Variation in the transcriptome response and detoxification gene diversity drives pesticide tolerance in fishes

Pesticides are critical for invasive species management, but often have negative effects on non-target native biota. Tolerance to pesticides should have an evolutionary basis, but this is poorly understood. Invasive sea lamprey (Petromyzon marinus) populations in North America have been controlled with a pesticide lethal to them at lower concentrations than native fishes. We addressed how interspecific variation in gene expression and detoxification gene diversity confer differential pesticide sensitivity in two fish species. We exposed sea lamprey and bluegill (Lepomis macrochirus), a tolerant native species, to TFM, a pesticide commonly used in sea lamprey control, and used whole-transcriptome sequencing of gill and liver to characterize the cellular response. Comparatively, bluegill exhibited a larger number of detoxification genes expressed and a larger number of responsive transcripts overall, which likely contributes to greater tolerance to TFM. Understanding the genetic and physiological basis for pesticide tolerance is crucial for managing invasive species.

Evolution of variable lymphocyte receptor B antibody loci in jawless vertebrates

Three types of variable lymphocyte receptor (VLR) genes, VLRA, VLRB, and VLRC, encode antigen recognition receptors in the extant jawless vertebrates, lampreys and hagfish. The somatically diversified repertoires of these VLRs are generated by serial stepwise copying of leucine-rich repeat (LRR) sequences into an incomplete germline VLR gene. Lymphocytes that express VLRA or VLRC are T cell–like, while VLRB-expressing cells are B cell–like. Here, we analyze the composition of the VLRB locus in different jawless vertebrates to elucidate its configuration and evolutionary modification. The incomplete germline VLRB genes of two hagfish species contain short noncoding intervening sequences, whereas germline VLRB genes in six representative lamprey species have much longer intervening sequences that exhibit notable genomic variation. Genomic clusters of potential LRR cassette donors, fragments of which are copied to complete VLRB gene assembly, are identified in Japanese lamprey and sea lamprey. In the sea lamprey, 428 LRR cassettes are located in five clusters spread over a total of 1.7 Mbp of chromosomal DNA. Preferential usage of the different donor cassettes for VLRB assemblage is characterized in our analysis, which reveals evolutionary modifications of the lamprey VLRB genes, elucidates the organization of the complex VLRB locus, and provides a comprehensive catalog of donor VLRB cassettes in sea lamprey and Japanese lamprey.

Tissue and salinity specific Na+/Cl− cotransporter (NCC) orthologues involved in the adaptive osmoregulation of sea lamprey (Petromyzon marinus)

Two orthologues of the gene encoding the Na+-Cl− cotransporter (NCC), termed ncca and nccb, were found in the sea lamprey genome. No gene encoding the Na+-K+-2Cl− cotransporter 2 (nkcc2) was identified. In a phylogenetic comparison among other vertebrate NCC and NKCC sequences, the sea lamprey NCCs occupied basal positions within the NCC clades. In freshwater, ncca mRNA was found only in the gill and nccb only in the intestine, whereas both were found in the kidney. Intestinal nccb mRNA levels increased during late metamorphosis coincident with salinity tolerance. Acclimation to seawater increased nccb mRNA levels in the intestine and kidney. Electrophysiological analysis of intestinal tissue ex vivo showed this tissue was anion absorptive. After seawater acclimation, the proximal intestine became less anion absorptive, whereas the distal intestine remained unchanged. Luminal application of indapamide (an NCC inhibitor) resulted in 73% and 30% inhibition of short-circuit current (Isc) in the proximal and distal intestine, respectively. Luminal application of bumetanide (an NKCC inhibitor) did not affect intestinal Isc. Indapamide also inhibited intestinal water absorption. Our results indicate that NCCb is likely the key ion cotransport protein for ion uptake by the lamprey intestine that facilitates water absorption in seawater. As such, the preparatory increases in intestinal nccb mRNA levels during metamorphosis of sea lamprey are likely critical to development of whole animal salinity tolerance.

Expression of Kisspeptin 1 in the Brain of the Adult Sea Lamprey Petromyzon marinus

Kisspeptin peptides play major roles in the regulation of reproduction and puberty onset in mammals. While most mammals only have one kisspeptin gene, other jawed vertebrates present two or three genes. Recent data also revealed the presence of two genes in lampreys (jawless vertebrates). However, apart from gene sequence data, there is almost no information on the kisspeptinergic system of lampreys. Here, we report phylogenetic and cluster-based analyses showing that the duplication of the ancestral kisspeptin gene occurred before the separation of jawless and jawed vertebrates. We also studied the expression of the kisspeptin transcripts in the brain of post-metamorphic juveniles and upstream migrating adult sea lampreys. Our in situ hybridization results revealed expression of kisspeptin 1 in hypothalamic neurons, which indicates that the hypothalamic expression of kisspeptins is an ancestral character in vertebrates. We also observed the presence of kisspeptin 1 expressing neurons in the paratubercular (posterior tubercle) nucleus of the diencephalon. This is the first description of the presence of kisspeptin 1 expressing neurons in this brain region in any vertebrate. We did not detect expression of kisspeptin 2 in the juvenile or adult sea lamprey brain with in situ hybridization. Our data provides an anatomical basis to study the role of kisspeptin 1 in the hypothalamic-pituitary system of lampreys and the contribution of diencephalic kisspeptinergic neurons to different circuits of the lamprey brain.

Evaluation of health benefits of sea lamprey (Petromyzon marinus) isolates using in vitro antiinflammatory and antioxidant assays

Sea lamprey (Petromyzon marinus), a parasitic fish which survives on blood of other fishes, is consumed as a delicacy in many countries. Our earlier studies on sea lamprey compounds that showed potential to deter adult sea lampreys yielded several sterols, glycerides, free fatty acids, amino acids, organic acids and nitrogenous compounds. Therefore, this study was to assess the health-benefits of these compounds including additional isolates from HPLC fractions that kept aside due to lack of activity in sea lamprey deterrent assays. In vitro cyclooxygenase enzymes (COX-1 and -2) and lipid peroxidation (LPO) inhibitory assays, respectively, were used to determine antiinflammatory and antioxidant activities. Among the tested sterols, cholesteryl eicosapentaenoate and cholesteryl arachidonate exhibited IC50 values of 14.6 and 17.7 μg/mL for COX-1 and 17.3 and 20.8 μg/mL for COX-2, respectively. Cholesteryl palmitate and cholesteryl oleate showed moderate COX-1 and COX-2 enzyme inhibition at 25 μg/mL. Amino acids arginine, tyrosine, glutamic acid, tryptophan and asparagine also showed moderate COX-1 and COX-2 inhibition at the same concentration. Among the twelve new isolates from fractions that we did not investigate earlier, a novel uracil derivative petromyzonacil showed COX-1 and COX-2 inhibition at 25 μg/mL by 35 and 15%, respectively. Cholesterol esters tested at 25 μg/mL exhibited LPO inhibition between 38 and 82 percent. Amino acids cysteine, methionine, aspartic acid, threonine, tryptophan, histidine, glutamic acid, phenylalanine and tyrosine at 25 μg/mL showed LPO inhibition between 37 and 58% and petromyzonacil by 32%. These assay results indicate that consumption of sea lamprey offer health-benefits in addition to nutritional benefits.

Next Generation Lampricides: A Three-Stage Process to Develop Improved Control Tools for Invasive Sea Lamprey

Successful integrated management of the invasive predatory sea lamprey (Petromyzon marinus) in the Laurentian Great Lakes of North America is owed largely to the long history of beneficial use of two lampricides: 3 trifluoromethyl 4 nitrophenol (TFM) and 2’,5-dichloro-4’-nitrosalicylanilide (niclosamide). Ensuring continued successful sea lamprey control necessitates consideration of possible next-generation lampricides to supplement or replace current lampricides. This review identifies fifteen hallmarks of success for current lampricides to be used as design criteria in a search for next-generation lampricides. A three-stage research approach is outlined. Targeted research using omics, computer modelling, and high-throughput technology to define molecular mechanisms and high probability molecular targets for sea lamprey selective toxic action is crucial to prioritizing chemical candidates. Targeted delivery or identifying synergists to existing or new lampricides can provide increased efficiency and reduced environmental impact. Ultimate development of next-generation lampricides will rely on traditional toxicity testing methodologies to ensure safety and regulatory compliance.