Occurrence of sex steroid hormones and their binding proteins in Octopus vulgaris lam

Let's talk about sex: Mechanisms of neural sexual differentiation in Bilateria

In multicellular organisms, sexed gonads have evolved that facilitate release of sperm versus eggs, and bilaterian animals purposefully combine their gametes via mating behaviors. Distinct neural circuits have evolved that control these physically different mating events for animals producing eggs from ovaries versus sperm from testis. In this review, we will describe the developmental mechanisms that sexually differentiate neural circuits across three major clades of bilaterian animals-Ecdysozoa, Deuterosomia, and Lophotrochozoa. While many of the mechanisms inducing somatic and neuronal sex differentiation across these diverse organisms are clade-specific rather than evolutionarily conserved, we develop a common framework for considering the developmental logic of these events and the types of neuronal differences that produce sex-differentiated behaviors. This article is categorized under: Congenital Diseases > Stem Cells and Development Neurological Diseases > Stem Cells and Development.

Exploring the Effect of Age on the Reproductive and Stress Physiology of Octopus bimaculoides Using Dermal Hormones

Our goal was to validate the use of dermal swabs to evaluate both reproductive and stress physiology in the California two-spot octopus, Octopus bimaculoides. Our objectives were to (1) use dermal swabs to evaluate glucocorticoids and reproductive hormones of O. bimaculoides; (2) determine the influence of life stage on hormone production (glucocorticoids in all individuals; testosterone, estrogen, and progesterone in females; and testosterone in males) of reproductive (n = 4) and senescent (n = 8) individuals to determine the effect of age on hormonal patterns; and (3) determine whether these hormones change significantly in response to an acute stressor. For the stress test, individuals were first swabbed for a baseline and then chased around the aquarium with a net for 5 min. Afterward, individuals were swabbed for 2 h at 15 min intervals to compare to the pre-stress test swab. Reproductive individuals responded to the stressor with a 2-fold increase in dermal cortisol concentrations at 15 and 90 min. Six of the eight senescent individuals did not produce a 2-fold increase in dermal cortisol concentrations. Reproductive individuals had significantly higher sex hormone concentrations compared to senescent individuals (progesterone and estradiol measured in females, and testosterone for both sexes). After the stressor, only reproductive males produced a 2-fold increase in dermal testosterone concentrations, while sex hormones in females showed no change. The stress hormone cortisol was significantly higher in senescent than in reproductive individuals, independent of sex. Dermal corticosterone concentrations were highest in senescent females followed by senescent males, and lowest in reproductive individuals regardless of sex. Dermal swabs provide an effective and noninvasive means for evaluating octopus hormones. Application of these indicators may be imperative as cephalopods are more commonly cultured in captivity for experimentation, display, and consumption.

Status in molluscan cell line development in last one decade (2010–2020): impediments and way forward

Despite the attempts that have started since the 1960s, not even a single cell line of marine molluscs is available. Considering the vast contribution of marine bivalve aquaculture to the world economy, the prevailing viral threats, and the dismaying lack of advancements in molluscan virology, the requirement of a marine molluscan cell line is indispensable. This synthetic review discusses the obstacles in developing a marine molluscan cell line concerning the choice of species, the selection of tissue and decontamination, and cell culture media, with emphasis given on the current decade 2010-2020. Detailed accounts on the experiments on the virus cultivation in vitro and molluscan cell immortalization, with a brief note on the history and applications of the molluscan cell culture, are elucidated to give a holistic picture of the current status and future trends in molluscan cell line development.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10616-022-00539-x.

Determining the effectiveness of using dermal swabs to evaluate the stress physiology of laboratory cephalopods: A preliminary investigation

To better comprehend the physiology of cephalopods, we used a minimal invasive technique of skin mucus swabs to measure immunoreactive corticosteroids in three cephalopod species commonly kept in captivity and promoted as new model organisms: Euprymna berryi, Sepia bandensis, and Octopus chierchiae. We compared results between sexes and age classes and then evaluated their stress responses during acclimation to a new habitat. To better understand glucocorticoid production, we conducted an adrenocorticotropic hormone, using Cosyntropin (an adrenocorticotropin (ACTH) analogue) challenge with a saline control and swabbed their mantles at 15-minute intervals for 2 h. Results showed cortisol was higher for younger individuals. Additionally, cortisol and corticosterone concentrations decreased by 2-fold after 2 to 4 days of acclimation to a new habitat. We were able to successfully measure 2-fold increase in immunoreactive corticosteroids which reacted with cortisol and corticosterone assays for all the species following ACTH injection, although not all individuals responded similarly. With further investigation, this technique can increase our understanding and management of cephalopods in captivity.

Effects of Whole-Lake Additions of Ethynylestradiol on Leech Populations

Leeches are widespread, found in many freshwater habitats, and have diverse dietary habits. Despite their close phylogenetic relationships to Mollusca, a phylum with species affected by exogenous estrogens, it is unclear whether Hirudinea may also be impacted. A whole-lake experiment was done at the Experimental Lakes Area in Ontario, Canada, to assess whether 17α-ethynylestradiol (EE2) affected fishes and other species. Herein, we examined whether EE2 impacted leech community composition, species abundance, growth rates, gonad size, and cocoon production, when compared with reference lakes using a before-after-control-impact design. Each month baited leech traps were set overnight in the littoral zone at 10 sites around experimental Lake 260 and 2 reference lakes, and individuals were identified, weighed, and measured. Male and female organs of common species Haemopis marmorata were measured. Across all lakes, 9 species representing 3 families were collected. There were no apparent effects of EE2 on numbers, species richness, or community composition; however, condition in 1 of 5 species increased significantly after EE2 exposures. Total gonadosomatic index (GSI) and the GSI for all male or all female organs combined for H. marmorata were not affected by EE2 additions. However, some individual reproductive organs including relative sperm sac length (+), relative epididymis weight (-), relative vaginal bulb length (+), and relative ovisac + albumen gland length (+) changed after EE2 additions. Finally, whereas overall cocoon production was similar, it occurred earlier in the EE2-amended lake. In summary, few individual through community measures of leeches responded to low ng/L concentrations of EE2, suggesting that Hirudinea are less sensitive to this endocrine disruptor than other invertebrates and vertebrates. Environ Toxicol Chem 2020;39:1608-1619. © 2020 SETAC.

Environmental estrogen exposure disrupts sensory processing and nociceptive plasticity in the cephalopod Euprymna scolopes

Endogenous estrogens affect multiple sensory systems, including those involved in processing noxious and painful stimuli. Extensive evidence demonstrates that estrogenic environmental pollutants have profound, negative effects on growth and reproductive physiology, but there is limited information about how estrogenic pollutants might affect sensory systems known to be modulated by endogenous estrogens. Here, we show that ethinyl estradiol, the most common artificial estrogen found in coastal marine environments, disrupts normal behavioral and neural responses to tissue injury in the sepiolid Euprymna scolopes (Hawaiian bobtail squid), which inhabits shallow tropical waters close to dense human habitation. Behavioral hypersensitivity and neural plasticity that occur normally after tissue injury were impaired both under chronic estrogen exposure beginning during embryogenesis and after a single, high dose co-incident with injury. This suggests that these naturally selected responses to injury, which function to protect animals from predation and infection risk, may be impaired by anthropogenic pollution.

The utility of vitellogenin as a biomarker of estrogenic endocrine disrupting chemicals in molluscs

Estrogenic endocrine disrupting chemicals (EDCs) are natural hormones, synthetic compounds or industrial chemicals that mimic estrogens due to their structural similarity with estrogen's functional moieties. They typically enter aquatic environments through wastewater treatment plant effluents or runoff from intensive livestock operations. Globally, most natural and synthetic estrogens in receiving aquatic environments are in the low ng/L range, while industrial chemicals (such as bisphenol A, nonylphenol and octylphenol) are present in the μg to low mg/L range. These environmental concentrations often exceed laboratory-based predicted no effect concentrations (PNECs) and have been evidenced to cause negative reproductive impacts on resident aquatic biota. In vertebrates, such as fish, a well-established indicator of estrogen-mediated endocrine disruption is overexpression of the egg yolk protein precursor vitellogenin (Vtg) in males. Although the vertebrate Vtg has high sensitivity and specificity to estrogens, and the molecular basis of its estrogen inducibility has been well studied, there is growing ethical concern over the use of vertebrate animals for contaminant monitoring. The potential utility of the invertebrate Vtg as a biomonitor for environmental estrogens has therefore gained increasing attention. Here we review evidence providing support that the molluscan Vtg holds promise as an invertebrate biomarker for exposure to estrogens. Unlike vertebrates, estrogen signalling in invertebrates remains largely unclarified and the classical genomic pathway only partially explains estrogen-mediated activation of Vtg. In light of this, in the latter part of this review, we summarise recent progress towards understanding the molecular mechanisms underlying the activation of the molluscan Vtg gene by estrogens and present a hypothetical model of the interplay between genomic and non-genomic pathways in the transcriptional regulation of the gene.

Uptake and metabolism of water-borne progesterone by the mussel, Mytilus spp. (Mollusca)

Previous studies have shown that mussels can pick up 17β-estradiol [E₂] and testosterone [T] from water, metabolize them and conjugate them to fatty acids (esterification), leading to their accumulation in tissue. A key requirement for the esterification process is that a steroid must have a 'reactive' hydroxyl group to conjugate to a fatty acid (which in T, and probably E₂, is the β-hydroxyl group on carbon 17). Progesterone (P) lacks any hydroxyl groups and theoretically cannot be esterified and hence should not accumulate in mussels in the same way as E₂ or T. However, it is already known that mussels have an enzyme that can achieve 5α-reduction of the A ring of T and P and that there is also another reductase that can transform the 3-oxo group of the 5α-reduced A ring of T into a hydroxyl group. We hypothesized that, although intact P cannot be directly esterified, it might nevertheless be transformed into metabolites that can. To test this hypothesis, we investigated the rate and capacity of uptake, metabolism and potential depuration of tritiated P by the common mussel, Mytilus spp. We found that tritiated P was taken up from water at a similar rate to E₂ and T (mean clearance rate 49mL^-1 animal^-1h^-1) and that, as found with the other steroids, the rate of uptake could not be saturated by the addition of non-radioactive steroid (even at 7.6μgL^-1). We found that up to 66% of the radioactivity that was taken up was present in the ester fraction, suggesting that hydroxylation of the P must indeed have occurred. We then definitively identified two metabolites in the ester fraction: 5α-pregnane-3β,20β-diol and 3β-hydroxy-5α-pregnan-20-one. These same two steroids were also present in the free steroid fraction. Intact P was not detected in either of the fractions. When undergoing depuration (under semi-static conditions), the radioactivity in the ester fractions remained at the same concentration in the animals for at least 10 days. Our findings suggest that the lack of reactive hydroxyl groups on P does not preclude it from being taken up, metabolized and subsequently stored. Many questions remain, not least of which is why, when P seems to be so rapidly metabolized, two previous studies on mussels have reported concentrations of up to 30ngg^-1 wet weight of P in their flesh.

Sex Reversal and Analyses of Possible Involvement of Sex Steroids in Scallop Gonadal Development in Newly Established Organ-Culture Systems

Many molluscs perform sex reversal, and sex hormones may be involved in the process. In adult scallops, Patinopecten yessoensis, gonadotropin releasing hormone and 17β-estradiol (E₂) are involved in male sexual maturation, however, little is known about the effects of E₂ and testosterone (T) on the gonadal differentiation in young scallops. In the present study, scallop gonadal development was analyzed to determine the sex reversal stage in Funka bay, and effects of E₂ and T were examined. In Funka bay, almost all scallops were male at month 12. Scallops equipped with ambiguous gonads were 61.1% at month 16 and disappeared at month 18. Therefore, sex reversal in Funka bay occurs at around month 16. For establishment of organ culture systems for bivalves, Manila clam gonads were cultured in 15% L-15 medium diluted with HBSS containing 10% KSR on agarose gel at 10°C, and the gonads survived for 14 days. Scallop gonads were also able to be cultured in 30% L15 medium diluted with ASW containing 10% KSR on agarose gel for seven days. At mature stage, Foxl2 and Tesk were predominantly expressed in ovary and testis, respectively. When scallop gonads at sex reversal stage were organ-cultured, sex steroid treatment decreased Tesk expression in the majority of scallop gonads at sex reversal stage. However, no obvious change in Foxl2 and Tesk expression was detected in mature gonads in response to either E₂ or T in culture, suggesting sex steroid treatment might affect gonadal development at sex reversal stage.

Spermatogenic Cycle and Steroidogenic Control of Spermatogenesis in Mytilus galloprovincialis Collected in the Bay of Naples

The aim of the present article was to study the spermatogenic cycle of Mytilus galloprovincialis collected in the Bay of Naples during a whole year and to acquire new insights into the mechanism of control. Knowledge of the Mytilus cycle in this geographic area is of particular interest as, to the best of our knowledge, the male gonad cycle has been hitherto unexplored. Testis organization was evaluated together with the localization of the enzymes 3β-HSD, 17β-HSD, and P450-aromatase, which are strictly connected to the synthesis of two key hormones involved in the testis activity: testosterone and 17β-estradiol. It was demonstrated that: (1) the spermatogenic cycle starts in late Summer-early Fall and continues until early Winter, when the first spawning occurs; after rapid gonad restoration, several spawning events take place until June, when the testis becomes non-active again; (2) in the testis, true Leydig and Sertoli cells are present; (3) during the reproductive period, Sertoli, Leydig, germ, and adipogranular cells (ADGs) are positive to 3β-HSD and 17β-HSD, while only germ cells are positive to P450 aromatase; by contrast, during the resting period, only ADGs are positive to 3β-HSD and 17β-HSD, and P450-aromatase is no longer recognizable. The presence of a hermaphrodite sample is also described. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 300:1881-1894, 2017. © 2017 Wiley Periodicals, Inc.

Oct-GnRH, the first protostomian gonadotropin-releasing hormone-like peptide and a critical mini-review of the presence of vertebrate sex steroids in molluscs

In protostome and deuterosome invertebrates, neurosecretory cells play major roles in the endocrine system. The optic glands of cephalopods are indicators of sexual maturation. In mature octopuses, optic glands enlarge and secrete a gonadotropic hormone. A peptide with structural features similar to that of vertebrate gonadotropin-releasing hormone (GnRH) was isolated from the octopus, Octopus vulgaris, and was named oct-GnRH. The discovery of oct-GnRH has triggered structural determinations and predictions of other mollusc GnRH-like peptides in biochemical and in silico studies. Interestingly, cephalopods studied so far are characterized by a single molecular form of oct-GnRH with a C-terminal -Pro-Gly-NH2 sequence, which is critical for gonadotropin-releasing activity in vertebrates. Other molluscan GnRH-like peptides lack the C-terminal -Pro-Gly-NH2 sequence but have -X-NH2 or -Pro-Gly although all protostome GnRH-like peptides have yet to be sequenced. In marine molluscs, relationships between GnRH-like peptides and sex steroids have been studied to verify the hypothesis that molluscs have vertebrate-type sex steroid system. However, it is currently questionable whether such sex steroids are present and whether they play endogenous roles in the reproductive system of molluscs. Because molluscs uptake and store steroids from the environment and fishes release sex steroids into the external environment, it is impossible to rule out the contamination of vertebrate sex steroids in molluscs. The function of key enzymes of steroidogenesis within molluscs remains unclear. Thus, evidence to deny the existence of the vertebrate-type sex steroid system in molluscs has been accumulated. The elucidation of substances, which regulate the maturation and maintenance of gonads and other reproductive functions in molluscs will require rigorous and progressive scientific study.

Cloning and expression analysis of the 17β hydroxysteroid dehydrogenase type 12 (HSD17B12) in the neogastropod Nucella lapillus

HSD17B12 is a member of the hydroxysteroid dehydrogenase superfamily, a multifunctional group of enzymes involved in the metabolism of steroids, retinoids, bile and fatty acids. Whether the main role of HSD17B12 in mammals is in steroid or fatty acid metabolism is a subject of intense debate. In mollusks it has been shown that an HSD17B12 orthologue can convert estrone into estradiol in vitro, although its primary in vivo function remains unknown. To gain insight into its role in gastropods, we provide here the first cloning of Hsd17b12 in Nucella lapillus and its detailed tissue distribution through quantitative PCR. Furthermore, given that the endocrine disruptor tributyltin (TBT) has been reported to unbalance steroid and lipid levels in gastropods, we tested its impact in on NlHsd17b12 transcript expression. Our results show that NlHsd17b12 is ubiquitously expressed in all tissues analyzed, with higher levels in organs with high metabolic rates, such as kidney and digestive gland, a pattern consistent with an involvement in lipid metabolism. Exposure to TBT chloride at 100 ng Sn/L caused a decrease in NlHsd17b12 mRNA levels in digestive gland, after one and two months, while no effect was observed in gonads. Overall, these results suggest that in mollusks, as in mammals, this enzyme is likely to be involved in lipid metabolism, and emphasize the need to perform more detailed studies on its in vivo function, in order to understand its physiological role and the biological impact of its disruption by pollutants such as TBT.

Evolution of minimal specificity and promiscuity in steroid hormone receptors

Most proteins are regulated by physical interactions with other molecules; some are highly specific, but others interact with many partners. Despite much speculation, we know little about how and why specificity/promiscuity evolves in natural proteins. It is widely assumed that specific proteins evolved from more promiscuous ancient forms and that most proteins' specificity has been tuned to an optimal state by selection. Here we use ancestral protein reconstruction to trace the evolutionary history of ligand recognition in the steroid hormone receptors (SRs), a family of hormone-regulated animal transcription factors. We resurrected the deepest ancestral proteins in the SR family and characterized the structure-activity relationships by which they distinguished among ligands. We found that that the most ancient split in SR evolution involved a discrete switch from an ancient receptor for aromatized estrogens—including xenobiotics—to a derived receptor that recognized non-aromatized progestagens and corticosteroids. The family's history, viewed in relation to the evolution of their ligands, suggests that SRs evolved according to a principle of minimal specificity: at each point in time, receptors evolved ligand recognition criteria that were just specific enough to parse the set of endogenous substances to which they were exposed. By studying the atomic structures of resurrected SR proteins, we found that their promiscuity evolved because the ancestral binding cavity was larger than the primary ligand and contained excess hydrogen bonding capacity, allowing adventitious recognition of larger molecules with additional functional groups. Our findings provide an historical explanation for the sensitivity of modern SRs to natural and synthetic ligands—including endocrine-disrupting drugs and pollutants—and show that knowledge of history can contribute to ligand prediction. They suggest that SR promiscuity may reflect the limited power of selection within real biological systems to discriminate between perfect and “good enough.”

The functions of most proteins are defined by their interactions with other biological substances, such as DNA, nutrients, hormones, or other proteins. Some proteins are highly specific, but others are more promiscuous and can interact with a variety of natural substances, as well as drugs and pollutants. Understanding molecular interactions is a key goal in pharmacology and toxicology, but there are few general principles to help explain or predict protein specificity. Because every biological entity is the result of evolution, understanding a protein's history might help explain why it interacts with the substances to which it is sensitive. In this paper, we used ancestral protein reconstruction to experimentally trace how specificity evolved in an ancient group of proteins, the steroid hormone receptors (SRs), a family of proteins that regulate reproduction and other biological processes in animals. We show that SRs evolved according to a principle of minimal specificity: at each point in time, these proteins evolved to be specific enough to distinguish among the substances to which they were naturally exposed, but not more so. Our findings provide an historical explanation for modern SRs' diverse sensitivities to natural and man-made substances; they show that knowledge of history can contribute to predicting the ligands to which a modern protein will respond and indicate that promiscuity reflects the limited power of natural selection to discriminate between perfect and “good enough.”

Do mollusks use vertebrate sex steroids as reproductive hormones? Part I: Critical appraisal of the evidence for the presence, biosynthesis and uptake of steroids

The consensus view is that vertebrate-type steroids are present in mollusks and perform hormonal roles which are similar to those that they play in vertebrates. Although vertebrate steroids can be measured in molluscan tissues, a key question is 'Are they formed endogenously or they are picked up from their environment?'. The present review concludes that there is no convincing evidence for biosynthesis of vertebrate steroids by mollusks. Furthermore, the 'mollusk' genome does not contain the genes for key enzymes that are necessary to transform cholesterol in progressive steps into vertebrate-type steroids; nor does the mollusk genome contain genes for functioning classical nuclear steroid receptors. On the other hand, there is very strong evidence that mollusks are able to absorb vertebrate steroids from the environment; and are able to store some of them (by conjugating them to fatty acids) for weeks to months. It is notable that the three steroids that have been proposed as functional hormones in mollusks (i.e. progesterone, testosterone and 17β-estradiol) are the same as those of humans. Since humans (and indeed all vertebrates) continuously excrete steroids not just via urine and feces, but via their body surface (and, in fish, via the gills), it is impossible to rule out contamination as the sole reason for the presence of vertebrate steroids in mollusks (even in animals kept under supposedly 'clean laboratory conditions'). Essentially, the presence of vertebrate steroids in mollusks cannot be taken as reliable evidence of either endogenous biosynthesis or of an endocrine role.

Molecular cloning and characterization of estrogen receptor gene in the scallop Chlamys farreri: expression profiles in response to endocrine disrupting chemicals

In order to gain insights into the mechanism of sex steroid signaling in molluscs, the full-length cDNA of estrogen receptor (ER) was isolated and characterized from Chlamys farreri for the first time. The positions of cysteine residues and other residues around them that constitute the two zinc finger motifs and the P-box are conserved. Phylogenetic analysis revealed that the CfER is an ortholog of the other mollusk ERs. Tissue distribution analysis of the CfER mRNA revealed that the expression of ER mRNA was observed in various tissues, and highest in the gonad of males and females. C. farreri were exposed for 10 days to endocrine disrupting chemicals including Benzo(a)pyrene (B(a)p) and polybrominated diphenyl ethers (BDE-47). B(a)p exposure at 0.4 and 2 μg/L caused significant increase in mRNA expression of ER and VTG, but B(a)p at 10 μg/L down-regulated CfER and VTG mRNA expression compared to control. Varying increase of ER and VTG mRNA transcripts was resulted in by BDE-47 at 0.1, 1 and 10 μg/L. These results elucidate potential roles of CfER induced by xenobiotics in C. farreri and can be helpful for investigating the mechanism of sex steroid signaling in bivalve mollusks.

Biosynthesis and metabolism of steroids in molluscs

Molluscs are the second most diverse animal group, they are ecologically important and they are considered excellent indicators of ecosystem health. Some species have been widely used in pollution biomonitoring programs; however, their endocrinology is still poorly known. Despite some studies reporting the presence of (vertebrate-type) steroids in molluscs, information regarding enzymatic pathways involved in steroid synthesis and further catabolism of those steroids is still fragmentary. Regarding steroidogenesis, a number of excellent studies were performed in the 70s using different radio-labelled steroid precursors and detecting the formation of different metabolites. But, since then a long gap of research exist until the late 90s when the 'endocrine disruption' issue raised the need of a better knowledge of mollusc (and invertebrate) endocrinology in order to assess alterations caused by pollutants. Here we summarize past and recent studies dealing with steroid biosynthesis and metabolism in different mollusc species. Most of these studies suggest the involvement of steroids in mollusc reproduction. However, the knowledge is still fragmentary and many questions remain to be answered.

Thyroid hormones and D-aspartic acid, D-aspartate oxidase, D-aspartate racemase, H2O2, and ROS in rats and mice

Total concentrations of thyroid hormones T(3) and T(4), and of their free forms, FT(3) and FT(4), D-aspartic acid (D-Asp), D-aspartate oxidase (D-AspO), D-aspartate racemase, H(2)O(2), and ROS (reactive oxygen species) were determined in rats and mice. T(3) and T(4) were 1 and 50 ng/ml, respectively, in serum, and 750 and 40000 ng/g, respectively, in thyroid. Concentrations of the free forms FT(3) and FT(4) were ca. 250 times lower than their respective total concentrations. The endogenous content of D-Asp in thyroid gland was ca. 100 nmol/g tissue, whereas the activity of D-AspO was ca. 80 units/mg thyroid, and that of D-aspartate racemase was ca. 15 units/mg thyroid. H(2)O(2) Concentration in rat and mouse thyroid gland was ca. 290 pmol/g thyroid, and the concentration of ROS was ca. 10 pmol/DCF/min/mg protein. H(2)O(2) is essential for the iodination of the tyrosyl residues to produce mono- and diiodotyrosine that are the precursors for the synthesis of T(3) and T(4). Production of H(2)O(2) in thyroid glands occurs by oxidation of endogenous D-Asp by D-AspO (D-Asp+O(2)+H(2)O-->alpha-oxaloacetate+NH(3)+H(2)O(2)). D-Aspartate racemase catalyzes the in vivo production of D-Asp from L-Asp. Thus, interaction of endogenous D-Asp, D-AspO, and D-aspartate racemase in thyroid gland constitutes an additional biochemical pathway for the production of H(2)O(2) and consequently for the synthesis of thyroid hormones.

Regulatory actions of neuropeptides and peptide hormones on the reproduction of molluscsThe present review is one of a series of occasional review articles that have been invited by the Editors and will feature the broad range of disciplines and expertise represented in our Editorial Advisory Board

Reproductive success of individual animals is essential for the survival of any species. Molluscs have adapted to a wide variety of environments (freshwater, brackish water, seawater, and terrestrial habits) and have evolved unique tactics for reproduction. Both of these features attract the academic interests of scientists. Because neuropeptides and peptide hormones play critical roles in neural and neurohormonal regulation of physiological functions and behaviors in this animal group, the regulatory actions of these messengers in reproduction have been extensively investigated. In this review, we will briefly summarize how peptidergic messengers are involved in various aspects of reproduction, using some peptides such as egg-laying hormone, caudo-dorsal cell hormone, APGWamide, and gonadotropin-releasing hormone as typical examples.

Fecal hormones measured within giant Pacific octopuses Enteroctopus dofleini

The captive husbandry of giant Pacific octopuses Enteroctopus dofleini is well understood, but their endocrine signatures are not well documented. The major vertebrate reproductive hormones--estrogen, progesterone, and testosterone--and the stress-related hormone corticosterone are relatively well known for many vertebrate species. However, few studies on these hormones within invertebrates have been conducted. Our hypothesis was that endocrine signatures within octopuses are similar to those found within vertebrates in response to reproductive activity and stress. Using standard immunoassay techniques, we measured fecal steroids within fecal samples collected from five female and three male giant Pacific octopuses housed at the Seattle Aquarium. The mean estrogen level ranged from 3.67 to 99.39 ng/g of feces, progesterone ranged from 44.35 to 231.71 ng/g feces, testosterone ranged from 9.30 to 18.18 ng/g feces, and corticosterone ranged from 10.91 to 22.14 ng/g feces. The results suggest that octopus fecal hormones are similar to those in vertebrates and may be useful in measuring ovarian activity and stress within captive female giant Pacific octopuses.

Endocrine interactions between plants and animals: Implications of exogenous hormone sources for the evolution of hormone signaling

Hormones are central to animal physiology, metabolism and development. Details on signal transduction systems and regulation of hormone synthesis, activation and release have only been studied for a small number of animal groups, notably arthropods and chordates. However, a significant body of literature suggests that hormonal signaling systems are not restricted to these phyla. For example, work on several echinoderm species shows that exogenous thyroid hormones (THs) affect larval development and metamorphosis and our new data provide strong evidence for endogenous synthesis of THs in sea urchin larvae. In addition to these endogenous sources, these larvae obtain THs when they consume phytoplankton. Another example of an exogenously acquired hormone or their precursors is in insect and arthropod signaling. Sterols from plants are essential for the synthesis of ecdysteroids, a crucial group of insect morphogenic steroids. The availability of a hormone or hormone precursor from food has implications for understanding hormone function and the evolution of hormonal signaling in animals. For hormone function, it creates an important link between the environment and the regulation of internal homeostatic systems. For the evolution of hormonal signaling it helps us to better understand how complex endocrine mechanisms may have evolved.

Octopus gonadotrophin-releasing hormone: a multifunctional peptide in the endocrine and nervous systems of the cephalopod

The optic gland, which is analogous to the anterior pituitary in the context of gonadal maturation, is found on the upper posterior edge of the optic tract of the octopus Octopus vulgaris. In mature octopus, the optic glands enlarge and secrete a gonadotrophic hormone. A peptide with structural features similar to that of vertebrate gonadotrophin-releasing hormone (GnRH) was isolated from the brain of octopus and was named oct-GnRH. Oct-GnRH showed luteinising hormone-releasing activity in the anterior pituitary cells of the Japanese quail Coturnix coturnix. Oct-GnRH immunoreactive signals were observed in the glandular cells of the mature optic gland. Oct-GnRH stimulated the synthesis and release of sex steroids from the ovary and testis, and elicited contractions of the oviduct. Oct-GnRH receptor was expressed in the gonads and accessory organs, such as the oviduct and oviducal gland. These results suggest that oct-GnRH induces the gonadal maturation and oviposition by regulating sex steroidogenesis and a series of egg-laying behaviours via the oct-GnRH receptor. The distribution and expression of oct-GnRH in the central and peripheral nervous systems suggest that oct-GnRH acts as a multifunctional modulatory factor in feeding, memory processing, sensory, movement and autonomic functions.

Gonad development during the early life of Octopus maya (Mollusca: Cephalopoda)

Gonad development during the early life of Octopus maya is described in terms of histological, morphometric, oocytes growth, and somatic-oocyte relationship data obtained from octopus cultured at the UMDI-UNAM, in Sisal, Yucatan, Mexico. This study is the first publication on gonad development during the early life of Octopus maya. A total of 83 O. maya specimens were used; their sizes ranged from 6.5 to 76 mm of total length (TL), 4 to 28 mm of dorsal mantle length (DML), 2.5 to 20 mm of ventral mantle length (VML), and 0.0180 to 7.2940 g of fixed body weight (fBW). Animals were weighed and measured only after preservation. A loss of 10% of living weight was estimated for juvenile octopuses after formalin preservation. The relation of length to weight (VML, DML, TL/fBW) pooled for both sexes had a strong positive correlation (r), as shown by a potential power function that was quite close to 1. Compound images were produced from numerous microscopic fields. The histological examination revealed that, 4 months after hatching, male octopus (24.5 mm DML and 7.2940 g fBW) were in gonad stages 2 (maturing) to 3 (mature), with spermatogonia and spermatocytes in the tubule wall and abundant spermatids and spermatozoa in the central lumen of the seminiferous tubules, suggesting the occurrence of different phases of gonad development at different maturity stages. In contrast, females (22.5 mm DML and 4.8210 g fBW) at the same time since hatching were immature (stage 1), with many oogonia, few oocytes, and germinal epithelium. This suggests that males reach maturity earlier than females, indicating a probable onset of maturity for males at around 4 months of culture or 8 g of wet body weight. Our results indicate the possibility that the size-at-weight can be recognized early with a degree of certainty that allows the sexes to be separated for culture purposes; but more detailed studies on reproduction in relation to endocrinology and nutrition are needed.

Sex differences in spatial cognition in an invertebrate: the cuttlefish

Evidence of sex differences in spatial cognition have been reported in a wide range of vertebrate species. Several evolutionary hypotheses have been proposed to explain these differences. The one best supported is the range size hypothesis that links spatial ability to range size. Our study aimed to determine whether male cuttlefish (Sepia officinalis; cephalopod mollusc) range over a larger area than females and whether this difference is associated with a cognitive dimorphism in orientation abilities. First, we assessed the distance travelled by sexually immature and mature cuttlefish of both sexes when placed in an open field (test 1). Second, cuttlefish were trained to solve a spatial task in a T-maze, and the spatial strategy preferentially used (right/left turn or visual cues) was determined (test 2). Our results showed that sexually mature males travelled a longer distance in test 1, and were more likely to use visual cues to orient in test 2, compared with the other three groups. This paper demonstrates for the first time a cognitive dimorphism between sexes in an invertebrate. The data conform to the predictions of the range size hypothesis. Comparative studies with other invertebrate species might lead to a better understanding of the evolution of cognitive dimorphism.

The evolution of the ligand/receptor couple: a long road from comparative endocrinology to comparative genomics

Comparative endocrinology considers the evolution of bioregulatory systems and the anatomical structures and molecules that constitute the neuroendocrine and endocrine systems. One aim of comparative endocrinology is to trace the origins of the main endocrine systems. The understanding of the evolution of the ligand/receptor couple is central to this objective. One classical approach to tackle this question is the characterization of receptors and ligands in various types of non-model organisms using as a starting point the knowledge accumulated on classical models such as mammals (mainly human and mouse) and arthropods (with Drosophila among other insects). In this review we discuss the potential caveats associated to this two-by-two comparison between a classical model and non-model organisms. We suggest that the use of an evolutionary approach involving comparisons of several organisms in a coherent framework permits reconstruction of the most probable scenarios. The use of the vast amount of genomic data now available, coupled to functional experiments, offers unprecedented possibilities to trace back the origins of the main ligand/receptor couples.

Endocrine-related reproductive effects in molluscs

Research on endocrine disruption has been a major topic of the past decade. Although most studies concentrated on vertebrate species, invertebrates are now gaining more attention. In particular, data on molluscs is increasing. One of the best-documented and more relevant examples of endocrine disruption is the imposex phenomenon affecting some gastropod species. But the increasing interest is also due to the fact that molluscs, especially bivalves, are good bioindicators used for decades in environmental studies and that progress have been made in the understanding of the physiology and endocrinology of some mollusc species. Recent results suggest that molluscs can be adversely affected by compounds that alter their reproduction and that vertebrate-type sex-steroids metabolism or mechanism of action could be involved in these effects. Nevertheless, the endocrine system of molluscs appears to be dissimilar in many aspects to those of vertebrates and sex-steroids might not have the same importance in all mollusc species. This diversity constitutes an important opportunity to examine and understand new and alternative mechanisms for endocrine disruption.

Estrogen binding sites in the sea scallop: Characterization and possible involvement in reproductive regulation

Previous reports have suggested that estrogen is involved in bivalve reproduction and have also hypothesized that its effects are mediated through binding sites on specific receptors. In this study, we provide initial characterization of the estrogen binding sites in the gonads of both female and male sea scallops (Placopecten magellanicus). Saturation analyses indicated two binding sites in fractions which have classically been used to represent the cytosol and the nucleus. One binding site is characterized by high affinity and limited binding capacity while the other site is characterized by low affinity and high capacity. Competitive binding analyses demonstrated that these sites can bind natural and synthetic estrogens with high affinity but only bind testosterone and progesterone at high concentrations. Comparison of binding capacity in scallops at different sexual maturation stages suggested that these sites may be involved in reproductive regulation in sea scallops.

Sex steroid receptor evolution and signalling in aquatic invertebrates

In vertebrate reproductive endocrinology sex steroids play a pivotal role via binding to receptors. However, information on the origin and relevance of sex steroids in invertebrates is limited. This review highlights current literature on steroid receptors in aquatic invertebrates and reports on some new findings. It has been shown that invertebrates of the deuterostome clade, such as Acrania and Echinodermata, respond to estrogens and androgens and, at least in Branchiostoma, an estrogen receptor has been cloned. Within the protostomes, most findings are related to aquatic molluscs. Sex steroid receptor-like proteins are abundant in gastropods, bivalves and cephalopods and also sex hormone signalling shows partial similarity to the deuterostomes. In ecdysozoans, however, the impact of sex steroids is still a matter of debate even though there is evidence on the presence of estrogen receptor-like proteins in Crustacea and on physiological effects of estrogens in both Nematoda and Crustacea. Recent findings suggest the presence of an estrogen receptor alpha-like protein of unclear physiological role in Gammarus fossarum (Crustacea). Binding studies revealed the crustacean Hyalella azteca to possess specific binding sites only for androgens but not for estrogens suggesting a possible limitation to functional androgen receptors in this species. Further studies have to be conducted to shed more light into the discussion about the controversy about sex steroid receptors in invertebrates.

Sex steroids and potential mechanisms of non-genomic endocrine disruption in invertebrates

The review reports on the presence and metabolism of sex steroids in several invertebrate species and provides detailed information on possible mechanisms of endocrine disruption other than the interaction with nuclear receptors. The presence of most vertebrate sex steroids in invertebrate tissues has been demonstrated by liquid or gas chromatography coupled to mass spectrometry. In addition, enzymatic pathways involved in the steroidogenic pathway have been described in at least some invertebrate phyla. Some endocrine disruptors induce alterations in these metabolic pathways and might lead to changes in steroid levels. Growing evidence suggests that estradiol can act through non-genomic pathways in molluscs, and that xenobiotics can as well interfere in these signalling cascades. In spite of these recent advances, most question marks on the action and function of sex steroids in invertebrates remain to be answered.

Steroids in aquatic invertebrates

Steroid molecules are present in all invertebrates, and some of them have established hormonal roles: this is the case for ecdysteroids in arthropods and, to a lesser extent, for vertebrate-type steroids in molluscs. Steroids are not only hormones, they may also fulfill many other functions in chemical communication, chemical defense or even digestive physiology. The increasing occurrence of endocrine disruption problems caused by environmental pollutants, which interfere in particular with reproductive physiology of vertebrates but also of invertebrates has made necessary to better understand the endocrine physiology of the latter and the role of steroids in these processes. So many attempts are being made to better understand the endocrine roles of steroids in arthropods and molluscs, and to establish whether they also fulfill similar functions in other invertebrate phyla. At the moment, both the precise identification of these steroids, the determination of their origin (endogenous versus exogenous) and of their mechanism of action are under active investigation. This research takes profit of the development of genome sequencing programs on many invertebrate species, which allow the identification of receptors and/or biosynthetic enzymes, when related to their vertebrate counterparts, but the story is not so simple, as will be exemplified by estrogen receptors of molluscs.

Identification of the steroid fatty acid ester conjugates formed in vivo in Mytilus edulis as a result of exposure to estrogens

Vertebrate-type sex steroids have been detected in a number of mollusk species and may play a role in the reproductive physiology of the animal. Mollusks are also exposed to exogenous estrogenic steroids that are present in sewage effluents, and these may add to the estrogenic burden of exposed animals. We investigated the uptake of estrogens in the blue mussel, Mytlius edulis and report for the first time the identity of estrogen fatty acid ester metabolites formed in vivo in an invertebrate. We exposed mussels to waterborne radiolabeled [(14)C]-17beta-estradiol (E2) or estrone (E1) and determined the nature of their metabolites using radio-HPLC and mass spectrometry (MS). After 13 days of exposure to 10ng/L E2, concentrations of radiolabeled residues were 2428-fold higher in M. edulis soft tissues compared with the ambient water concentration of E2. All the E2 residues in the mussel were present as a lipophilic ester which, in depuration studies, had a half-life of 8.3 days. Exposure of mussels to [(14)C]-E1 (70ng/L) resulted in formation of a similar lipophilic metabolite that after hydrolysis released [(14)C]-E2. Tandem MSMS analyses of the purified steroid ester fraction isolated from mussels exposed to either E2 or E1 revealed that they had the same composition and comprised C16:0, C16:1 and C16:2 esters of E2. This work reveals that in vivo E1 is rapidly metabolized to E2 in mussels prior to conjugation to C16 fatty acid esters, proving that C17-ketoreductase and C16 fatty acid acyl-CoA:E2 acyltransferase are important enzymes for the metabolism of estrogens in M. edulis.

Neuropeptidergic control of Octopus oviducal gland

The oviducal gland of the female of Octopus vulgaris lies about halfway along the oviduct. Progesterone and 17beta-estradiol receptors have been immunolocalized in the nuclei of the cells of the glandular compartment of previtellogenic glands. We also have evidence of FMRFamide-like and cGnRH-I-like immunoreactivity in the nerve endings that reach the oviducal gland. Moreover, we have recently shown APGWamide immunoreactivity in the glandular cells of the inner part of the oviducal gland. Here we report a review on these findings as well as our latest studies on the effect that neuropeptides may exert on the secretory activity of the oviducal gland. cAMP seems to be a possible second messenger involved in such a process. We discuss the findings of a neuropeptidergic action on the glandular cells of oviducal gland in a more complex frame of molecules, such as steroids, biogenic amines and neuromodulators, controlling the activity of the gland.

Tissue preferential expression of estrogen receptor gene in the marine snail, Thais clavigera

Sex steroid hormones have been widely detected in molluscs, and experiments have shown the importance of sex steroids in sex determination, gonadal tissue maturation and gametogenesis. Nevertheless, the signaling pathways of sex steroids in invertebrates have not yet been elucidated. In order to gain insights into the mechanism of sex steroid signaling in molluscs, we have, therefore, tried to isolate molluscan estrogen receptors from the prosobranch mollusc Thais clavigera. Cerebral ganglia of T. clavigera (Mollusca, Gastropoda, Prosobranchia) were subjected to RNA extraction, and degenerate primers for amino acid sequences conserved in vertebrate estrogen receptors were designed. PCR amplification using cerebral RNA and degenerate primers followed by 5'- and 3'-RACE identified the cDNA encoding T. clavigera estrogen receptor 1 (tcER1). The deduced amino acid sequence showed 93% identity in the DNA-binding domain and 72% identity in the ligand binding domain when compared to Aplysia estrogen receptor. Reporter gene assay revealed that tcER1 is constitutively active and unresponsive to estrogen. Quantitative analysis of the tcER1 mRNA level demonstrated the preferential expression in the ovary. Furthermore, cerebral ganglia expressed tcER1 at a high level in the spring followed by subsequent enlargement of the ovary in later seasons. These results suggest importance of tcER1 in the seasonal development of reproductive organs in T. clavigera.

The Octopus vulgaris estrogen receptor is a constitutive transcriptional activator: evolutionary and functional implications

Steroid hormones such as estrogens and androgens are important regulators of reproduction, physiology, and development in a variety of animal taxa, including vertebrates and mollusks. Steroid hormone receptors, which mediate the classic cellular responses to these hormones, were thought to be vertebrate specific, which left the molecular mechanisms of steroid action in invertebrates unresolved. Recently an estrogen receptor (ER) ortholog was isolated from the sea hare Aplysia californica, but the functional significance of the receptor was unclear because estrogens and other steroids are not known to be important in that species. Furthermore, the Aplysia ER was found to be a constitutive transcriptional activator, but it was unclear whether the estrogen independence of the ER was an Aplysia-specific novelty or a more ancient character general to the mollusks. Here we report on the isolation and functional characterization of the first ER ortholog from an invertebrate in which estrogens are produced and play an apparent role, the cephalopod Octopus vulgaris. We show that the Octopus ER is a strong constitutive transcriptional activator from canonical estrogen response elements. The receptor does not bind estradiol and is unresponsive to estrogens and other vertebrate steroid hormones. These characteristics are similar to those observed with the Aplysia ER and support the hypothesis that the evolving ER gained constitutive activity deep in the mollusk lineage. The apparent reproductive role of estrogens in Octopus and other mollusks is unlikely to be mediated by the ER and may take place through an ancient, non-ER-mediated pathway.

Sexual dimorphism in esterified steroid levels in the gastropod Marisa cornuarietis: the effect of xenoandrogenic compounds

Molluscs can conjugate a variety of steroids to form fatty acid esters. In this work, the freshwater ramshorn snail Marisa cornuarietis was used to investigate sex differences in endogenous levels of esterified steroids. Testosterone and estradiol were mainly found in the esterified form in the digestive gland/gonad complex of M. cornuarietis, and males had higher levels of esterified steroids than females (4-10-fold). Additionally, the ability of several xenobiotics, namely tributyltin (TBT), methyltestosterone (MT) and fenarimol (FEN) to interfere with the esterification of testosterone and estradiol was investigated. All three compounds induced imposex - appearance of male sexual characteristics in females. Exposure to TBT led to a decrease in both esterified testosterone (60-85%) and estradiol (16-53%) in females after 100 days exposure, but had no effect on males. Exposure to FEN and MT did not alter levels of esterified steroids in males or in females, although exposed females developed imposex after 150 days exposure. The decrease in esterified steroids by TBT could not be directly linked with a decrease in microsomal acyl-CoA:testosterone acyltransferase (ATAT) activity, which catalyzes the esterification of steroids. In fact, ATAT activity was marginally induced in organisms exposed to TBT for 50 days (1.3-fold), and significantly induced in males and females exposed to MT for 50 days (1.8- and 1.5-fold, respectively), whereas no effect on ATAT activity was observed after 150 days exposure.

Steroid levels and steroid metabolism in the mussel Mytilus edulis: the modulating effect of dispersed crude oil and alkylphenols

Significant amounts of oil and alkylphenols are released into the sea by petroleum installations as a result of discharges of produced water. Some of these pollutants elicit estrogenic responses in fish, but their effects on the endocrine system of molluscs are largely unknown. In this study, mussels Mytilus edulis were exposed to North Sea oil (O) and the mixture of North Sea oil+alkylphenols (OAP), and the effects on tissue steroid levels and steroid metabolism (P450-aromatase and estradiol-sulfotransferase) were monitored. Levels of free testosterone and free estradiol were much higher in gonad tissue than in peripheral tissue, whereas esterified steroids (released after saponification) were of the same order of magnitude in both tissues. Levels of free steroids determined in gonads were not affected by exposure, but esterified steroids significantly increased in OAP exposed mussels (up to 2.4-fold). The sulfation of estradiol was investigated as a conjugation pathway, and increased activities were observed in digestive gland cytosol of both O and OAP exposure groups (up to 2.8-fold). Additionally, increased P450-aromatase activity was determined in OAP exposed mussels (up to three-fold, both in gonad and digestive gland), but not in the O group. Altogether, the results indicate that North Sea oil leads to increased sulfation of estradiol, and that in combination with alkylphenols, additional alterations are observed: increased P450-aromatase, and increased levels of esterified-steroids in gonads. Nonetheless, mussels are able to maintain gonad concentrations of free steroids unaltered, possibly via homeostatic mechanisms such as the conjugation with fatty acid or the formation of sulphate conjugates.

Molecular and functional characterization of a novel gonadotropin-releasing-hormone receptor isolated from the common octopus (Octopus vulgaris)

GnRH (gonadotropin-releasing hormone) plays a pivotal role in the regulation of reproduction in vertebrates through interaction with a specific receptor. Previously, we isolated a GnRH homologue, oct-GnRH, from the common octopus (Octopus vulgaris). In the present study, we have identified a GnRH receptor (oct-GnRHR) specific for oct-GnRH from Octopus brain. Oct-GnRHR includes domains and motifs typical of vertebrate GnRH receptors. The intron-inserted positions are conserved between oct-GnRHR and the chordate GnRHR genes. The oct-GnRHR expressed in Xenopus (South African clawed frog) oocytes was responsive to oct-GnRH, but not to any other HPLC fractions of the Octopus brain extract. These results show that oct-GnRHR is an authentic receptor for oct-GnRH. Southern blotting of reverse-transcription PCR products revealed that the oct-GnRHR mRNA was widely distributed in the central and peripheral nervous systems and in several peripheral tissues. In situ hybridization showed that oct-GnRHR mRNA was expressed in some regions involved in autonomic functions, feeding, memory and movement. Oct-GnRH was shown to induce steroidogenesis of testosterone, progesterone and 17beta-oestradiol in Octopus ovary and testis, where oct-GnRHR was abundantly expressed. These results suggest that oct-GnRH, like its vertebrate counterparts, acts as a multifunctional neurotransmitter, neuromodulator and hormone-like factor, both in Octopus central nervous system and peripheral tissues, and that both structure and functions of the GnRH family are, at least partially, evolutionarily conserved between octopuses and chordates.

Regulation of vitellogenesis in Nereis virens (Annelida: Polychaeta): effect of estradiol-17beta on eleocytes

In the marine polychaete Nereis virens, the yolk protein precursor vitellogenin (Vg) is synthesized in specialized coelomic cells (eleocytes) during oogenesis. This process was visualized by immunohistochemistry using antibodies raised against the yolk protein. Transversal sections from male and female worms confirmed that eleocytes from females but not from males produce Vg. In order to investigate the hormonal regulation of Vg synthesis, eleocytes were incubated in vitro with estradiol-17beta (E(2)) at a concentration of 1 microg/l for up to three days. A strong increase in Vg secretion was detected by ELISA in culture media of treated eleocytes from vitellogenic females. In contrast, no response to the hormonal treatment was detectable in immature worms. Our results showed that Vg synthesis is under a complex regulation, which involves endocrine factors like estrogens. The role of E(2) in vitellogenesis of N. virens rather resembles the situation found in vertebrate than the one in insects.