Gamete Release Research Articles

Follicle-intrinsic and spatially distinct molecular programs drive follicle rupture and luteinization during ex vivo mammalian ovulation

During ovulation, the apical wall of the preovulatory follicle breaks down to facilitate gamete release. In parallel, the residual follicle wall differentiates into a progesterone-producing corpus luteum. Disruption of ovulation, whether through contraceptive intervention or infertility, has implications for women’s health. In this study, we harness the power of an ex vivo ovulation model and machine-learning guided microdissection to identify differences between the ruptured and unruptured sides of the follicle wall. We demonstrate that the unruptured side exhibits clear markers of luteinization after ovulation while the ruptured side exhibits cell death signals. RNA-sequencing of individual follicle sides reveals 2099 differentially expressed genes (DEGs) between follicle sides without ovulation induction, and 1673 DEGs 12 h after induction of ovulation. Our model validates molecular patterns consistent with known ovulation biology even though this process occurs in the absence of the ovarian stroma, vasculature, and immune cells. We further identify previously unappreciated pathways including amino acid transport and Jag-Notch signaling on the ruptured side and glycolysis, metal ion processing, and IL-11 signaling on the unruptured side of the follicle. This study yields key insights into follicle-inherent, spatially-defined pathways that underlie follicle rupture, which may further understanding of ovulation physiology and advance women’s health.

An ulvophycean marine green alga produces large parthenogenetic isogametes as predicted by the gamete dynamics model for the evolution of anisogamy.

In eukaryotes, gamete size difference between the two sexes (anisogamy) evolved from gametes of equal size in both mating types (isogamy). The gamete dynamics (GD) model for anisogamy evolution combines gamete limitation and competition and predicts that if gametes of both mating types can develop parthenogenetically (i.e. without fusing with the opposite mating type), large isogamy can evolve under gamete-limited conditions. Ulvophycean marine green algae that have been claimed to exhibit various gametic systems from isogamy to anisogamy are important models for testing such theories. However, in most previous papers, whether a species is isogamous or anisogamous has not been examined statistically. Caution is necessary regarding claims of slight anisogamy because of gamete size variation. We reveal (i) that the gametic system of Struvea okamurae is large isogamy using a generalized linear mixed model, which accounted for the variation of gamete size among individual gametophytes, and (ii) that gametes of this alga can actually develop parthenogenetically, contrary to a previous report. Its habitat environments and protracted duration of gamete release suggest that this alga might experience gamete-limited conditions. Struvea okamurae seems to produce large parthenogenetic isogametes following GD model predictions, as an adaptation to deep waters.

Antidepressants as new endocrine disruptors? – transcriptomic profiling in gonads of Mytilus trossulus exposed to norfluoxetine

In this study an impact of norfluoxetine (NFLU) on Mytilus trossulus gonads was investigated focusing on sex-related differences in hormonal changes, gene expression, and transcriptomic profiling. Sex-specific differences in gonadal serotonin levels were found. NFLU stimulates serotonin synthesis and/or transport in female gonads, potentially accelerating oocyte maturation and gamete release. In males, NFLU decreases serotonin level what likely leads to impeding sperm maturation and thus spawning delay. Transcriptomic analyses highlighted the presence of NFLU-induced changes in gene expression related to gametogenesis and neurotransmission. In females, NFLU upregulated genes associated with oocyte development and downregulated those involved in sperm maturation. NFLU-treated males exhibited mixed effects in their genes in relation to spermatogenesis. Additionally, sex-related differences in the expression of the CYP450 genes responsible for detoxification were found. Overall, norfluoxetine acts as an endocrine-disrupting chemical and impacts gonadal serotonin levels and gene expression, potentially disrupting reproductive success of M. trossulus.

Gonadal Cycle of Corbicula largillierti (Bivalvia: Cyrenidae) in a Pampean Streams, Argentina

The reproductive cycle of non-native species is indicative of their capacity for dispersal, invasion, and competition, and the alteration in biodiversity. Corbicula spp. are successful invaders of aquatic ecosystems. We studied the reproductive cycle of Corbicula largillierti from a Pampean stream, Argentina, at its southern distribution in South America. Specimens were collected monthly from January 2003 to April 2005 and processed using traditional histological techniques. Three gonadal stages (active gametogenesis, mature, and spawned) were recognized. In the studied population, most individuals were hermaphroditic with a dominant female gonadal portion. The three gonadal stages were observed during the whole sampling period with rapid gonadal recovery; no resting period was observed. Five oocyte spawning events were recognized, occurring in autumn and spring. Expanding the knowledge of reproductive features of the Corbicula largillierti allows the understanding of current distributions. The results highlight the difficulty of identifying patterns of gamete release and spawning behavior in this invasive species, as it is recorded for other Corbicula spp.

A rare case of intra-ovarian oocyte maturation.

The intra-ovarian presence of ootids, i.e. female gametes that have completed meiosis, is considered exceptional in the animal kingdom. The present study explores the first such case to be reported in a sea cucumber (Echinodermata: Holothuroidea). In the overwhelming majority of animals, including holothuroids, oocytes (i.e. immature female gametes) that are developing in the ovary undergo a primary arrest at the prophase stage of meiosis, which may last from days to decades. In free-spawning taxa, this arrest is normally lifted only during or shortly before transit in the gonoduct, when gamete release (spawning) is imminent. However, oocytes of the holothuroid Chiridota laevis were discovered to have resumed the second meiotic division including the completion of germinal vesicle breakdown and polar-body expulsion inside the ovary, effectively reaching the ootid stage concomitantly with ovulation (i.e. escape from follicle cells) prior to spawning. The potential drivers and significance of this exceptionally rare case of full intra-ovarian oogenic maturation are discussed.

Potential sexual pheromones of sea cucumber Apostichopus japonicus and their functions on aggregative and spawning behavior

The surging market demand for sea cucumbers (Apostichopus japonicus) has fueled a thriving growth in the sea cucumber breeding industry. Pheromones are molecules that evolve signals in defined proportions in the case of multicomponent pheromones, emitted by one individual and received by a second individual of the same species to cause a specific response. It remains an enigma as to how the species of sea cucumber, devoid of visual, auditory, and olfactory senses, aggregate and communicate within their groups, as well as coordinate gamete release during the breeding period. We hypothesize that pheromones may serve as the medium for facilitating these behaviors and propose conducting experiments centered around pheromonal investigation. In this study, we aimed to analyze common metabolites of male A. japonicus using LC-MS/MS technology and bioinformatics. Coelomic fluid and ejaculate fluid were analyzed, with aquaculture water serving as the control. Eight target pheromones were analyzed, and eight of metabolite analogs were tested for aggregation and spawning behaviors. Results showed that β-sitosterol at a concentration of 10 μg·L−1 significantly promoted aggregation (21.25 % average rate) and induced a significant increase in spawning rate (58 %) of A. japonicus. The significance of this study lies in the fact that by collecting and utilizing pheromones of A. japonicus, farmers can accurately determine the reproductive cycle and optimal breeding season for A. japonicus. This enables fish farmers to implement effective breeding management strategies at the appropriate time, thereby increasing the success rate of reproduction and providing valuable technical support for the cultivation of A. japonicus seedlings.

Conservation of Protein Kinase A Substrates in the Cnidarian Coral Spermatozoa Among Animals and Their Molecular Evolution.

The coral Acropora spp., known for its reef-building abilities, is a simultaneous hermaphroditic broadcast spawning species. Acropora spp. release gametes into seawater, activating sperm motility. This activation is mediated by adenylyl cyclase (AC) and protein kinase A (PKA). Notably, membrane-permeable cAMP (8-bromo-cAMP) promotes sperm motility activation of Acropora florida. While the signal transduction for PKA-dependent motility activation is highly conserved among animals, the downstream signaling of PKA remains unclear. In this study, we used mass spectrometry (MS) analyses to identify sperm proteins in the coral Acropora digitifera, as well as the serine/threonine residues of potential PKA substrates, and then, we investigated the conservation of these proteins from corals to vertebrates. We identified 148 sperm proteins of A. digitifera with typical PKA recognition motifs, namely RRXT and RRXS. We subsequently used ORTHOSCOPE to screen for orthologs encoding these 148 proteins from corals to vertebrates. Among the isolated orthologs, we identified positive selection in 48 protein-encoding genes from 18 Acropora spp. Subsequently, we compared the conservation rates of the PKA phosphorylation motif residues between the orthologs under positive and purifying selections. Notably, the serine residues of the orthologs under positive selection were more conserved. Therefore, adaptive evolution might have occurred in the orthologs of PKA substrate candidates from corals to vertebrates, accompanied by phosphorylation residue conservation. Collectively, our findings suggest that while PKA signal transduction, including substrates in sperm, may have been conserved, the substrates may have evolved to adapt to diverse fertilization conditions, such as synchronous broadcast spawning.

Investigating the timing of spawning of two sea urchins (Tripneustes gratilla and Toxopneustes pileolus)

AbstractMany marine organisms broadcast gametes for external fertilization, thus conspecifics need to concentrate the time of gamete release through synchronization with environmental factors. We investigated the timing of spawning in two sea urchin species, Tripneustes gratilla and Toxopneustes pileolus, by assessing the spawning potential of individuals using both surveys and experiments in southern Taiwan from March to November 2010. We developed a new method to observe the spawning potential without sacrificing any individuals, defining those individuals‐initiated spawning within 30 min after 10 s of exposure to air as having the spawning potential. We discovered that the percentage of individuals with spawning potential, that is, the spawning ratios of the population, varied greatly from 0% to 80% in To. pileolus and from 0% to 50% in Tr. gratilla within the reproductive seasons. We evaluated the possibility of a lunar/semilunar rhythm of spawning ratios of the population and tested three environmental factors, that is, light intensity, tide, and temperature that could potentially affect the spawning potential of the sea urchins by experiments. Individuals with spawning potential were neither randomly nor evenly distributed among days but were aggregated on certain days; however, no lunar/semilunar rhythm of the spawning ratios was detected within the reproductive season. The possible role of the tidal factor within a day was not found in experiments in either species. However, when water temperature was >27°C in our surveys, significantly higher spawning ratios were observed in To. pileolus, but not in Tr. gratilla in the reproductive season. A further temperature experiment in To. pileolus supported the positive role of high temperature on the spawning ratios of individuals. In addition, To. pileolus was more likely to spawn during the day than at night, and the light/dark experiments suggested that the spawning potential was controlled by an endogenous biological clock rather than by the ambient light conditions directly. The lack of rhythmic pattern and yet concentrated spawning of these sea urchins may be adaptive to avoid predation.

Overwintering and summer survival of Ulva prolifera in sediments: Indoor simulation of temperature impacts

Green tides, a globally prevalent marine ecological anomaly observed in coastal regions, have received substantial attention. However, there is limited research on the burial of Ulva prolifera in sediments during the late stages of green tide outbreaks. This study investigates the effect of temperature on U. prolifera buried in sediment over 30 days. The measurements included the length, biomass, relative growth rate, chlorophyll composition and maximum quantum yield (Fv/Fm) of PS II at different stages. The results indicate that at −20 °C, numerous seedlings emerged after 14 days of recovery culture, suggesting the release of spores or gametes; survival was possible from −2 °C to 15 °C; but at 20 °C and 30 °C, all U. prolifera died. The U. prolifera buried in sediment during the late stage of green tide outbreaks may serve as one of the sources for the subsequent year's green tide eruption. This research provides insights into the origins of green tide outbreaks in the southern Yellow Sea.

Reproductive cycle of the mangrove oyster Crassostrea rhizophorae (Guilding, 1828) in Delta do Parnaíba, Brazil

This study describes some aspects of the reproductive biology of the native oyster Crassostrea rhizophorae in the Delta do Parnaíba estuary, located between the states of Maranhão and Piauí, Brazil. The oysters were acquired from landings at Porto dos Tatus (Ilha Grande - PI) between June 2017 and May 2018. Approximately 50 individuals per month (n=611) with an average total shell length of 74.44 mm (±14.31 SD) were collected for analysis of gonadal development and condition index and correlated with temporal variations in local rainfall. The C. rhizophorae population in the Parnaíba Delta estuary showed a sex ratio of 2.18 females to 1 male and continuous reproduction. The condition index (CI) values in the dry period were higher, coinciding with a greater proportion of individuals in the gametogenesis and pre-spawning stages. In the rainy season, there was a reduction in the CI as a result of animals in the gamete release stage.

Efficacy of salmon GnRHa, Ovaprim® and hCG for hormonal stimulation of spermiation in the Fowler's toad (Anaxyrus fowleri).

Ex situ amphibian populations can experience reproductive dysfunction due to the absence of environmental cues that trigger reproductive events. Assisted reproductive technologies (ART) for amphibians, specifically exogenous hormone regimens, can circumvent these external signals to induce gametogenesis and gamete release. Currently, the use of the mammalian reproductive hormones gonadotropin-releasing hormone (GnRH) and human chorionic gonadotropin (hCG) are used in a species-specific manner to stimulate amphibian breeding. Hormones or hormone mixtures that are effective in all breeding scenarios would provide the best option for conservation practitioners and some commercial products are already in use for breeding other ectotherms. Ovaprim®, which contains salmon GnRH analogue (sGnRHa) and the dopamine antagonist domperidone (DOM), is effective in fish aquaculture and may be effective for amphibians. To test this hypothesis, we treated Fowler's toads (Anaxyrus fowleri) with either sGnRHa alone, a high or low dose of Ovaprim® or hCG. We then compared spermiation response, sperm quantity and quality parameters, and changes in animal mass over time within each treatment. We found administration of Ovaprim® resulted in more males producing sperm with better motility compared to administration of sGnRHa alone. In addition, the Ovaprim® and sGnRHa treatments resulted in lower response rates, lower sperm motilities, more abnormal sperm, and higher aggregations of sperm compared to the hCG treatment. Furthermore, Ovaprim®-treated males gained significant mass, suggesting an anti-diuretic effect of DOM. Together, these results show that neither Ovaprim® nor sGnRHa, at the concentrations tested, are likely suitable replacements for hCG in ex situ bufonid breeding programmes and that hormone mixtures developed for fish may have limited transferability to new world toad species.

Reproductive performance of the fluted clams (Tridacna squamosa) through different serotonin hormone doses for spawning induction

Exploring the reproductive performance one of the giant clam species being cultured in Indonesia. The fluted clams (Tridacna squamosa) are a keystone species for Indonesia’s marineculture and restocking program, categorized as a protected commodities by Convention on International Trade in Endangered Species (CITES) due to anthropogenic pressure on wild population. To assess and improve their reproductive performance, induction of different serotonin was applied consisting of control (0 mM), T1 (1.1 mM), T2 (1.4 mM), and T3 (1.7 mM). New significant insights emerge, results indicate response’s time of pre-spawning T1 and T2 were approximately 45 s, while T3 was 60 s, respectively T2 is highest spawning success at 91.67%, contrasting with 50% by T3, also spawning latency varied, with the quickest gamete release (3 min) by T2, on the contrary T3 (4 min). Observed eggs released at approximately 24 min (T2), 84 min (T1) with an egg diameter of 128.72±1.56 μm yet absent in T3. Polynomial regression of fecundity from differential dosing approach attained an R² = 0.3885, highlights an optimal 1.36 mM dosage for maximizing spawning performance, indicating T2 as an adequate dose with moderate egg abnormalities 8.7% and. FR, HR, and SR ranged from to 70-80% respectively.

Synthesis and Scope of the Role of Postmating Prezygotic Isolation in Speciation.

How barriers to gene flow arise and are maintained are key questions in evolutionary biology. Speciation research has mainly focused on barriers that occur either before mating or after zygote formation. In comparison, postmating prezygotic (PMPZ) isolation-a barrier that acts after gamete release but before zygote formation-is less frequently investigated but may hold a unique role in generating biodiversity. Here we discuss the distinctive features of PMPZ isolation, including the primary drivers and molecular mechanisms underpinning PMPZ isolation. We then present the first comprehensive survey of PMPZ isolation research, revealing that it is a widespread form of prezygotic isolation across eukaryotes. The survey also exposes obstacles in studying PMPZ isolation, in part attributable to the challenges involved in directly measuring PMPZ isolation and uncovering its causal mechanisms. Finally, we identify outstanding knowledge gaps and provide recommendations for improving future research on PMPZ isolation. This will allow us to better understand the nature of this often-neglected reproductive barrier and its contribution to speciation.

Spawning acts as a metabolic stressor enhanced by hypoxia and independent of sex in a broadcast marine spawner

Broadcast spawners, like the blue mussel Mytilus edulis, experience substantial energy expenditure during spawning due to extensive gamete release that can divert energy from other functions. This energetic cost might be intensified by environmental stressors, including hypoxia that suppress aerobic metabolism. However, the energy implications of spawning in marine broadcast spawners have not been well studied. We examined the effects of short-term hypoxia (7 days) and spawning on mitochondrial activity, reactive oxygen species (ROS) production, and cellular energy allocation (ratio of tissue energy reserves to energy demand) in somatic tissues of M. edulis. Under normoxic conditions, post-spawning (72 h) recovery correlated with increased phosphorylation (OXPHOS) rate in mitochondria from the digestive gland, while hypoxia inhibited this response. Regardless of oxygen levels, mitochondrial ROS production decreased after spawning, indicating M. edulis' ability to prevent oxidative stress. Spawning led to reduced energy reserves in somatic tissues (the gills and the digestive gland), highlighting significant energy cost of spawning primarily fueled by lipid and protein breakdown. Additionally, cellular energy allocation dropped 3 h post-spawning, indicating a shift in energy demand and supply. Normoxic conditions allowed recovery in 72 h, but hypoxia hindered recuperation. These findings underscore spawning's bioenergetic challenge for broadcast spawners like M. edulis, potentially elevating post-spawning mortality risk, especially in hypoxic coastal habitats.

The marine fish Terapon theraps calling in tropical Australia

Calling by fish of the family Terapontidae, primarily Terapon theraps, is a dominant component of sea noise recorded in northern Australian tropical coastal waters. These fish produce nightly choruses over a few hours at frequencies from 50 Hz to a few kilohertz, with spectral peaks up to 30 dB above background. Choruses are heard over muddy bottoms <30 m depth. The two commonly heard calls range from 73–260 ms in length and comprised 11–21 pulses with repetition rates of 87–121 Hz. Calls were produced by muscle action on a two chambered swim bladder, and differed by muscle contraction rates, damping, and possibly the opening state of a sphincter separating chambers. Swimbladder carrier frequencies varied from 570–1465 Hz. Source levels varied from 141–154 dB re 1 mPa @ 1 m. Heavily damped alarm calls were sometimes heard. Chorusing fish schools were up to 2 km across although they were diffuse and actively calling fish extended beyond this region. A chorus could be detected out to 8 km from its center, well beyond the detection range of an individual call. Choruses may advertise school location during spawning, be used for mate attraction or mediate gamete release in dark turbid waters.

The protobranch Aequiyoldia eightsii (Jay, 1839) (Nuculanida: Sareptidae) reveals uncommon siphonal anatomy among bivalves

ABSTRACT Siphons represent a remarkable example of evolutionary convergence in different bivalve lineages. In Protobranchia, the siphons, when present, are used exclusively to channel the water currents used for respiration, waste removal and gamete release. Their emergence is thought to be associated with the taxonomic and morphological diversification within the Nuculanida. While siphons have been extensively studied in other bivalve groups, particularly the Heterodonta, gaps remain in the knowledge of protobranch siphons, especially on their morphology, including the musculature and innervation, and their functioning. The few data on Protobranchia siphons are restricted to some Nuculanoidea, and information is still missing for other nuculanid lineages, such as the Sareptoidea. The present study provides a description of the siphonal morphology of Aequiyoldia eightsii, a sareptid bivalve. Histological data were obtained to investigate their organization and infer their functioning. All traits observed were compared with those of heterodont siphons. In A. eightsii, the siphons are fused with each other and distinguished by their reduced longitudinal musculature in bundles that do not form layers, by the presence of a blood lacunal system that fills most of the wall of the siphon and by the innervation that is likely diffuse. This suggests that the siphons are hydrostatic organs with a hydraulic mechanism whose expansion occurs when the lacunar system is filled with blood. Our results provide the first morphological and functional details of a protobranch siphon and thus contribute to knowledge on the comparative anatomy of Bivalvia.

Radial spoke protein 9 is necessary for axoneme assembly in Plasmodium but not in trypanosomatid parasites.

Flagella are important for eukaryote cell motility, including in sperm, and are vital for life cycle progression of many unicellular eukaryotic pathogens. The "9+2" axoneme in most motile flagella comprises nine outer doublet and two central-pair singlet microtubules. T-shaped radial spokes protrude from the outer doublets towards the central pair and are necessary for effective beating. We asked if there were radial spoke adaptations associated with parasite lineage-specific properties in apicomplexans and trypanosomatids. Following an orthologue search for experimentally uncharacterised radial spoke proteins (RSPs), we identified and analysed RSP9. Trypanosoma brucei and Leishmania mexicana, have an extensive RSP complement including two divergent RSP9 orthologs, necessary for flagellar beating and swimming. Detailed structural analysis showed that neither ortholog is needed for axoneme assembly in Leishmania. In contrast, Plasmodium has a reduced set of RSPs including a single RSP9 ortholog. deletion of which in Plasmodium berghei leads to failure of axoneme formation, failed male gamete release, greatly reduced fertilisation and inefficient life cycle progression in the mosquito. This indicates contrasting selection pressures on axoneme complexity, likely linked with the different mode of assembly of trypanosomatid versus Plasmodium flagella.

Localization of relaxin-like gonad-stimulating peptide expression in starfish reveals the gonoducts as a source for its role as a regulator of spawning.

Oocyte maturation and gamete release (spawning) in starfish are triggered by relaxin-like gonad-stimulating peptide (RGP), a neuropeptide that was first isolated from the radial nerve cords of these animals. Hitherto, it has generally been assumed that the radial nerve cords are the source of RGP that triggers spawning physiologically. To investigate other sources of RGP, here we report the first comprehensive anatomical analysis of its expression, using both in situ hybridization and immunohistochemistry to map RGP precursor transcripts and RGP, respectively, in the starfish Asterias rubens. Cells expressing RGP precursor transcripts were revealed in the ectoneural epithelium of the radial nerve cords and circumoral nerve ring, arm tips, tube feet, cardiac stomach, pyloric stomach, and, most notably, gonoducts. Using specific antibodies to A. rubens RGP, immunostaining was revealed in cells and/or fibers in the ectoneural region of the radial nerve cords and circumoral nerve ring, tube feet, terminal tentacle and other arm tip-associated structures, body wall, peristomial membrane, esophagus, cardiac stomach, pyloric stomach, pyloric caeca, and gonoducts. Our discovery that RGP is expressed in the gonoducts of A. rubens proximal to its gonadotropic site of action in the gonads is important because it provides a new perspective on how RGP may act as a gonadotropin in starfish. Thus, we hypothesize that it is the release of RGP from the gonoducts that triggers gamete maturation and spawning in starfish, while RGP produced in other parts of the body may regulate other physiological/behavioral processes.

An Overview of the Female Reproductive System: A Narrative Literature Review

The female reproductive system is a biological system that is responsible for producing, transporting, and storing eggs and facilitating the meeting between eggs and sperm for fertilization. The female reproductive system consists of internal and external organs. This literature review aimed to describe the female reproductive system. Internal organs include the ovaries (ovaries), fallopian tubes (oviducts), uterus (womb), cervix (cervix), and vagina. The ovary is the main female reproductive organ. The two main functions of the ovaries are the secretion of female sex hormones and the development and release of female gametes, or ova. The almond-shaped ovaries are located on either side of the uterus and are supported and supported by the halves mesovarium of the broad, ovarian, and suspensory ligaments. The female reproductive system is also influenced by reproductive hormones such as estrogen, progesterone, and gonadotropins which are produced by the pituitary gland and ovaries.

Induced spawning with gamete release from body ruptures during reproduction of Xenoturbella bocki

Xenoturbella is a marine invertebrate with a simple body plan, with recent phylogenomic studies suggesting that it forms the phylum Xenacoelomorpha together with the acoelomorphs. The phylogenetic position of the phylum is still under debate, whether it is an early branching bilaterian or a sister group to the Ambulacraria. Phylogenetic traits often appear during development, and larva resembling the cnidarian planula has been reported for Xenoturbella. However, subsequent developmental studies on Xenoturbella have been scarce. This is mainly due to the difficulties in collecting and keeping adult animals, resulting in the lack of data on the reproduction of the animal, such as the breeding season and the spawning pattern. Here we report on the reproduction of X. bocki and confirm that its breeding season is winter. Spawning induction resulted in gametes being released from body ruptures and not the mouth. No evidence supported the animal as a simultaneous hermaphrodite.