Influence of reproductive activity, sex steroids, and seasonality on epigonal organ cellular proliferation in the skate (Leucoraja erinacea)

Immunological and hemato-biochemical effects on catfish (Clarias gariepinus) exposed to dexamethasone

Dexamethasone (glucocorticoid) was recently shown to be a life-saving drug for the treatment of SARS-CoV-2 disease. Water and sediments can be contaminated by sewage treatment plants when this product is widely used. Accordingly, we evaluated the effects of dexamethasone as pharmaceutical residue on Clarias gariepinus, following exposure and post-exposure recovery on blood biochemical, antioxidant, and cytokine markers. Three experimental groups were examined. Control, fish exposed to 0.3 mg/L of dexamethasone, and fish exposed to 3 mg/L of dexamethasone for 7 days, followed by a 15-days recovery period. Hematological indices, such as red blood cell number, hemoglobin (Hb), platelets, mean corpuscular hemoglobin concentration, and large lymphocytes, were significantly declined following the exposure to dexamethasone compared to control. In contrast, hematocrit (Ht), mean corpuscular volume, monocytes, small lymphocytes, and mean corpuscular hemoglobin increased significantly depending on the dose–concentration. Liver and kidney functions, other biochemical parameters (albumin and globulin), cortisol, and cytokine (IL-1β and IL-6) concentrations increased significantly after exposure to dexamethasone compared to control. Antioxidants and acetylcholinesterase enzymes were significantly decreased in catfish treated with dexamethasone cumulatively with doses. After a recovery period, blood biochemical, antioxidant, and cytokine markers were still elevated compared with the control group. In conclusion, dexamethasone at concentrations present in water bodies causes deleterious effects on blood biomarkers, biochemical, and antioxidant as well as immune upregulation in catfish until after depuration period.

Occurrence, Fate, Effects, and Risks of Dexamethasone: Ecological Implications Post-COVID-19

The recent outbreak of respiratory syndrome-coronavirus-2 (SARS-CoV-2), which causes coronavirus disease (COVID-19), has led to the widespread use of therapeutics, including dexamethasone (DEXA). DEXA, a synthetic glucocorticoid, is among the widely administered drugs used to treat hospitalized COVID-19 patients. The global COVID-19 surge in infections, consequent increasing hospitalizations, and other DEXA applications have raised concerns on eminent adverse ecological implications to aquatic ecosystems. Here, we aim to summarize published studies on DEXA occurrence, fate, and effects on organisms in natural and engineered systems as, pre-COVID, the drug has been identified as an emerging environmental contaminant. The results demonstrated a significant reduction of DEXA in wastewater treatment plants, with a small portion, including its transformation products (TPs), being released into downstream waters. Fish and crustaceans are the most susceptible species to DEXA exposure in the parts-per-billion range, suggesting potential deleterious ecological effects. However, there are data deficits on the implications of DEXA to marine and estuarine systems and wildlife. To improve DEXA management, toxicological outcomes of DEXA and formed TPs should entail long-term studies from whole organisms to molecular effects in actual environmental matrices and at realistic exposure concentrations. This can aid in striking a fine balance of saving human lives and protecting ecological integrity.

Sex steroid hormones and the associated morphological changes in the reproductive tract of free-living males of the cururu stingray Potamotrygon wallacei

This study analyzed sex steroid hormones and morphology of the reproductive tract in free-living adult males of the cururu stingray (Potamotrygon wallacei). These stingrays were captured during the transition between drought and rising waters in the middle Rio Negro basin, which coincides with the reproductive period (spermatogenesis and copulation) of this endemic species. Levels of the plasma steroid hormones testosterone (T), 17 β-estradiol (E₂), and progesterone (P₄), the gonadosomatic and hepatosomatic indices, as well as histological characteristics of the testis and epididymis were evaluated. Three reproductive maturational stages were observed: regression males, capable to reproduce males, and active males. Plasma T levels were increasing and parallel with the rising water period in the middle Rio Negro basin and were associated with the progress of spermatogenesis. This was not observed for E₂, which did not vary significantly among the different reproductive stages. The high P₄ concentrations in males in regression and males capable of reproducing appeared to regulate the progression of spermatogenesis. Increases in this hormone in the plasma of active males was associated with spermiogenesis and spermiation events. These findings have not been previously observed in Amazonian freshwater stingrays and demonstrate that the reproductive activity of P. wallacei males is concomitant to the period of rising waters in the middle Rio Negro basin, and is regulated by the action of gonadal steroids, mainly testosterone.

A role for the CXCR4-CXCL12 axis in the little skate, Leucoraja erinacea

The interaction between C-X-C chemokine receptor type 4 (CXCR4) and its cognate ligand C-X-C motif chemokine ligand 12 (CXCL12) plays a critical role in regulating hematopoietic stem cell activation and subsequent cellular mobilization. Extensive studies of these genes have been conducted in mammals, but much less is known about the expression and function of CXCR4 and CXCL12 in non-mammalian vertebrates. In the present study, we identify simultaneous expression of CXCR4 and CXCL12 orthologs in the epigonal organ (the primary hematopoietic tissue) of the little skate, Leucoraja erinacea. Genetic and phylogenetic analyses were functionally supported by significant mobilization of leukocytes following administration of Plerixafor, a CXCR4 antagonist and clinically important drug. Our results provide evidence that, as in humans, Plerixafor disrupts CXCR4/CXCL12 binding in the little skate, facilitating release of leukocytes into the bloodstream. Our study illustrates the value of the little skate as a model organism, particularly in studies of hematopoiesis and potentially for preclinical research on hematological and vascular disorders.

Prenatal stress from trawl capture affects mothers and neonates: a case study using the southern fiddler ray (Trygonorrhina dumerilii)

Assessing fishing effects on chondrichthyan populations has predominantly focused on quantifying mortality rates. Consequently, sub-lethal effects of capture stress on the reproductive capacity of chondrichthyans are largely unknown. We investigated the reproductive consequences of capture on pregnant southern fiddler rays (Trygonorrhina dumerilii) collected from Swan Bay, Australia, in response to laboratory-simulated trawl capture (8 h) followed immediately by air exposure (30 min). Immediately prior to, and for up to 28 days post trawling, all females were measured for body mass (BM), sex steroid concentrations (17-β estradiol, progesterone, testosterone) and granulocyte to lymphocyte (G:L) ratio. At parturition, neonates were measured for total length (TL), BM and G:L ratio. Trawling reduced maternal BM and elevated the G:L ratio for up to 28 days. Trawling did not significantly affect any sex steroid concentrations relative to controls. Neonates from trawled mothers were significantly lower in BM and TL than control animals, and had an elevated G:L ratio. Our results show that capture of pregnant T. dumerilii can influence their reproductive potential and affect the fitness of neonates. We suggest other viviparous species are likely to be similarly affected. Sub-lethal effects of capture, particularly on reproduction, require further study to improve fisheries management and conservation of chondrichthyans.

Effects of trophic exposure to dexamethasone and diclofenac in freshwater fish

Steroidal and non-steroidalanti-inflammatories are pharmaceutical prescribed in human medicine and have the potential to contaminate water and sediments via inputs from sewage treatment plants. Their impacts on humans and ecosystems are emerging issues in environmental health. The aim of the present work was to evaluate the effects of diclofenac and dexamethasone in male fish Hoplias malabaricus after trophic exposure. Fish were fed twice every week with Astyanax sp. submitted to intraperitoneal inoculation with diclofenac (0; 0.2; 2.0 or 20.0 μg/kg) or dexamethasone (0; 0.03; 0.3 or 3.0 μg/kg). After 12 doses, blood was collected for testosterone dosage. The gonad and liver were collected to calculate gonadosomatic (GSI) and hepatosomatic index (HSI). Antioxidants enzymes activity and biotransformation were also evaluated in liver and gonads. In liver, diclofenac caused oxidative stress with increased superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities and lipoperoxidation (LPO). The GST activity was reduced by diclofenac in liver. Trophic exposure of H. malabaricus to dexamethasone caused an increase in antioxidant system (GPx, CAT, GST, and GSH) and LPO in liver. However, it reduced antioxidant system (GPX and GST activities and GSH) in gonads. Both diclofenac and dexamethasone reduced the levels of testosterone, causing impairment to reproduction. Diclofenac reduced HSI at the 0.2 μg/kg, but not GSI. Our results suggest that the anti-inflammatory drugs diclofenac and dexamethasone caused oxidative stress and reduced testosterone levels that can have a negative impact in aquatic organisms.

The epigonal organ and mature pole of the testis in the recreationally fished blue shark (Prionace glauca): histochemico-functional correlates

The exact role of the immune system in normal spermatogenesis is poorly understood. The attachment, however, of the lymphomyeloid epigonal organ specifically to the testis's mature pole in many shark species is a curious finding. Unlike the histology of the lymphomyeloid tissues of many other elasmobranchs, the epigonal organ leukocytes of wild-caught blue shark (Prionace glauca), besides exhibiting extensive nuclear heterogeneity, contain some of the largest known granules ever seen in vertebrate white blood cells. It was previously shown that the blue shark epigonal organ remains unremarkable and functionally unchanged despite cestode parasites embedded into its surface, suggesting that it might have other functions in addition to microbial defense. We show here that Prionace epigonal leukocytes shed their granule-laden cytoplasm into the cyst resorption zone (RZ) of the testis, i.e. the region separating the spermatogenic tissue from the epigonal organ, as they begin to migrate into the RZ. Using the immunoreactivity of the conserved transcription factor (proliferating cell nuclear antigen) as marker, it is shown that the granule-lacking leukocytes exclusively infiltrated spermatozoal cysts leftover after the wave of wide-spread multinuclear cell death in summer-breeding males in a seasonally dependent manner. By contrast, Prionace caught 2 months later showed fully recovered testes containing numerous completely intact spermatozoal cysts. Conversely, degenerating immature spermatids were gradually phagocytized by their accompanying Sertoli cells, and leukocytes did not infiltrate such cysts. The autoimmune response described here resembles in every aspect the testicular autoimmune response induced experimentally in a teleost fish. These observations suggest functional adaptation of shark leukocytes in response to specific changes in the testicular microenvironment.

Cell and molecular biology of the spiny dogfish Squalus acanthias and little skate Leucoraja erinacea: insights from in vitro cultured cells

Two of the most commonly used elasmobranch experimental model species are the spiny dogfish Squalus acanthias and the little skate Leucoraja erinacea. Comparative biology and genomics with these species have provided useful information in physiology, pharmacology, toxicology, immunology, evolutionary developmental biology and genetics. A wealth of information has been obtained using in vitro approaches to study isolated cells and tissues from these organisms under circumstances in which the extracellular environment can be controlled. In addition to classical work with primary cell cultures, continuously proliferating cell lines have been derived recently, representing the first cell lines from cartilaginous fishes. These lines have proved to be valuable tools with which to explore functional genomic and biological questions and to test hypotheses at the molecular level. In genomic experiments, complementary (c)DNA libraries have been constructed, and c. 8000 unique transcripts identified, with over 3000 representing previously unknown gene sequences. A sub-set of messenger (m)RNAs has been detected for which the 3' untranslated regions show elements that are remarkably well conserved evolutionarily, representing novel, potentially regulatory gene sequences. The cell culture systems provide physiologically valid tools to study functional roles of these sequences and other aspects of elasmobranch molecular cell biology and physiology. Information derived from the use of in vitro cell cultures is valuable in revealing gene diversity and information for genomic sequence assembly, as well as for identification of new genes and molecular markers, construction of gene-array probes and acquisition of full-length cDNA sequences.

Community annotation and bioinformatics workforce development in concert--Little Skate Genome Annotation Workshops and Jamborees

Recent advances in high-throughput DNA sequencing technologies have equipped biologists with a powerful new set of tools for advancing research goals. The resulting flood of sequence data has made it critically important to train the next generation of scientists to handle the inherent bioinformatic challenges. The North East Bioinformatics Collaborative (NEBC) is undertaking the genome sequencing and annotation of the little skate (Leucoraja erinacea) to promote advancement of bioinformatics infrastructure in our region, with an emphasis on practical education to create a critical mass of informatically savvy life scientists. In support of the Little Skate Genome Project, the NEBC members have developed several annotation workshops and jamborees to provide training in genome sequencing, annotation and analysis. Acting as a nexus for both curation activities and dissemination of project data, a project web portal, SkateBase (http://skatebase.org) has been developed. As a case study to illustrate effective coupling of community annotation with workforce development, we report the results of the Mitochondrial Genome Annotation Jamborees organized to annotate the first completely assembled element of the Little Skate Genome Project, as a culminating experience for participants from our three prior annotation workshops. We are applying the physical/virtual infrastructure and lessons learned from these activities to enhance and streamline the genome annotation workflow, as we look toward our continuing efforts for larger-scale functional and structural community annotation of the L. erinacea genome.

Effects of a glucocorticoid receptor agonist, dexamethasone, on fathead minnow reproduction, growth, and development

Synthetic glucocorticoids are pharmaceutical compounds prescribed in human and veterinary medicine as anti-inflammatory agents and have the potential to contaminate natural watersheds via inputs from wastewater treatment facilities and confined animal-feeding operations. Despite this, few studies have examined the effects of this class of chemicals on aquatic vertebrates. To generate data to assess potential risk to the aquatic environment, we used fathead minnow 21-d reproduction and 29-d embryo-larvae assays to determine reproductive toxicity and early-life-stage effects of dexamethasone. Exposure to 500 µg dexamethasone/L in the 21-d test caused reductions in fathead minnow fecundity and female plasma estradiol concentrations and increased the occurrence of abnormally hatched fry. Female fish exposed to 500 µg dexamethasone/L also displayed a significant increase in plasma vitellogenin protein levels, possibly because of decreased spawning. A decrease in vitellogenin messenger ribonucleic acid (mRNA) expression in liver tissue from females exposed to the high dexamethasone concentration lends support to this hypothesis. Histological results indicate that a 29-d embryo-larval exposure to 500 µg dexamethasone/L caused a significant increase in deformed gill opercula. Fry exposed to 500 µg dexamethasone/L for 29 d also exhibited a significant reduction in weight and length compared with control fry. Taken together, these results indicate that nonlethal concentrations of a model glucocorticoid receptor agonist can impair fish reproduction, growth, and development.

Testicular structure and spermatogenesis of Amazonian freshwater cururu stingray Potamotrygon cf. histrix

The cururu stingray Potamotrygon cf. histrix, a new and endemic Amazonian freshwater species, presents appropriate characteristics for fish keeping and is exploited from its natural environment. The present study identified the testicular structure and spermatogenesis of this species. Gonads from adult male specimens were dissected, fixed and processed for histological analysis. The testes were of testicular/epigonial type. The presence of germinal papillae was observed in the upper portion of organ with primordial germ cells and Sertoli cell precursors. The testis was lobular with zonal organization and cystic gametogenesis, with the occurrence of spermatoblasts. The Sertoli cells underwent morphological modifications over the course of gamete formation. The spermatozoids had long heads and were spiraled on their own axis. Information on the reproductive biology will serve as basis for studies on the reproduction and phylogeny of this peculiar group of cartilaginous fish.

Morphological relationships and leukocyte influence on steroid production in the epigonal organ-ovary complex of the skate, Leucoraja erinacea

In elasmobranchs, a unique association exists between an immune tissue, the epigonal organ (EO), and the gonads. In this study, the histological and vascular relationships of the EO and ovarian follicles of the little skate, Leucoraja erinacea, were assessed. Perfusions of Evans blue dye and Batson's monomer showed a shared vascular pathway from the gonadal artery into the epigonal-ovary complex, with blood first entering the EO and then perfusing the ovarian follicles. Histological studies demonstrated direct cellular contact between epigonal leukocytes and the follicle wall (FW), as well as the presence of leukocytes between the steroidogenic theca and granulosa cells. In vitro analyses demonstrated that epigonal cells co-cultured with FW cells cause a dose-dependent inhibition of estrogen (E2) and testosterone (T) production. In contrast, conditioned media from epigonal leukocytes, stimulated or unstimulated with lipopolysaccharide (10 microg/ml), increase the production of E2 and T from FW cells of the ovaries. These studies provide a basis for further investigations of leukocyte secreted factors and cell contact modulation of follicular steroid production.