least two hepcidin variants with eight cysteines. We confirmed the formation process of activated mature hepcidins from D. mawsoni in Chinese hamster ovary (CHO) cell line, obtained recombinant hepcidin protein from prokaryotes, and characterized its binding ability and antibacterial activity against varying bacteria. The expression of hepcidin in CHO cell line showed that the prepropeptide of Dmhep_8cysV1 and Dmhep_8cysV2 cleavage into smaller mature peptide. The antibacterial assay and flow cytometry showed that Dmhep_8cysV1, Dmhep_8cysV2, and Drhep bound to different bacteria and killed them with different minimum inhibitory concentration. These data suggest that hepcidin plays an important role in the innate immunity of D. mawsoni and is of great value in improving resistance to pathogens.
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Project description:Freezing avoidance conferred by different types of antifreeze proteins in various polar and subpolar fishes represents a remarkable example of cold adaptation, but how these unique proteins arose is unknown. We have found that the antifreeze glycoproteins (AFGPs) of the predominant Antarctic fish taxon, the notothenioids, evolved from a pancreatic trypsinogen. We have determined the likely evolutionary process by which this occurred through characterization and analyses of notothenioid AFGP and trypsinogen genes. The primordial AFGP gene apparently arose through recruitment of the 5' and 3' ends of an ancestral trypsinogen gene, which provided the secretory signal and the 3' untranslated region, respectively, plus de novo amplification of a 9-nt Thr-Ala-Ala coding element from the trypsinogen progenitor to create a new protein coding region for the repetitive tripeptide backbone of the antifreeze protein. The small sequence divergence (4-7%) between notothenioid AFGP and trypsinogen genes indicates that the transformation of the proteinase gene into the novel ice-binding protein gene occurred quite recently, about 5-14 million years ago (mya), which is highly consistent with the estimated times of the freezing of the Antarctic Ocean at 10-14 mya, and of the main phyletic divergence of the AFGP-bearing notothenioid families at 7-15 mya. The notothenioid trypsinogen to AFGP conversion is the first clear example of how an old protein gene spawned a new gene for an entirely new protein with a new function. It also represents a rare instance in which protein evolution, organismal adaptation, and environmental conditions can be linked directly.
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Project description:Scavenging of gas- and aerosol-phase organic pollutants by rain is an efficient wet deposition mechanism of organic pollutants. However, whereas snow has been identified as a key amplification mechanism of fugacities in cold environments, rain has received less attention in terms of amplification of organic pollutants. In this work, we provide new measurements of concentrations of perfluoroalkyl substances (PFAS), organophosphate esters (OPEs), and polycyclic aromatic hydrocarbons (PAHs) in rain from Antarctica, showing high scavenging ratios. Furthermore, a meta-analysis of previously published concentrations in air and rain was performed, with 46 works covering different climatic regions and a wide range of chemical classes, including PFAS, OPEs, PAHs, polychlorinated biphenyls and organochlorine compounds, polybromodiphenyl ethers, and dioxins. The rain-aerosol (KRP) and rain-gas (KRG) partition constants averaged 105.5 and 104.1, respectively, but showed large variability. The high field-derived values of KRG are consistent with adsorption onto the raindrops as a scavenging mechanism, in addition to gas-water absorption. The amplification of fugacities by rain deposition was up to 3 orders of magnitude for all chemical classes and was comparable to that due to snow. The amplification of concentrations and fugacities by rain underscores its relevance, explaining the occurrence of organic pollutants in environments across different climatic regions.
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