The use of reference gene selection programs to study the silvering transformation in a freshwater eel Anguilla australis: a cautionary tale

The induction of oocyte maturation and ovulation in the European eel (Anguilla anguilla): in vitro and in vivo comparison of progesterone with 17α,20β-dihydroxy-4-pregnen-3-one

Ovulation in European eel is induced by injection of 17α,20β-dihydroxy-4-pregnen-3-one (DHP) as the maturation-inducing hormone (MIH). Female eels need to ovulate within 18 h after injection to release good quality eggs. Progesterone (P), as an upstream precursor of DHP, may promote endogenous DHP production and improve egg quality. The purpose of this study was therefore to compare treatment of P with DHP on batch level, in vitro, to determine dose-response effects, and in vivo, at a single dose. For the in vitro experiment, ovarian tissue was extracted and placed in culture plates containing hormone-free medium and media supplemented with the treatment: DHP at 1, 10 and 100 ng mL-1, or P at 10, 100 and 1,000 ng mL-1. At the start of incubation, the folliculated oocytes were sampled for histology, microscopy and qPCR. After incubation for 12 and 18 h, the oocytes were sampled for microscopy and qPCR analysis. For the in vivo experiment, females were either injected with DHP or P at a dose of 2 mg kg-1 to assess their effects on ovulation and reproductive success. At the moment of release, eggs were sampled for RNA sequencing to compare effects of DHP and P on the expression of genes involved in egg quality aspects. Remaining eggs were fertilized and larval viability was recorded. Both DHP and P were able to induce GVBD (DHP at 10 and 100 ng mL-1, P at 100 and 1,000 ng mL-1) in vitro. Expression of genes involved in oocyte maturation and ovulation was similar in vitro for both DHP and P treatments. Regarding the in vivo results, RNAseq results reflected similar DHP and P effects on the expression of genes involved in egg quality aspects. Females injected with either DHP or P ovulated, released eggs, and were equally able to produce larvae without any differences in reproductive success. Our results support the conclusion that DHP and P work equally well in vitro and in vivo. P is more attractive to apply as the price is 3,000 times lower than the price of DHP.

Lipoprotein receptors in ovary of eel, Anguilla australis: molecular characterisation of putative vitellogenin receptors

Lipoprotein receptors, including low-density lipoprotein receptor (LDLr) relatives (Lrs) and LDLr-related proteins (Lrps), belong to the LDLr supergene family and participate in diverse physiological functions. In this study, novel sequences of lr and lrp genes expressed in the ovary of the short-finned eel, Anguilla australis, during early gonadal development are presented. The genes encoding the LDLr-like, Lrp1-like, Lrp1b-like, Lrp3, Lrp4-like, Lrp5-like, Lrp6, Lrp10, Lrp11, Lrp12-like, and Lr11-like proteins were found and identified by sequence and structure analysis, in addition to phylogenetic analysis. Genes encoding proteins previously implicated in follicle development and vitellogenin (Vtg) uptake in oviparous vertebrates were also identified, i.e. lr8 (including lr8 + and lr8- variants) and lrp13; their identification was reinforced by conserved synteny with orthologues in other teleost fish. Compared to other lr/lrp genes, the genes encoding Lr8 + , Lr8-, and Lrp13 were highly expressed in ovary during early development, decreasing as oocyte development advanced when induced by hypophysation. Furthermore, lr8 + , lr8-, and lrp13 were dominantly expressed in the ovary when compared with 17 other tissues. Finally, this study successfully detected the expression of both lr8 variants, which showed different expression patterns to those reported in other oviparous vertebrates and provided the first characterisation of Lrp13 in Anguilla sp. We propose that lr8 + , lr8-, and lrp13 encode putative Vtg receptors in anguillid eels.

Evaluation of housekeeping genes as references for quantitative real-time PCR analysis of European eel, Anguilla anguilla

Eels are important aquaculture species for which an increasing number of reference genes are being identified and applied. In this study, five housekeeping genes [RPL7 (ribosomal protein L7), 18 S (18 S ribosomal RNA), EF1A (elongation factor 1α), ACTB (β-actin) and GAPDH (glyceraldehyde-3-phosphate dehydrogenase)] were chosen to evaluate their reliability as reference genes for quantitative real-time PCR (qPCR) for the study of Anguilla anguilla. The expression of the selected genes in different eel tissues was determined using qPCR at different growth stages or upon challenge by Anguillid herpesvirus (AngHV), and the expression levels of these genes were then compared and evaluated using the geNorm and NormFinder algorithms. Then, RefFinder was used to comprehensively rank the examined housekeeping genes. Interestingly, the expression of the evaluated housekeeping genes exhibited tissue-dependent and treatment-dependent variations. In different growth periods A. anguilla tissues, the most stable genes were the following: ACTB in mucus; 18 S in skin and kidney; RPL7 in muscle, gill, intestine and brain; EF1A in heart and liver; and GAPDH in spleen. In contrast, in AngHV-challenged A. anguilla tissues, the most stable genes were the following: 18 S in mucus; RPL7 in skin, gill, heart, spleen, kidney and intestine; EF1A in muscle and liver; and ACTB in brain. Further comparison analysis indicated that the expression of RPL7 and EF1A was stable in multiple A. anguilla tissues in different growth periods and in eels challenged by AngHV. Nonetheless, the expression level of GAPDH in eel tissues was lower, and it was unstable in several tissues. These results indicated that the selection of reference genes for qPCR analysis in A. anguilla should be made in accordance with experimental parameters, and both RPL7 and EF1A could be used as reference genes for qPCR study of A. anguilla at different growth stages or upon challenge by AngHV. The reference genes identified in this study could improve the accuracy of qPCR data and facilitate further studies aimed at understanding the biology of eels.

Steroid implants for the induction of vitellogenesis in feminized European silver eels (Anguilla anguilla L.)

Assisted propagation of the European eel will lead to a closed production cycle supplying the aquaculture industry with juvenile glass eels. Females require long-term weekly treatment with pituitary extract (PE), which is stressful and causes abnormalities in oogenesis. We tested the effects of 17α-methyltestosterone (17 MT), as potent androgen activating the androgen receptor, and 17β-estradiol (E2), as an inducer of vitellogenesis, to shorten the duration of PE treatment.Four groups of feminized eels were subjected to a simulated migration and subsequent injection with implants containing 17 MT (17 MT-group), E2 (E2-group) or 17 MT plus E2 (17 MT + E2-group) to test for synergistic effects, or without any steroids as controls (C-group). The effects of a 2-months treatment were investigated by determining the eye index (EI), hepatosomatic and gonadosomatic index (HSI and GSI, respectively), plasma steroid concentrations by liquid chromatography mass spectrometry (LCMS), gonadal histology, expression of androgen receptors a and b (ara, arb); estrogen receptor 1 (esr1); FSH receptor (fshr); vitellogenin receptor (vtgr) and aromatase (cyp19), and the required number of weekly PE injections to fully mature. For many parameters, both the 17 MT and E2 groups showed an increase vs. controls, with the 17 MT + E2 group showing a synergistic effect, as seen for EI, GSI (3.4 for 17 MT and for E2, 6.6 for 17 MT + E2), oocyte diameter and ara, arb and esr1 expression. Concentrations of almost all focal steroids decreased with simulated migration and steroid treatment. Only eels of the 17 MT-group showed increased expression of cyp19 and of fshr, while fshr expression increased 44-fold in the 17 MT + E2 group, highlighting that co-implantation is most effective in raising fshr mRNA levels. Specific for eels of the E2 groups were vitellogenesis-associated changes such as an increase of HSI, plasma E2, and presence of yolk in the oocytes. Steroid treatments reduced the duration of PE treatment, again synergistically for co-implantation. In conclusion, E2 is necessary to start vitellogenesis, but 17 MT has specific effects on cyp19 and fshr expression. The combination is necessary for synergistic effects and as such, steroid implants could be applied in assisted reproduction protocols for European eel to improve oocyte quality leading to the production of more vital larvae.

Expression Profiles of Estrogen-Regulated MicroRNAs in Cancer Cells

MicroRNAs play critical roles through their impact on posttranscriptional gene regulation. In cancer, they can act as oncogenes or tumor suppressors and can also function as biomarkers. Here, we describe a method for robust characterization of estrogen-regulated microRNA profiles. The activity of estrogen is mediated by two nuclear receptors, estrogen receptor alpha and estrogen receptor beta, and a transmembrane G-protein coupled estrogen receptor 1. This chapter details how to prepare cells for optimal estrogen response, directions for estrogen treatment, RNA extraction, different microRNA profiling approaches, and subsequent confirmations.

Current Practices for Reference Gene Selection in RT-qPCR of Aspergillus: Outlook and Recommendations for the Future

Aspergillus is a genus of filamentous fungi with vast geographic and ecological distributions. Species within this genus are clinically, agriculturally and biotechnologically relevant, leading to increasing interest in elucidating gene expression dynamics of key metabolic and physiological processes. Reverse-transcription quantitative Polymerase Chain Reaction (RT-qPCR) is a sensitive and specific method of quantifying gene expression. A crucial step for comparing RT-qPCR results between strains and experimental conditions is normalisation to experimentally validated reference gene(s). In this review, we provide a critical analysis of current reference gene selection and validation practices for RT-qPCR gene expression analyses of Aspergillus. Of 90 primary research articles obtained through our PubMed query, 17 experimentally validated the reference gene(s) used. Twenty reference genes were used across the 90 studies, with beta-tubulin being the most used reference gene, followed by actin, 18S rRNA and glyceraldehyde 3-phosphate dehydrogenase. Sixteen of the 90 studies used multiple reference genes for normalisation. Failing to experimentally validate the stability of reference genes can lead to conflicting results, as was the case for four studies. Overall, our review highlights the need to experimentally validate reference genes in RT-qPCR studies of Aspergillus.

What Goes Wrong during Early Development of Artificially Reproduced European Eel Anguilla anguilla? Clues from the Larval Transcriptome and Gene Expression Patterns

Simple Summary

Closing the life cycle of the European eel in captivity is urgently needed to gain perspective for the commercial production of juvenile glass eels. Larvae are produced weekly at our facilities, but large variations in larval mortality are observed during the first week after hatching. Although much effort has been devoted to investigating ways to prevent early larval mortality, it remains unclear what the causes are. The aim of this study was to perform a transcriptomic study on European eel larvae in order to identify genes and physiological pathways that are differentially regulated in the comparison of larvae from batches that did not survive for longer than three days vs. larvae from batches that survived for at least a week up to 22 days after hatching (non-viable vs. viable larvae). In contrast to earlier published studies on European eel, we conclude that larvae exhibit immune competency. Non-viable larvae initiated an inflammatory and host protection immune response and tried to maintain osmoregulatory homeostasis. As a perspective, microbial control and salinity reduction might benefit eel larvae in terms of lower mortality and improved development by lowering the costs of immune functioning and osmoregulation.

Abstract

In eels, large variations in larval mortality exist, which would impede the viable production of juvenile glass eels in captivity. The transcriptome of European eel larvae was investigated to identify physiological pathways and genes that show differential regulation between non-viable vs. viable larvae. Expression of genes involved in inflammation and host protection was higher, suggesting that non-viable larvae suffered from microbial infection. Expression of genes involved in osmoregulation was also higher, implying that non-viable larvae tried to maintain homeostasis by strong osmoregulatory adaptation. Expression of genes involved in myogenesis, neural, and sensory development was reduced in the non-viable larvae. Expression of the major histocompatibility complex class-I (mhc1) gene, M-protein (myom2), the dopamine 2B receptor (d2br), the melatonin receptor (mtr1), and heat-shock protein beta-1 (hspb1) showed strong differential regulation and was therefore studied in 1, 8, and 15 days post-hatch (dph) larvae by RT-PCR to comprehend the roles of these genes during ontogeny. Expression patterning of these genes indicated the start of active swimming (8 dph) and feed searching behavior (15 dph) and confirmed immunocompetence immediately after hatching. This study revealed useful insights for improving larval survival by microbial control and salinity reduction.

Reference gene selection for transcriptional profiling in Cryptocercus punctulatus, an evolutionary link between Isoptera and Blattodea

The subsocial life style and wood-feeding capability of Cryptocercus gives us an evolutionary key to unlock some outstanding questions in biology. With the advent of the Genomics Era, there is an unprecedented opportunity to address the evolution of eusociality and the acquisition of lignocellulases at the genetic level. However, to quantify gene expression, an appropriate normalization strategy is warranted to control for the non-specific variations among samples across different experimental conditions. To search for the internal references, 10 housekeeping genes from a gut transcriptome of a wood-feeding cockroach, Cryptocercus punctulatus, were selected as the candidates for the RT-qPCR analysis. The expression profiles of these candidates, including ACT, EF1α, GAPDH, HSP60, HSP70, αTUB, UBC, RPS18, ATPase and GST, were analyzed using a panel of analytical tools, including geNorm, NormFinder, BestKeeper, and comparative ΔC_T method. RefFinder, a comprehensive ranking system integrating all four above-mentioned algorithms, rated ACT as the most stable reference gene for different developmental stages and tissues. Expression analysis of the target genes, Hex-1 and Cell-1, using the most or the least appropriate reference genes and a single or multiple normalizers signified this research. Our finding is the first step toward establishing a standardized RT-qPCR analysis in Cryptocercus.

Spatiotemporal expression of activin receptor-like kinase-5 and bone morphogenetic protein receptor type II in the ovary of shortfinned eel, Anguilla australis

In the eel ovary, the expression of growth differentiation factor-9 (Gdf9) appears to be largely confined to the germ cell in early stages of oogenesis. However, both the target tissue and the function of Gdf9 in fish remain unknown. This study aimed to describe the abundance and localization of activin receptor-like kinase-5 (Alk5) and bone morphogenetic protein receptor type II (Bmpr2), which together mediate the Gdf9 signal, in the ovary of a basal teleost, the shortfinned eel, Anguilla australis, during early folliculogenesis. The cDNA encoding eel alk5 and bmpr2 genes were cloned, characterized and the transcript abundances of these receptors quantified by quantitative real-time PCR. Ovarian transcript abundance for both receptors, along with that of gdf9 and of its paralogue bmp15, increased from the previtellogenic to early vitellogenic stage. Localization of receptor mRNAs by in situ hybridization revealed that these receptors are located in the somatic cells surrounding the oocyte. Furthermore, tissue distribution analysis showed that the expression of alk5 and bmpr2 were highest in ovary and thyroid, respectively. Unexpectedly, however, bmpr2 mRNA levels were lower in the ovary than in any of the other 17 tissues examined, and indeed, lower than ovarian gdf9 transcript abundance. These findings, together with the ovarian expression pattern of Gdf9, suggest that Gdf9, and conceivably, Bmp15, from the oocyte can signal through receptors that are located on the somatic cells surrounding the oocyte; this, in turn, facilitates elucidation of the function of these growth factors during oogenesis in teleost fish.

Synergistic effects of estradiol and 11-ketotestosterone on vitellogenin physiology in the shortfinned eel (Anguilla australis)

Estradiol-17β (E2) and 11-ketotestosterone (11KT) have been implicated in vitellogenesis and in regulating expression of the follicle-stimulating hormone receptor (fshr), respectively. To override the captivity-induced reproductive block in shortfinned eel, Anguilla australis, we hypothesized that in combination, 11KT and E2 would stimulate ovarian uptake of vitellogenin (Vtg). Early pubertal eels received hormone implants containing varying concentrations of E2 (0, 0.2, 2, 5 mg) with or without 11KT (1 mg). Vtg levels were determined in plasma, liver, and ovarian tissues by histological examination, qPCR, immunoblotting, or single radial immunodiffusion. The expression of gonadotropin-beta subunits and gonadotropin receptors in the pituitary and ovary, respectively, were analyzed to determine mechanisms by which steroid effects may be exerted. When administered alone, E2 increased hepatic production and plasma levels of Vtg. In contrast, 11KT decreased plasma levels of Vtg, seemingly reducing its production. Neither 11KT nor E2 could induce uptake of Vtg into oocytes, although E2 treatment appeared necessary for uptake to occur. This was the case despite 11KT dramatically increasing both oocyte size and fshr mRNA levels. Astonishingly, the uptake of Vtg was successfully induced by co-treatment with 11KT and E2, suggesting that 11KT might facilitate the incorporation of Vtg into the developing oocyte. These results highlight the potential of sex steroid co-treatment, an approach aimed at mimicking oogenesis in wild eels, to induce vitellogenesis, specifically ovarian yolk deposition, even in the absence of exogenous gonadotropin treatment.

Induction of oocyte development in previtellogenic eel, Anguilla australis

The role of gonadotropins during early ovarian development in fish remains little understood. Concentrations of gonadotropins were therefore experimentally elevated in vivo by administration of recombinant follicle-stimulating hormone (rec-Fsh) or human chorionic gonadotropin (hCG) and the effects on ovarian morphology, sex steroid levels and mRNA levels of genes expressed in pituitary and ovary examined. Hormones were injected thrice at weekly intervals in different doses (20, 100 or 500 µg/kg BW for rec-Fsh and 20, 100 or 500 IU/kg BW for hCG). All treatments, especially at the highest doses of either rec-Fsh or hCG, induced ovarian development, reflected in increased oocyte size and lipid uptake. Both gonadotropins up-regulated follicle-stimulating hormone receptor (fshr) mRNA levels and plasma levels of estradiol-17β (E2). Exogenous gonadotropins largely decreased the expression of follicle-stimulating hormone β-subunit (fshb) and had little effect on those of luteinizing hormone β-subunit (lhb) in the pituitary. It is proposed that the effects of hCG on ovarian development in previtellogenic eels could be indirect as a significant increase in plasma levels of 11-ketotestosterone (11-KT) was found in eels treated with hCG. Using rec-Fsh and hCG has potential for inducing puberty in eels in captivity, and indeed, in teleost fish at large.

Expressional regulation of gonadotropin receptor genes and androgen receptor genes in the eel testis

Receptors for follicle-stimulating hormone (Fshr), luteinizing hormone (Lhcgr1 and Lhcgr2) and androgens (Ara and Arb) transduce the hormonal signals that coordinate spermatogenesis, but the factors that regulate the abundance of these transducers in fish testes remain little-understood. To mend this paucity of information, we first determined changes in transcript abundance for these receptors (fshr, lhcgr1, ara and arb) during spermatogenesis induced by human chorionic gonadotropin (hCG) injection in the eel, Anguilla australis. We related our findings to testicular production of the fish androgen, 11-ketotestosterone (11-KT), and to the levels of the transcripts encoding steroidogenic acute regulatory protein (star) and 11β-hydroxylase (cyp11b), and subsequently evaluated the effects of hCG or 11-KT on mRNA levels of these target genes in vitro. Testicular 11-KT production was greatly increased by hCG treatment, both in vivo and in vitro, and associated with up-regulation of star and cyp11b transcripts. In situ hybridization indicated that testicular fshr mRNA levels were higher in the early stages of hCG-induced spermatogenesis, while lhcgr1 transcripts were most abundant later, once spermatids were observed. In vitro experiments further showed that hCG and its steroidal mediator 11-KT significantly increased fshr transcript abundance. These data provide new angles on the interactions between gonadotropin and androgen signaling during early spermatogenesis. Increases in levels of 11-KT following hCG injection elevated testicular fshr mRNA levels augmenting Fsh sensitivity in the testis. This evidence is suggestive of a positive feedback loop between gonadotropins and 11-KT that may be key to regulating early spermatogenesis in fish.

A mechanistic model for studying the initiation of anguillid vitellogenesis by comparing the European eel (Anguilla anguilla) and the shortfinned eel (A. australis)

An inverse relation exists between the maturation stage at the start of the oceanic reproductive migration and the migration distance to the spawning grounds for the various eel species. The European eel Anguilla anguilla migrates up to 5-6000 km and leaves in a previtellogenic state. The shortfinned eel A. australis migrates 2-4000 km and leaves in an early vitellogenic state. In this study, we compared the early pubertal events in European silver eels with those in silver shortfinned eels to gain insights into the initiation of vitellogenesis. Immediately after being caught, yellow and silver eels of both species were measured and sampled for blood and tissues. Eye index (EI), gonadosomatic index (GSI) and hepatosomatic index (HSI) were calculated. Plasma 11-ketotestosterone (11-KT) and 17β-estradiol (E2) levels were measured by radioimmunoassay. Pituitary, liver and ovaries were dissected for quantitative real-time PCR analyses (pituitary dopamine 2b receptor d2br, gonadotropin-releasing hormone receptors 1 and 2 gnrhr1 and gnrhr2, growth hormone gh and follicle-stimulating hormone-β fshb; liver estrogen receptor 1 esr1; gonad follicle-stimulating hormone receptor fshr, androgen receptors α and β ara and arb, vitellogenin receptor vtgr and P450 aromatase cyp19). Silver eels of both species showed a drop in pituitary gh expression, progressing gonadal development (GSI of ∼1.5 in European eels and ∼3.0 in shortfinned eels) and steroid level increases. In shortfinned eels, but not European eels, expression of fshb, gnrhr1 and gnrhr2, and d2br in the pituitary was up-regulated in the silver-stage as compared to yellow-stage females, as was expression of fshr, ara and arb in the ovaries. Expression of esr1 in European eels remained low while esr1 expression was up-regulated over 100-fold in silver shortfinned eels. The mechanistic model for anguillid vitellogenesis that we present suggests a first step that involves a drop in Gh and a second step that involves Fsh increase when switching in the life history trade-off from growth to reproduction. The drop in Gh is associated with gonadal development and plasma steroid increase but precedes brain-pituitary-gonad axis (BPG) activation. The Fsh increase marks BPG activation and increased sensitivity of the liver to estrogenic stimulation, but also an increase in D2br-mediated dopaminergic signaling to the pituitary.

Expression of gonadotropin subunit and gonadotropin receptor genes in wild female New Zealand shortfinned eel (Anguilla australis) during yellow and silver stages

Despite tremendous importance of follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh) as primary controllers of reproductive development, information on the expression profiles of the genes encoding gonadotropin subunits and gonadotropin receptors (Fshr and Lhr) in wild eels are essentially non-existent. This study investigated pituitary fshb and lhb mRNA levels and ovarian fshr and lhr mRNA levels of wild shortfinned eels, Anguilla australis at different stages of oogenesis. Protein expression of Fsh in the pituitary was also quantified and visualized using slot blot and immunohistochemistry. Pituitary fshb and lhb mRNA levels showed a differential expression pattern, fshb mRNA levels increasing significantly from the perinucleolus (PN) to the oil droplet stage (OD) before slightly decreasing (not significantly) in the early vitellogenic stage (EV). A similar trend was observed in relative Fsh protein levels analyzed by slot blot and immunohistochemistry, but this trend was not reflected in the plasma levels of sex steroids. In contrast, pituitary lhb mRNA levels increased significantly from the PN to EV stage. A higher expression of Fsh at both mRNA and protein levels in the pituitary of eels at the OD stage compared to other investigated stages suggests that synthesis of Fsh production in the pituitary may reach a peak at the OD stage. In the ovary, transcript abundances of fshr and lhr gradually increased during previtellogenic follicle growth, but markedly and significantly increased thereafter. Taken together, our data suggest i) that Fsh release may be very limited, or absent, prior to onset of puberty in shortfinned eels and ii) that Lh is not functionally important in this fish during the EV stage.

Does silvering or 11-ketotestosterone affect osmoregulatory ability in the New Zealand short-finned eel (Anguilla australis)?

Silvering has been associated with advancing osmoregulatory ability. Given the demonstrated role of 11-ketotestosterone (11KT) in mediating many of the silvering-related changes, we investigated the role of 11KT in driving this advanced osmoregulatory ability in the New Zealand short-finned eel (Anguilla australis). Yellow (non-migratory) eels with or without 11KT implants and blank-implanted silver (migratory) eels, either held in freshwater or subjected to seawater challenge, were sampled to determine serum [Na⁺] and [Cl^-], pituitary prolactin mRNA levels, gill Na⁺/K⁺-ATPase activity and gill mRNA levels for Na⁺/K⁺-ATPase-α1 subunit and for Na⁺/K⁺/2Cl^- co-transporter-1α-subunit. Developmental stage and 11KT treatment advanced the eels' osmoregulatory ability. Thus, serum [Na⁺] and [Cl^-] were affected by developmental stage and 11KT treatment upon seawater challenge. However, seawater challenge, not 11KT treatment or developmental stage, produced the strongest and the most consistent effects on A. australis osmoregulatory processes, inducing significant effects in all the relevant parameters we measured. In light of our results and in view of the eel's marine ancestry, we contend that A. australis, or freshwater eels in general, are highly tolerant and able to adapt quickly to changing salinities even at the yellow stage, which may preclude a critical need for an advanced osmoregulatory ability at silvering.

The effects of migratory stage and 11-ketotestosterone on the expression of rod opsin genes in the shortfinned eel (Anguilla australis)

The androgen 11-ketotestosterone (11KT) can induce many of the changes associated with silvering, i.e., the transformation of a non-migrating 'yellow' eel into a migrating 'silver' eel. We posited that plasticity in spectral sensitivity of the eye, accompanied by expression of different opsins in the retina during silvering, is controlled by 11KT. To test this hypothesis, mRNA levels of freshwater (fwo) and seawater (swo) opsins and of the two androgen receptors (ara and arb) in retinas of wild-caught female shortfinned eels, Anguilla australis were compared. Swo expression was much higher (3-4 orders of magnitude) and fwo expression substantially lower in silver than in yellow eels, whereas mRNA levels of both ars did not differ between stages. Yellow eel retinas exposed to 11KT in vitro exhibited a robust dose-dependent increase in swo, but weak decreasing effects on fwo transcript abundance were inconsistent. Similarly, increased retinal swo expression was seen after in vivo treatment of yellow eels with 11KT implants, whereas expression of fwo remained unaffected. Lastly, co-treatment with 11KT and the androgen receptor blocker flutamide was undertaken to determine whether 11KT exerts its effects through nuclear androgen receptors. Flutamide did not block 11KT-affected expression of any target gene, neither in vivo nor in vitro. We conclude that 11KT greatly increases the abundance of swo, identifying the androgen as an important regulator of the opsin switch during silvering in freshwater eels.

Effects of GnRHa treatment during vitellogenesis on the reproductive physiology of thermally challenged female Atlantic salmon (Salmo salar)

Tasmanian Atlantic salmon (S. salar) broodstock can experience temperatures above 20 °C, which impairs reproductive development and inhibits ovulation. The present study investigated the prolonged use of gonadotropin releasing hormone analogue (GnRHa) during vitellogenesis as a means of maintaining endocrine function and promoting egg quality at elevated temperature in maiden and repeat spawning S. salar. GnRHa-treatment during vitellogenesis did not compensate for the negative effects of thermal challenge on the timing of ovulation, egg size, egg fertility or embryo survival in any fish maintained at 22 °C relative to 14 °C. The lack of effectiveness was reflected by the endocrine data, as plasma follicle stimulating hormone and luteinising hormone levels were not different between treated and untreated groups at 22 °C. Furthermore, plasma testosterone and E2 levels were unchanged in GnRHa-treated fish at 22 °C, and plasma levels were generally lower in both groups maintained at 22 °C relative to 14 °C. Transcription of vitellogenin, and zona pellucida B and C was not enhanced in GnRHa-treated fish relative to untreated fish at 22 °C, presumably due to observed suppression of plasma E2. These results indicate that thermal impairment of reproduction is likely to occur on multiple levels, and is difficult to overcome via hormonal manipulation.

Environmentally relevant concentrations of nitrate increase plasma testosterone concentrations in female American alligators (Alligator mississippiensis)

Anthropogenic nitrogen is a ubiquitous environmental contaminant that is contributing to the degradation of freshwater, estuarine, and coastal ecosystems worldwide. The effects of environmental nitrate, a principal form of nitrogen, on the health of aquatic life is of increasing concern. We exposed female American alligators to three concentrations of nitrate (0.7, 10 and 100mg/L NO₃-N) for a duration of five weeks and five months from hatch. We assessed growth, plasma sex steroid and thyroid hormone concentrations, and transcription levels of key genes involved in steroidogenesis (StAR, 3β-HSD, and P450_scc) and hepatic clearance (Cyp1a, Cyp3a). Exposure to 100mg/L NO₃-N for both five weeks and five months resulted in significantly increased plasma testosterone (T) concentrations compared with alligators in the reference treatment. No differences in 17β-estradiol, progesterone, or thyroid hormones were observed, nor were there differences in alligator weight or the mRNA abundance of steroidogenic or hepatic genes. Plasma and urinary nitrate concentrations increased with increasing nitrate treatment levels, although relative plasma concentrations of nitrate were significantly lower in five month, versus five week old animals, possibly due to improved kidney function in older animals. These results indicate that environmentally relevant concentrations of nitrate can increase circulating concentrations of T in young female alligators.

Expression Profiles of Estrogen-Regulated MicroRNAs in Breast Cancer Cells

Molecular signaling through both estrogen and microRNAs are critical for breast cancer development and growth. The activity of estrogen is mediated by transcription factors, the estrogen receptors. Here we describe a method for robust characterization of estrogen-regulated microRNA profiles. The method details how to prepare cells for optimal estrogen response, directions for estrogen treatment, RNA extraction, microRNA large-scale profiling, and subsequent confirmations.

A comparative study of vitellogenesis in Echinodermata: Lessons from the sea star

The provision of yolk precursor proteins to the oviparous egg is crucial for normal embryo development. In Echinodermata, a transferrin-like yolk component termed major yolk protein (MYP) is a major precursor protein in Echinoidea and Holothuroidea. In contrast, in Asteroidea a single vitellogenin (Vtg) was recently identified, but its role as primary yolk protein remains unclear. To resolve the apparent MYP-Vtg dichotomy in sea stars and to understand the dynamics of candidate yolk protein gene expression during the reproductive cycle, we investigated the molecular structures of sea star Vtg and MYP and quantified their transcript levels during oogenesis. By combining protein sequencing of the predominant proteins in ovulated eggs of Patiriella regularis with ovarian transcriptome sequencing and molecular cloning, we characterized two cDNAs encoding two bona fide Vtgs (PrVtg1 and PrVtg2) and a partial cDNA encoding MYP (PrMYP). PrMYP mRNA was found in low abundance in growing oocytes, possibly as maternal transcripts for translation after ovulation. In contrast, PrVtg transcripts, whose levels varied during the reproductive cycle, were not found in developing oocytes - rather, they were detected in ovarian follicle cells and pyloric caeca, indicating an extra-oocytic origin. Vtg accumulating in oocytes was stored in the form of cleaved products, which constituted the most abundant yolk polypeptides in ovulated sea star eggs; their levels decreased during early embryonic and larval development. Together, these traits are the hallmarks of a classical yolk protein - and hence, we contend that Vtg, and not MYP, is the main yolk protein in asteroids.

Validation of putative reference genes for gene expression studies in heat stressed and α-MSH treated melanocyte cells of Bos indicus using real-time quantitative PCR

Normalization of cellular mRNA data using internal reference gene (IRG) is an essential step in expression analysis studies. MIQE guidelines ensure that the choice and appropriateness of IRG should be validated for particular tissues or cell types and specific experimental designs. The objective of the present study was to assess 15 IRGs from different functional classes that could serve as best IRGs for Bos indicus (Tharparkar cattle) melanocyte cells under heat stress and hormonal treatment. We implemented the use of geNorm, NormFinder and BestKeeper algorithm to measure the stability of the gene transcript. A total of 15 IRGs (ACTB, BZM, EEF1, GAPDH, GTP, HMBS, HPRT, RPL22, RPL4, RPS15, RPS18, RPS23, RPS9, UBC and UXT) from different functional classes were evaluated. Pair wise comparisons using geNorm revealed that HPRT and RPS23 were the most stable combination of IRGs with M-value of 0.29 followed by UXT (0.30) and RPL4 (0.31). The NormFinder analysis also identified the same set of stably expressed genes (UXT, RPL4, RPS23 and HPRT); however, the rank order was little different. The UXT gene showed lowest crossing point SD and CV values of 0.30 and 1.17, respectively indicating its maximum expression stability through BestKeeper analysis. The present study indicated that, ACTB and HMB were not reliable IRGs for melanocytes cells on account of their lower expression stability. Current study further revealed that UXT, HPRT and RPS23 are the best IRGs for normalization of qPCR data in Bos indicus melanocyte cells under heat stress and hormonal treatment.

Triacylglyceride physiology in the short-finned eel, Anguilla australis--the effects of androgen

The importance of androgens (especially 11-ketotestosterone) during previtellogenesis in eels is well established. In wild pubertal migrants, circulating 11-ketotestosterone levels correlate with a number of morphological and molecular changes. Here, we test the prediction that this correlation represents a causal relationship by artificially raising the levels of circulating 11-ketotestosterone in prepubertal nonmigratory female and pubertal, migratory male short-finned eels (Anguilla australis) using sustained-release hormone implants. In females, increases in hepatosomatic index and transcript copy numbers of hepatic apolipoprotein B and microsomal triacylglyceride transfer protein indicated increased repackaging of endogenously sourced triacylglycerides. These changes in liver measures were reflected in increased concentrations of serum triacylglycerides. However, despite a small increase in gonadosomatic index, ovarian lipoprotein receptor transcript abundances were not affected by 11-ketotestosterone. Interestingly, no such changes in hepatic gene expression were detected in a dose-response experiment using males. We propose that the androgens are inducing the observed changes in previtellogenic females, although it remains unclear to what extent these effects are direct or indirect.

Evaluation of housekeeping genes as references for quantitative real-time PCR analysis of gene expression in the murrel Channa striatus under high-temperature stress

Quantitative real-time polymerase chain reaction is the most advanced method of quantifying gene expression studies; however, the significance of the obtained results strongly depends on the normalization of the data to compensate for differences between the samples. In the present study, expression analysis of six different constitutively expressed genes viz. 18S ribosomal RNA, glyceraldehyde-3-phosphate dehydrogenase (gapdh), beta actin (βactin), ribosomal binding protein L13, tubulin and TATA-box-binding protein (tbp) were carried out to test their efficacy as reference genes in three different tissues, namely liver, gill and muscle of murrel Channa striatus exposed to high temperature for variable time periods. The stability and suitability of the genes were determined by using bioinformatic tools: GeNorm, NormFinder and BestKeeper. Based on the results, tub/βactin could be used as the reference genes for liver and gill tissues and βactin/gapdh could be the reference genes for muscle tissues in Channa striatus under both short- and long-term thermal stress.

Selection of best-performing reference gene products for investigating transcriptional regulation across silvering in the European eel (Anguilla anguilla)

The focus of the present study was to set a methodological approach for evaluating molecular mechanisms underlying silvering transformation in the European eel, Anguilla anguilla. Silvering is a tightly controlled process during which eels undergo significant morphological, physiological and behavioral changes, pre-adapting for the oceanic spawning migration. Female eels showing different silver indexes were caught in different seasons in the Comacchio Lagoon (North Adriatic Sea, Italy). Isolated hepatocytes from these eels were selected as the experimental model given the relevant role of these cells in metabolic functions potentially altered during silvering. Expression profiles of 7 candidate reference transcripts were analyzed seeking the most viable and robust strategies for accurate qPCR data normalization during silvering. Stability analysis and further statistical validation identified transcripts encoding the ribosomal proteins L13 and ARP as the appropriate reference genes in studies on A. anguilla through silvering. The identified reference transcripts were further used to evaluate expression profiles of target transcripts encoding the thyroid hormone receptor β (THRβ) and vitellogenin (vtg), known to be involved in silvering processes. To the best of our knowledge, this is the first study comparing THRβ expression in European eels across silvering.

Triacylglyceride physiology in the short-finned eel, Anguilla australis—changes throughout early oogenesis

During certain stages in an animal's life cycle, energy requirements may exceed energy intake from the diet. The spawning migration of temperate eels is a textbook example of negative energy balance, forcing these fish to rely on stored fats (triacylglycerides) to provide their muscles with energy for swimming and their growing oocytes with the nutrients needed to develop and support healthy offspring. We predicted broad implications of this great need for endogenous triacylglycerides in terms of their packaging, transport, and ovarian uptake. To test this, serum lipid concentrations and transcript abundances of intestinal and hepatic triacylglyceride packagers and ovarian triacylglyceride modifiers and receivers were investigated throughout previtellogenesis (feeding phase) and into early vitellogenesis (fasting phase) in short-finned eels. A switch from exogenous to endogenous triacylglyceride packaging was seen as the liver upregulated transcript levels of apolipoprotein B and microsomal triacylglyceride transport protein and downregulated those of apolipoprotein E and lipoprotein lipase. In the intestine, the reverse response was observed. Furthermore, ovarian transcript abundances of triacylglyceride modifiers and receivers increased (apolipoprotein E, lipoprotein lipase, and vitellogenin receptor), indicative of increased triacylglyceride uptake during previtellogenesis. We propose that increased hepatic apolipoprotein B production is a conserved vertebrate response to prolonged periods of negative energy balance.

Development and partial characterisation of an antiserum against apolipoprotein B of the short-finned eel, Anguilla australis

Despite its key role in transportation of triacylglycerides in blood, the distribution, localisation and molecular weight variants of apolipoprotein B (Apob) in teleost fish have essentially escaped study. To address this, a specific short-finned eel (Anguilla australis) Apob antiserum was produced by an immunised rabbit, purified and partially characterised. Localisation of Apob at both the mRNA (in situ hybridisation) and protein (immunohistochemistry) levels mirrored that of mammals; thus immunostaining was confined to the interstitial spaces of the liver and the vascular core of the intestinal villi. Immunostaining of proteins by Western blotting, followed by high-resolution LC-MS, indicated that peptide sequence coverage of Apob in low-density lipoproteins spanned the full-length protein. We conclude that only full-length Apob is produced by eels and that both liver and intestine are key sites for its synthesis.

Profiling of estrogen-regulated microRNAs in breast cancer cells

Estrogen plays vital roles in mammary gland development and breast cancer progression. It mediates its function by binding to and activating the estrogen receptors (ERs), ERα, and ERβ. ERα is frequently upregulated in breast cancer and drives the proliferation of breast cancer cells. The ERs function as transcription factors and regulate gene expression. Whereas ERα's regulation of protein-coding genes is well established, its regulation of noncoding microRNA (miRNA) is less explored. miRNAs play a major role in the post-transcriptional regulation of genes, inhibiting their translation or degrading their mRNA. miRNAs can function as oncogenes or tumor suppressors and are also promising biomarkers. Among the miRNA assays available, microarray and quantitative real-time polymerase chain reaction (qPCR) have been extensively used to detect and quantify miRNA levels. To identify miRNAs regulated by estrogen signaling in breast cancer, their expression in ERα-positive breast cancer cell lines were compared before and after estrogen-activation using both the µParaflo-microfluidic microarrays and Dual Labeled Probes-low density arrays. Results were validated using specific qPCR assays, applying both Cyanine dye-based and Dual Labeled Probes-based chemistry. Furthermore, a time-point assay was used to identify regulations over time. Advantages of the miRNA assay approach used in this study is that it enables a fast screening of mature miRNA regulations in numerous samples, even with limited sample amounts. The layout, including the specific conditions for cell culture and estrogen treatment, biological and technical replicates, and large-scale screening followed by in-depth confirmations using separate techniques, ensures a robust detection of miRNA regulations, and eliminates false positives and other artifacts. However, mutated or unknown miRNAs, or regulations at the primary and precursor transcript level, will not be detected. The method presented here represents a thorough investigation of estrogen-mediated miRNA regulation.

Steroidogenic acute regulatory protein transcript abundance in the eel, Anguilla australis: changes during the induced reproductive cycle and effects of follicle-stimulating hormone during previtellogenesis

Steroidogenic acute regulatory protein (StAR) mRNA levels in the eel ovary were assayed by quantitative PCR and related to plasma steroid levels throughout oogenesis in order to shed light on the previously considered 'aberrant' prematurational increase in plasma levels of estradiol-17β (E2). Total ovarian StAR transcript abundance mirrored circulating levels of E2, but not of 11-ketotestosterone (11KT). The study was complemented by evaluation of in vitro effects of follicle-stimulating hormone (FSH) on ovarian StAR transcript abundance and on short-term ('acute') radiolabelled pregnenolone-supported steroid metabolism by ovarian fragments to understand how the production of steroids during previtellogenic oocyte growth is regulated. We observed a significant effect of FSH on StAR mRNA levels within 24h of incubation, but these were no longer evident by 4 days of culture. Unexpectedly, FSH had no effect on substrate-supported steroidogenesis, as comparable yields of steroid products were detected using semi-quantitative HPLC and scintillation counting. We conclude that the eel ovarian follicle can respond to FSH from a very early stage of development (early oil droplet stage) by increasing StAR mRNA levels, but that there is no evidence for acute effects of FSH on bioactive steroid production downstream of cytochrome P450 side-chain cleavage. Furthermore, the prematurational increase in StAR mRNA in vivo is in keeping with general teleost models and is likely to be a 'normal' response to reaching advanced stages of development.

The effects of 11-ketotestosterone on ovarian physiology of previtellogenic captive hapuku (Polyprion oxygeneios)

The present study investigated, for the first time in a perciform teleost, the effects of in vivo 11-ketotestosterone (11-KT) treatment using slow-release implants on ovarian development and gonadotropin receptor mRNA levels in captive previtellogenic females of hapuku (Polyprion oxygeneios). At the cellular/functional level, ovarian development and ovarian and hepatic total lipid levels were examined. At the molecular level, transcript abundance of ovarian follicle-stimulating hormone receptor (FSH-R) and luteinizing hormone receptor (LH-R) was measured. Additionally, cyclic adenosine monophosphate (cAMP) levels in ovarian fragments from placebo and 11-KT implanted fish incubated with or without human chorionic gonadotropin (hCG) in vitro were compared between groups. There were no significant differences between treatments with regard to oocyte size and lipid contents of liver and ovary. Messenger RNA levels of FSH-R and LH-R were significantly lower in the treated females. Similarly, cAMP levels were significantly lower in the ovarian fragments of the 11-KT implanted females. These results suggest that 11-KT specifically, but possibly androgens in general, may not have an important function in regulating gonadal development of previtellogenic female hapuku; indeed, if anything, 11-KT appeared to have a detrimental effect and its use will not be beneficial in advancing sexual maturity of hapuku in aquaculture.

Androgen-specific regulation of FSH signalling in the previtellogenic ovary and pituitary of the New Zealand shortfinned eel, Anguilla australis

The evidence for androgens having a pivotal role in the functioning of the female reproductive axis--such as initiating puberty or vitellogenesis--is mounting. However, the use of aromatizable androgens and the tissue-specific focus of most studies often make it unclear if androgenic effects throughout the axis proceed via androgen or estrogen signalling mechanisms. In this study, we assessed the effects of 11-ketotestosterone (11KT, a non-aromatizable androgen) on the pituitary and ovary of previtellogenic (PV) freshwater eels Anguilla australis, comparing them with eels naturally undergoing early vitellogenesis (EV). We found that 11KT treatment produces molecular and morpho-physiological phenotypes that were generally intermediate between PV and EV. Most notably, we demonstrated that 11KT induces effects on follicle-stimulating hormone (FSH) signalling in the pituitary and ovaries that are in opposition to each other. Thus, 11KT significantly reduced fshβ subunit expression in the pituitary. At the same time, 11KT dramatically increased mRNA levels of ovarian FSH receptor and plasma levels of estradiol-17β, very likely sensitizing the previtellogenic follicle to the FSH signal. Androgens therefore may be important in facilitating puberty in the eel.

Hepatic reference gene selection in adult and juvenile female Atlantic salmon at normal and elevated temperatures

BACKGROUND

The use of quantitative real-time polymerase chain reaction (qPCR) has become widespread due to its specificity, sensitivity and apparent ease of use. However, experimental error can be introduced at many stages during sample processing and analysis, and for this reason qPCR data are often normalised to an internal reference gene. The present study used three freely available algorithms (GeNorm, NormFinder and BestKeeper) to assess the stability of hepatically expressed candidate reference genes (Hprt1, Tbp, Ef1α and β-tubulin) in two experiments. In the first, female Atlantic salmon (Salmo salar) broodstock of different ages were reared at either 14 or 22 °C for an entire reproductive season, therefore a reference gene that does not respond to thermal challenge or reproductive condition was sought. In the second, estrogen treated juvenile salmon were maintained at the same temperatures for 14 days and a reference gene that does not respond to temperature or estrogen was required. Additionally, we performed independent statistic analysis to validate the outputs obtained from the program based analysis.

RESULTS

Based on the independent statistical analysis performed the stability of the genes tested was Tbp > Ef1α > Hprt1 > β-tubulin for the temperature/reproductive development experiment and Ef1α > Hprt1 > Tbp for the estrogen administration experiment (β-tubulin was not analysed). Results from the algorithms tested were quite ambiguous for both experiments; however all programs consistently identified the least stable candidate gene. BestKeeper provided rankings that were consistent with the independent analysis for both experiments. When an inappropriate candidate reference gene was used to normalise the expression of a hepatically expressed target gene, the ability to detect treatment-dependent changes in target gene expression was lost for multiple groups in both experiments.

CONCLUSIONS

We have highlighted the need to independently validate the results of reference gene selection programs. In addition, we have provided a reference point for those wishing to study the effects of thermal challenge and/or hormonal treatment on gene stability in Atlantic salmon and other teleost species.

Use of Maximum Likelihood-Mixed Models to select stable reference genes: a case of heat stress response in sheep

Background

Reference genes with stable expression are required to normalize expression differences of target genes in qPCR experiments. Several procedures and companion software have been proposed to find the most stable genes. Model based procedures are attractive because they provide a solid statistical framework. NormFinder, a widely used software, uses a model based method. The pairwise comparison procedure implemented in GeNorm is a simpler procedure but one of the most extensively used. In the present work a statistical approach based in Maximum Likelihood estimation under mixed models was tested and compared with NormFinder and geNorm softwares. Sixteen candidate genes were tested in whole blood samples from control and heat stressed sheep.

Results

A model including gene and treatment as fixed effects, sample (animal), gene by treatment, gene by sample and treatment by sample interactions as random effects with heteroskedastic residual variance in gene by treatment levels was selected using goodness of fit and predictive ability criteria among a variety of models. Mean Square Error obtained under the selected model was used as indicator of gene expression stability. Genes top and bottom ranked by the three approaches were similar; however, notable differences for the best pair of genes selected for each method and the remaining genes of the rankings were shown. Differences among the expression values of normalized targets for each statistical approach were also found.

Conclusions

Optimal statistical properties of Maximum Likelihood estimation joined to mixed model flexibility allow for more accurate estimation of expression stability of genes under many different situations. Accurate selection of reference genes has a direct impact over the normalized expression values of a given target gene. This may be critical when the aim of the study is to compare expression rate differences among samples under different environmental conditions, tissues, cell types or genotypes. To select reference genes not only statistical but also functional and biological criteria should be considered. Under the method here proposed SDHA/MDH1 have arisen as the best set of reference genes to be used in qPCR assays to study heat shock in ovine blood samples.