Sex reversal by implantations of ethanol-treated androgenic glands of female isopods, Armadillidium vulgare (Malacostraca, crustacea)

Chemical synthesis of insulin-like peptide 1 and its potential role in vitellogenesis of the kuruma prawn Marsupenaeus japonicus

The insulin superfamily comprises a group of peptides with diverse physiological functions and is conserved across the animal kingdom. Insulin-like peptides (ILPs) of crustaceans are classified into four major types: insulin, relaxin, gonadulin, and androgenic gland hormone (AGH)/insulin-like androgenic gland factor (IAG). Of these, the physiological functions of AGH/IAG have been clarified to be the regulation of male sex differentiation, but those of the other types have not been uncovered. In this study, we chemically synthesized Maj-ILP1, an ILP identified in the ovary of the kuruma prawn Marsupenaeus japonicus, using a combination of solid-phase peptide synthesis and regioselective disulfide bond formation reactions. As the circular dichroism spectral pattern of synthetic Maj-ILP1 is typical of other ILPs reported thus far, the synthetic peptide likely possessed the proper conformation. Functional analysis using ex vivo tissue incubation revealed that Maj-ILP1 significantly increased the expression of the yolk protein genes Maj-Vg1 and Maj-Vg2 in the hepatopancreas and Maj-Vg1 in the ovary of adolescent prawns. This is the first report on the synthesis of a crustacean ILP other than IAGs and also shows the positive relationship between the reproductive process and female-dominant ILP.

Investigating the Molecular Genetic Basis of Cytoplasmic Sex Determination Caused by Wolbachia Endosymbionts in Terrestrial Isopods

In animals, sexual differences between males and females are usually determined by sex chromosomes. Alternatively, sex may also be determined by vertically transmitted intracellular microbial endosymbionts. The best known cytoplasmic sex manipulative endosymbiont is Wolbachia which can, for instance, feminize genetic males into phenotypic females in the terrestrial isopod Armadillidium vulgare. However, the molecular genetic basis of cytoplasmic sex determination is unknown. To identify candidate genes of feminization induced by Wolbachia strain wVulC from A. vulgare, we sequenced the genome of Wolbachia strain wCon from Cylisticus convexus, the most closely related known Wolbachia strain to wVulC that does not induce feminization, and compared it to the wVulC genome. Then, we performed gene expression profiling of the 216 resulting wVulC candidate genes throughout host developmental stages in A. vulgare and the heterologous host C. convexus. We identified a set of 35 feminization candidate genes showing differential expression during host sexual development. Interestingly, 27 of the 35 genes are present in the f element, which is a piece of a feminizing Wolbachia genome horizontally transferred into the nuclear genome of A. vulgare and involved in female sex determination. Assuming that the molecular genetic basis of feminization by Wolbachia and the f element is the same, the 27 genes are candidates for acting as master sex determination genes in A. vulgare females carrying the f element.

Characterization of distinct ovarian isoform of crustacean female sex hormone in the kuruma prawn Marsupenaeus japonicus

The eyestalk hormone, crustacean female sex hormone (CFSH), regulates the development of female secondary sexual characteristics in the blue crab Callinectes sapidus. After its discovery, several CFSH gene orthologs have been identified in some species of the suborder Pleocyemata as well. Similarly, in species of another suborder (Dendrobranchiata), an ortholog (Maj-CFSH) has been characterized as an eyestalk factor expressed in both females and males of the kuruma prawn, Marsupenaeus japonicus. In this study, another novel CFSH isoform was identified in the same species using cDNA cloning, expression analysis, and recombinant protein production. The isoform has "CFSH-family" structural characteristics but is dominantly expressed in the ovary, and was therefore designated as Maj-CFSH-ov. Its mRNA and protein levels in vitellogenic ovaries are higher than those in non-vitellogenic ovaries. In the vitellogenic ovary, both mRNA and protein expression of Maj-CFSH-ov are localized to oogonia and previtellogenic oocytes that occupy a small portion of vitellogenic ovaries, but not to the major developing oocytes. A vitellogenesis-inhibiting peptide of M. japonicus (Pej-SGP-I) reduced the expression of vitellogenin in incubated ovarian fragments, but not that of Maj-CFSH-ov. These results indicate that M. japonicus possesses two CFSH isoforms that are derived from distinct tissues, the central X-organ/sinus gland complex and peripheral ovaries. The expression profile of Maj-CFSH-ov suggests its involvement in some reproductive process other than vitellogenesis.

Isolation and Tissue Distribution of an Insulin-Like Androgenic Gland Hormone (IAG) of the Male Red Deep-Sea Crab, Chaceon quinquedens

The insulin-like androgenic gland hormone (IAG) found in decapod crustaceans is known to regulate sexual development in males. IAG is produced in the male-specific endocrine tissue, the androgenic gland (AG); however, IAG expression has been also observed in other tissues of decapod crustacean species including Callinectes sapidus and Scylla paramamosain. This study aimed to isolate the full-length cDNA sequence of IAG from the AG of male red deep-sea crabs, Chaceon quinquedens (ChqIAG), and to examine its tissue distribution. To this end, we employed polymerase chain reaction cloning with degenerate primers and 5′ and 3′ rapid amplification of cDNA ends (RACE). The full-length ChqIAG cDNA sequence (1555 nt) includes a 366 nt 5′ untranslated region a 453 nt open reading frame encoding 151 amino acids, and a relatively long 3′ UTR of 733 nt. The ORF consists of a 19 aa signal peptide, 32 aa B chain, 56 aa C chain, and 44 aa A chain. The putative ChqIAG amino acid sequence is most similar to those found in other crab species, including C. sapidus and S. paramamosain, which are clustered together phylogenetically.

Phase-specific expression of an insulin-like androgenic gland factor in a marine shrimp Lysmata wurdemanni: Implication for maintaining protandric simultaneous hermaphroditism

BACKGROUND

Shrimp in the genus Lysmata have a unique and rare sexual system referred to as protandric simultaneous hermaphroditism, whereby individuals mature first as male (male phase), and then the female function may also develop as the shrimp grow, so that the gonad is able to produce both eggs and sperms simultaneously, a condition called simultaneous hermaphroditism (euhermaphrodite phase). To date, the mechanisms of sex control in this sexual system still remain poorly understood. Many studies indicate that an insulin-like androgenic gland factor (IAG) is involved in controlling sex differentiation in gonochoric crustaceans, but its role in the protandric simultaneous hermaphrodite is still not clear.

RESULTS

To determine whether an IAG is involved in sex control in the hermaphrodite, here we, for the first time, cloned the IAG gene cDNA sequence from Lysmata wurdemanni (termed Lw-IAG: L. wurdemanni insulin-like AG factor), a protandric simultaneous hermaphroditic shrimp. The IAG contains an open reading frame of 528 bp, corresponding to 176 amino acids, which consists of a signal peptide, B chain, C peptide, and A chain. The organization is similar to the IAGs found in other decapods. The IAG gene was expressed in both male and euhermaphrodite phases, but the expression level was significantly higher in the male phase than in the euhermaphrodite phase. Immunofluorescence analysis and Western Blotting revealed that the IAG protein was expressed in the androgenic gland, and its expression level was higher in the male phase than in the euhermaphrodite phase.

CONCLUSIONS

Data presented here suggest that the IAG gene may be a factor controlling sex in the protandric simultaneous hermaphrodite, and that the euhermaphrodite phase is maintained by reduced gene expression, i.e., the presence of the androgenic gland (or the androgenic hormone it produces) completely inhibits ovarian development in the male phase, and incomplete degeneration of the androgenic gland in the euhermaphrodite phase results in simultaneous hermaphroditism. The findings presented in the current study can help to reveal how protandric simultaneous hermaphroditism evolved in crustaceans.

Two spliced variants of insulin-like androgenic gland hormone gene in the Chinese shrimp, Fenneropenaeus chinensis

More and more evidence indicates that the insulin-like androgenic gland hormone (IAG) plays an important role in male sexual differentiation in crustaceans. In the present study, two IAG isoforms (Fc-IAG1 and Fc-IAG2) were identified from the penaeid shrimp Fenneropenaeus chinensis. Sequence analysis of IAG gene (Fc-IAG) showed that Fc-IAG1 and Fc-IAG2 were generated by alternative splicing of Fc-IAG pre-mRNA, and they shared almost the same deduced amino acid sequence. Both of them were composed of signal peptide, B chain, C peptide and A chain. They both contained the six conserved cysteine residues and a putative N-linked glycosylated site like IAGs reported in other crustacean species. Tissue distribution and in situ hybridization analysis revealed that they had the highest expression level in the androgenic gland. The transcripts of Fc-IAG1 and Fc-IAG2 could also be detected in hepatopancreas and nerve cord of both sexes at a low expression level. Analysis on their temporal expression profiles showed that they expressed at all embryonic and post-larvae stages. The expression of Fc-IAG1 at different developmental stages displayed a low and stable manner, while the expression of Fc-IAG2 began to increase from post-larvae stages, which suggested that Fc-IAG2 might be involved in male sexual differentiation. In the 5' flanking sequence of Fc-IAG, putative binding sites for transcription factors regulating transcription of hormone genes and genes related to sexual development were predicted, which provided us a primary understanding on the regulation mechanism of Fc-IAG gene. This is the first time to report the gene structure of IAG gene and distinct variants of IAG transcripts in crustaceans.

Cloning of an insulin-like androgenic gland factor (IAG) from the blue crab, Callinectes sapidus: implications for eyestalk regulation of IAG expression

In malacostracan crustaceans, sex differentiation is uniquely regulated by a hormone secreted by the male-specific androgenic gland (AG). An isopod AG hormone was the first to be structurally elucidated and was found to belong to the insulin superfamily of proteins. Recently, it has been found that the AGs of several decapod crustaceans express insulin-like androgenic gland factors (IAGs), whose function is believed to be similar to that of the isopod AG hormone. Here we report the isolation from the blue crab Callinectes sapidus of the full-length cDNA encoding a candidate insulin-like AG hormone, termed Cas-IAG. The predicted protein Cas-IAG was encoded as a precursor consisting of a signal peptide, the B chain, the C peptide, and the A chain in that order. While the AG was the main source of Cas-IAG expression, as found in other decapod species, the hepatopancreas of male Callinectes sapidus crabs displayed minor Cas-IAG expression. Eyestalk ablation confirmed the presence of a possible endocrine axis between the eyestalk ganglia and the AG, implying that Cas-IAG expression is negatively regulated by (a) substance(s) present in the eyestalk ganglia.

Reproductive regulators in decapod crustaceans: an overview

Control of reproductive development in crustaceans requires neuropeptides, ecdysone and methyl farnesoate (MF). A major source of neuropeptides is the X-organ-sinus gland (XO-SG) complex located in the eyestalk ganglia of crustaceans. The other regulatory factors (either peptides or neuromodulators) are produced in the brain and thoracic ganglia (TG). Two other regulatory non-peptide compounds, the steroid ecdysone and the sesquiterpene MF, are produced by the Y-organs and the mandibular organs, respectively. In the current review, I have tried to recapitulate recent studies on the role of gonadal regulatory factors in regulating crustacean reproduction.

A sexual shift induced by silencing of a single insulin-like gene in crayfish: ovarian upregulation and testicular degeneration

In sequential hermaphrodites, intersexuality occurs naturally, usually as a transition state during sexual re-differentiation processes. In crustaceans, male sexual differentiation is controlled by the male-specific androgenic gland (AG). An AG-specific insulin-like gene, previously identified in the red-claw crayfish Cherax quadricarinatus (designated Cq-IAG), was found in this study to be the prominent transcript in an AG cDNA subtractive library. In C. quadricarinatus, sexual plasticity is exhibited by intersex individuals in the form of an active male reproductive system and male secondary sex characters, along with a constantly arrested ovary. This intersexuality was exploited to follow changes caused by single gene silencing, accomplished via dsRNA injection. Cq-IAG silencing induced dramatic sex-related alterations, including male feature feminization, a reduction in sperm production, extensive testicular degeneration, expression of the vitellogenin gene, and accumulation of yolk proteins in the developing oocytes. Upon silencing of the gene, AG cells hypertrophied, possibly to compensate for low hormone levels, as reflected in the poor production of the insulin-like hormone (and revealed by immunohistochemistry). These results demonstrate both the functionality of Cq-IAG as an androgenic hormone-encoding gene and the dependence of male gonad viability on the Cq-IAG product. This study is the first to provide evidence that silencing an insulin-like gene in intersex C. quadricarinatus feminizes male-related phenotypes. These findings, moreover, contribute to the understanding of the regulation of sexual shifts, whether naturally occurring in sequential hermaphrodites or abnormally induced by endocrine disruptors found in the environment, and offer insight into an unusual gender-related link to the evolution of insulins.

Can you feminise a crustacean?

The ability of anthropogenic chemicals to cause reproductive disorders has been the focus of toxicologists for many years. Whilst the focus of endocrine disrupting chemicals has mainly been associated with vertebrate groups, there have been continued calls for more research on the invertebrates. Surprisingly, within the Crustacea, many studies have focussed on female or growth/moulting related endpoints despite many of the vertebrate studies highlighting male related effects such as abnormal male reproductive development. Furthermore, a large number of the invertebrate studies have focussed on vertebrate estrogens or their mimics. Considering the biology of the crustacean endocrine systems, this paper shall argue that unlike the vertebrates, it is a lot more difficult to feminise a crustacean than it is to de-masculinise one. Consequently, crustacean toxicologists, by following the tact of vertebrate biologists, may have been trying to address the right questions, but in the wrong way. Studies have shown that intersexuality in crustaceans may arise through the masculinisation of heterogametic (WZ) females or the de-masculinisation of males through aberrations in male androgenic gland activity. It is recommended that the focus be put on understanding the mechanisms of sex determination in Crustacea, and the expression of male secondary sexual characteristics at the molecular, biochemical and physiological level are fully explored so that appropriate assessments can be made as to whether sexual endocrine disruption is occurring in this ecologically important group.

Inhibitory effects of the androgenic gland on ovarian development in the mud crab Scylla paramamosain

Isolation and characterization of androgenic hormone in decapod crustaceans depend on an effective bioassay of its action. In the present study, the effect of androgenic gland on ovarian development in the mud crab Scylla paramamosain was investigated with a view to develop a bioassay for androgenic hormone. Ovarian regression with degeneration of oocytes occurred in some female crabs implanted with androgenic gland in vivo. In vitro incubation of ovarian tissues at secondary vitellogenesis in extract of androgenic gland resulted in a significant decrease in amino acid uptake by the tissues. We propose that this inhibitory effect could be established as an effective bioassay for the isolation of androgenic hormone in the mud crab.

Developmental toxicity of testosterone in the crustacean Daphnia magna involves anti-ecdysteroidal activity

Testosterone has been shown to cause developmental arrest of embryonic daphnids (Daphnia magna). The present study was undertaken to determine whether this toxicity might be due to anti-ecdysteroidal activity associated with testosterone. The effect of testosterone on molt frequency of early instar daphnids was first evaluated to determine whether testosterone interfered with this ecdysteroid-regulated process. Molt frequency was delayed by exposure to testosterone and this effect was mitigated by co-exposure to the ecdysteroid 20-hydroxyecdysone. Testosterone exposure concentrations that interfered with molting also elicited developmental abnormalities among neonatal organisms produced by maternal organisms that were continuously exposed to testosterone or among embryos that were removed from unexposed mothers and exposed directly to the hormone. Embryos were significantly protected against the developmental toxicity of testosterone by co-exposure to 20-hydroxyecdysone. Taken together, these results demonstrated that the embryo toxicity of testosterone to daphnids is due largely to its ability to interfere with ecdysteroid control of development. Experiments next were conducted to determine whether testosterone interfered with ecdysteroidal activity by acting as an ecdysone receptor antagonist or by reducing endogenous ecdysone levels. Testosterone significantly antagonized the action of 20-hydroxyecdysone in an ecdysone-responsive cell line. Testosterone had no discernable effect on endogenous ecdysone levels in daphnids. These results demonstrated that (1). ecdysteroids regulate critical processes in daphnid embryo development, (2). testosterone elicits embryo toxicity to daphnids by interfering with ecdysteroid activity, and (3). ecdysteroid receptor antagonism could be one mechanism by which testosterone elicits these effects.

Effects of implantation of hypertrophied androgenic glands on sexual characters and physiology of the reproductive system in the female red claw crayfish, Cherax quadricarinatus

The role of the androgenic gland (AG), an organ unique to male Crustacea, in the development of sex characters and physiology of the reproductive system has not been fully documented in the red claw crayfish, Cherax quadricarinatus. To investigate the role of the AG in this species, the effect of implanting hypertrophied AGs into immature female animals was followed. Of the female animals with AG implants, 91.6% developed male-like propodi, including the red patch characteristic of males of this species. The development of female secondary sex characteristics such as a wider abdomen, a wider endopod, and simple setation was inhibited. At the end of the experiment, the ovaries of the AG-implanted females contained mostly lipid-stage oocytes, with a small number of oocytes at the early yolk stage. The gonadosomatic index of the AG-implanted females was significantly lower than that of the control (sperm duct-implanted or sham-operated) females, which had mature oocytes with a well-defined perinuclear zone and yolk globules. An immunohistochemical test using an antibody developed against a 106-kDa secondary vitellogenic polypeptide showed only slight immunoreactivity in the oocytes of AG-implanted females compared with abundant immunoreactivity in control ovaries. In the polypeptide profile of the high-density lipoprotein (HDL) from the hemolymph of AG-implanted females, the 206- and 79-kDa secondary vitellogenesis-specific polypeptides were not found, whereas they were present in the profile of control females. In contrast, the female-specific 177-kDa polypeptide was present in the polypeptide profile of hemolymph HDL of both AG-implanted females and control females. It seems therefore that while secondary sex characters were masculinized under the influence of the implanted AG, the process of vitellogenesis was suppressed but not fully eliminated in the AG-implanted females.

Characterization and cDNA cloning of androgenic gland hormone of the terrestrial isopod Armadillidium vulgare

The sex differentiation in crustaceans is known to be controlled by a peptide hormone called androgenic gland hormone (AGH). AGH was extracted and purified from the androgenic glands (AGs) of the male isopod Armadillidium vulgare by high-performance liquid chromatography. AGH consisted of two peptide chains and their N-terminal amino acid sequences were determined. A cDNA encoding AGH was cloned by PCR and sequenced. The cDNA had an open reading frame of 432 bp, which encoded a preproAGH consisting of a signal peptide (21 residues), B chain (44 residues), C peptide (46 residues), and A chain (29 residues). Through processing, the A and B chains might form a heterodimer interlinked by disulfide bonds. The A chain possessed a putative N-linked glycosylation site. A Northern blot analysis using the cDNA as a probe detected a hybridization signal with 0.8 kb in the RNA preparation only from the AGs.

Androgenic gland hormone is a sex-reversing factor but cannot be a sex-determining factor in the female crustacean isopods Armadillidium vulgare

Sex reversal of female isopods, Armadillidium vulgare, has been induced by implantation of the androgenic gland (AG) into individuals after the initiation of morphological sex differentiation. The focus of the present study is to examine whether female gonads are reversed by the androgenic gland hormone (AGH) during the sexually undifferentiated period through postembryonic development in A. vulgare. Instead of injections of AGH, three AGs were implanted into each genetic female at various developmental stages to induce sex reversal. Before implantation fresh AGs were treated with ethanol to stop AGH synthesis, but then still contained AGH. These AGs have been referred to as ethanol-treated AGs (t-AGs). Development of a testis was used as an indicator of gonadal sex reversal. The gonads of genetic females were transformed into testes by implantations of t-AGs during the sex differentiation period. However, when genetic females received implants at sexually undifferentiated stages, development of their gonads was not reversed in the male direction. These results suggest that after the onset of gonadal sex differentiation, AGH is a sex-reversing factor that can turn a female gonad into a male gonad. AGH cannot be a sex-determining factor in female A. vulgare, as undifferentiated gonads of genetic females are not sex reversed by the hormone.