Nervous control of reproduction in Octopus vulgaris: a new model

Chronic thermal stress on Octopus maya embryos down-regulates epigenome-related genes and those involved in the nervous system development and morphogenesis

Red Octopus maya is strongly influenced by temperature. Recent studies have reported negative reproduction effects on males and females when exposed to temperatures higher than 27 °C. Embryos under thermal stress show morphological and physiological alterations; similar phenotypes have been reported in embryos from stressed females, evidencing transgenerational consequences. Transcriptomic profiles were characterized along embryo development during normal-under thermal stress and epigenetic alterations through DNA methylation and damage quantification. Total RNA in organogenesis, activation, and growth stages in control and thermal stress were sequenced with Illumina RNA-Seq. Similarly, total DNA was used for DNA methylation and damage quantification between temperatures and embryo stages. Differential gene expression analyses showed that embryos express genes associated with oxygen transport, morphogenesis, nervous system, neuroendocrine cell differentiation, spermatogenesis, and male sex differentiation. Conversely, embryos turn off genes involved mainly in nervous system development, morphogenesis, and gene expression regulation when exposed to thermal stress - consistent with O. maya embryo phenotypes showing abnormal arms, eyes, and body development. No significant differences were observed in quantifying DNA methylation between temperatures but they were for DNA damage quantification. Epigenetic alterations are hypothesized to occur since several genes found downregulated belong to the epigenetic machinery but at histone tail level.

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.

Concomitant downregulation of neuropeptide genes in a marine snail with consecutive sexual maturation after a nuclear disaster in Japan

Consecutive sexual maturation (CSM), an abnormal reproductive phenomenon of a marine snail, Reishia clavigera, has occurred since 2017 in the vicinity of the Fukushima Daiichi Nuclear Power Plant after the nuclear disaster there. We hypothesized that alterations in animal physiology mediated through genetic/epigenetic changes could sensitively reflect environmental pollution. Understanding the mechanism of this rapid biological response should enable us to quantitatively evaluate long-lasting effects of the nuclear disaster. To determine the molecular basis for CSM, we conducted transcriptome profiling in the ganglia of normal and CSM snails. We assembled the short-read cDNA sequences obtained by Illumina sequencing, and succeeded in characterizing more than 60,000 gene models that include 88 kinds of neuropeptide precursors by BLAST search and experimental curation. GO-enrichment analysis of the differentially expressed genes demonstrated that severe downregulation of neuropeptide-related genes occurred concomitantly with CSM. In particular, significant decreases of the transcripts of 37 genes among 88 neuropeptide precursor genes, including those for myomodulin, PentaFVamide, maturation-associated peptide-5A and conopressin, were commonly observed in female and male CSM snails. By contrast, microseminoprotein precursor was the only exceptional case where the expression was increased in CSM snails. These results indicate that down-regulation of neuropeptide precursors is a remarkable feature of CSM. We also found that factors involved in epigenetic modification rather than transcription factors showed altered patterns of expression upon CSM. Comprehensive expression panels of snail neuropeptide precursors made in this study will be useful tools for environmental assessment as well as for studying marine reproductive biology.

Sex-specific role of the optic gland in octopus maya: A transcriptomic analysis

The optic glands (OG) of cephalopods are a source of molecules associated with the control of reproductive traits and lifecycle events such as sexual maturation, reproductive behavior, feeding, parental care, and senescence. However, little is known about the role of the optic gland in Octopus maya adults during mating and egg laying. RNA sequencing, de novo transcriptome assembly, ubiquity and differential expression analysis were performed. First, we analyzed the expression patterns of transcripts commonly associated with OG regulatory functions to describe their possible role once the maturation of the gonad is complete. The transcriptomic profiles of the optic gland of both sexes were compared with emphasis on the signaling pathways involved in the dimorphism of reproductive traits. Results suggest that in the OG of males, the reproductive condition (mated or non-mated) did not affect the general expression profile. In contrast, more differentially expressed genes were observed in females. In mated females, the mRNA metabolic process and the response to norepinephrine were enriched, suggesting a high cellular activity in preparation for the laying of the embryos. Whereas in egg-laying females, energetic and metabolic processes were the most represented, including the oxidation-reduction process. Finally, the gene expression patterns in senescence females suggest a physiological response to starvation as well as upregulation of genes involved retrotransposon activity. In conclusion, more substantial fluctuations in gene expression were observed in the optic glands of the fertilized females compared to the males. Such differences might be associated with the regulation of the egg-laying and the onset of senescence.

Oviducal gland transcriptomics of Octopus maya through physiological stages and the negative effects of temperature on fertilization

Background

Elevated temperatures reduce fertilization and egg-laying rates in the octopus species. However, the molecular mechanisms that control the onset of fertilization and egg-laying in the octopus' oviducal gland are still unclear; and the effect of temperature on the expression of key reproductive genes is unknown. This study aims to better understand the molecular bases of octopus fertilization and egg-laying, and how they are affected by elevated temperatures.

Method

RNA-seq of oviducal glands was performed for samples before, during, and after fertilization and their transcriptomic profiles were compared. Also, at the fertilization stage, the optimal and thermal-stress conditions were contrasted. Expression levels of key reproductive genes were validated via RT-qPCR.

Results

In mated females before egg-laying, genes required for the synthesis of spermine, spermidine, which may prevent premature fertilization, and the myomodulin neuropeptide were upregulated. Among the genes with higher expression at the fertilization stage, we found those encoding the receptors of serotonin, dopamine, and progesterone; genes involved in the assembly and motility of the sperm flagellum; genes that participate in the interaction between male and female gametes; and genes associated with the synthesis of eggshell mucoproteins. At temperatures above the optimal range for reproduction, mated females reduced the fertilization rate. This response coincided with the upregulation of myomodulin and APGW-amide neuropeptides. Also, genes associated with fertilization like LGALS3, VWC2, and Pcsk1 were downregulated at elevated temperatures. Similarly, in senescent females, genes involved in fertilization were downregulated but those involved in the metabolism of steroid hormones like SRD5A1 were highly expressed.

Mapping of neuropeptide Y expression in Octopus brains

Neuropeptide Y (NPY) is an evolutionarily conserved neurosecretory molecule implicated in a diverse complement of functions across taxa and in regulating feeding behavior and reproductive maturation in Octopus. However, little is known about the precise molecular circuitry of NPY-mediated behaviors and physiological processes, which likely involve a complex interaction of multiple signal molecules in specific brain regions. Here, we examined the expression of NPY throughout the Octopus central nervous system. The sequence analysis of Octopus NPY precursor confirmed the presence of both, signal peptide and putative active peptides, which are highly conserved across bilaterians. In situ hybridization revealed distinct expression of NPY in specialized compartments, including potential "integration centers," where visual, tactile, and other behavioral circuitries converge. These centers integrating separate circuits may maintain and modulate learning and memory or other behaviors not yet attributed to NPY-dependent modulation in Octopus. Extrasomatic localization of NPY mRNA in the neurites of specific neuron populations in the brain suggests a potential demand for immediate translation at synapses and a crucial temporal role for NPY in these cell populations. We also documented the presence of NPY mRNA in a small cell population in the olfactory lobe, which is a component of the Octopus feeding and reproductive control centers. However, the molecular mapping of NPY expression only partially overlapped with that produced by immunohistochemistry in previous studies. Our study provides a precise molecular map of NPY mRNA expression that can be used to design and test future hypotheses about molecular signaling in various Octopus behaviors.

Octopus maya white body show sex-specific transcriptomic profiles during the reproductive phase, with high differentiation in signaling pathways

White bodies (WB), multilobulated soft tissue that wraps the optic tracts and optic lobes, have been considered the hematopoietic organ of the cephalopods. Its glandular appearance and its lobular morphology suggest that different parts of the WB may perform different functions, but a detailed functional analysis of the octopus WB is lacking. The aim of this study is to describe the transcriptomic profile of WB to better understand its functions, with emphasis on the difference between sexes during reproductive events. Then, validation via qPCR was performed using different tissues to find out tissue-specific transcripts. High differentiation in signaling pathways was observed in the comparison of female and male transcriptomic profiles. For instance, the expression of genes involved in the androgen receptor-signaling pathway were detected only in males, whereas estrogen receptor showed higher expression in females. Highly expressed genes in males enriched oxidation-reduction and apoptotic processes, which are related to the immune response. On the other hand, expression of genes involved in replicative senescence and the response to cortisol were only detected in females. Moreover, the transcripts with higher expression in females enriched a wide variety of signaling pathways mediated by molecules like neuropeptides, integrins, MAPKs and receptors like TNF and Toll-like. In addition, these putative neuropeptide transcripts, showed higher expression in females' WB and were not detected in other analyzed tissues. These results suggest that the differentiation in signaling pathways in white bodies of O. maya influences the physiological dimorphism between females and males during the reproductive phase.

Transcriptome analysis for identifying possible causes of post-reproductive death of Sepia esculenta based on brain tissue

BACKGROUND

The subpeduncle lobe/olfactory lobe-optic gland axis is called the endocrine regulation center of cephalopods. However, little is known about the mechanism of the subpeduncle lobe/olfactory lobe-optic gland axis regulate the sexual maturation and post-reproductive death of Sepia esculenta Hoyle.

OBJECTIVES

The primary objective of this study was to provide basic information for revealing the mechanism of the subpeduncle lobe/olfactory lobe-optic axis regulating the rapid post-reproductive death of S. esculenta.

METHODS

In this paper, Illumina sequencing based transcriptome analysis was performed on the brain tissue of female S. esculenta in the three key developmental stages: growth stage (BG), spawning stage (BS), and post-reproductive death stage (BA).

RESULTS

A total of 66.19 Gb Illumina sequencing data were obtained. A comparative analysis of the three stages showed 2609, 3333, and 170 differentially expressed genes (DEGs) in BG-vs-BA, BG-vs-BA, and BS-vs-BA, respectively. The Gene Ontology (GO) enrichment analysis of DEGs revealed that the regulation of cyclin-dependent protein serine/threonine kinase activity, oxidative phosphorylation, and respiratory chain were significantly enriched. The significant enrichment analysis of the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway identified pathways associated with the regulation of death, such as the mammalian target of rapamycin (mTOR) signaling pathway, AMPK signaling pathway, oxidative phosphorylation, and cell cycle.

CONCLUSION

The post-reproductive death of S. esculenta was found to be a complex energy steady-state regulation network system. The mTOR acted as an energy receptor and had a key role in regulating energy homeostasis.

Identification and Characterization of Neuropeptides by Transcriptome and Proteome Analyses in a Bivalve Mollusc Patinopecten yessoensis

Neuropeptides play essential roles in regulation of reproduction and growth in marine molluscs. But their function in marine bivalves – a group of animals of commercial importance – is largely unexplored due to the lack of systematic identification of these molecules. In this study, we sequenced and analyzed the transcriptome of nerve ganglia of Yesso scallop Patinopecten yessoensis, from which 63 neuropeptide genes were identified based on BLAST and de novo prediction approaches, and 31 were confirmed by proteomic analysis using the liquid chromatography-tandem mass spectrometry (LC-MS/MS). Fifty genes encode known neuropeptide precursors, of which 20 commonly exist in bilaterians and 30 are protostome specific. Three neuropeptides that have not yet been reported in bivalves were identified, including calcitonin/DH31, lymnokinin and pleurin. Characterization of glycoprotein hormones, insulin-like peptides, allatostatins, RFamides, and some reproduction, cardioactivity or feeding related neuropeptides reveals scallop neuropeptides have conserved molluscan neuropeptide domains, but some (e.g., GPB5, APGWamide and ELH) are characterized with bivalve-specific features. Thirteen potentially novel neuropeptides were identified, including 10 that may also exist in other protostomes, and 3 (GNamide, LRYamide, and Vamide) that may be scallop specific. In addition, we found neuropeptides potentially related to scallop shell growth and eye functioning. This study represents the first comprehensive identification of neuropeptides in scallop, and would contribute to a complete understanding on the roles of various neuropeptides in endocrine regulation in bivalve molluscs.

Expression profile and reproductive regulation of APGWamide in Pacific abalone (Haliotis discus hannai)

Neuropeptides in the central nervous system regulate reproductive activities in vertebrates. Ala-Pro-Gly-Trp-NH₂ (APGWamide), a neuromediator expressed in the neural ganglia of mollusks, controls sexual maturation and reproduction. To clarify the role of APGWamide in sexual behavior regulation and gamete cell maturation in mollusks, we cloned the cDNA of APGWamide precursor (Hdh-APGWamide) and examined the spatiotemporal expression of the transcript in the Pacific abalone Haliotis discus hannai. The 222-amino acid sequence of the precursor deduced from the cDNA sequence showed typical features of gastropod APGWamide precursors. Phylogenetic analysis revealed that Hdh-APGWamide is classified with other gastropod APGWamide precursors, which form a separate branch from those of the bivalves. Hdh-APGWamide mRNA was highly expressed in the neural ganglia in both sexes. In females, the three ganglia (pleuro-pedal ganglion, PPG; branchial ganglion, and cerebral ganglion) showed similar expression in immature and mature animals, whereas in males, the level in the PPG only was higher at maturity (P < 0.05). In vivo injection of APGWamide or 5-hydroxytryptamine (10^-3 M) increased the frequency of spawning and the number of released sperm cells by mature males (P < 0.05), while concentrations above 10^-7 M enhanced germinal vesicle breakdown in fully developed cultured oocytes (P < 0.05). Thus, the phylogenetic branch of the APGWamide precursor gene in Haliotidae was separate from the other branches under the phylum Mollusca, and this gene exhibited ganglion-specific expression, indicating that it may induce final maturation and spawning in both sexes of Haliotis spp.

Distribution of the neuro-regulatory peptide galanin in the human eye

Galanin (GAL) is a neuro-regulatory peptide involved in many physiological and pathophysiological processes. While data of GAL origin/distribution in the human eye are rather fragmentary and since recently the presence of GAL-receptors in the normal human eye has been reported, we here systematically search for sources of ocular GAL in the human eye. Human eyes (n=14) were prepared for single- and double-immunohistochemistry of GAL and neurofilaments (NF). Cross- and flat-mount sections were achieved; confocal laser-scanning microscopy was used for documentation. In the anterior eye, GAL-immunoreactivity (GAL-IR) was detected in basal layers of corneal epithelium, endothelium, and in nerve fibers and keratinocytes of the corneal stroma. In the conjunctiva, GAL-IR was seen throughout all epithelial cell layers. In the iris, sphincter and dilator muscle and endothelium of iris vessels displayed GAL-IR. It was also detected in stromal cells containing melanin granules, while these were absent in others. In the ciliary body, ciliary muscle and pigmented as well as non-pigmented ciliary epithelium displayed GAL-IR. In the retina, GAL-IR was detected in cells associated with the ganglion cell layer, and in endothelial cells of retinal blood vessels. In the choroid, nerve fibers of the choroidal stroma as well as fibers forming boutons and surrounding choroidal blood vessels displayed GAL-IR. Further, the majority of intrinsic choroidal neurons were GAL-positive, as revealed by co-localization-experiments with NF, while a minority displayed NF- or GAL-IR only. GAL-IR was also detected in choroidal melanocytes, as identified by the presence of intracellular melanin-granules, as well as in cells lacking melanin-granules, most likely representing macrophages. GAL-IR was detected in numerous cells and tissues throughout the anterior and posterior eye and might therefore be an important regulatory peptide for many aspects of ocular control. Upcoming studies in diseased tissue will help to clarify the role of GAL in ocular homeostasis.

Olfactory organ of Octopus vulgaris: morphology, plasticity, turnover and sensory characterization

The cephalopod olfactory organ was described for the first time in 1844 by von Kölliker, who was attracted to the pair of small pits of ciliated cells on each side of the head, below the eyes close to the mantle edge, in both octopuses and squids. Several functional studies have been conducted on decapods but very little is known about octopods. The morphology of the octopus olfactory system has been studied, but only to a limited extent on post-hatching specimens, and the only paper on adult octopus gives a minimal description of the olfactory organ. Here, we describe the detailed morphology of young male and female Octopus vulgaris olfactory epithelium, and using a combination of classical morphology and 3D reconstruction techniques, we propose a new classification for O. vulgaris olfactory sensory neurons. Furthermore, using specific markers such as olfactory marker protein (OMP) and proliferating cell nuclear antigen (PCNA) we have been able to identify and differentially localize both mature olfactory sensory neurons and olfactory sensory neurons involved in epithelium turnover. Taken together, our data suggest that the O. vulgaris olfactory organ is extremely plastic, capable of changing its shape and also proliferating its cells in older specimens.

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.

Invertebrate neuroscience and CephsInAction at the Mediterranean Society for Neuroscience Meeting Cagliari 2015

Invertebrate neuroscience, and in particular cephalopod research, is well represented in the Mediterranean region. Therefore, the recent meeting of the Mediterranean Society for Neuroscience in Santa Margherita di Pula, Sardinia (12-15 June 2015) provided an excellent opportunity for invertebrate contributions. Furthermore, the Chair of an EU COST Action for cephalopod research (FA1301; www.cephsinaction.org ), Giovanna Ponte, together with Graziano Fiorito from the Stazione Zoologica, Naples, aligned a meeting of research groups working in the field of cephalopod neurophysiology from across Europe to coincide with the neuroscience meeting. This provided an exciting forum for exchange of ideas. Here we provide brief highlights of both events and an explanation of the activities of the COST Action for the broader invertebrate neuroscience community.

In Vivo Administration of Scallop GnRH-Like Peptide Influences on Gonad Development in the Yesso Scallop, Patinopecten yessoensis

Existing research on the role of gonadotropin-releasing hormone (GnRH) in bivalve reproduction is inadequate, even though a few bivalve GnRH orthologs have been cloned. The objective of this paper was to elucidate the in vivo effect of GnRH administration in Yesso scallop reproduction. We performed in vivo administration of scallop GnRH (py-GnRH) synthetic peptide into the developing gonad, and analyzed its effect on gonad development for 6 weeks during the reproductive season. The resulting sex ratio in the GnRH administered (GnRH(+)) group might be male biased, whereas the control (GnRH(-)) group had an equal sex ratio throughout the experiment. The gonad index (GI) of males in the GnRH(+) group increased from week 2 to 24.8% at week 6. By contrast the GI of the GnRH(-) group peaked in week 4 at 16.6%. No significant difference was seen in female GI between the GnRH(+) and GnRH(-) groups at any sampling point. Oocyte diameter in the GnRH(+) group remained constant (about 42–45 μm) throughout the experiment, while in the GnRH(-) group it increased from 45 to 68 μm i.e. normal oocyte growth. The number of spermatogonia in the germinal acini of males in the GnRH(+) group increased from week 4 to 6. Hermaphrodites appeared in the GnRH(+) group in weeks 2 and 4. Their gonads contained many apoptotic cells including oocytes. In conclusion, this study suggests that py-GnRH administration could have a potential to accelerate spermatogenesis and cause an inhibitory effect on oocyte growth in scallops.

Role of olfaction in Octopus vulgaris reproduction

The olfactory system in any animal is the primary sensory system that responds to chemical stimuli emanating from a distant source. In aquatic animals "Odours" are molecules in solution that guide them to locate food, partners, nesting sites, and dangers to avoid. Fish, crustaceans and aquatic molluscs possess sensory systems that have anatomical similarities to the olfactory systems of land-based animals. Molluscs are a large group of aquatic and terrestrial animals that rely heavily on chemical communication with a generally dispersed sense of touch and chemical sensitivity. Cephalopods, the smallest class among extant marine molluscs, are predators with high visual capability and well developed vestibular, auditory, and tactile systems. Nevertheless they possess a well developed olfactory organ, but to date almost nothing is known about the mechanisms, functions and modulation of this chemosensory structure in octopods. Cephalopod brains are the largest of all invertebrate brains and across molluscs show the highest degree of centralization. The reproductive behaviour of Octopus vulgaris is under the control of a complex set of signal molecules such as neuropeptides, neurotransmitters and sex steroids that guide the behaviour from the level of individuals in evaluating mates, to stimulating or deterring copulation, to sperm-egg chemical signalling that promotes fertilization. These signals are intercepted by the olfactory organs and integrated in the olfactory lobes in the central nervous system. In this context we propose a model in which the olfactory organ and the olfactory lobe of O. vulgaris could represent the on-off switch between food intake and reproduction.