Pattern of vitellogenesis and follicle maturational competence during the ovarian follicular cycle of Fundulus heteroclitus

Evaluation of Black Soldier Fly Larvae Meal on Growth, Body Composition, Immune Responses, and Antioxidant Capacity of Redclaw Crayfish (Cherax quadricarinatus) Juveniles

This study investigated the effects of substituting fish meal (FM) with black soldier fly (Hermetia illucens) meal (BSM) on the growth performance, body composition, immune response, and antioxidant enzyme activity of juvenile redclaw crayfish (Cherax quadricarinatus). Four isonitrogenous (41%) and isolipidic (11%) diets (i.e., FM substitutes) were formulated from BSM prepared using larvae that were fed soybean meal (BSM-S), fishery byproducts (BSM-F), or pitaya (BSM-P). The experimental diets were fed twice daily to triplicate groups of juvenile redclaw crayfish (0.56 ± 0.04 g). After the feed trial, the FM and BSM-F groups exhibited significantly lower feed conversion ratios and significantly higher weight gain; specific growth rates; and concentrations of saturated fatty acids, highly unsaturated fatty acids, eicosapentaenoic acid, and docosahexaenoic acid in the muscle. Among the tested groups, the BSM-F group exhibited significantly enhanced immune responses and increased antioxidant enzyme activity (i.e., superoxide dismutase, phenoloxidase, and glutathione peroxidase); the BSM-P group exhibited a significantly higher feed intake and hepatopancreatic index; and the FM group exhibited a significantly higher muscle body index and apparent digestibility for the dry matter of crude protein. The findings indicate that the juvenile redclaw crayfish fed BSM-F achieved the highest weight gain among the groups.

Acute cold stress leads to zebrafish ovarian dysfunction by regulating miRNA and mRNA

Temperature is a critical factor that regulates the reproduction processes in teleost. However, the gonadal response mechanism to cold stress in fish remains largely unknown. In the present study, female zebrafish were exposed to different extents of low temperatures at 18 °C and 10 °C for 48 h. The ovarian histology was remarkably damaged after cold stress exposure. Integrated analysis of miRNA-mRNA was used to investigate the ovarian response to acute cold stress. A large number of mRNAs and miRNAs were altered by cold stress, which are involved in extensive biological processes. It is indicated that the signal transduction of MAPK and Calcium signaling pathway is highly engaged in zebrafish ovary to adapt to cold stress. The immune system was dysregulated by cold stress while the ovarian autophagy was activated. Remarkably increased gene number related to reproductive functions was identified in the cold stress at 10 °C compared to the control. The cold stress-induced dysregulated reproductive genes include star, hsd3b1, hsd17b1, inha, insl3, amh, nanos1 and foxl2. Combined with the dysregulated insulin, IGF and progesterone signaling, it is suggested that cold stress affects ovarian function in multiple aspects, including oocyte meiosis, folliculogenesis, final maturation and ovarian maintenance. On the other hand, the ovarian miRNA-mRNA regulatory network response to cold stress was also constructed. Overall, our result revealed the ovarian response to cold stress in zebrafish and provided insight into the fish adaptation mechanism to acute temperature change.

The Still Dark Side of the Moon: Molecular Mechanisms of Lunar-Controlled Rhythms and Clocks

Starting with the beginning of the last century, a multitude of scientific studies has documented that the lunar cycle times behaviors and physiology in many organisms. It is plausible that even the first life forms adapted to the different rhythms controlled by the moon. Consistently, many marine species exhibit lunar rhythms, and also the number of documented "lunar-rhythmic" terrestrial species is increasing. Organisms follow diverse lunar geophysical/astronomical rhythms, which differ significantly in terms of period length: from hours (circalunidian and circatidal rhythms) to days (circasemilunar and circalunar cycles). Evidence for internal circatital and circalunar oscillators exists for a range of species based on past behavioral studies, but those species with well-documented behaviorally free-running lunar rhythms are not typically used for molecular studies. Thus, the underlying molecular mechanisms are largely obscure: the dark side of the moon. Here we review findings that start to connect molecular pathways with moon-controlled physiology and behaviors. The present data indicate connections between metabolic/endocrine pathways and moon-controlled rhythms, as well as interactions between circadian and circatidal/circalunar rhythms. Moreover, recent high-throughput analyses provide useful leads toward pathways, as well as molecular markers. However, for each interpretation, it is important to carefully consider the, partly substantially differing, conditions used in each experimental paradigm. In the future, it will be important to use lab experiments to delineate the specific mechanisms of the different solar- and lunar-controlled rhythms, but to also start integrating them together, as life has evolved equally long under rhythms of both sun and moon.

Mummichog (Fundulus heteroclitus) are less sensitive to 17α-ethinylestradiol (EE2) than other common model teleosts: A comparative review of reproductive effects

The environmental estrogen 17α-ethinylestradiol (EE₂) will depress or completely inhibit egg production in many common model teleosts at low concentrations (≤0.5 ng/L; Runnalls et al., 2015). This inhibition is not seen in the estuarine killifish, or mummichog (Fundulus heteroclitus), even when exposed to 100 ng/L EE₂. This relative insensitivity to EE₂ exposure indicates species-specific mechanisms for compensating for exogenous estrogenic exposure. This review compares various reproductive responses elicited by EE₂ in mummichog to other common model teleosts, such as zebrafish (Danio rerio) and fathead minnow (Pimephales promelas), identifying key endpoints where mummichog differ from other studied fish. For example, EE₂ accumulates primarily in the liver/gall bladder of mummichog, which is different than zebrafish and fathead minnow in which accumulation is predominantly in the carcass. Despite causing species-specific differences in fecundity, EE₂ has been shown to consistently induce hepatic vitellogenin in males and cause feminization/sex reversal during gonadal differentiation in larval mummichog, similar to other species. In addition, while gonadal steroidogenesis and plasma steroid levels respond to exogenous EE_2, it is generally at higher concentrations than observed in other species. In mummichog, production of 17β-estradiol (E₂) by full grown ovarian follicles remains high; unlike other teleost models where E₂ synthesis decreases as 17α,20β-dihydroxy-4-prenen-3-on levels increase to induce oocyte maturation. New evidence in mummichog indicates some dissimilarity in gonadal steroidogenic gene expression responses compared to gene expression responses in zebrafish and fathead minnow exposed to EE₂. The role of ovarian physiology continues to warrant investigation regarding the tolerance of mummichog to exogenous EE₂ exposure. Here we present a comprehensive review, highlighting key biological differences in response to EE₂ exposure between mummichog and other commonly used model teleosts.

Gonadal development and reproductive period of the characin Astyanax aff. bimaculatus (Characiformes: Characidae) in a tropical reservoir in southeastern Brazil

The gonadal development of the characin Astyanax aff. bimaculatus from Funil Reservoir, an impoundment in the middle reaches of the Paraiba do Sul River in southeastern Brazil was analysed through histological, histochemical and histometric techniques, and the spawning season was determined. Unbalanced sex ratio was found, with females outnumbering and reaching larger sizes than males. The following stages of oogenic cell development were identified for females: primary growth, pre-vitellogenic (cortical alveolar) and vitellogenic. In males, the following stages were determined: spermatogonia primary and secondary, spermatocyte primary and secondary, spermatid and spermatozoa. The spawning occurs most of the year, peaking in January-February, as indicated by the gonadosomatic index. In the peak of the spawning period, the condition factor and hepatosomatic indices decreased suggesting use of stored body energy reserves during the reproduction. Spawning in batches, small-sized oocytes and a long reproductive season suggest that Astyanax aff. bimaculatus fits to an opportunist strategy. Such strategy may facilitate the use of a wide range of lentic and lotic body waters in the Neotropical region.

Temperature affects sexual maturation through the control of kisspeptin, kisspeptin receptor, GnRH and GTH subunit gene expression in the grass puffer during the spawning season

Water temperature is an environmental factor of primary importance that influences reproductive function in fish. To understand the molecular and physiological mechanisms underlying the regulation of reproduction by temperature, we examined changes in expression of genes encoding kisspeptin (kiss2), kisspeptin receptor (kiss2r) and three gonadotropin-releasing hormones (gnrh1, gnrh2 and gnrh3) in the brain and genes encoding gonadotropin (GTH) subunits (gpa, fshb and lhb) in the pituitary of grass puffer exposed to a low temperature (14°C), normal temperature (21°C) and high temperature (28°C) for 7days. In addition, the plasma levels of cortisol were examined after exposed to three temperature conditions. The gonadosomatic index was significantly decreased in both low and high temperature conditions. The levels of kiss2 and kiss2r mRNAs were significantly decreased at both low and high temperature conditions compared to normal temperature (control) condition. gnrh1 but not gnrh2 were significantly decreased in both temperature conditions, while gnrh3 showed a decreasing tendency in low temperature. Consequently, the levels of fshb and lhb mRNAs were significantly decreased in both low and high temperature conditions. Interestingly, the plasma levels of cortisol were significantly increased in low temperature but remain unchanged in high temperature, suggesting that the fish were under stress in the low temperature conditions but not in the high temperature conditions. Taken together, the present results indicate that anomalous temperature have an inhibitory effect on reproductive function through suppressing kiss2/kiss2r/gnrh1/fshb and lhb expression and these changes may occur in a normal physiological response as well as in a malfunctional stress response.

Reproductive and parental care physiology of Cichlasoma dimerus males

The South American cichlid fish Cichlasoma dimerus presents a high breeding frequency and biparental care of the eggs and larvae. The male parental care period was divided in four different phases according to the developmental degree of the offspring: pre-spawning activity (MP, day 0), guarding eggs (ME, one day after fertilization (1 DAF)), guarding hatched larvae (MHL, 3 DAF), and guarding swimming larvae (MSL, 8 DAF). The aim of this study was to characterize male reproductive physiology by measuring steroid hormone plasma levels and analyzing testes cellular composition. Males exhibiting pre-spawning activity showed 8.4 times higher 11-ketotestosterone and 5.63 times higher testosterone levels than MHL. No differences were observed in estradiol and cortisol levels among the different phases. The cellular composition of the testes varied during the reproductive and parental care periods. Testes of MP were composed of 50% of spermatozoa, whereas spermatogonia type B and spermatocytes were predominant in the subsequent parental phases. A morphometric analysis of Leydig cells nuclear area revealed that MP and ME's Leydig cells averaged 1.27 times larger than that those of MHL and MSL and was positively correlated with circulating 11-KT and T levels. Hence, C. dimerus males showed important changes in its hormonal profiles and testicular cellular composition throughout the reproductive and parental care period.

Chronic exposure of killifish to a highly polluted environment desensitizes estrogen-responsive reproductive and biomarker genes

Reproductive and endocrine disruption is commonly reported in aquatic species exposed to complex contaminant mixtures. We previously reported that Atlantic killifish (Fundulus heteroclitus) from the chronically contaminated Newark Bay, NJ, exhibit multiple endocrine disrupting effects, including inhibition of vitellogenesis (yolk protein synthesis) in females and false negative vitellogenin biomarker responses in males. Here, we characterized the effects on estrogen signaling and the transcriptional regulation of estrogen-responsive genes in this model population. First, a dose-response study tested the hypothesis that reproductive biomarkers (vtg1, vtg2, chg H, chg Hm, chg L) in Newark Bay killifish are relatively less sensitive to 17β-estradiol at the transcriptional level, relative to a reference (Tuckerton, NJ) population. The second study assessed expression for various metabolism (cyp1a, cyp3a30, mdr) and estrogen receptor (ER α, ER βa, ER βb) genes under basal and estrogen treatment conditions in both populations. Hepatic metabolism of 17β-estradiol was also evaluated in vitro as an integrated endpoint for adverse effects on metabolism. In the third study, gene methylation was evaluated for promoters of vtg1 (8 CpGs) and vtg2 (10 CpGs) in both populations, and vtg1 promoter sequences were examined for single nucleotide polymorphism (SNPs). Overall, these studies show that multi-chemical exposures at Newark Bay have desensitized all reproductive biomarkers tested to estrogen. For example, at 10ng/g 17β-estradiol, inhibition of gene induction ranged from 62% to 97% for all genes tested in the Newark Bay population, relative to induction levels in the reference population. The basis for this recalcitrant phenotype could not be explained by a change in 17β-estradiol metabolism, nuclear estrogen receptor expression, promoter methylation (gene silencing) or SNPs, all of which were unaltered and normal in the Newark Bay population. The decreased transcriptional sensitivity of estrogen-responsive genes is suggestive of a broad effect on estrogen receptor pathway signaling, and provides insight into the mechanisms of the endocrine disrupting effects in the Newark Bay population.

Temperature differentially regulates the two kisspeptin systems in the brain of zebrafish

Kisspeptins encoded by the kiss1 and kiss2 genes play an important role in reproduction through the stimulation of gonadotropin-releasing hormone (GnRH) secretion by activating their receptors (KissR1 EU047918 and KissR2 EU047917). To understand the mechanism through which temperature affects reproduction, we examined kiss1 and kiss2 and their respective receptor (kissr1 and kissr2) gene expression in the brain of male zebrafish exposed to a low temperature (15°C), normal temperature (27°C), and high temperature (35°C) for 7-days. kiss1 mRNA levels in the brain were significantly increased (2.9-fold) in the low temperature compared to the control (27°C), while no noticeable change was observed in the high temperature conditions. Similarly, kissr1 mRNA levels were significantly increased (1.5-2.2-folds) in the low temperature conditions in the habenula, the nucleus of the medial longitudinal fascicle, oculomotor nucleus, and the interpeduncular nucleus. kiss2 mRNA levels were significantly decreased (0.5-fold) in the low and high temperature conditions, concomitant with kissr2 mRNA levels (0.5-fold) in the caudal zone of the periventricular hypothalamus and the posterior tuberal nucleus. gnrh3 but not gnrh2 mRNA levels were also decreased (0.5-fold) in the low and high temperature conditions. These findings suggest that while the kiss1/kissr1 system is sensitive to low temperature, the kiss2/kissr2 system is sensitive to both extremes of temperature, which leads to failure in reproduction.

Probiotics can induce follicle maturational competence: the Danio rerio case

In the present study, the effects of the probiotic Lactobacillus rhamnosus IMC 501 on the acquisition of oocyte maturational competence was examined in zebrafish (Danio rerio). L. rhamnosus administration induced the responsiveness of incompetent follicles (stage IIIa) to 17,20-dihydroxy-4-pregnen-3-one and their in vitro maturation. Acquisition of competence by the stage IIIa follicles was further validated by changes of lhr, mprb, inhbaa (activin betaA1), tgfb1, and gdf9 gene expression, which have recently emerged as key regulators of oocyte acquisition of maturational competence, and pou5f1 gene expression, which in other models has been shown to govern the establishment of developmental competence of oocytes. In addition, a DNA microarray experiment was conducted using the same follicles, and with relative gene ontology (GO) data analysis, the molecular effects of probiotic administration emerged. Molecular analysis using PCR-DGGE (denaturing gradient gel electrophoresis) approach, providing information about only the most abundant bacterial members of the microbial community, revealed that the probiotic was able to populate the gastrointestinal tract and modulate the microbial communities, causing a clear shift in them and specifically enhancing the presence of the lactic acid bacteria Streptococcus thermophilus. At the same time, PCR-DGGE analysis revealed that the probiotic was not directly associated with the ovaries. Finally, the effects of probiotic treatment on zebrafish follicle development were also analyzed by FPA (focal plane array) Fourier transform-infrared (FT-IR) imaging, a technique that provides the overall biochemical composition of samples. Changes were found above all in stage IIIa follicles from probiotic-exposed females; the modifications, observed in protein secondary structures as well as in hydration and in bands related to phosphate moieties, allowed us to hypothesize that probiotics act at this follicle stage, affecting the maturation phase.

Fundulus heteroclitus: ovarian reproductive physiology and the impact of environmental contaminants

Fundulus heteroclitus, the mummichog or Atlantic killifish, is the dominant small-bodied fish species of the east coast estuaries and salt marshes of Canada and the USA, where it is present as two subspecies, the northern F. h. macrolepidotus and the southern F. h. heteroclitus. Recently identified as the premier teleost model in environmental biology, the species has long been of value in understanding evolved tolerance to toxicants and more lately in adding to our knowledge about reproductive effects of environmental endocrine disruptors. The body of literature on F. heteroclitus ovarian physiology and reproduction, from both field and laboratory studies, provides the foundation for present work focused on understanding the reproductive effects and modes of action of environmental toxicants. In this paper, we review the environmental and endocrine factors controlling ovarian and reproductive cycling in F. heteroclitus, noting specifics related to field and laboratory studies on the two subspecies as well as key research gaps compared to other fish species. We also summarize recent development of methodologies to study the effects of environmental contaminants on endocrine signalling and egg production in F. heteroclitus. Continued efforts to progress both our fundamental understanding of reproductive physiology in mummichog, coupled with studies focused on the modes of action of environmental contaminants, have high potential to further develop this teleost model. While the model may presently lag behind those based on other species of fish, the unique biochemical and physiological adaptations which allow F. heteroclitus to adapt to changing environmental and toxic conditions provide a valuable experimental system for comparative physiologists, ecotoxicologists and evolutionary biologists.

Decreased vitellogenin inducibility and 17β-estradiol levels correlated with reduced egg production in killifish (Fundulus heteroclitus) from Newark Bay, NJ

Aquatic species inhabiting polluted estuaries are exposed to complex mixtures of xenobiotics which can alter normal reproduction. We previously reported that female Atlantic killifish (Fundulus heteroclitus) from the highly contaminated Newark Bay, NJ (USA) exhibited an inhibition of oocyte development due to reduced vitellogenin (egg-yolk precursor) levels. Our hypothesis was that the inhibition of oocyte development in Newark Bay killifish is due to (1) deficient levels of circulating 17β-estradiol, and (2) a decreased sensitivity of the vitellogenin pathway to physiological doses of 17β-estradiol. In the first study, adult naïve killifish from Tuckerton, NJ (reference) were caged at Tuckerton and Newark Bay. After 1 month, males caged at Newark Bay exhibited inductions of hepatic vitellogenin and estrogen receptor α, which were transient and returned to basal levels after 2 months (p≤0.05). In the second study, fecundity and 17β-estradiol levels were measured in reproductively active adult females from Tuckerton and Newark Bay. Tuckerton females produced 140 eggs per female and Newark Bay females produced 11 eggs per female. Embryos from Newark Bay had 34% greater mortality and 28% less hatch, relative to Tuckerton. In addition, embryo mass and yolk-volume of Newark Bay embryos compared to Tuckerton embryos was 16% and 25% lower, respectively. Circulating 17β-estradiol levels in Newark Bay females (0.26 ng/mL) were measured to be 8-fold lower than Tuckerton females (2.25 ng/mL). In the third study, adult killifish from both sites were dosed with 17β-estradiol to assess the sensitivity of the vitellogenin pathway. At doses of 0.01, 0.1, 1 and 10 ng/g body weight, induction levels of circulating vitellogenin in Newark Bay males were significantly inhibited by 97, 99, 98 and 44%, respectively, compared to Tuckerton males. At doses of 0.01, 0.1, 1, 10 and 100 ng/g body weight, induction levels of circulating vitellogenin in Newark Bay females were inhibited by 89, 79, 61, 40 and 30%, respectively, compared to Tuckerton females. These differences in inducibility could not be explained by altered hepatic expression of estrogen receptors α, βa or βb. Based on the caged and dose-response studies, contaminants that down-regulate vitellogenin would interfere with its ability to be used as a biomarker for xeno-estrogen exposures. These studies demonstrate that contaminants within Newark Bay exert both estrogenic and anti-estrogenic responses which results in an overtly anti-estrogenic phenotype (reduced egg production due to inhibition of vitellogenesis).

Experimentally nonylphenol-polluted diet induces the expression of silent genes VTG and ERα in the liver of male lizard Podarcis sicula

Endocrine Disruptor Chemicals (EDCs) with estrogen-like properties i.e nonylphenol (NP) induce vitellogenin (VTG) synthesis in males of aquatic and semi-aquatic species. In the oviparous species VTG is a female-specific oestrogen dependent protein. Males are unable to synthesize VTG except after E2 treatment. This study aimed to verify if NP, administered via food and water, is able to induce the expression of VTG even in males of vertebrates with a terrestrial habitat such as the lizard Podarcis. By means of ICC, ISH, W/B and ELISA we demonstrated that NP induces the presence of VTG in the plasma and its expression in the liver. VTG, undetectable in untreated males, reaches the value of 4.34 μg/μl in the experimental ones. Expression analysis and ISH in the liver showed that an NP-polluted diet also elicits the expression of ERα in the liver which is known to be related to VTG synthesis in Podarcis.

Cathepsin B differential expression and enzyme processing and activity during Fundulus heteroclitus embryogenesis

The role of lysosomal proteases such as cathepsin B (Ctsb) and one of the paralogs of cathepsin L (Ctsla) during yolk metabolism in fish oocytes is well established. However, the function of Ctsb during embryogenesis, particularly in marine teleosts, has been poorly documented. In this study, the spatio-temporal expression of Ctsb and Ctsla, their enzymatic activities, and the processing of the Ctsb and its cellular localization, was investigated in developing embryos of the killifish (Fundulus heteroclitus). Both fhctsb and fhctsla transcript levels, as well as cathepsin B- and L-like activities, gradually increased in embryos from the 2-4 cell stage up to 7 days post-fertilization. During the morula to gastrula transition an increase of the active FhCtsb single chain form was followed by a rise in cathepsin B activity, which were apparently regulated by post-transcriptional mechanisms. During neurulation, a 8-fold increase in cathepsin B activity was accompanied by a more moderate increase in cathepsin L activity, which was 6-fold enhanced by 7 dpf. These increased catalytic activities were well-correlated to changes in the electrophoretic pattern of yolk proteins and a strong expression of fhctsb and its protein product in the yolk syncytial layer. The increase of cathepsin B activity was further correlated with an increment of the relative amount of the FhCtsb single and double chain forms, both active forms of FhCtsb. These results suggest that FhCtsb may be involved in the mechanisms underlying the onset of gastrulation in F. heteroclitus embryos, and may play complementary roles with FhCtsla during yolk metabolism.

Impaired reproductive health of killifish (Fundulus heteroclitus) inhabiting Newark Bay, NJ, a chronically contaminated estuary

A battery of biomarkers were used to evaluate the reproductive health and contaminant exposure of Atlantic killifish (Fundulus heteroclitus) inhabiting the heavily industrialized Newark Bay and a reference population from Great Bay, Tuckerton, NJ. The biomarkers investigated included classical endpoints (gonad and liver histopathology, body and tissue morphometrics), hepatic mRNA expression (CYP1A and vitellogenin I), hepatic protein levels (CYP1A and vitellogenin), gonadal aromatase mRNA expression, and chemical exposure analyses (bile PAHs). Our data showed no significant differences between populations for body size and body weight. However, Newark Bay killifish exhibited molecular and morphological changes indicative of impaired reproductive health and endocrine disruption compared to the reference population. Newark Bay males had decreased gonad weight, altered testis development and decreased gonadal aromatase mRNA expression. Newark Bay females had decreased gonad weight, inhibited gonadal development, decreased hepatic vitellogenin production (mRNA and protein) and increased mRNA expression of gonadal aromatase. In addition, Newark Bay females had a significant increase in the percent of pre-vitellogenic follicles (43% at Tuckerton, 64% at Newark Bay) and a significantly decreased percent of follicles at the mid-vitellogenic and mature stages (25% mature at Tuckerton and 3% at Newark Bay). In addition to reproductive endpoints, killifish at Newark Bay exhibited high basal levels of CYP1A mRNA and protein expression which indicated exposure to aryl hydrocarbon receptor (AhR) agonists. An inverse relationship between hepatic CYP1A protein and hepatic vitellogenin mRNA expression was established suggesting a possible link between AhR agonist exposure and vitellogenesis. Killifish in the NY-NJ Harbor Estuary are exposed to a number of chemicals that can interact with the AhR pathway and stimulate enzymatic activity along with chemicals that can modify reproductive success in this indigenous species. Similar effects on the reproductive development in less resilient species may limit their ability to repopulate the NY-NJ Harbor Estuary and similarly contaminated water systems.

Adaptive plasticity of killifish (Fundulus heteroclitus) embryos: dehydration-stimulated development and differential aquaporin-3 expression

Embryos of the marine killifish Fundulus heteroclitus are adapted to survive aerially. However, it is unknown if they are able to control development under dehydration conditions. Here, we show that air-exposed blastula embryos under saturated relative humidity were able to stimulate development, and hence the time of hatching was advanced with respect to embryos continuously immersed in seawater. Embryos exposed to air at later developmental stages did not hatch until water was added, while development was not arrested. Air-exposed embryos avoided dehydration probably because of their thickened egg envelope, although it suffered significant evaporative water loss. The potential role of aquaporins as part of the embryo response to dehydration was investigated by cloning the aquaporin-0 (FhAqp0), -1a (FhAqp1a), and -3 (FhAqp3) cDNAs. Functional expression in Xenopus laevis oocytes showed that FhaAqp1a was a water-selective channel, whereas FhAqp3 was permeable to water, glycerol, and urea. Expression of fhaqp0 and fhaqp1a was prominent during organogenesis, and their mRNA levels were similar between water- and air-incubated embryos. However, fhaqp3 transcripts were highly and transiently accumulated during gastrulation, and the protein product was localized in the basolateral membrane of the enveloping epithelial cell layer and in the membrane of ingressing and migrating blastomers. Interestingly, both fhaqp3 transcripts and FhAqp3 polypeptides were downregulated in air-exposed embryos. These data demonstrate that killifish embryos respond adaptively to environmental desiccation by accelerating development and that embryos are able to transduce dehydration conditions into molecular responses. The reduced synthesis of FhAqp3 may be one of these mechanisms to regulate water and/or solute transport in the embryo.

Local expression of CYP19A1 and CYP19A2 in developing and adult killifish (Fundulus heteroclitus)

P450 aromatase (CYP19) is the terminal enzyme in the steroidogenic pathway and catalyzes the conversion of androgens to estrogens. Fundulus heteroclitus like other teleosts, express two CYP19 genes, CYP19A1 and CYP19A2. The expression of CYP19s in Fundulus was measured by in situ hybridization throughout development. In 90 dpf (day post-fertilization) fish and adult fish, CYP19A1 was expressed in the ooplasm of early stage I oocytes (primary growth stage). Expression of CYP19A1 was localized in the follicle cell layer of late stage I (previtellogenic stage) and stage II (vitellogenic stage) follicles, but by stage III (early maturational follicles) CYP19A1 expression was localized in the vitelline envelope. Overall, CYP19A1 oocyte membrane expression gradually declined from highest expression at late stage I to nondetectable levels by stage IV. Highest expression of CYP19A2 was detected in the brain including the hypothalamus from 4, 6, 8, 10, 14 dpf embryos, 90 dpf fry fish and adult fish brain. In females compared to males, there was higher CYP19A2 expression in olfactory bulb. In addition to the brain, there was strong CYP19A2 signal in adrenal/kidney cells in 6-14 dpf embryos. This work establishes the localization and constitutive expression of CYP19s in Fundulus which can then be compared with potential disruption of CYP19A1 and CYP19A2 expression and physiological consequences caused by environmental contaminants.

Fundulus as the premier teleost model in environmental biology: opportunities for new insights using genomics

A strong foundation of basic and applied research documents that the estuarine fish Fundulus heteroclitus and related species are unique laboratory and field models for understanding how individuals and populations interact with their environment. In this paper we summarize an extensive body of work examining the adaptive responses of Fundulus species to environmental conditions, and describe how this research has contributed importantly to our understanding of physiology, gene regulation, toxicology, and ecological and evolutionary genetics of teleosts and other vertebrates. These explorations have reached a critical juncture at which advancement is hindered by the lack of genomic resources for these species. We suggest that a more complete genomics toolbox for F. heteroclitus and related species will permit researchers to exploit the power of this model organism to rapidly advance our understanding of fundamental biological and pathological mechanisms among vertebrates, as well as ecological strategies and evolutionary processes common to all living organisms.

What is normal? A characterization of the values and variability in reproductive endpoints of the fathead minnow, Pimephales promelas

Jensen et al. [Jensen, K.M., Korte, J.J., Kahl, M.D., Pasha, M.S., Ankley, G.T., 2001. Aspects of basic reproductive biology and endocrinology in the fathead minnow (Pimephales promelas). Comp. Biochem. Physiol. C 128, 127-141.] investigated aspects of the normal reproductive biology of the fathead minnow (FHM, P. promelas), and subsequent studies have generated a large amount of additional reproductive data for endpoints such as plasma steroid hormone and vitellogenin concentrations, spawn interval, and secondary sex characteristics (i.e., nuptial tubercle score and fat pad weight). These data were analyzed and fitted with statistical distributions to improve understanding of the variability in normal, unexposed, adult male (n=154) and female (n=186) FHM. Summary statistics for most endpoints were consistent with results from other more limited studies of FHMs. Male fat pad weight, and in both sexes gonad and liver weights were found to be proportional to body weight. Multiple statistical distributions were found to characterize each endpoint with the exception of spawn interval. Based on one of the largest datasets ever compiled for controlled studies, results presented herein provide a robust point of reference for the quantitative assessment of reproductive processes in the fathead minnow.

Role of inhibin and activin in the modulation of gonadotropin- and steroid-induced oocyte maturation in the teleost Fundulus heteroclitus

BACKGROUND

Activin and inhibin are glycoproteins structurally related to the transforming growth factor-beta superfamily. These peptides were first described as factors that regulate the follicle-stimulating hormone (FSH) at the pituitary level. The possible role of inhibin and activin, at the ovarian level, in mediating the stimulatory actions of a Fundulus pituitary extract (FPE) and 17alpha,20beta-dihydroprogesterone (DHP) on oocyte maturation was investigated in this study.

METHODS

In vitro culture of ovarian follicles and induction of oocyte maturation were carried out in 75% Leibovitz L-15 medium. Follicles or denuded oocytes were exposed to FPE, inhibin, activin, ethanol vehicle (control group), or DHP. The competence of the follicles or denuded oocytes to respond to the hormones was assessed by scoring germinal vesicle breakdown (GVBD) used as an indication of the reinitiation of meiosis or oocyte maturation. DHP level was measured by radioimmunoassay.

RESULTS

Addition of FPE promoted the synthesis of DHP by the granulose cells of fully grown ovarian follicles and thus stimulated GVBD in the oocyte. Presence of porcine inhibin did not hinder the synthesis of DHP stimulated by FPE, although it did inhibit the subsequent GVBD in a dose-dependent manner, suggesting that the action of inhibin was at the oocyte level. Similarly to the findings with FPE, inhibin also blocked the DHP-induced GVBD in intact follicles, as well as the spontaneous and steroid-induced GVBD of denuded oocyte. Inhibin straightforwardly blocked the response to a low dose of DHP throughout the culture period, while higher doses of the steroid appeared to overcome the inhibitory effect especially at later times. In contrast to inhibin, recombinant human activin A significantly enhanced DHP-induced GVBD in a dose-dependent manner after 48 hr, although activin alone was not able to induce GVBD without the presence of the steroid.

CONCLUSION

Taking together with our previous studies that demonstrate the presence of activin/inhibin subunits in the ovary of F. heteroclitus, these in vitro findings indicate that inhibin and activin are local regulators in the teleost ovary and have opposing effects in modulating oocyte maturation.

Phylogenetic relationships and gene expression pattern of three different cathepsin L (Ctsl) isoforms in zebrafish: Ctsla is the putative yolk processing enzyme

Certain cysteine proteases, such as cathepsin L (Ctsl), have been involved in yolk processing mechanisms in oocytes and embryos of lower vertebrates. In zebrafish (Danio rerio), three different ctsl genes, ctsla, ctslb and ctslc, have been found in the genome, but their pattern of expression, as well as information on which the encoded enzymes are potentially involved in yolk absorption during embryogenesis, is unknown. Here, phylogenetic and gene structure analysis revealed that zebrafish ctsla and ctslb genes are similar, showing a highly conserved structure in comparison with human ctsl, while ctslc presents different exon organization together with an earlier evolution. Thus, ctslc appears to be evolved from a common ancestral ctsl-like gene, possibly through an early duplication event, whereas ctsla and ctslb may be originated from a second duplication mechanism. Zebrafish ctsla, ctslb and ctslc also showed different patterns of mRNA expression during embryogenesis and in adult tissues. While Ctsla transcripts were accumulated in embryos throughout development and in the adult ovary, those encoding Ctslb were detected only in embryos around the time of hatching as previously reported, and those for Ctslc appeared only in larvae and in some adult tissues, but not in the ovary. In zebrafish and killifish (Fundulus heteroclitus) embryos, Ctsla mRNA was first detected in blastomers, and later in development it was localized in cells of the yolk syncytial layer, an embryonic structure involved in yolk absorption. These data therefore suggested that Ctsla is most likely the putative protease involved in yolk processing in fish embryos, while Ctslc seems not to be required during early embryogenesis in zebrafish.

Ovarian cysteine proteinases in the teleost Fundulus heteroclitus: molecular cloning and gene expression during vitellogenesis and oocyte maturation

The cysteine proteinases cathepsins B and L are members of the multigene family of lysosomal proteases that have been implicated in the processing of yolk proteins (YPs) in teleost oocytes. However, the full identification of the type of cathepsins expressed in fish ovarian follicles and embryos, as well as their regulatory mechanisms and specific function(s), are not yet elucidated. In this study, cDNAs encoding cathepsins B, L, F, K, S, Z, C, and H have been isolated from the teleost Fundulus heteroclitus, and the analysis of their deduced amino acid sequences revealed highly similar structural features to vertebrate orthologs, and confirmed in this species the existence of cathepsin L-like, cathepsin B-like, and cathepsin F-like subfamilies of cysteine proteinases. While all identified cathepsins were expressed in ovarian follicles, the corresponding mRNAs showed different temporal expression patterns. Thus, similar mRNA levels of cathepsins L, F, S, B, C, and Z were found throughout the oocyte growth or vitellogenesis period, whereas those for cathepsin H and K appeared to decrease as vitellogenesis advanced. During oocyte maturation, a transient accumulation of cathepsins L, S, H, and F mRNAs, approximately a 3-, 1.5-, 1.6-, and 6-fold increase, respectively, was detected in ovarian follicles within the 20-25 hr after hormone stimulation, coincident with the maximum proteolysis of the oocyte major YPs. The specific temporal pattern of expression of these genes may indicate a potential role of cathepsin L-like and cathepsin F proteases in the YP processing events occurring during fish oocyte maturation and/or early embryogenesis.

Multihormonal control of vitellogenesis in lower vertebrates

The comparative approach on how and when vitellogenesis occurs in the diverse reproductive strategies displayed by aquatic and terrestrial lower vertebrates is presented in this chapter; moreover, attention has been paid to the multihormonal control of hepatic vitellogenin synthesis as it is related to seasonal changes and to vitellogenin use by growing oocytes. The hormonal mechanisms regulating vitellogenin synthesis are also considered, and the effects of environmental estrogens on the feminization process in wildlife and humans have been reported. It is then considered how fundamental nonmammalian models appear to be, for vitellogenesis research, addressed to clarifying the yolkless egg and the evolution of eutherian viviparity.

Vitellogenin precursors in the liver of the oviparous lizard, Podarcis sicula

In reptiles, as in the other oviparous vertebrates, vitellogenin (VTG) synthesis is stimulated in the liver by ovarian estrogens. In this article, the presence of VTG precursors was detected in liver subcellular fractions of the oviparous lizard, Podarcis sicula, in the reproductive period. The rough endoplasmic reticulum (RER) and the smooth microsomal fraction (SMF), which includes smooth endoplasmic reticulum and Golgi complex, were separated by means of two different sucrose gradients. The successful separation was controlled at the electron microscope. The contents of the different compartments were extracted by means of n-octyl-beta-D-glucopiranoside detergent and subjected to SDS-PAGE. Western Blotting with homologous anti/VTG antibody revealed two immunoreactive proteins of about 84 and 70 kDa in the RER, and four proteins of about 180, 150, 60, 50 kDa in the SMF; all these proteins appeared phosphorylated and glycosylated. The differences in the molecular weight of these VTG precursors are discussed.

Gonadotropin and activin enhance maturational competence of oocytes in the zebrafish (Danio rerio)

In most teleosts, 17alpha,20beta-dihydroxy-4-pregnen-3-one (DHP) serves as the most potent maturation-inducing steroid (MIS) to initiate final oocyte maturation. The maturational competence or the responsiveness of oocytes to DHP increases when the ovarian follicles approach the final stage of growth. In the zebrafish, we demonstrated in the present study that full-grown oocytes (approximately 0.7 mm) exhibited the highest maturational competence, which diminished progressively with decreasing size of the follicles. Using midvitellogenic follicles (0.49-0.56 mm), which had little response to DHP, as the material, the present study aimed at investigating the endocrine and paracrine mechanisms that regulate maturational competence of the oocytes. In agreement with the results of studies in other teleost fish, pretreatment of follicles with gonadotropin (hCG) significantly enhanced the responsiveness of midvitellogenic oocytes to DHP in a clear time- and dose-dependent manner. Interestingly, activin, an ovarian growth factor, also had a potent stimulatory effect on the acquisition of oocyte maturational competence. Pretreatment with either recombinant human activin A or goldfish activin B significantly increased the rate of DHP-induced oocyte maturation from approximately 3% to approximately 70%, also in a clear dose-dependent manner. Similar to the results with hCG, pretreatment with activin alone had no effect in inducing maturation of midvitellogenic oocytes without subsequent DHP treatment, although both exhibited a strong effect in promoting maturation of full-grown oocytes. The effect of activin on maturational competence of oocytes could be reduced by cotreatment with follistatin, a potent activin-binding protein. Interestingly, follistatin treatment also significantly reduced the effect of hCG on maturational competence of oocytes, suggesting a mediating role for endogenous activin or activin-related molecules in the action of gonadotropin. The effects of hCG and activin on maturational competence of oocytes could be significantly inhibited by actinomycin D (1 microg/ml) and completely blocked by cycloheximide (1 microg/ml), suggesting that the hCG and activin-induced acquisition of oocyte maturational competence involves de novo protein synthesis at both the transcriptional and translational levels.

Preparation and use of specific antibodies to the beta-I and beta-II subunits of gonadotropic hormone from Fundulus heteroclitus pituitary

Fundulus heteroclitus naturally spawns with a semilunar periodicity throughout most of the year in its southernmost habitat, an activity that can be maintained in the laboratory. The alpha and two beta subunits comprising F. heteroclitus gonadotropic hormones (GtHs) I and II have been sequenced, and antibodies have been raised against unique peptides found in each of the two beta subunits. On immunoblots of pituitary proteins, each antibody recognizes a single band with a molecular mass of 16-17 kDa, somewhat larger than the deduced sizes (11-13 kDa) of the unglycosylated subunits. Each antibody also recognizes a different subset of pituitary cells in the central (GtH I) and peripheral (GtH II) proximal pars distalis, regions that display the typical tinctorial properties of gonadotrops. The distribution and distinct separation of cells containing GtH beta subunits I and II thus differ from those found for previously described teleost species, most of which are salmonids that engage in a single spawning episode during the year. The availability of these antibodies thus makes F. heteroclitus an inexpensive, easily manipulated model system for studies on the hormonal regulation of fractional spawning common to a large class of commercially important species other than salmonids.

Aspects of basic reproductive biology and endocrinology in the fathead minnow (Pimephales promelas)

The fathead minnow (Pimephales promelas) has been proposed as a model species for assessing the adverse effects of endocrine-disrupting chemicals (EDCs) on reproduction and development. The purpose of these studies was to develop baseline reproductive biology and endocrinology data for this species to support interpretation of tests with potential EDCs. Pairs of reproductively-active fathead minnows (n=70) were evaluated with respect to reproductive cyclicity in terms of spawning interval and fecundity. The mode and mean (+/-SE) spawning intervals for the fish in this study were 3.0 and 3.7+/-0.1 days, respectively. The mean number of eggs produced per spawn was 85+/-2.8. Animals were sacrificed at periodic intervals during the established spawning cycle and measurements made of gonadal condition (gonadosomatic index [GSI], histopathology) and plasma concentrations of vitellogenin and sex steroids (beta-estradiol, testosterone, 11-ketotestosterone). The GSI in females varied significantly as a function of spawning interval, with the largest values occurring day 2 post-spawn, just prior to the interval of maximum spawning activity. Plasma beta-estradiol concentrations in females also varied significantly relative to peak values in the GSI and spawning activity. Vitellogenin concentrations in the female, and male GSI and steroid concentrations did not vary significantly relative to position in the spawning cycle. Concentrations of beta-estradiol in females and 11-ketotestosterone in males were positively correlated with testosterone concentrations.

Sex steroids relative to alternative mating behaviors in the simultaneous hermaphrodite Serranus subligarius (Perciformes: Serranidae)

This study is the first investigation of reproductive endocrinology in a simultaneously hermaphroditic teleost, the belted sandfish (Serranus subligarius). We address two questions: (1) Do steroid hormone levels vary during the spawning season or during the daily spawning cycle of sandfish? (2) Do hormone levels vary relative to an individual's phenotype-size, frequency of spawning and aggressive behaviors, and proportion of testis in the gonad? We analyzed circulating estradiol-17beta (E2), testosterone (T), 11-ketotestosterone (11KT), 17alpha,20beta,21-trihydroxy-4-pregnen-3-one (20betaS), and 17alpha,20beta-dihydroxy-4-pregnen-3-one (DHP) concentrations in a field population. Only E2 levels were significantly higher at the new and full moon, suggesting peak periods of vitellogenesis at these times. Naturally spawning sandfish were sampled every 2 h during the photophase of a 25-h period (12 pm to 1 pm the following day) and gonadosomatic index, degree of oocyte hydration and ovulation, and plasma levels of E2, T, DHP, and 20betaS were analyzed. E2 and T levels did not vary during photophase, suggesting continuous recruitment of oocytes into vitellogenesis. The 20betaS levels peaked around the time of final oocyte maturation. Since frequency of spawning behaviors changes with body size, we captured individuals of various sizes throughout the spawning season and analyzed circulating levels of hormones. 11KT and 20betaS levels increased significantly with body size. In 1992, we quantified frequency of spawning and aggressive behaviors, circulating T and 11KT levels and testicular mass relative to ovotestis mass in focal animals. 11KT levels tended to be positively correlated with frequency of courting male behavior, but were unrelated to the frequency of aggressive behavior or testis mass. Because hormone levels increased with size and frequency of each spawning behavior changes with size, we propose that sex steroids influence growth-related changes in spawning tactics of individuals.

Oocyte sensitivity to serotonergic regulation during the follicular cycle of the teleost Fundulus heteroclitus

In the teleost Fundulus heteroclitus, serotonin (5-HT) reversibly inhibits oocyte maturation induced in vitro by the maturation-inducing steroid (MIS) 17,20beta-dihydroxy-4-pregnen-3-one (17,20betaP). The 5-HT inhibition of 17,20betaP-induced meiotic maturation was examined in ovarian follicles at different developmental stages or isolated at different times during the follicular cycle. Steroid treatment of late vitellogenic and early maturing follicles (1.2- to 1.7-mm diameter) promoted oocyte maturation in a size-dependent manner, and this maturation was inhibited by 5-HT in follicles of < 1.6- to 1.7-mm diameter. Thus, the 5-HT inhibition progressively decreased as follicles developed the ability to mature in the absence of 17,20betaP. The effectiveness of 5-HT to increase follicular cAMP remained similar within the same developmental stages, indicating that the reduction of 5-HT inhibitory action was not related to the competence of 5-HT to activate inhibitory signals in the oocyte. During the follicular cycle, fully grown follicles (1.3- to 1.4-mm diameter) showed a decreased maturational competence in response to gonadotropin or MIS stimulation after the follicular recruitment into maturation and spawning occurred, which coincided with an increase of the effectiveness of 5-HT at inhibiting 17,20betaP-induced maturation. In further experiments, preincubation of follicles with hCG was found to reduce 5-HT inhibitory action, but when follicles were incubated with either hCG in the presence of a steroidogenesis inhibitor or estradiol-17beta (E2), the 5-HT inhibition was unaffected. These findings suggest that 5-HT inhibition of the MIS-induced meiotic maturation is not under direct gonadotropin or E2 regulation but that it might be regulated in vivo by changes in the competence of the oocytes to undergo oocyte maturation after MIS stimulation.