Recent advances in understanding neurotoxicity,behavior and neurodegeneration in siluriformes

Occurrence of neurotoxic chemicals in the aquatic environment is on the rise posing a potential threat to aquatic biota including fish.In teleosts,zebrafish has become a popular model organism for toxicological studies and testing strategies.However,over the decade,siluriformes(catfish)are also finding ever increasing application being robust as well as their adaptability to adverse ecological conditions,surgical interventions,and tolerant models for toxicity studies and manipulations.Such information can infer potential effects occurring to other species exposed to neurotoxins in their aquatic environment and predicting potential risks of a chemical for the aquatic ecosystem.The aim of this review is to compare and interpret recent results published concerning neuro-behavioral and morphological disturbances caused by toxicants/pollutants providing a holistic view of potential neurotoxic outcomes in catfish.Overall,this review summarizes various effects of toxicants/pollutants in terms of neurotoxicity and neurodegeneration associated with behavioral phenotypes.

Neuroendocrine facets of behavior and toxicology

Professor B.Senthilkumaran,who I came to know as Senthil,came over to visit the University of Alberta in the summer of 2022 in connection with his Global Ambassador Fellowship program at University of Saskatechewan,Canada.So,there was that reason to visit,but there was another one as well,one that tied us together.Many years before Senthil had been considered for a postdoctoral fellowship with the legend that was Dick Peter.However,it didn’t materialize and then he moved to Japan to do his Post Doc Under Prof.Hirohiko Kagawa.Dick had been Dean and a preeminent endocrinologist at the U of A.I came to know Dick near the end of my PhD;he had brought me out to Bamfield Marine Sciences Centre to carryout research using their then-new,and very expensive,simulated river.Dick left an incredible mark on all of us that knew him;he represented all that was wonderful and achievable in science.Having spent time with him was akin to shaking Sinatra’s hand,at least in the world of biology in that era.With this common history,Senthil and I were fast friends.

Development and organisation of gonadal steroidogenesis in bony fishes - A review

Gonadal steroidogenesis is pivotal to synchronize various reproductive stages including sexual development,growth and maturation.In all vertebrates including teleost,steroidogenesis is triggered by the mobilization of cholesterol by steroidogenic acute regulatory protein from outer to inner mitochondrial membrane.Thereafter,the entire process occurs in endoplasmic reticulum or mitochondria wherein various steroidogenic enzyme genes play a crucial role.The onset of steroidogenesis during sexual development in teleost is essentially regulated by differential expression of several transcription as well as steroidogenesis-related factors.More specifically,the role of dmrt,sox9,sox3,other sox forms,ad4bp/sf-1,wt-1,foxl2,ftz-f1,gata4,gsdf,Activator protein-1,fgfs and growth factors and steroidogenic enzymes such as cytochrome P450aromatase(cyp19a1),hydroxysteroid 3β-dehydrogenase(hsd3b),hydroxysteroid 17β-dehydrogenase(hsd17b)have been well characterised.Recently,the role of pax2,THO complex(thoc),pentraxin(ptx)and few signalling molecules like wnt4/5 regulating teleostean steroidogenesis has been reported.In females,cyp19a1 appears to be critical as it converts androgens to estrogens during ovarian differentiation which suggests that estradiol-17βis indispensable for the event.Unlike females,males do not depend on testosterone for testicular determination,yet has a major role along with 11-ketotestosterone in testicular development and growth when compared to early testicular differentiation.In males,onset of sex determining or testis-related genes seems most essential.Considering these,the regulation of steroidogenesis is virtually critical at later stages.In view of this,several steroidogenic motifs pertaining to transcriptional regulation have been analysed in teleost,yet far below than the reports on mammals.In this context,the regulatory influence on HHG axis plays a critical role in teleost.Further,multiple gonadotropin-releasing hormones and duality of gonadotropins play a differential role in gonadal function.As for steroidogenic pathway,the synthesis of sex steroids predominantly usesΔ4,however,Δ5 pathway was also evident.The next aspect is shift in steroidogenesis that usually occurs in the maturing follicles during final oocyte maturation,yet such a mechanism is not clear in males.The review highlights the interactions of steroidogenic enzyme gene regulation in terms of HHG axis and other important transcription factors that are involved in the regulatory pathways as well as the influence of environmental and dietary factors by comparing both sexes to present a holistic view on steroidogenesis onset and organisation during gametogenesis in teleost.

Sexual plasticity in bony fishes:Analyzing morphological to molecular changes of sex reversal

Sex reversal is one of the characteristic properties of sexual plasticity in bony fishes wherein both natural and induced sex change happens at various stages of life cycle in different species.Sex determination in gonochoristic species is genetically regulated,wherein the same sex is retained throughout their life span whereas hermaphrodites change their sex during development or adulthood.In sequential hermaphrodites,serial sex change occurs at different points of life cycle.Concurrently,synchronous hermaphrodites function as both the sexes during spawning.Other variables like temperature,pH and social factors can trigger sex reversal in teleost.Sex reversal through gene mutations and chemicals/hormones,including sex steroids,can be induced mostly at early developmental stages but natural sex reversal can occur at any time.Sex reversal mechanism shows morphological to molecular changes,which are ideal for identification of sex-specific gene markers.In fact,gonadal transdifferentiation occurs at the molecular level through differential expression of transcription factors and steroidogenic enzyme genes vis-a-vis hormones,thereby imparting phenotypic or structural changes.In addition,brain shows sexual dimorphism which is mostly consequential to gonadal sex development and occasionally either causative.The major breakthrough in this line is the identification of sex determining genes such as dmy/dmrt1Yb,gsdfY,sox3 in the Japanese medaka and amhY in Patagonian pejerrey.Incidentally,the induction of mono-sex population by favouring one sex due to sex-specific differences in growth is an important economic boom for aquaculture.This review comprehensively highlights key molecular factors involved in natural and induced sex reversal conditions to illustrate teleostean sexual plasticity and its application perspectives.

Effect of copper nanoparticles exposure in the physiology of the common carp(Cyprinus carpio):Biochemical,histological and proteomic approaches

Copper nanoparticles(Cu-NPs)are serious water pollutants but their impact in teleosts performance remains poorly understood.In the present study,we have exposed juvenile carps(Cyprinus carpio),a freshwater teleost edible in India to two different doses(20 and 100 mg/L)of Cu-NPs for seven days.The doses selected were eco-relevant considering the contamination levels of certain water resources.The results indicated that the activity oxidative stress enzymes catalase,superoxide dismutase,and glutathione-S-transferase were significantly increased in the kidney,liver and gills of the treated groups when compared to control.Histological analysis revealed that after exposure,disruption of the secondary lamellae of gills,liver damage with pyknotic nuclei and structural disarray of the kidney occurred.Proteomic analysis of the liver showed down-regulation of several proteins including the ferritin heavy chain,rho guanine nucleotide exchange factor 17-like,cytoglobin-1 and up-regulation of diphosphomevalonate decarboxylase and selenide&water dikinase-1.Taken together,the results of suggest that short-term exposure of juvenile carp to Cu-NPs causes oxidative stress and impart serious deleterious effects in the tissues which may affect fish growth and development.

Endocrine disruptors in teleosts:Evaluating environmental risks and biomarkers

Endocrine disruptors(EDs)are synthetic or natural chemical molecules occurring in environment that have the potential to impart adverse effects on homeostasis of endocrine axis leading to neurological,developmental,immunological and reproductive disarray at organismal level.A wide range of structurally diverse EDs such as,sex-steroid hormone mimics,pesticides and fertilizers,prevail in the environment originating from waste of industries,pharmaceutics,sewage treatment plants and agriculture.In addition,some metals,such as Cu,Hg and Zn,have endocrine disrupting potency in their metallic as well as synthesized nano-particulate forms.There is an increasing concern in research for the plausible threat posed by EDs that can disrupt the endocrine system in aquatic fauna as these compounds are frequently discharged or run-off into water stream.Fishes are well known bio-indicators to understand toxicity of EDs as they are vulnerable to endocrine disruption.Furthermore,EDs have the potential to affect fish-feeding higher vertebrates including mammals and subsequently human,as they make their way up on the food web pyramid due to biomagnification.In light of this,several observations suggesting adverse effects of EDs and the mechanism contributing to endocrine disruption in fish are discussed extensively in this review.This article highlights the necessity to choose a credible model for assessing the toxic effects exerted by EDs.Furthermore,the toxic effects of EDs will be comprehensively reviewed with reference to sexual plasticity,neuroendocrine mechanisms,thyroid and immune modulation,gonadal development and maturation as well as changes in transcriptome/genome profile using fish models to imply ED-induced aquatic pollution in a larger perspective.For decades now,studies on EDs have challenged traditional concepts in toxicology to develop new molecular markers to improve methodologies and to assess the ecological risks associated with field conditions.In this regard,it is imperative to highlight the development of modern diagnostic tools including biosensors to monitor the inadvertent usage of EDs and the resultant environmental risks.Lastly,current limitations in knowledge along with future research perspectives in the field are also highlighted in this article.

Editorial Reproduction and gonadal development in bony fishes

Fish-is an important source of dietary protein around the globe.Aquaculture aims to fulfill the supply gaps created by insufficient number of fish captured from the wild to meet the ever-increasing demand.One approach to address this renewed yield goal is by enhancing reproduction in fish used in aquaculture.However,enhancing reproduction necessitates a deeper understanding of our fundamental knowledge on reproductive endocrinology and physiology of fishes.There are many teleost fishes used for human consumption and the species choice largely depends on regional availability and geographical factors.This creates a need to study individual species to better understand the species-specific biology of reproduction in fishes.In line with this,research by fish reproductive biologists is generating significant new knowledge on fishes of interest in aquaculture,many of which are endemic to specific regions where humans inhabit.

Germ cell markers in fishes-A review

Identification of germ cell markers in fishes is crucial to track the germ cell differentiation and migration for manipulation of the cells to study sexual differentiation as well as to carry out transgenic transplantation techniques.Several germ cell-specific markers such as vasa,cnbp,dnd,nanos3,cbx2,amh,dmrt1,Ly75/CD205 have been characterized so far in fishes using localization and expression analysis,which have highlighted the spatio-temporal pattern of expression in early gonadal development.Incidentally,seasonal breeders show dramatic changes during gonadal recrudescence,which might also influence germ cell differentiation and growth to entrain the reproductive cycle.Hence,an in-depth analysis of the gonadal cycle is required to delineate germ cell progress,differentiation,and maturation explicitly.In this context,fishes undergoing gonadal recrudescence for the seasonal cycle show germ cell proliferation differentially.Most of these germ cell markers belong to the DEAD-box protein family of ATP-dependent RNA helicases sharing consensus motifs and clustering in phylogenetic analysis.These markers were found to be well-conserved throughout evolution.In situ hybridization approaches confirmed the germ cell specific distribution of these molecular markers.In addition,several genes such as fgf and gsdf seem to facilitate germ cell development and differentiation.Hence,more detailed studies on these factors will facilitate a better understanding of germ cell development.This review highlights various germ cell markers in fishes and their immense potential to use these cells for germ cell transplantation.The extensive knowledge of the germ cell markers can also be exploited to carry out other biotechnological experiments aiming at the preservation of genetic information of endangered species or the analytical study of gonadogenesis.