Distinguishing between ante factum and post factum properties of animal cell lines and demonstrating their use in grouping ray-finned fish cell lines into invitromes

In this review, animal cell lines are considered to have two classes of attributes: "before-the-fact" (ante factum) and "after-the-fact" (post factum) properties. Fish cell lines from Actinopterygii (ray-finned fishes) are used to illustrate this distinction and to demonstrate how these properties can be used in various ways to categorize cell lines into groups or invitromes. Before-the-fact properties are set at initiation and are properties of the sample and species from which the cell line arose and of the scientist(s) who developed the cell line. On the basis of the Actinopterygii sample, invitromes exist for embryos, larvae, juveniles, adults, and spawning fish, and for most solid organs but rarely for biological fluids. For species, invitromes exist for only a small fraction of the Actinopterygii total. As to their development, scientists from around the world have contributed to invitromes. By contrast, after-the-fact properties are limitless and become apparent during development, characterization, use, and storage of the cell line. For ray-finned invitromes, cell lines appear to acquire immortality during development, are characterized poorly for differentiation potential, have numerous uses, and are stored formally only sporadically. As an example of applying these principles to a specific organ, the skeletal muscle invitrome is used. For ante factum properties, the cell lines are mainly from trunk muscle of economically important fish from 11 orders, 15 families, 19 genera, and 21 species of ray-finned fishes. For post factum properties, fibroblast-like and myogenic cell lines have been described but epithelial-like FHM is most widely used and curated. Considering cell lines by their before- and after-the-fact properties should facilitate integration of new cell lines into the literature and help incorporate the discipline of cell biology into other research areas, particularly the natural history of fishes.

A continuous myofibroblast precursor cell line from the tail muscle of Australasian snapper (Chrysophrys auratus) that responds to transforming growth factor beta and fibroblast growth factor

Chrysophrys auratus (Australasian snapper) is one of the largest and most valuable finfish from capture fisheries in New Zealand, yet no cell lines from this species are reported in the scientific literature. Here, we describe a muscle-derived cell line initiated from the tail of a juvenile snapper which has been designated CAtmus1PFR (Chrysophrys auratus, tail muscle, Plant & Food Research). The cell line has been passaged over 100 times in 3 years and is considered immortal. Cells are reliant on serum supplementation for proliferation and exhibit a broad thermal profile comparable to the eurythermic nature of C. auratus in vivo. The impact of exogenous growth factors, including insulin-like growth factors I and II (IGF-I and IGF-II), basic fibroblast growth factor (bFGF), and transforming growth factor beta (TGFβ), on cell morphology and proliferation was investigated. Insulin-like growth factors acted as mitogens and had minimal effect on cell morphology. TGFβ exposure resulted in CAtmus1PFR exhibiting a myofibroblast morphology becoming enlarged with actin bundling. This differentiation was confirmed through the expression of smooth muscle actin (sma), an increase in type 1 collagen (col1a) expression, and a loss of motility. Expression of col1a and sma was decreased when cells were exposed to bFGF, and no actin bundling was observed. These data indicate that CAtmus1PFR may be myofibroblastic precursor cells descending from mesenchymal progenitor cells present in the tail muscle myosepta.

Xela DS2 and Xela VS2: Two novel skin epithelial-like cell lines from adult African clawed frog (Xenopus laevis) and their response to an extracellular viral dsRNA analogue

The skin epithelial layer acts as an important immunological barrier against pathogens and is capable of recognizing and responding to pathogen-associated molecular patterns (PAMPs) in human and mouse models. Although presumed, it is unknown whether amphibian skin epithelial cells exhibit the ability to respond to PAMPs such as viral double-stranded RNA (dsRNA). To address this, two cell lines from the dorsal skin (Xela DS2) and ventral skin (Xela VS2) of the African clawed frog (Xenopus laevis) were established. Xela DS2 and Xela VS2 cells have an epithelial-like morphology, express genes associated with epithelial cells, and lack senescence-associated beta-galactosidase activity. Cells grow optimally in 70% Leibovitz's L-15 medium supplemented with 15% fetal bovine serum at 26 °C. Upon treatment with poly(I:C), a synthetic analogue of viral dsRNA and known type I interferon inducer, Xela DS2 and Xela VS2 exhibit marked upregulation of key antiviral and pro-inflammatory transcripts suggesting frog epithelial cells participate in the recognition of extracellular viral dsRNA and production of local inflammatory signals; similar to human and mouse models. Currently, these are the only known Xenopus laevis skin epithelial-like cell lines and will be important for future research in amphibian epithelial cell biology, initial host-pathogen interactions, and rapid screening of the effects of environmental stressors, including contaminants, on frog skin epithelial cells.

Screening of Fish Cell Lines for Piscine Orthoreovirus-1 (PRV-1) Amplification: Identification of the Non-Supportive PRV-1 Invitrome

Piscine reovirus (PRV) is the causative agent of heart and skeletal muscle inflammation (HSMI), which is detrimental to Atlantic Salmon (AS) aquaculture, but so far has not been cultivatable, which impedes studying the disease and developing a vaccine. Homogenates of head kidney and red blood cells (RBC) from AS in which PRV-1 had been detected were applied to fish cell lines. The cell lines were from embryos, and from brain, blood, fin, gill, gonads, gut, heart, kidney, liver, skin, and spleen, and had the shapes of endothelial, epithelial, fibroblast, and macrophage cells. Most cell lines were derived from the Neopterygii subclass of fish, but one was from subclass Chondrostei. Cultures were examined by phase contrast microscopy for appearance, and by quantitative polymerase chain reaction (qPCR) for PRV-1 RNA amplification and for the capacity to transfer any changes to new cultures. No changes in appearance and Ct values were observed consistently or transferable to new cultures. Therefore, 31 cell lines examined were unable to support PRV-1 amplification and are described as belonging to the non-supportive PRV-1 invitrome. However, these investigations and cell lines can contribute to understanding PRV-1 cellular and host tropism, and the interactions between virus-infected and bystander cells.

VHSV IVb infection and autophagy modulation in the rainbow trout gill epithelial cell line RTgill-W1

Autophagy modulation influences the success of intracellular pathogens, and an understanding of the mechanisms involved might offer practical options to reduce the impact of infectious disease. Viral haemorrhagic septicaemia virus (VHSV) can cause high mortality and economic loss in some commercial fish species. VHSV IVb was used to infect a rainbow trout gill cell line, RTgill-W1, followed by the treatment of the cells with different autophagy-modulating reagents. LC3II protein using Western blot was significantly (p < .05) decreased for two days following VHSV infection, and immunofluorescence confirmed that LC3II-positive intracytoplasmic puncta were also decreased. Infection with VHSV resulted in significantly decreased expression of the autophagy-related (Atg) genes atg4, at12, atg13 and becn1 after one day using quantitative PCR. Both viral gene copy number and VHSV N protein were significantly decreased by treating the cells with autophagy-blocking (chloroquine) and autophagy-inhibiting reagents (deoxynivalenol and 3-methyladenine) after three days, while autophagy induction (restricted nutrition and rapamycin) had limited effect. Only treatment of RTgill-W1 with deoxynivalenol resulted in a significant increase in expression of type I interferon. Therefore, the suppression of autophagy initially occurs after VHSV IVb infection, but the modulation of autophagy can also inhibit VHSV IVb infection in RTgill-W1 after three days.

Regulation of endogenous antigen presentation in response to suboptimal temperatures in a walleye skin fibroblast cell line

A skin fibroblast cell line WE-skin11f from walleye (Sander vitreus) was used to study the impact of temperature (26 °C, 20 °C, 14 °C, or 4 °C) on the transcript levels of genes involved in the endogenous antigen processing and presentation pathway (EAPP), which is an important antiviral pathway of vertebrates. Partial coding sequences were found for 4 previously unidentified walleye EAPP members, calreticulin, calnexin, erp57, and tapasin, and the constitutive transcript levels of these genes in WE-skin11f was unchanged by culture incubation temperature. The viral mimic poly (I:C) and viral haemorrhagic septicaemia virus (VHSV) IVb were used to study possible induction of EAPP transcripts (b2m, mhIa, and tapasin). The walleye cells were exquisitely sensitive to poly (I:C), losing adherence and viability at concentrations greater than 100 ng/mL, particularly at suboptimal temperatures. VHSV IVb viral particles were produced from infected WE-skin11f cells at 20 °C, 14 °C, and 4 °C but with much lower production at 4 °C. Under conditions where their impact on the viability of WE-skin11f cultures was slight, poly (I:C) and VHSV IVb were shown to induce b2m, mhIa, and tapasin transcript°s at 26 °C and 20 °C respectively. However, at 4 °C, the up-regulation of EAPP transcript levels was either delayed or completely impaired when compared to the 26 °C and 20 °C control temperatures of the respective experiments. These in vitro results suggest that suboptimal temperatures may be capable of modulating the regulation of the EAPP in walleye cells during viral infection.

Understanding the pathogenesis of Flavobacterium psychrophilum using the rainbow trout monocyte/macrophage-like cell line, RTS11, as an infection model

The life cycle of Flavobacterium psychrophilum (Fp), the causative agent of bacterial coldwater disease (BCWD) and rainbow trout fry syndrome (RTFS), appears to involve interactions with spleen and head kidney macrophages. To develop an in vitro model for studying this, F. psychrophilum was incubated with a rainbow trout splenic monocyte/macrophage-like cell line (RTS11) and fundamental macrophage functions evaluated. The animal cell basal medium, L15, supplemented with bovine serum (FBS) supports RTS11 maintenance, and surprisingly, L15 with 2% FBS (L15/FBS) also supported F. psychrophilum growth. L15/FBS in which the bacteria had been grown is referred to as F. psychrophilum conditioned medium (FpCM). Adding FpCM to RTS11 cultures caused a small, yet significant, percentage of cells to die, many cells to become more diffuse, and phagocytosis to be temporarily reduced. FpCM also significantly stimulated transcript expression for pro-inflammatory cytokines (IL-1β, TNFα and IL-6) and the anti-inflammatory cytokine (IL-10) after one day of exposure but this upregulation rapidly declined over time. Adding live F. psychrophilum to RTS11 cultures also altered the cellular morphology and stimulated cytokine expression more profoundly than FpCM. Additionally, the phagocytic activity of RTS11 was also significantly impaired by live F. psychrophilum, but not to the same extent as when exposed to FpCM. Adding heat-killed bacteria to RTS11 cultures elicited few changes. These bacteria/RTS11 co-cultures should be useful for gaining a deeper understanding of the pathogenesis of F. psychrophilum and may aid in the development of effective measures to prevent infection and spread of this troublesome disease.

Evolution of IFN subgroups in bony fish - 1:Group I-III IFN exist in early ray-finned fish, with group II IFN subgroups present in the Holostean spotted gar, Lepisosteus oculatus

The present study helps clarify when the fish type I IFN groups/subgroups evolved, by examination of the IFN genes present in the Holostean spotted gar, Lepisosteus oculatus, in relation to the IFN genes present in the Chondrostea (sturgeon). It confirms that all three IFN groups (I-III), and group II subgroups, existed prior to the appearance of teleost fish. Preliminary expression analysis in a gar cell line (GARL) suggests these IFN genes will have a role in antiviral defence in Holostean fish, in that they are induced by poly(I:C). A refined model of IFN evolution within the actinopterygian fish is proposed.

Effect of suboptimal temperature on the regulation of endogenous antigen presentation in a rainbow trout hypodermal fibroblast cell line

Rainbow trout (Oncorhynchus mykiss) face low environmental temperatures over winter months and during extreme low temperature events. Suboptimal temperatures are known to negatively impact the teleost immune system, although there is mixed evidence in rainbow trout as to the effect on the endogenous antigen processing and presentation pathway (EAPP). The EAPP is an important pathway for antiviral defense that involves the presentation of endogenous peptides on the cell surface for recognition by cytotoxic T cells. Using a rainbow trout hypodermal fibroblast (RTHDF) cell line as an in vitro model, we determined that constitutive EAPP transcript levels are not impaired at low temperature, but induction of up-regulation of these transcripts is delayed at the suboptimal temperature following exposure to poly(I:C) or viral haemorrhagic septicaemia virus IVb, which was still able to enter and replicate in the cell line at 4 °C, albeit with reduced efficiency. The delay in the induction of EAPP mRNA level up-regulation following poly(I:C) stimulation coincided with a delay in ifn1 transcript levels and secretion, which is important since interferon-stimulated response elements were identified in the promoter regions of the EAPP-specific members of the pathway, implying that IFN1 is involved in the regulation of these genes. Our results suggest that the ability of rainbow trout to mount an effective immune response to viral pathogens may be lessened at suboptimal temperatures.

Characterization of the continuous skin fibroblastoid cell line, WE-skin11f, from walleye (Sander vitreus)

A walleye dermal fibroblastoid cell line, WE-skin11f, was established and characterized. WE-skin11f was immunocytochemically positive for two known dermal fibroblast protein markers: vimentin and collagen I. At passage 26, WE-skin11f cultures contained both diploid and aneuploid populations. Ascorbic acid was required to produce extracellular collagen I fibres. Both of the skin fibroblastoid cell lines, WE-skin11f and rainbow trout-derived RTHDF, were not as good as the walleye caudal fin fibroblastoid cell line, WE-cfin11f, at forming abundant dense extracellular collagen matrices. The thermobiology of WE-skin11f was similar to that of other walleye cell lines with 26°C showing best temperature for growth and 4°C showing no growth but 100% viability. The transcript levels of b2m and mhIa genes of the major histocompatibility class I receptor in WE-skin11f were largely similar at all temperatures examined (4, 14, 20 and 26°C). Cortisol had a variety of effects on WE-skin11f cells: growth inhibition, morphological change from fibroblastoid to epithelioid, and enhancement of barrier function. Treatment of WE-skin11f cells with the physiologically relevant concentration of 100 ng/ml cortisol inhibited collagen I synthesis and matrix formation. Thus, WE-skin11f cell line could be useful in fish dermatology, endocrinology, and immunology research.

Improving a fish intestinal barrier model by combining two rainbow trout cell lines: epithelial RTgutGC and fibroblastic RTgutF

An in vitro model of the fish intestine is of interest for research and application in diverse fields such as fish physiology, aquaculture and chemical risk assessment. The recently developed epithelial barrier model of the fish intestine relies on the RTgutGC cell line from rainbow trout (Oncorhynchus mykiss), cultured in inserts on permeable membranes. Our aim was to extend the current system by introducing intestinal fibroblasts as supportive layer in order to reconstruct the epithelial-mesenchymal interface as found in vivo. We therefore initiated and characterized the first fibroblast cell line from the intestine of rainbow trout, which has been termed RTgutF. Co-culture studies of RTgutGC and RTgutF were performed on commercially available electric cell substrate for impedance sensing (ECIS) and on newly developed ultrathin, highly porous alumina membranes to imitate the cellular interaction with the basement membrane. Cellular events were examined with non-invasive impedance spectroscopy to distinguish between barrier tightness and cell density in the ECIS system and to determine transepithelial electrical resistance for cells cultured on the alumina membranes. We highlight the relevance of the piscine intestinal fibroblasts for an advanced intestinal barrier model, particularly on ultrathin alumina membranes. These membranes enable rapid crosstalk of cells cultured on opposite sides, which led to increased barrier tightening in the fish cell line-based epithelial-mesenchymal model.

Effect of selenomethionine on cell viability and heat shock protein 70 levels in rainbow trout intestinal epithelial cells at hypo-, normo-, and hyper-thermic temperatures

As global warming and environmental pollution modify aquatic environments, the thermal biology of fish could be affected by interactions between temperature and pollutants, such as selenium (Se). Therefore, selenomethionine (SeMet) was studied for effects on cell viability and on heat shock protein 70 (HSP70) levels in the rainbow trout intestinal epithelial cell, RTgutGC, at hypothermic (4 °C), normothermic (14 and 18 °C) and hyperthermic (26 °C) temperatures. RTgutGC cultures remained viable for at least a week at all temperatures, although energy metabolism as measured with Alamar Blue (resazurin) was appreciably diminished at 4 °C. Over a 7-day incubation, HSP 70 levels in cultures remained steady at 4 °C, declined at 18 °C, and increased slightly at 26 °C. When 125 μM SeMet was present, cultures remained viable and HSP70 levels were neither increased nor decreased relative to control cultures, regardless of the temperature. With 500 and 1000 μM SeMet, cell viability was profoundly impaired after 7 days in cultures at 14, 18 and 26 °C but was unchanged at 4 °C. Overall the results suggest that only hypothermia modulated the response of rainbow trout cells to SeMet.

Responses of rainbow trout intestinal epithelial cells to different kinds of nutritional deprivation

In order to develop an in vitro system to study the cell biology of starvation in the fish intestine, rainbow trout intestinal epithelial cells were subjected to three kinds of nutrient deprivation and evaluated for 7 days. The RTgutGC cell line was grown into monolayers in Leibovitz's basal medium supplemented with fetal bovine serum (L15/FBS) and then subjected to deprivation of serum (L15); of serum, amino acids, and vitamin (L15/ex); and of all nutrients (L15/salts). After 7 days of nutrient deprivation, the cells remained attached to the plastic surface as monolayers but changes were seen in shape, with the cells becoming more polygonal, actin and α-tubulin cytoskeleton organization, and in tight junction protein-1 (ZO-1) localization. Two barrier functions, transepithelial electrical resistance (TEER) and Lucifer Yellow (LY) retention, were impaired by nutrient deprivation. In L15/FBS, cells rapidly healed a gap or wound in the monolayer. In L15 and L15/ex, some cells moved into the gap, but after 7 days, the wound remained unhealed, whereas in L15/salts, cells did not even migrate into the gap. Upon nutrient replenishment (L15/FBS) after 7 days in L15, L15/ex, or L15/salts, cells proliferated again and healed a wound. After 7 days of nutrient deprivation, monolayers were successfully passaged with trypsin and cells in L15/FBS grew to again form monolayers. Therefore, rainbow trout intestinal epithelial cells survived starvation, but barrier and wound healing functions were impaired.

The characterization of γH2AX and p53 as biomarkers of genotoxic stress in a rainbow trout (Oncorhynchus mykiss) brain cell line

Rainbow trout cell cultures were exposed to three genotoxicants and examined for effects on γH2AX and p53 levels by western blotting and on cell viability using the indicator dyes Alamar Blue (AB) for energy metabolism and 5'-carboxyfluorescein diacetate acetoxymethyl ester (CFDA-AM) for plasma membrane integrity. Bleomycin induced γH2AX and p53 in a dose- and time-dependent manner and had little cytotoxic effect. However, induction was first seen at 0.3 μM for γH2AX but not until 16.5 μM for p53. Methyl methanesulfonate (MMS) increased H2AX phosphorylation but diminished p53 levels as the dose was increased from 908 μM up to 2724 μM. Over this dose range cell viability was progressively lost. 4-nitroquinoline N-oxide (NQO) induced both γH2AX and p53, beginning at 62.5 nM, which was also the concentration at which cell viability began to decline. As the NQO concentration increased further, elevated γH2AX was detected at up to 2.0 μM, while p53 was elevated up to 1.0 μM. Therefore, H2AX phosphorylation was superior to p53 levels as a marker of DNA damage caused by genotoxicants that act by introducing double-stranded DNA breaks (bleomycin), alkyl groups (MMS), and quinoline adducts (NQO).

Tapasin's protein interactions in the rainbow trout peptide-loading complex

Major histocompatibility complex (MHC) class I receptors play a key role in the immune system by presenting non-self peptides to T cell lymphocytes. In humans, the assembly of the MHC class I with a peptide is mediated by machinery in the endoplasmic reticulum referred as the peptide loading complex (PLC). Although, the identity of the PLC has been widely explored in humans, this complex has not been characterized in fish. Co-immunoprecipitation and mass spectrometry analysis revealed that the protein-protein interactions which exist in the human PLC are conserved in the monocyte/macrophage rainbow trout cell line (RTS11), in particular the interaction of tapasin with the transporter associated with antigen processing (TAP), MHC class I and ERp57. Importantly, a 20 kDa tapasin version that contains an intact C and N terminal domains was found to associate with ERp57 and form a 75 kDa heterodimer. These results suggest a possible novel alternative spliced version of tapasin may regulate the formation of the peptide-loading complex in teleosts.

Activation of an Aquareovirus, Chum Salmon Reovirus (CSV), by the Ciliates Tetrahymena thermophila and T. canadensis

For the first time, ciliates have been found to activate rather than inactivate a virus, chum salmon reovirus (CSV). Activation was seen as an increase in viral titre upon incubation of CSV at 22 °C with Tetrahymena canadenesis and two strains of T. thermophila: wild type (B1975) and a temperature conditional mutant for phagocytosis (NP1). The titre increase was not likely due to replication because CSV had no visible effects on the ciliates and no vertebrate virus has ever been shown unequivocally to replicate in ciliates. When incubated with B1975 and NP1 at 30 °C, CSV was activated only by B1975. Therefore, activation required CSV internalization because at 30 °C only B1975 exhibited phagocytosis. CSV replicated in fish cells at 18 to 26 °C but not at 30 °C. Collectively, these observations point to CSV activation being distinct from replication. Activation is attributed to the CSV capsid being modified in the ciliate phagosomal-lysosomal system and released in a more infectious form. When allowed to swim in CSV-infected fish cell cultures, collected, washed, and transferred to uninfected cultures, T. canadensis caused a CSV infection. Overall the results suggest that ciliates could have roles in the environmental dissemination of some fish viral diseases.

Structural and Kinetic Studies of the Potent Inhibition of Metallo-β-lactamases by 6-Phosphonomethylpyridine-2-carboxylates

There are currently no clinically available inhibitors of metallo-β-lactamases (MBLs), enzymes that hydrolyze β-lactam antibiotics and confer resistance to Gram-negative bacteria. Here we present 6-phosphonomethylpyridine-2-carboxylates (PMPCs) as potent inhibitors of subclass B1 (IMP-1, VIM-2, and NDM-1) and B3 (L1) MBLs. Inhibition followed a competitive, slow-binding model without an isomerization step (IC₅₀ values of 0.3-7.2 μM; K_i values of 0.03-1.5 μM). Minimum inhibitory concentration assays demonstrated potentiation of β-lactam (Meropenem) activity against MBL-producing bacteria, including clinical isolates, at concentrations at which eukaryotic cells remain viable. Crystal structures revealed unprecedented modes of binding of inhibitor to B1 (IMP-1) and B3 (L1) MBLs. In IMP-1, binding does not replace the nucleophilic hydroxide, and the PMPC carboxylate and pyridine nitrogen interact closely (2.3 and 2.7 Å, respectively) with the Zn2 ion of the binuclear metal site. The phosphonate group makes limited interactions but is 2.6 Å from the nucleophilic hydroxide. Furthermore, the presence of a water molecule interacting with the PMPC phosphonate and pyridine N-C2 π-bond, as well as the nucleophilic hydroxide, suggests that the PMPC binds to the MBL active site as its hydrate. Binding is markedly different in L1, with the phosphonate displacing both Zn2, forming a monozinc enzyme, and the nucleophilic hydroxide, while also making multiple interactions with the protein main chain and Zn1. The carboxylate and pyridine nitrogen interact with Ser221 and -223, respectively (3 Å distance). The potency, low toxicity, cellular activity, and amenability to further modification of PMPCs indicate these and similar phosphonate compounds can be further considered for future MBL inhibitor development.

Fish viruses stored in RNAlater can remain infectious and even be temporarily protected from inactivation by heat or by tissue homogenates

RNAlater is a commonly used transport and storage solution for samples collected for fish health investigations, particularly those potentially involving viruses. However, the infectivity of fish viruses after storage in RNAlater have not been determined. Nevertheless, knowledge of pathogen infectivity of preserved samples is crucial for ensuring safe transport and storage protocols. Therefore, the infectivity of three fish RNA viruses in RNAlater was examined at four temperatures: -80 °C, 4 °C, room temperature (RT, approximately 22 °C) and 37 °C. The viruses were viral hemorrhagic septicemia virus (VHSV), infectious pancreatic necrosis virus (IPNV) and chum salmon reovirus (CSV). Overall, three consistent outcomes were observed. First, all three viruses remained infectious in RNAlater at RT or lower. High log titres of these viruses remained over 30 d of storage in either RNAlater or PBS. Second, RNAlater delayed the thermal inactivation of these viruses when compared to PBS at 37 °C. For VHSV, the titre remained high in RNAlater after one day of incubation at 37 °C, but was inactivated to below threshold in PBS over the same period. For IPNV, the titre remained high in RNAlater after 30 d of incubation at 37 °C, but was inactivated to below threshold in PBS over the same period. For CSV, the titre was slightly higher in RNAlater than PBS at 37 °C over 7 d, and by day 30, only samples stored in RNAlater proved infectious at titres above the detection threshold. Third, RNAlater delayed the inactivation of these viruses when they were stored together with head kidney homogenates. For VHSV, infectious virus was recovered from samples stored at 4 °C in RNAlater by day 7 of incubation, whereas it was inactivated to below threshold in PBS over the same period. For both IPNV and CSV, infectious virus was recovered from samples stored at 37 °C in RNAlater for 7 d, but not so in PBS. In summary, fish viruses can remain infectious and are even temporarily protected from inactivation while in RNAlater. This makes RNAlater a potentially useful solution for the transport of fish viruses. At the same time, precautionary measures must be taken when transporting potentially infectious samples in RNAlater.

Atlantic salmon endothelial cells from the heart were more susceptible than fibroblasts from the bulbus arteriosus to four RNA viruses but protected from two viruses by dsRNA pretreatment

Heart diseases caused by viruses are major causes of Atlantic salmon aquaculture loss. Two Atlantic salmon cardiovascular cell lines, an endothelial cell line (ASHe) from the heart and a fibroblast cell line (BAASf) from the bulbus arteriosus, were evaluated for their response to four fish viruses, CSV, IPNV, VHSV IVa and VHSV IVb, and the innate immune agonist, double-stranded RNA mimic poly IC. All four viruses caused cytopathic effects in ASHe and BAASf. However, ASHe was more susceptible to all four viruses than BAASf. When comparing between the viruses, ASHe cells were found to be moderately susceptible to CSV and VHSV IVb, but highly susceptible to IPNV and VHSV IVa induced cell death. All four viruses were capable of propagating in the ASHe cell line, leading to increases in virus titre over time. In BAASf, CSV and IPNV produced more than one log increase in titre from initial infection, but VHSV IVb and IVa did not. When looking at the antiviral response of both cell lines, Mx proteins were induced in ASHe and BAASf by poly IC. All four viruses induced Mx proteins in BAASf, while only CSV and VHSV IVb induced Mx proteins in ASHe. IPNV and VHSV IVa suppressed Mx proteins expression in ASHe. Pretreatment of ASHe with poly IC to allow for Mx proteins accumulation protected the culture from subsequent infections with IPNV and VHSV IVa, resulting in delayed cell death, reduced virus titres and reduced viral proteins expression. These data suggest that endothelial cells potentially can serve as points of infections for viruses in the heart and that two of the four viruses, IPNV and VHSV IVa, have mechanisms to avoid or downregulate antiviral responses in ASHe cells. Furthermore, the high susceptibility of the ASHe cell line to IPNV and VHSV IVa can make it a useful tool for studying antiviral compounds against these viruses and for general detection of fish viruses.

Development and use of an Arctic charr cell line to study antiviral responses at extremely low temperatures

Arctic charr (Salvelinus alpinus) are the northernmost distributed freshwater fish and can grow at water temperatures as low as 0.2 °C. Other teleost species have impaired immune function at temperatures that Arctic charr thrive in, and thus, charr may maintain immune function at these temperatures. In this study, a fibroblastic cell line, named ACBA, derived from the bulbus arteriosus (BA) of Arctic charr was developed for use in immune studies at various temperatures. ACBA has undergone more than forty passages at 18 °C over 3 years, while showing no signs of senescence-associated β-galactosidase activity and producing nitric oxide. Remarkably, ACBA cells survived and maintained some mitotic activity even at 1 °C for over 3 months. At these low temperatures, ACBA also continued to produce MH class I proteins. After challenge with poly I:C, only antiviral Mx proteins were induced while MH proteins remained constant. When exposed to live viruses, ACBA was shown to permit viral infection and replication of IPNV, VHSV IVa and CSV at 14 °C. Yet at the preferred temperature of 4 °C, only VHSV IVa was shown to replicate within ACBA. This study provides evidence that Arctic charr cells can maintain immune function while also resisting infection with intracellular pathogens at low temperatures.

Responses of an American eel brain endothelial-like cell line to selenium deprivation and to selenite, selenate, and selenomethionine additions in different exposure media

The effect of selenium deprivation and addition on the American eel brain endothelial cell line (eelB) was studied in three exposure media: complete growth medium (L15/FBS), serum-free medium (L15), and minimal medium (L15/ex). L15/ex contains only galactose and pyruvate and allowed the deprivation of selenium on cells to be studied. In L15/ex, without any obvious source of selenium, eelB cells survived for at least 7 d, formed capillary-like structures (CLS) on Matrigel, and migrated to heal wounds. Three selenium compounds were added to cultures: selenite, selenate, and selenomethionine (SeMet). Adding selenite or selenate to eelB cell cultures for 24 h caused dose-dependent declines in cell viability, regardless of the exposure media. Although varying with exposure media and viability end point, selenite was approximately 70-fold more cytotoxic than selenate. By contrast, 24 h exposures to either DL- or L-SeMet in the three media caused little or no cytotoxicity. However for 7 d exposures in L15/ex, DL- and L-SeMet were very cytotoxic, even at the lowest tested concentration of 31 μM. By contrast in L15 and L15/FBS, cytotoxicity was only observed with 500 and 1000 μM L-SeMet. In L15/FBS, eelB continued to migrate and form CLS in the presence of SeMet but at 500 μM, cell migration appeared stimulated. As judged from a colony-forming assay over 14 d in L15/FBS, 500 and 1000 μM DL- and L-SeMet inhibited cell proliferation. Overall, the responses of eel cells to selenium depended on the selenium form, concentration, and exposure media, with responses to SeMet being most dependent on exposure media.

Development of an Atlantic salmon heart endothelial cell line (ASHe) that responds to lysophosphatidic acid (LPA)

As diseases and abnormalities of the heart can interfere with the aquaculture of Atlantic salmon, the heart was investigated as a source of cell lines that could be used to study the cellular basis of these conditions. An Atlantic salmon heart endothelial cell line, ASHe, was developed and characterized for growth properties, endothelial cell characteristics, and responsiveness to lysophosphatidic acid (LPA). AHSe cells stained negative for senescence associated ß-galactosidase and grew well in 10 and 20% FBS/L15 at high cell density, but not in L15 medium supplemented with calf serum. It displayed many endothelial cell-like characteristics including a cobblestone morphology, capillary-like structures formation on Matrigel, and expression of von Willebrand factor and endothelial cell-related tight junction proteins ZO-1, claudin 3, and claudin 5. ASHe cells responded to the cardiovascular modulator, LPA, in two contrasting ways. LPA at 5 and 25 μM inhibited the ability of ASHe cells to heal a wound but stimulated their proliferation, especially as evaluated by colony formation in low-density cultures. The enhancement of proliferation by LPA parallels what has been observed previously in mammalian endothelial cell cultures exposed to LPA, whereas the LPA slowing of ASHe cell migration contrasted with the LPA-enhanced migration of some mammalian cells. Therefore, this cell line is a potentially useful model for future comparative studies on piscine and mammalian cardiovascular cell biology and for studies on diseases of Atlantic salmon in aquaculture.

Temporary protection of rainbow trout gill epithelial cells from infection with viral haemorrhagic septicaemia virus IVb

The branchial epithelium is not only a primary route of entry for viral pathogens, but is also a site of viral replication and subsequent shedding may also occur from the gill epithelium. This study investigated the potential of agents known to stimulate innate immunity to protect rainbow trout epithelial cells (RTgill-W1) from infection with VHSV IVb. RTgill-W1 cells were pretreated with poly I:C, FuGENE(®) HD + poly I:C, lipopolysaccharide (LPS), LPS + poly I:C or heat-killed VHSV IVb and then infected with VHSV IVb 4 days later. Cytopathic effect (CPE) was determined at 2, 3, 4, 7 and 11 days post-infection. Virus in cells and supernatant was detected using quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). All of the treatments delayed the onset of CPE (per cent of monolayer destruction), compared with untreated controls; however, killed VHSV or poly I:C combined with LPS was the most effective. Similarly, the detection of viral RNA in the supernatant was delayed, and the quantity was significantly (P < 0.05) reduced by all treatments with the exception of LPS alone (4 days). Unlike many of the other treatments, pretreatment of RTgill-W1 with heat-killed VHSV did not upregulate interferon 1, 2 or MX 1 gene expression.

Evaluating the toxic potential of benzothiazoles with the rainbow trout cell lines, RTgill-W1 and RTL-W1

Benzothiazole (BTHs) are environmental contaminants of emerging concern for which little toxicological information is available. Therefore the toxic potential of twelve BTHs was evaluated with two rainbow trout epithelial cell lines, RTgill-W1 and RTL-W1. The BTHs were benzothiazole (BTH), 3,3'-diethylthia dicarbocyanine iodide (DTDC), C.I. sulphur orange 1 (SO), 2-mercaptobenzothiazole (2MBTH), zinc 2-mercaptobenzothiazole (ZnMBTH), sodium 2-mercaptobenzothiazole (NaMBTH), 2-hydroxy-benzothiazole (OHBTH), 2- aminobenzothiazole (2ABTH), C.I. vat yellow 2 (VY), N,N-dicyclohexyl-2-benzothiazolsulfene amide (NNA), 2,2'-dithiobis (benzothiazole) (DBTH) and 2-(p-aminophenyl)-6-methylbenzothiazole-7-sulfonic acid (MBTHS). All BTHs, except for NNA, DBTH, and MBTHS, caused both cytotoxicity and a transitory elevation in reactive oxygen species (ROS) levels. Yet, neither N-acetyl cysteine (NAC) nor IM-54 inhibited cytotoxicity, suggesting that ROS imbalance did not contribute to cell death. Cell death was not blocked by Necrostatin-1 nor accompanied by DNA laddering, suggesting that neither necroptosis nor apoptosis took place. The comet assay revealed DNA strand breaks after exposures to 2ABTH and OHBTH for 1 day and to BTH for 12 days. In RTL-W1, cytochrome P4501A was induced noticeably by 2ABTH, OHBTH, and MBTHS and weakly by NaMBTH, ZnMBTH, SO, VY, and NNA, suggesting that these BTHs have the potential to alter xenobiotic metabolism and activate the aryl hydrocarbon receptor. In summary, several toxic actions were initiated in vitro by some but not all BTHs, warranting further study of these BTHs in vivo.

Differential viral haemorrhagic septicaemia virus genotype IVb infection in fin fibroblast and epithelial cell lines from walleye, Sander vitreus (Mitchill), at cold temperatures

A cell line, WE-cfin11e, with an epithelial-like morphology was developed from a caudal fin of walleye, Sander vitreus (Mitchill), characterized as distinct from the established walleye caudal fin fibroblast-like cell line, WE-cfin11f, and compared with WE-cfin11f for susceptibility to VHSV IVb. Immunocytochemistry and confocal microscopy were used to localize the intermediate filament protein, vimentin, the tight junction protein, zonula occludens-1 (ZO-1), the extracellular matrix protein, collagen I, and the viral protein, G. Although both cell lines contained vimentin, only WE-cfin11e stained for ZO-1 and only WE-cfin11f stained for collagen I. Ascorbic acid increased the accumulation of collagen I and caused the appearance of collagen fibres only in WE-cfin11f cultures. At 14 °C, both cell lines produced VHSV IVb, but the infection developed more rapidly in WE-cfin11f. At 4 °C, both cell lines became infected with VHSV IVb as judged by the expression of viral proteins, N and G, but only WE-cfin11f produced virus. The results suggest that cold temperatures can modulate viral tropism.

Use of the rainbow trout cell lines, RTgill-W1 and RTL-W1 to evaluate the toxic potential of benzotriazoles

Epithelial cell lines, RTgill-W1 and RTL-W1 from respectively gill and liver of rainbow trout, Onchorhynchus mykiss (Walbaum), were used to evaluate the toxic potential of six benzotriazoles (BTRs) and tolytriazole (TT), which is a commercial mixture of 4-methyl-1H-benzotriazole (4MBTR) and 5-methyl-1H-benzotriazole (5MBTR). The other BTRs were 1H-benzotriazole (1H-BTR), 5-chlorobenzotriazole (5CBTR), 1-hydroxybenzotriazole (1OHBTR) and 5,6-dimethyl-1H-benzotriazole monohydrate (DM). Except for DM, all BTRs were cytotoxic at concentrations above 15mg/L and transitorily elevated reactive oxygen species (ROS) levels. Neither N-acetyl cysteine (NAC) nor IM-54 inhibited cytotoxicity, suggesting that ROS were not the major cause of the cell death. Cell death was not blocked by Necrostatin nor accompanied by DNA laddering, suggesting that the cell death mechanism was neither necroptosis nor apoptosis. As judged by the comet assay, DNA strand breaks were detected with three BTRs: 4MBTR, 5MBTR and 5CBTR. In RTL-W1, the BTRs weakly induced cytochrome P4501A, suggesting that they have the potential to alter xenobiotic metabolism and activate the aryl hydrocarbon receptor. In summary, the toxic potential of BTRs appears to be limited to only high concentrations, which are higher than have been measured in the environment to date.

Demonstration of primary cilia and acetylated α-tubulin in fish endothelial, epithelial and fibroblast cell lines

Primary cilia (PC) were demonstrated for the first time in fish endothelial, epithelial and fibroblast cell lines through immunofluorescence staining with the monoclonal antibody, 6-11B-1, against acetylated α-tubulin. The study was carried out with eight recently developed cell lines from the walleye, Sander vitreus (Mitchill). These were three fibroblast-like cell lines, WE-cfin11f, WE-skin11f and WE-liver3 from, respectively, the caudal fin, skin and liver, and three epithelial-like cell lines, WE-cfin11e, WE-spleen6 and WErpe from, respectively, the caudal fin, spleen and retina. Also, endothelial-like WEBA from the bulbus arteriosus and glial-like WE-brain5 from the brain were used. Immunocytochemistry revealed strong staining for acetylated α-tubulin in mitotic spindles and midbodies for all cell lines, and in PC for all cell lines except WE-skin11f. Staining of cytoplasmic microtubules (fibrils) was absent in three cell lines, including WEBA, but present in the others, especially WE-skin11f, which might have obscured PC detection in these cells. Tubacin, an inhibitor of histone deacetylase 6, induced cytoplasmic fibrils in WEBA and the intensity of their staining in WE-cfin11f. These results suggest that the cell lines might differ in their deacetylase activities, making them useful for studying this tubulin modification in teleosts, as well as for studying PC.

The p53 inhibitor, pifithrin-α, disrupts microtubule organization, arrests growth, and induces polyploidy in the rainbow trout gill cell line, RTgill-W1

Pifithrin-α (PFT-α) blocks p53-dependent transcription and is an example of the many drugs being developed to target the p53 pathway in humans that could be released into the environment with potential impacts on aquatic animals if they were to become successful pharmaceuticals. In order to understand how p53 drugs might act on fish, the effects of PFT-α on rainbow trout gill epithelial cell line, RTgill-W1, were studied. PFT-α was not cytotoxic to RTgill-W1 in cultures with or without fetal bovine serum (FBS), but at 5.25μg/ml, PFT-α completely arrested proliferation. When FBS was present, PFT-α increased the number of polyploid cells over 12days. Those results suggest that like in mammals, p53 appears to regulate ploidy in fish. However, several effects were seen that have not been observed with mammalian cells. PFT-α caused a transient rise in the mitotic index and a disruption in cytoskeletal microtubules. These results suggest that in fish cells PFT-α affects microtubules either directly through an off-target action on tubulin or indirectly through an on-target action on p53-regulated transcription.

Walleye Sander vitreus (Mitchill) are relatively resistant to experimental infection with VHSV IVb and extant walleye strains vary in susceptibility

Compared to fathead minnow, walleye demonstrate low susceptibility to experimental infection with VHSV IVb, regardless of route of exposure or water temperature at time of infection. In triplicate and duplicate groups, walleye were intraperitoneally (i.p.) injected (10² -10⁸  pfu/fish) or waterborne-exposed (w; 1.4 × 10⁷  pfu mL^-1 ) with VHSV IVb. High cumulative mortality (64-100%) and severe gross lesions associated with VHSV IVb infection were evident only in fish i.p. injected with 10⁸  pfu at 12 °C. These fish had multifocal necrosis of several tissues including the gill and heart. There was no difference in mortality between walleye infected (w or i.p.) at 12 °C (spring stocking) compared with a declining temperature profile from 18 to 12 °C (fall stocking). There were significant differences (P < 0.05) in mortality between four extant walleye strains following i.p. infection, indicating that the choice of walleye strain for stocking might be an important consideration. Viral antigen was found in both i.p. and w-exposed walleye using immunohistochemistry, mostly within the gill and skin of w-exposed fish and most prominently in dermal fibrocytes. VHSV IVb was detected in multiple tissues from 6 to 21 days post-infection using reverse transcriptase quantitative polymerase chain reaction (RT-qPCR).

Development of a walleye spleen stromal cell line sensitive to viral hemorrhagic septicemia virus (VHSV IVb) and to protection by synthetic dsRNA

A cell line, WE-spleen6, has been developed from the stromal layer of primary spleen cell cultures. On conventional plastic, WE-spleen6 cells had a spindle-shaped morphology at low cell density but grew to become epithelial-like at confluency. On the commercial extracellular matrix (ECM), Matrigel, the cells remained spindle-shaped and formed lumen-like structures. WE-spleen6 cells had intermediate filament protein, vimentin and the ECM protein, collagen I, but not smooth muscle α-actin (SMA) and von Willebrand factor (vWF) and lacked alkaline phosphatase and phagocytic activities. WE-spleen6 was more susceptible to infection with VHSV IVb than a fibroblast and epithelial cell lines from the walleye caudal fin, WE-cfin11f and WE-cfin11e, respectively. Viral transcripts and proteins appeared earlier in WE-spleen6 cultures as did cytopathic effect (CPE) and significant virus production. The synthetic double-stranded RNA (dsRNA), polyinosinic: polycytidylic acid (pIC), induced the antiviral protein Mx in both cell lines. Treating WE-spleen6 cultures with pIC prior to infection with VHSV IVb inhibited the early accumulation of viral transcripts and proteins and delayed the appearance of CPE and significant viral production. Of particular note, pIC caused the disappearance of viral P protein 2 days post infection. WE-spleen6 should be useful for investigating the impact of VHSV IVb on hematopoietic organs and the actions of pIC on the rhabdovirus life cycle.

Development of a walleye cell line and use to study the effects of temperature on infection by viral haemorrhagic septicaemia virus group IVb

A cell line, WE-cfin11f, with a fibroblast-like morphology was developed from a walleye caudal fin and used to study the intersection of thermobiology of walleye, Sander vitreus (Mitchill), with the thermal requirements for replication of viral haemorrhagic septicaemia virus (VHSV) IVb. WE-cfin11f proliferated from 10 to 32 °C and endured as a monolayer for at least a week at 1-34 °C. WE-cfin11f adopted an epithelial shape and did not proliferate at 4 °C. Adding VHSV IVb to cultures at 4 and 14 °C but not 26 °C led to cytopathic effects (CPE) and virus production. At 4 °C, virus production developed more slowly, but Western blotting showed more N protein accumulation. Infecting monolayer cultures at 4 °C for 7 days and then shifting them to 26 °C resulted in the monolayers being broken in small areas by CPE, but with time at 26 °C, the monolayers were restored. These results suggest that at 26 °C, the VHSV IVb life cycle stages responsible for CPE can be completed, but the production of virus and the initiation of infections cannot be accomplished.

Delineating cellular interactions between ciliates and fish by co-culturing Tetrahymena thermophila with fish cells

Although several species of Tetrahymena are often described as histophagous and opportunistic pathogens of fish, little is known about ciliate/fish cell interactions, but one approach for studying these is in vitro with cell lines. In this study, T. thermophila, B1975 (wild type) and NP1 (temperature sensitive mutant for phagocytosis) were cultured on monolayers of 3 fish epithelial cell lines, CHSE-214, RTgill-W1, and ZEB2J, and the rabbit kidney epithelial cell line, RK-13. Generally the ciliates flourished, whereas the monolayers died, being completely consumed over several days. The destruction of monolayers required that the ciliates could make contact with the animal cells through swimming, which appeared to dislodge or loosen cells so that they could be phagocytosed. The ciliates internalized into food vacuoles ZEB2J from cell monolayers as well as from cell suspensions. Phagocytosis was essential for monolayer destruction as monolayers remained intact under conditions where phagocytosis was impeded, such as 37°C for NP1 and 4°C for B1975. Monolayers of fish cells supported the proliferation of ciliates. Thus T. thermophila can 'eat' animal cells or be histophagous in vitro, with the potential to be histophagous in vivo.

Expression of tapasin in rainbow trout tissues and cell lines and up regulation in a monocyte/macrophage cell line (RTS11) by a viral mimic and viral infection

Tapasin is a transmembrane glycoprotein that acts as a bridge between the transporter associated with antigen processing and the MHC class I receptor in mammals. Through the development of antibody against trout tapasin, this report demonstrates the detection of trout tapasin as a N-glycosylated 48 kDa protein. Tissue and cell line distribution revealed that tapasin protein is expressed mainly in immune system organs and in rainbow trout epithelial cell lines from gill (RTgill-W1), liver (RTL-W1), and intestine (RTgutGC). An additional 20 kDa band was observed in tissues and cell lines, and appeared to be most prominent in RTgutGC but was absent in peripheral blood leukocytes. Tapasin 48 kDa protein was most strongly expressed in RTS11 (monocyte/macrophage cell line) and its regulation following dsRNA stimulation was explored. Upon poly I:C treatment and Chum Salmon Reovirus (CSV) infection, tapasin protein expression was upregulated up to 3.5 fold and 3 fold respectively, in parallel with increased expression of the glycosylated MH class I heavy chain, whereas the expression of the 20 kDa form remained unchanged. Overall this work demonstrates the induction of tapasin protein by dsRNA stimulation, which implies its possible conserved regulation during viral infection in teleost cells.

Induction of rainbow trout MH class I and accessory proteins by viral haemorrhagic septicaemia virus

Major histocompatibility (MH) class I receptors are glycoproteins which play a critical role during responses to intracellular pathogens by presenting endogenous peptides to cytotoxic T cell lymphocytes (CD8+). To date, little is known about MH class I regulation at the protein level during viral infections in fish. In this study, we characterised the MH class I pathway response to polyinosinic-polycytidylic acid (poly I:C) and upon infection with viral haemorrhagic septicemia virus (VHSV) genotype IVa using the rainbow trout monocyte/macrophage cell line RTS11. A 14-day challenge with VHSV IVa at 14°C demonstrated enhanced expression of the class I heavy chain, β2 microglobulin (β2M) and tapasin, while the expression of other accessory molecules ERp57 and calreticulin remained unchanged. However, when infection occurred at 2°C no change in expression levels of any of these molecules was observed. β2M accumulated in the media of RTS11 over time, however the β2M concentrations were 2 fold higher in cultures infected with VHSV 14 days post infection. Strikingly, when cells were maintained at 2°C the secretion of β2M was significantly reduced in both infected and non-infected cultures. These results indicate that VHSV infection alters the kinetics of β2M release as well as the expression of MH class I and suggests that cellular immunity against VHSV can be compromised at low temperatures which may increase host susceptibility to this virus during the winter.

Rainbow trout (Oncorhynchus mykiss) contain two calnexin genes which encode distinct proteins

Calnexin (IP90/P88) is an integral membrane protein of the endoplasmic reticulum that binds newly synthesized N-linked glycoproteins during their folding in the ER including MHC class I molecule. This manuscript reports the identification of two unique cDNA clones of calnexin in rainbow trout. Both encode putative mature proteins of 579 and 592 aa respectively in addition to a 24 aa signal peptide. Sequence analysis revealed that only one of the two cDNA clones encodes a putative ER retention signal, K/QEDDL, followed by a serine phosphorylation site conserved with mammalian homologs. Amino acid sequence alignment illustrated conservation of the calnexin luminal domain, which consists of a globular and a P domain, in both copies. Southern blotting revealed that there are at least two copies of the calnexin gene in the trout genome and northern blotting showed a wide tissue distribution of an estimated 3 kbp calnexin transcript with an additional minor transcript of 2.3 kbp expressed only in head kidney, spleen PBLs and strongly in RTS11. Importantly, the smaller transcript was predominantly upregulated in RTS11 after a 24h treatment with the calcium ionophore A23187. In western blots, calnexin was detected primarily as a 120 kDa protein and upon A23187 treatment; a 100 kDa band was most prominently expressed. These results suggest that in salmonids there are two differentiated versions of the calnexin gene which encode proteins that may have diverged to perform unique biological functions.

The p53/HSP70 inhibitor, 2-phenylethynesulfonamide, causes oxidative stress, unfolded protein response and apoptosis in rainbow trout cells

The effect of 2-phenylethynesulfonamide (PES), which is a p53 and HSP70 inhibitor in mammalian cells, was studied on the rainbow trout (Oncorhynchus mykiss) gill epithelial cell line, RTgill-W1, in order to evaluate PES as a tool for understanding the cellular survival pathways operating in fish. As judged by three viability assays, fish cells were killed by 24h exposures to PES, but cell death was blocked by the anti-oxidant N-acetylcysteine (NAC). Cell death had several hallmarks of apoptosis: DNA laddering, nuclear fragmentation, Annexin V staining, mitochondrial membrane potential decline, and caspases activation. Reactive oxygen species (ROS) production peaked in several hours after the addition of PES and before cell death. HSP70 and BiP levels were higher in cultures treated with PES for 24h, but this was blocked by NAC. As well, PES treatment caused HSP70, BiP and p53 to accumulate in the detergent-insoluble fraction, and this too was prevented by NAC. Of several possible scenarios to explain the results, the following one is the simplest. PES enhances the generation of ROS, possibly by inhibiting the anti-oxidant actions of p53 and HSP70. ER stress arises from the ROS and from PES inhibiting the chaperone activities of HSP70. The ER stress in turn initiates the unfolded protein response (UPR), but this fails to restore ER homeostasis so proteins aggregate and cells die. Despite these multiple actions, PES should be useful for studying fish cellular survival pathways.

The use of fish-derived cell lines for investigation of environmental contaminants: an update following OECD's fish toxicity testing framework No. 171

Protocols for evaluating chemical toxicity at the cellular level using fish cell lines are described in this unit. Routine methodologies for growing salmonid cell lines, and using them in aquatic toxicology studies that support the mandate of the Organization for Economic Co-operation and Development (OECD) to reduce the use of whole animals in toxicity testing, are presented. Rapid, simple, cost-effective tests evaluating viability of cells with three indicator dyes per sample provides a broad overview of the sensitivity of cells to chemical contaminants. This fluorometric assay involves: (1) alamar blue for metabolic activity, (2) CFDA-AM for membrane integrity, and (3) neutral red for lysosomal function. These protocols are conveniently performed in semi-unison within the same multiwell plates and read at three different wavelengths. Detailed step-by-step descriptions of the assays, parameters to consider, troubleshooting, and guidelines for data interpretation are provided as essential tools for investigating environmental aquatic contaminants at the cellular level.

Survival and growth of Tetrahymena thermophila in media that are conventionally used for piscine and mammalian cells

The transfer of Tetrahymena thermophila from normosmotic solutions (~20-80 mOsm/kg H(2)O) to hyperosmotic solutions (> 290 mOsm/kg H(2)O) was investigated. During the first 24 h of transfer from proteose peptone yeast extract (PPYE) to either 10 mM HEPES or PPYE with added NaCl to give ~300 mOsm/kg H(2)O, most ciliates died in HEPES but survived in PPYE. Supplementing hyperosmotic HEPES or PPYE with fetal bovine serum (FBS) enhanced survival. When ciliates were transferred from PPYE to a basal medium for vertebrate cells, L-15 (~320 mOsm/kg H(2)O), only a few survived the first 24 h but many survived when the starting cell density at transfer was high (100,000 cells/ml) or FBS was present. These results suggest that nutrients and/or osmolytes in either PPYE or FBS helped ciliates survive the switch to hyperosmotic solutions. FBS also stimulated T. thermophila growth in normosmotic HEPES and PPYE and in hyperosmotic L-15. In L-15 with 10% FBS, the ciliates proliferated for several months and could undergo phagocytosis and bacterivory. These cell culture systems and results can be used to explore how some Tetrahymena species function in hyperosmotic hosts and act as opportunistic pathogens of vertebrates.

Differential effects of viral hemorrhagic septicaemia virus (VHSV) genotypes IVa and IVb on gill epithelial and spleen macrophage cell lines from rainbow trout (Oncorhynchus mykiss)

The two most prominent genotypes of viral hemorrhagic septicemia virus (VHSV) are -I in the Northeastern Atlantic region and -IV in North America, but much more is known about the cellular pathogenesis of genotype -I than -IV. VHSV genotype -IV is divided into -IVa from the Northeast Pacific Ocean and -IVb from the Great Lakes and both of which are less virulent to rainbow trout than genotype -I. In this work, infections of VHSV-IVa and -IVb have been studied in two rainbow trout cell lines, RTgill-W1 from the gill epithelium, and RTS11 from spleen macrophages. RTgill-W1 produced infectious progeny of both VHSV-IVa and -IVb. However, VHSV-IVa was more infectious than -IVb toward RTgill-W1: -IVa caused cytopathic effect (CPE) at a lower viral titre, elicited CPE earlier, and yielded higher titres. By contrast, no CPE and no increase in viral titre were observed in RTS11 cultures infected with either genotype. Yet in RTS11 all six VHSV genes were expressed and antiviral genes, Mx2 and Mx3, were up regulated by VHSV-IVb and -IVa. However, replication appeared to terminate at the translational stage as viral N protein, presumably the most abundant of the VSHV proteins, was not detected in either infected RTS11 cultures. In RTgill-W1, Mx2 and Mx3 were up regulated to similar levels by both viral genotypes, while VHSV-IVa induced higher levels of IFN1, IFN2 and LGP2A than VHSV-IVb.

The cloning and inducible expression of the rainbow trout ERp57 gene

ERp57 is a member of a protein disulfide isomerase family and is a chaperone responsible for the correct folding of newly synthesized glycoproteins in the endoplasmic reticulum and in the assembly of the major histocompatibility complex class I in the endogenous pathway of antigen presentation. This study reports the identification of a full length ERp57 cDNA in rainbow trout that encodes a putative 477aa mature protein with an additional signal sequence of 16aa. The trout protein shared 75% identity with the human homolog, but interestingly did not include either a C terminal endoplasmic reticulum retention signal, Q/KEDL in humans, or a nuclear localization signal which is highly conserved in mammals. Amino acid sequence alignment revealed conservation of four classical domains in trout ERp57 and two conserved active CXXC redox motifs. Trout ERp57 protein was identified as a single band around 57 kDa. Southern blotting analysis revealed that there two copies of the ERp57 gene in the trout genome and northern blotting showed a wide tissue distribution of gene expression in various tissues with the highest expression in liver and egg. This study showed for the first time in teleost that ERp57 transcript is upregulated in response to immune stimuli such as double stranded RNA or phytohemagglutinin. Furthermore, upon treatment with ER stress inducer A23187, trout ERp57 protein expression levels were increased both in peripheral blood leukocytes and the RTS11 macrophage like cell line after 6 and 8 h respectively. These findings suggest a possible conserved function for trout ERp57 in the ER and during the activation of the immune response.

The use of fish-derived cell lines for investigation of environmental contaminants

This unit describes protocols for growing salmonid cell lines and using them in in vitro toxicology studies. Cell viability of cultures is assessed with three indicator dyes: alamar blue for metabolic activity, CFDA-AM for membrane integrity, and neutral red for lysosomal activity. These protocols are essential tools for investigating environmental toxicity at the cellular level.

The rad1 gene in Rainbow Trout (Oncorhynchus mykiss) is highly conserved and may express proteins from non-canonical spliced isoforms

Cell-cycle checkpoint proteins maintain genomic integrity by sensing damaged DNA and initiating DNA repair or apoptosis. RAD1 is a checkpoint protein involved in the sensing of damaged DNA and is a part of the 9-1-1 complex. In this project rainbow trout rad1 (rtrad1) was cloned, sequenced, expressed as a recombinant protein and anti-rtRAD1 antibodies were developed. RAD1 protein levels were characterized in various rainbow trout tissues. It was determined that an 840 bp open-reading frame encodes 279 aa with a predicted protein size of 31 kDa. The rtRAD1 amino-acid sequence is highly conserved and contains conserved exonuclease and leucine zipper domains. RT-PCR was used to identify three non-canonical splice variants of rtrad1, two of which are capable of forming functional proteins. The rad1 splice variant that encodes an 18 kDa protein appears to be abundant in rainbow trout spleen, heart and gill tissue and in the RTgill-W1 cell-line. Based on the genomic rtrad1 sequence the splice variants contain only partial exons which are consistent with the splicing of rad1 variants in mammals. This is the first time that rad1 has been fully characterized in a fish species.

Methodology for demonstrating and measuring the photocytotoxicity of fluoranthene to fish cells in culture

Methodology was developed for quantifying the photocytotoxicity of fluoranthene to a gill cell line from rainbow trout for future use in screening polycyclic aromatic hydrocarbons for their relative photocytotoxicity to fish. Solubilization in a modified culture medium was achieved with and without foetal bovine serum (FBS) and with and without dimethyl sulfoxide (DMSO). FBS caused most of the fluoranthene to remain in solution and blocked photocytotoxicity if present during UV irradiation. DMSO had little effect on fluoranthene distribution in cell cultures but caused cells to be slightly more sensitive to the phototoxicity of fluoranthene. The indicator dyes alamar Blue() and 5-carboxyfluorescein diacetate acetoxymethyl ester were used to quantify cytotoxicity in two different ways-singly in two separate assays, and mixed together in a novel single assay, which saved time and material. With UV irradiation for 2 hr at a photon fluence rate of either 1.4 mumol UV-B/m(2)/sec (UV-A:UV-B, 1.5) or 1.1 mumol UV-B/m(2)/sec (UV-A:UV-B, 9.7), both dyes indicated increasing loss of viability with increasing doses of fluoranthene. EC(50) values ranged from 18 to 44 ng/ml (89-217 nM), with the alamar Blue assay being slightly more sensitive.

Carbon nanotube compared with carbon black: effects on bacterial survival against grazing by ciliates and antimicrobial treatments

The ingestion and digestion of Escherichia coli by the ciliated protozoan, Tetrahymena thermophila, was investigated after an initial exposure to either water-soluble single-walled carbon nanotubes (SWNT) or to carbon black (CB). Both SWNT and CB were internalised and visible in food vacuoles of ciliates. When presented with E. coli expressing green-fluorescent protein (GFP), these ciliates internalised bacteria as well. However, ciliates that had first internalised SWNT but not CB subsequently externalised or egested vesicle-like structures with fluorescent bacteria inside. These egested bacteria were viable and less susceptible than planktonic E. coli to killing either by the antibiotic, chloramphenicol or the disinfectant, glutaraldehyde. These results suggest that SWNT can alter the intracellular trafficking of vesicles within ciliates, leading to bacterial prey being packaged externally and protected for a time from environmental killing, which could have implications for sewage treatment and for public health.

Proteomic profiles of white sucker (Catostomus commersonii) sampled from within the Thunder Bay Area of Concern reveal up-regulation of proteins associated with tumor formation and exposure to environmental estrogens

White sucker (Catostomus commersonii) sampled from the Thunder Bay Area of Concern were assessed for health using a shotgun approach to compile proteomic profiles. Plasma proteins were sampled from male and female fish from a reference location, an area in recovery within Thunder Bay Harbour, and a site at the mouth of the Kaministiquia River where water and sediment quality has been degraded by industrial activities. The proteins were characterized using reverse-phase liquid chromatography tandem to a quadrupole-time-of-flight (LC-Q-TOF) mass spectrometer and were identified by searching in peptide databases. In total, 1086 unique proteins were identified. The identified proteins were then examined by means of a bioinformatics pathway analysis to gain insight into the biological functions and disease pathways that were represented and to assess whether there were any significant changes in protein expression due to sampling location. Female white sucker exhibited significant (p = 0.00183) site-specific changes in the number of plasma proteins that were related to tumor formation, reproductive system disease, and neurological disease. Male fish plasma had a significantly different (p < 0.0001) number of proteins related to neurological disease and tumor formation. Plasma concentrations of vitellogenin were significantly elevated in females from the Kaministiquia River compared to the Thunder Bay Harbour and reference sites. The protein expression profiles indicate that white sucker health has benefited from the remediation of the Thunder Bay Harbour site, whereas white sucker from the Kaministiquia River site are impacted by ongoing contaminant discharges.

Characterization of p53 expression in rainbow trout

The tumour suppressor protein p53 is a critical component of cell cycle checkpoint responses. It upregulates the expression of cyclin-dependent kinase inhibitors in response to DNA damage and other cellular perturbations, and promotes apoptosis when DNA repair pathways are overwhelmed. Given the high incidence of p53 mutations in human cancers, it has been extensively studied, though only a small fraction of these investigations have been in non-mammalian systems. For the present study, an anti-rainbow trout p53 polyclonal antibody was generated. A variety of rainbow trout (Oncorhynchus mykiss) tissues and cell lines were examined through western blot analysis of cellular protein extracts, which revealed relatively high p53 levels in brain and gills. To evaluate the checkpoint response of rainbow trout p53, RTbrain-W1 and RTgill-W1 cell lines were exposed to varying concentrations of the DNA damaging agent bleomycin and ribonucleotide reductase inhibitor hydroxyurea. In contrast to mammals, these checkpoint-inducing agents provoked no apparent increase in rainbow trout p53 levels. These results infer the presence of alternate DNA damage checkpoint mechanisms in rainbow trout cells.