Mature Gametes Research Articles

A novel homozygous mutation in the NLRP2 gene causes early embryonic arrest.

Successful reproduction in humans requires maturation and fertilization of gametes as well as early embryonic development. Any deviation from these processes leads to infertility. Early embryonic arrest (EEA) is common in female infertility and is primarily attributed to genetic factors. Mutations in the NLRP2 gene have been identified as the causative factors for EEA. In the present study, a novel mutation identified in NLRP2 underscored the novel homozygous variant and phenotypes that might contribute to its inclusion in the genetic counseling of infertile patients. We recruited a proband from a consanguineous family with a diagnosis of EEA. Peripheral blood samples were collected from the proband and family members for whole-exome sequencing to identify the genes and inheritance patterns associated with infertility; the results were substantiated by Sanger sequencing. All genetic variants and protein structures were analyzed based on computational predictions. Wild-type and mutant plasmids were constructed and transfected into HeLa cells. Subsequent in vitro analyses elucidated the functional impact of the variant. A novel homozygous mutation in NLRP2 was identified in the proband. The patient harbored a frameshift deletion mutation (c.195delC: p.Tyr66Thrfs*32) in the pyrin structural domain. This genetic alteration resulted in the down-regulation of NLRP2 mRNA expression, truncation of the protein structure, and altered protein localization in cells. The current findings broaden the spectra of NLRP2 variants, especially concerning EEA. Also, potential diagnostic markers for patients experiencing recurrent IVF/ICSI failure were identified, and a solid foundation was laid for genetic counseling for female infertility.

Mechano-regulation of Germline Development, Maintenance, and Differentiation

Biochemical signaling arising from mechanical force-induced physical changes in biological macromolecules is a critical determinant of key physiological processes across all biological lengths and time scales. Recent studies have deepened our understanding of how mechano-transduction regulates somatic tissues such as those in alveolar, gastrointestinal, embryonic, and skeleto-muscular systems. The germline of an organism has a heterogeneous composition - of germ cells at different stages of maturation and mature gametes, often supported and influenced by their accessory somatic tissues. While biochemical signaling underlying germline functioning has been extensively investigated, a deeper interest in their mechanical regulation has been gaining traction in recent years. In this review, we delve into the myriad ways in which germ cell development, maintenance, and functions are regulated by mechanical forces.

Revolutionizing Infertility Management through Novel Peptide-based Targets.

Around 48 million couples and 186 million people worldwide have infertility; of these, approximately 85% have an identifiable cause, the most common being ovulatory dysfunctions, male infertility, polycystic ovary syndrome, and tubule disease. The remaining 15% have infertility for unknown reasons, including lifestyle and environmental factors. The regulation of the hypothalamic- pituitary-adrenal axis (HPA) is crucial for the secretion of gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH), which are essential for female reproductive functions. GnRH is the primary reproductive axis regulator. The pattern of GnRH, FSH, and LH release is determined by its pulsatile secretion, which in turn controls endocrine function and gamete maturation in the gonads. Peptides called Kisspeptin (KP), Neurokinin-B (NKB), and Orexin influence both positive and negative feedback modulation of GnRH, FSH, and LH secretion in reproduction. This review article mainly focuses on the historical perspective, isoform, and signaling pathways of KP, NKB, and Orexin novel peptide-based targets including clinical and preclinical studies and having a promising effect in the management of infertility.

Spawning is accompanied by increased thermal performance in blue mussels

Climate change is causing extreme short-term warming with greater intensity and more frequent occurrence. Reproduction and subsequent recruitment of coastal ecosystem engineers, such as the blue mussel, may be impacted by the extreme temperatures because these vital functions are sensitive to the timing of short-term changes in abiotic factors. We exposed intertidal blue mussels, Mytilus edulis, to a thermal challenge from 10 to 29 °C using an ecologically relevant heating rate of 4 °C/h. We assessed their reproductive status by observing spawning activity and by analyzing histological sections of their gonad tissue. In addition, we monitored their heart rates and valve gaping behavior to determine their thermal performance. We identified three spawning groups: non-spawners that had mature gonads but did not release gametes, post-spawners that released mature gametes prior to the thermal challenge, and active spawners that released mature gametes during the thermal challenge. Across temperatures, active spawners had significantly higher heart rates and their heart rate peaked at the temperatures 3.9 and 3.2 °C higher compared to those of non-spawners or post-spawners, respectively. Post-spawners had significantly narrower valve gapes across temperatures compared to both other spawning groups. Hence, the metabolic response to warming strongly depends on the reproductive status, with active spawners experiencing increased thermal stress due to heightened metabolism, non-spawners showing heat-induced metabolic depression, and post-spawners adopting an energy-conserving strategy indicated by reduced gaping. Considered together, spawning during recurring short-term warming events may elevate mortality risk with potential consequences for the local biodiversity in a future climate.

Ex situ spawning, larval development, and settlement in massive reef‐building corals (Porites) in Palau

AbstractReproduction, embryological development, and settlement of corals are critical for survival of coral reefs through larval propagation. Yet, for many species of corals, a basic understanding of the early life‐history stages is lacking. In this study, we report our observations for ex situ reproduction in the massive reef‐building coral Porites cf. P. lobata across 2 years. Spawning occurred in April and May, on the first day after the full moon with at least 2 h of darkness between sunset and moonrise, on a rising tide. Only a small proportion of corals observed had mature gametes or spawned (14–35%). Eggs were 185–311 μm in diameter, spherical, homogenous, and provisioned with 95–155 algal cells (family Symbiodiniaceae). Males spawned before females, and ex situ fertilization rates were high for the first 2 h after egg release. Larvae were elliptical, ~300 μm long, and symbiotic. Just 2 days after fertilization, many larvae swam near the bottom of culture dishes and were competent to settle. Settlers began calcification 2 days after metamorphosis, and tentacles were developed 10 days after attachment. Our observations contrast with previous studies by suggesting an abbreviated pelagic larval period in Porites cf. P. lobata, which could lead to the isolation of some populations. The high thermal tolerance and broad geographic range of Porites cf. P. lobata suggest that this species could locally adapt to a wide range of environmental conditions, especially if larvae are locally retained. The results of this study can inform future work on reproduction, larval biology, dispersal, and recruitment in Porites cf. P. lobata, which could have an ecological advantage over less resilient coral species under future climate change.

Fertility Treatment and Preservation Options for Transgender and Gender Diverse People.

Years of growing research demonstrate that transgender and gender diverse (TGD) people desire fertility counseling and family building, however social and medical factors can impact future fertility options. Fortunately, TGD individuals have many viable options for family building using their own gametes and/or reproductive organs. However, the nuanced ways in which different gender affirming treatments affect reproduction, the interplay with non-treatment related infertility factors, and mitigation of likely dysphoria triggers are all critical to actual utilization. This review focuses on fertility treatment and preservation options for TGD patients and highlights these influential social and medical factors. Fertility treatments may be associated with worsening gender dysphoria in TGD people, and an affirming clinical environment and conscientious provider approach is paramount to treatment success. However, reducing gender dysphoria can also require specific changes to medically assisted reproduction and sperm collection protocols, some which carry the potential for diminished outcomes or unknown effects. Adolescents undergoing fertility preservation treatments may need more support or additional protocol modifications, and outcomes may be poorer in this age group compared with adults. Testicular and ovarian tissue cryopreservation may present a fertility preservation option for prepubertal TGD children, however in-vitro gamete maturation remains experimental in this situation.

Single-nucleus multiomics reveals the gene-regulatory networks underlying sex determination of murine primordial germ cells.

Accurate specification of female and male germ cells during embryonic development is critical for sexual reproduction. Primordial germ cells (PGCs) are the bipotential precursors of mature gametes that commit to an oogenic or spermatogenic fate in response to sex-determining cues from the fetal gonad. The critical processes required for PGCs to integrate and respond to signals from the somatic environment in gonads are not understood. In this study, we developed the first single-nucleus multiomics map of chromatin accessibility and gene expression during murine PGC development in both XX and XY embryos. Profiling of cell-type specific transcriptomes and regions of open chromatin from the same cell captured the molecular signatures and gene networks underlying PGC sex determination. Joint RNA and ATAC data for single PGCs resolved previously unreported PGC subpopulations and cataloged a multimodal reference atlas of differentiating PGC clusters. We discovered that regulatory element accessibility precedes gene expression during PGC development, suggesting that changes in chromatin accessibility may prime PGC lineage commitment prior to differentiation. Similarly, we found that sexual dimorphism in chromatin accessibility and gene expression increased temporally in PGCs. Combining single-nucleus sequencing data, we computationally mapped the cohort of transcription factors that regulate the expression of sexually dimorphic genes in PGCs. For example, the gene regulatory networks of XX PGCs are enriched for the transcription factors, TFAP2c, TCFL5, GATA2, MGA, NR6A1, TBX4, and ZFX. Sex-specific enrichment of the forkhead-box and POU6 families of transcription factors was also observed in XY PGCs. Finally, we determined the temporal expression patterns of WNT, BMP, and RA signaling during PGC sex determination, and our discovery analyses identified potentially new cell communication pathways between supporting cells and PGCs. Our results illustrate the diversity of factors involved in programming PGCs towards a sex-specific fate.

Особенности развития генеративных структур некоторых цветковых растений

The paper presents the results of a comparative study of the reproductive biology of a number of Crimean flora species and valuable plants introduced to the south of Russia belonging to various families (Magnoliaceae, Annonaceae, Ericaceae, Campanulaceae, Anacardiaceae, Lamiaceae, Ranunculaceae, Davidiaceae, Nyssaceae, Onagraceae, Papaveraceae), which made it possible to establish some features and regularities in the formation of the generative structures of the reproductive system, consisting in the conjugation of the development of male and female elements, the maturation of sexual gametes and the process of pollination in entomophilous plants. A conclusion was drawn concerning the high reproductive potential of the studied species, which is expressed in the formation of a sufficient number of full-fledged seeds to reproduce. The possibilities of using the knowledge of the reproductive processes of flowering plants in solving certain issues of taxonomy, determining the strategy of reproduction and conservation of phytodiversity, and showing the importance of antecological aspects in plant reproduction, breeding and nature protection were demonstrated. The material is of scientific interest to botanists, ecologists, breeders and other specialists.

Sendai virus-mediated RNA delivery restores fertility to congenital and chemotherapy-induced infertile female mice.

Current infertility treatment strategies focus on mature gametes, leaving a significant proportion of cases with gamete progenitors that stopped complete differentiation. On the other hand, recent advancements in next-generation sequencing have identified many candidate genes that may promote maturation of germ cells. Although gene therapy has shown success in mice, concerns about the integration of DNA vectors into oocytes hinder clinical applications. Here, we present the restoration of fertility in female mice through Sendai virus (SeV)-mediated RNA delivery. Ovaries lacking Kitl expression exhibit only primordial follicles due to impaired signaling to oocytes expressing the KIT tyrosine kinase. Despite SeVs being immunogenic and larger than the blood-follicle barrier, the administration of Kitl-expressing SeVs reinitiated oogenesis in genetically infertile mice that have only primordial follicles, resulting in the birth of normal offspring through natural mating. This virus also effectively addressed iatrogenic infertility induced by busulfan, a widely used cancer chemotherapy agent. Offspring born through SeV administration and natural mating displayed normal genomic imprinting patterns and fertility. Since SeVs pose no genotoxicity risk, the successful restoration of fertility by SeVs represents a promising approach for treating congenital infertility with somatic cell defects and protecting fertility of cancer patients who may become infertile due to loss of oocytes during cancer therapy.

Elevated temperature impairs gonadal development by suppressing the expression of the genes for kisspeptin, GnRH1 and GTH subunits in Nile tilapia Oreochromis niloticus

Temperature is a preeminent factor in the regulation of fish reproduction and hinders gonadal development beyond a specific threshold. To comprehend the molecular mechanism responsible for reproductive suppression at different temperature, expression of the genes encoding kisspeptin (kiss2), gonadotropin-releasing hormone (gnrh1) and their receptors (gpr54, gnrh1r) in the brain, and the gonadotropin (GTH) subunits (fshb and lhb) in the pituitary were studied in juvenile Nile tilapia (Oreochromis niloticus) along with gonadal histology. Fish were acclimatized to three distinct temperatures, including 31 °C, 34 °C and 37 °C for 14 days. The mRNA levels of kiss2, gpr54, gnrh1, and gnrh1r were significantly decreased at 37 °C compared to 31 °C and 34 °C in the both sexes. In parallel, the expression level of fshb in the both sexes and lhb in the female were significantly lower at 37 °C in the pituitary. Histologically, the gonads of both sexes had normal growth of gametes at control temperature (31 °C), whereas the spermatogenesis and oocyte maturation were slowed down and atretic oocytes were found in the ovary at 37 °C acclimation temperature. Taken together, the results imply that elevated temperature beyond the specific threshold may have a negative impact on reproduction by suppressing the gene expressions of kisspeptin/GnRH1/GTH system and eventually restrains normal growth and maturation of gametes in the both sexes of Nile tilapia.

P-550 Monoallelic CCNB2 variants may cause oocyte maturation defects and embryo developmental arrest

Abstract Study question Have all the genes that may cause embryo development arrest and oocyte maturation defects been identified in female patients? Summary answer We identified a variant in CCNB2 in our patient. To our knowledge, this is first time that meiotic arrest can be caused by mutated-CCNB2. What is known already Successful reproduction involves the maturation of gametes, fertilization, and early development of the embryo. Oocyte maturation involves a sequence of both morphological and molecular transformations, progressing from germinal vesicle oocytes to metaphase I oocytes and ultimately to metaphase II oocytes. Any disruption in the process of oocyte maturation can result in infertility. With the widespread use of whole exome sequencing (WES), several genes that influence oocyte maturation at different stages have been recently identified. Study design, size, duration We here report the case of repeated ART failure due to oocyte maturation defect and embryo developmental arrest. Participants/materials, setting, methods A 30-year-old female and 38-year-old male applied to our clinic due to unexplained infertility for 4 years. The first ART attempt resulted in 2 of 13 oocytes with late MII. During ART performed in our center, germinal vesicle and meiotic arrest were observed in all oocytes. No mature oocytes were obtained. Her grandfather’s sister was also infertile. WES and Sanger analysis were performed to detect any mutation in known/candidate genes and show familial segregation Main results and the role of chance WES analysis revealed no mutation in genes that were previously reported as a cause of oocyte maturation defect or early embryo development in human. We do a further analysis of genes highly or specifically expressed in oocytes or expressed at low levels yet previous studies have suggested its role in embryo development. We identified a c.787C>T, p.Arg263* heterozygous nonsense variant in the CCNB2 gene that was extremely rare in both multiple databases and our in-house database. Multiple lines of computational evidence support the deleterious effect of the variant on the gene product. This variant was transmitted from her healthy father. CCNNB2 is not expressed in any cells other than oocytes in human. The activity of the M phase-promoting factor (MPF) is crucial for advancing through both mitosis and meiosis. CCNB2 plays a vital role by contributing to the activity of pre-MPF during prophase, necessary for generating enough MPF to proceed through maturation. Furthermore, CCNB2 is significantly involved in mouse oocyte meiosis, playing a key role in both the G2/M and MI/anaphase I transitions. Limitations, reasons for caution New disease-causing variants in this gene should be demonstrated in larger cohorts with female infertility. In addition, further functional studies should be carried out both in CCNB2-mutated human and animals. Wider implications of the findings This study may provide a better understanding background of female infertility and the failure of the ART process. CCNB2 may have a crucial role in the oocyte maturation process and can be utilized as a female infertility genetic marker. Trial registration number NA

Low-Dose Ionizing Radiation Exposure on Human Male Gametes: Damage or Benefit.

With the improvement of medical devices for diagnosis and radiotherapy, concerns about the effects of low doses of ionizing radiation are also growing. There is no consensus among scientists on whether they might have beneficial effects on humans in certain cases or pose more risks, making the exposure unreasonable. While the damaging consequences of high-dose radiation have been known since the discovery of radioactivity, low-dose effects present a much bigger investigative challenge. They are highly specific and include radio-adaptive responses, bystander effects, and genomic instability. Current data regarding the consequences of exposure to low-dose radiation on the quality of male gametes and fertility potential are contradictory. The reports suggest two directions: indirect impact on male gametes-through spermatogenesis-or direct effects at low doses on already mature spermatozoa. Although mature gametes are used for observation in both models, they are fundamentally different, leading to varied results. Due to their unique physiological characteristics, in certain cases, exposure of spermatozoa to low-dose ionizing radiation could have positive effects. Despite the findings indicating no beneficial effects of low-dose exposure on male fertility, it is essential to research its impact on mature spermatozoa, as well.

Gametogenesis and seminatural reproduction of the Amazon twospot astyanax Astyanax bimaculatus (Linnaeus, 1758) cultivated in an enriched environment

Environmental enrichment is used to provide well-being to the animals, such as fish, in captive conditions, mimicking their natural habitat. It may influence fish behavior, physiology, and survival. In terms of reproduction, however, the relationship between environment enrichment and successful reproduction in captivity is still poorly explored in fish species. Aiming to understand any possible benefits of structural enrichment on fish reproduction, 10-days-hatched larvae of the twospot astyanax Astyanax bimaculatus were raised for 18 weeks in tanks with different elements of structural environmental enrichment (PVC pipes, stones, and artificial plants). In the 5th month of life, those animals were hormonally induced to reproduce to assess gamete formation and offspring quality. Animals raised in a sterile-reared environment (non-enriched) showed earlier spawning than the enriched one, presenting significant quantities of Postovulatory follicle complexes (POCs) and cells in atresia in female ovaries, indicating possible reproductive dysfunction or stress, as well as a greater quantity of empty testicular lumen in males, indicating great release of sperm. On the contrary, animals cultivated in enriched environments showed gonads filled with semen in males and vitellogenic oocytes in females. Furthermore, offspring from the sterile-reared group presented significant rates of larval abnormality compared to the enriched group. In conclusion, the results of this study show that environmental enrichment can interfere with the reproduction of fish in captivity, mainly by preventing early maturation of gametes, which can result in low-quality offspring and, consequently, low production of fish species.

Influence of extracellular ATP on mammalian sperm physiology.

In addition to its central role in cellular metabolism, adenosine 5'-triphosphate (ATP) is an important extracellular signalling molecule involved in various physiological processes. In reproduction, extracellular ATP participates in both autocrine and paracrine paths regulating gametogenesis, gamete maturation and fertilisation. This review focusses on how extracellular ATP modulates sperm physiology with emphasis on the mammalian acrosome reaction. The presence of extracellular ATP in the reproductive tract is primarily determined by the ion channels and transporters that influence its movement within the cells comprising the tract. The main targets of extracellular ATP in spermatozoa are its own transporters, particularly species-specific sperm purinergic receptors. We also discuss notable phenotypes from knock-out mouse models and human Mendelian inheritance related to ATP release mechanisms, along with immunological, proteomic, and functional observations regarding sperm purinergic receptors and their involvement in sperm signalling.

Reproductive Health-Oriented Development in Assisted Reproductive Technologies

Assisted reproductive technologies (ARTs) are core components of the field of reproductive medicine, encompassing multiple pivotal stages of early development from gamete maturation and fertilization to embryo development. Against the backdrop of a deteriorating trend of global decline in fertility rates, patients with infertility problems increasingly turn to ARTs to realize their dreams of parenthood. However, concomitant with this trend is a growing apprehension regarding the potential adverse effects of ARTs. Herein, we endeavor to discuss several common ARTs procedures utilized in clinical settings and the relevant cutting-edge advancements. The ARTs discussed in the article include in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI), biphasic in vitro maturation (biphasic IVM), frozen embryo transfer (FET), preimplantation genetic testing (PGT), non-invasive PGT (niPGT), etc. In addition, we reevaluated their roles within the broader context of assisted reproduction aimed at promoting reproductive health. Additionally, we will delve into the impact of ARTs on the reproductive health of the offspring. By prioritizing the reproductive well-being of both patients and their offspring, the ongoing development and improvement of ARTs to enhance their efficacy and safety will contribute significantly to the advancement of human reproductive health.

Emerging Contributions of Pluripotent Stem Cells to Reproductive Technologies in Veterinary Medicine.

The generation of mature gametes and competent embryos in vitro from pluripotent stem cells has been successfully achieved in a few species, mainly in mice, with recent advances in humans and scarce preliminary reports in other domestic species. These biotechnologies are very attractive as they facilitate the understanding of developmental mechanisms and stages that are generally inaccessible during early embryogenesis, thus enabling advanced reproductive technologies and contributing to the generation of animals of high genetic merit in a short period. Studies on the production of in vitro embryos in pigs and cattle are currently used as study models for humans since they present more similar characteristics when compared to rodents in both the initial embryo development and adult life. This review discusses the most relevant biotechnologies used in veterinary medicine, focusing on the generation of germ-cell-like cells in vitro through the acquisition of totipotent status and the production of embryos in vitro from pluripotent stem cells, thus highlighting the main uses of pluripotent stem cells in livestock species and reproductive medicine.

Application of ultrasonography in abalone gonadal evaluation

The precise assessment of the gonad status and gamete development level is an essential step in abalone breeding. However, traditional methods are damaging to the animals, causing the waste of a quality parent. Ultrasound imaging as a noninvasive technique is a candidate substitute. This study aimed to verify the application of ultrasonography to the assessment of abalone gonad condition. Pacific abalones (n = 20) were randomly selected for ultrasonography, another six abalones in different gonad maturation stages (mature, between mature and immature, and immature) were also subjected to the same detection and histological analysis. Abalones (n = 10) were induced to spawn, and the changes in the gonad index and the types of germ cells were determined before and after spawning. Thirty-six female abalones were selected and divided into a high-gonad index group (HGI) and a low-gonad index group (LGI) according to the gonad index determined by ultrasonography, and their reproductive performance was compared during the entire breeding process. There was no significant difference in gonad index or gonad relative average thickness (GRAT) obtained from ultrasonography and histological methods. The gonad index and GRAT measured by ultrasound images significantly decreased after spawning. After spawning, a minimal quantity of mature gametes remained in gonad tissue as reflected in histology images. In a reproductive trial, the HGI group showed comprehensive and overwhelming reproductive advantages compared to the LGI group in total fecundity, relative fecundity, fertilization rate, hatching rate, abnormality rate, and attachment rate. Ultrasonography was demonstrated to be useful as a noninvasive method to evaluate abalone gonad condition. The ultimate goal is to achieve tracing and monitoring the abalone reproductive cycle through the ultrasound technique.

Coral mariculture using abandoned abalone farming ponds in northeastern Taiwan

Stony corals are ecologically and economically important marine organisms. Coral aquaculture is essential to provide live coral materials for the marine ornamental trade, reef restoration programs, and environmental education. This study sought to establish coral farms in Taiwan. To culture corals, we adopted an abandoned abalone farming pond built along the northeastern coast of Taiwan, and investigated whether it is possible to propagate corals in this artificial environment. Stainless steel underwater tables were anchored to the pond floor, and fragments of Acropora tumida, Pocillopora damicornis, Stylophora pistillata, Favites pentagona, and Porites lobata were cultured on the tables for one year. Environmental factors in the pond were also monitored. The mean surface temperature was 23.07 °C, ranging from >30 °C in summer to 18 °C in winter. The mean salinity and pH were about 35 ppt and 8.14, respectively. Survivorship of these five species after one year ranged from 100% to 67%, with a 1.37–1.51-fold increase in weight and a 3.22–3.38-fold increase in area, demonstrating that although environmental factors fluctuate depending on the season and weather, long-term and stable asexual propagation of corals is feasible in the pond. For further optimization of culture conditions, the effects of initial fragment size for culture on subsequent survival and growth were investigated. Fragments of 3 sizes (1.5, 3.0, and 4.5 cm) were prepared from parental colonies of A. tumida, P. damicornis, and S. pistillata and cultured for 6 months by hanging them under the table. There were no significant differences in survivorship among these sizes. Differences were observed in biomass (weight) increase. In A. tumida, 3-cm fragments showed significantly more weight gain than other lengths, while 1.5-cm fragments showed a significant weight increase in P. damicornis. In S. pistillata, no significant difference in weight increase was observed among size groups, suggesting the necessity to optimize the initial fragment size for culture for each species before mass culture. Histological analysis showed that mature gametes were formed in some cultured corals, suggesting that sexual propagation may also be possible in the future. The established coral farm, which is culturing >4000 coral fragments now, will be able to support not only basic and applied coral research, but also sustainable reef development and marine ornamental trade.

Roles of endogenous retroviral elements in the establishment and maintenance of imprinted gene expression.

DNA methylation (DNAme) has long been recognized as a host defense mechanism, both in the restriction modification systems of prokaryotes as well as in the transcriptional silencing of repetitive elements in mammals. When DNAme was shown to be implicated as a key epigenetic mechanism in the regulation of imprinted genes in mammals, a parallel with host defense mechanisms was drawn, suggesting perhaps a common evolutionary origin. Here we review recent work related to this hypothesis on two different aspects of the developmental imprinting cycle in mammals that has revealed unexpected roles for long terminal repeat (LTR) retroelements in imprinting, both canonical and noncanonical. These two different forms of genomic imprinting depend on different epigenetic marks inherited from the mature gametes, DNAme and histone H3 lysine 27 trimethylation (H3K27me3), respectively. DNAme establishment in the maternal germline is guided by transcription during oocyte growth. Specific families of LTRs, evading silencing mechanisms, have been implicated in this process for specific imprinted genes. In noncanonical imprinting, maternally inherited histone marks play transient roles in transcriptional silencing during preimplantation development. These marks are ultimately translated into DNAme, notably over LTR elements, for the maintenance of silencing of the maternal alleles in the extraembryonic trophoblast lineage. Therefore, LTR retroelements play important roles in both establishment and maintenance of different epigenetic pathways leading to imprinted expression during development. Because such elements are mobile and highly polymorphic among different species, they can be coopted for the evolution of new species-specific imprinted genes.

Growth, survival and reproductive traits of chemical induced and tetraploid-derived triploid Hong Kong oysters (Crassostrea hongkongensis)

Chemical induction (inhibition of polar body II release) and crossing between tetraploid and diploid oysters (mating triploids) are 2 distinct and typical methods for obtaining triploids, and systematic comparative analysis on the phenotypic traits of these two triploids is rare. We tracked and compared the growth, survival, reproductive characteristics and ploidy composition of diploids, induced triploids, and mating triploids, and conducted interaction analysis between genotypes and sites. The results showed that the shell height of larvae showed a significant decrease trend of 3 NTD > 3 NCB > 2 N, while the D larval rate and survival rate of 3 NCB were the lowest, which may be related to the long-term effects of CB toxicity. During offshore farming, from the 180th to 700th day, the shell heights of the three groups followed a significantly decreasing order at both sites, namely 3 NTD > 3 NCB > 2 N (except on the 270th day at Beihai site), and the triploid advantage of shell height in 3 NTD was generally higher than that in 3 NCB, with the same trend in the whole weight. Genotypes and sites always had significant effects on shell height, but their interactions were not significant. The incremental survival rates of the 2 triploid groups were higher than that of the diploid at both sites on the 270th and 700th day, while that of the 3 NTD was significantly higher than the 3 NCB only on the 270th day. In addition, both triploids had some individuals fertile and could produce mature gametes, but the proportion was much lower than that of diploids. Triploid gonadal development is characterized by feminization and a high proportion of hermaphroditism. The fertility ratio and gamete production of 3 NTD were higher than that of 3 NCB, but the relatively high fertility of 3 NTD had no significant effect on its growth and survival. Ploidy composition tracking found that the ploidy composition of 2 N and 3 NTD groups was stable, but the ploidy composition of 3 NCB varied over time. These results indicate that 3 NTD has better performance and higher triploid advantages than 3 NCB, making it more suitable for the commercial production and promotion of triploid C. hongkongensis.