Zinc availability regulates exit from meiosis in maturing mammalian oocytes

Using Machine Learning to Construct the Blood-Follicle Distribution Models of Various Trace Elements and Explore the Transport-Related Pathways with Multiomics Data

Permeabilities of various trace elements (TEs) through the blood-follicle barrier (BFB) play an important role in oocyte development. However, it has not been comprehensively described as well as its involved biological pathways. Our study aimed to construct a blood-follicle distribution model of the concerned TEs and explore their related biological pathways. We finally included a total of 168 women from a cohort of in vitro fertilization-embryo transfer conducted in two reproductive centers in Beijing City and Shandong Province, China. The concentrations of 35 TEs in both serum and follicular fluid (FF) samples from the 168 women were measured, as well as the multiomics features of the metabolome, lipidome, and proteome in both plasma and FF samples. Multiomics features associated with the transfer efficiencies of TEs through the BFB were selected by using an elastic net model and further utilized for pathway analysis. Various machine learning (ML) models were built to predict the concentrations of TEs in FF. Overall, there are 21 TEs that exhibited three types of consistent BFB distribution characteristics between Beijing and Shandong centers. Among them, the concentrations of arsenic, manganese, nickel, tin, and bismuth in FF were higher than those in the serum with transfer efficiencies of 1.19-4.38, while a reverse trend was observed for the 15 TEs with transfer efficiencies of 0.076-0.905, e.g., mercury, germanium, selenium, antimony, and titanium. Lastly, cadmium was evenly distributed in the two compartments with transfer efficiencies of 0.998-1.056. Multiomics analysis showed that the enrichment of TEs was associated with the synthesis and action of steroid hormones and the glucose metabolism. Random forest model can provide the most accurate predictions of the concentrations of TEs in FF among the concerned ML models. In conclusion, the selective permeability through the BFB for various TEs may be significantly regulated by the steroid hormones and the glucose metabolism. Also, the concentrations of some TEs in FF can be well predicted by their serum levels with a random forest model.

Stage-specific exposure of Caenorhabditis elegans to cadmium identifies unique transcriptomic response cascades and an uncharacterized cadmium responsive transcript

Age/stage sensitivity is considered a significant factor in toxicity assessments. Previous studies investigated cadmium (Cd) toxicosis in Caenorhabditis elegans, and a plethora of metal-responsive genes/proteins have been identified and characterized in fine detail; however, most of these studies neglected age sensitivity and stage-specific response to toxicants at the molecular level. This present study compared the transcriptome response between C. elegans L3 vs L4 larvae exposed to 20 µM Cd to explore the transcriptional hallmarks of stage sensitivity. The results showed that the transcriptome of the L3 stage, despite being exposed to Cd for a shorter period, was more affected than the L4 stage, as demonstrated by differences in transcriptional changes and magnitude of induction. Additionally, T08G5.1, a hitherto uncharacterized gene located upstream of metallothionein (mtl-2), was transcriptionally hyperresponsive to Cd exposure. Deletion of one or both metallothioneins (mtl-1 and/or mtl-2) increased T08G5.1 expression, suggesting that its expression is linked to the loss of metallothionein. The generation of an extrachromosomal transgene (PT08G5.1:: GFP) revealed that T08G5.1 is constitutively expressed in the head neurons and induced in gut cells upon Cd exposure, not unlike mtl-1 and mtl-2. The low abundance of cysteine residues in T08G5.1 suggests, however, that it may not be involved directly in Cd sequestration to limit its toxicity like metallothionein, but might be associated with a parallel pathway, possibly an oxidative stress response.

Minerals and the Menstrual Cycle: Impacts on Ovulation and Endometrial Health

The role of minerals in female fertility, particularly in relation to the menstrual cycle, presents a complex area of study that underscores the interplay between nutrition and reproductive health. This narrative review aims to elucidate the impacts of minerals on key aspects of the reproductive system: hormonal regulation, ovarian function and ovulation, endometrial health, and oxidative stress. Despite the attention given to specific micronutrients in relation to reproductive disorders, there is a noticeable absence of a comprehensive review focusing on the impact of minerals throughout the menstrual cycle on female fertility. This narrative review aims to address this gap by examining the influence of minerals on reproductive health. Each mineral's contribution is explored in detail to provide a clearer picture of its importance in supporting female fertility. This comprehensive analysis not only enhances our knowledge of reproductive health but also offers clinicians valuable insights into potential therapeutic strategies and the recommended intake of minerals to promote female reproductive well-being, considering the menstrual cycle. This review stands as the first to offer such a detailed examination of minerals in the context of the menstrual cycle, aiming to elevate the understanding of their critical role in female fertility and reproductive health.

Electrochemical Nanopipette Sensor for In Vitro/In Vivo Detection of Cu2+ Ions

In vitro/in vivo detection of copper ions is a challenging task but one which is important in the development of new approaches to the diagnosis and treatment of cancer and hereditary diseases such as Alzheimer's, Wilson's, etc. In this paper, we present a nanopipette sensor capable of measuring Cu2+ ions with a linear range from 0.1 to 10 μM in vitro and in vivo. Using the gold-modified nanopipette sensor with a copper chelating ligand, we evaluated the accumulation ability of the liposomal form of an anticancer Cu-containing complex at three levels of biological organization. First, we detected Cu2+ ions in a single cell model of human breast adenocarcinoma MCF-7 and in murine melanoma B16 cells. The insertion of the nanoelectrode did not result in leakage of the cell membrane. We then evaluated the distribution of the Cu-complex in MCF-7 tumor spheroids and found that the diffusion-limited accumulation was a function of the depth, typical for 3D culture. Finally, we demonstrated the use of the sensor for Cu2+ ion detection in the brain of an APP/PS1 transgenic mouse model of Alzheimer's disease and tumor-bearing mice in response to injection (2 mg kg-1) of the liposomal form of the anticancer Cu-containing complex. Enhanced stability and selectivity, as well as distinct copper oxidation peaks, confirmed that the developed sensor is a promising tool for testing various types of biological systems. In summary, this research has demonstrated a minimally invasive electrochemical technique with high temporal resolution that can be used for the study of metabolism of copper or copper-based drugs in vitro and in vivo.

Cellular zinc metabolism and zinc signaling: from biological functions to diseases and therapeutic targets

Zinc metabolism at the cellular level is critical for many biological processes in the body. A key observation is the disruption of cellular homeostasis, often coinciding with disease progression. As an essential factor in maintaining cellular equilibrium, cellular zinc has been increasingly spotlighted in the context of disease development. Extensive research suggests zinc's involvement in promoting malignancy and invasion in cancer cells, despite its low tissue concentration. This has led to a growing body of literature investigating zinc's cellular metabolism, particularly the functions of zinc transporters and storage mechanisms during cancer progression. Zinc transportation is under the control of two major transporter families: SLC30 (ZnT) for the excretion of zinc and SLC39 (ZIP) for the zinc intake. Additionally, the storage of this essential element is predominantly mediated by metallothioneins (MTs). This review consolidates knowledge on the critical functions of cellular zinc signaling and underscores potential molecular pathways linking zinc metabolism to disease progression, with a special focus on cancer. We also compile a summary of clinical trials involving zinc ions. Given the main localization of zinc transporters at the cell membrane, the potential for targeted therapies, including small molecules and monoclonal antibodies, offers promising avenues for future exploration.

Zn2+ is essential for Ca2+ oscillations in mouse eggs

Changes in the intracellular concentration of free calcium (Ca2+) underpin egg activation and initiation of development in animals and plants. In mammals, the Ca2+ release is periodical, known as Ca2+ oscillations, and mediated by the type 1 inositol 1,4,5-trisphosphate receptor (IP3R1). Another divalent cation, zinc (Zn2+), increases exponentially during oocyte maturation and is vital for meiotic transitions, arrests, and polyspermy prevention. It is unknown if these pivotal cations interplay during fertilization. Here, using mouse eggs, we showed that basal concentrations of labile Zn2+ are indispensable for sperm-initiated Ca2+ oscillations because Zn2+-deficient conditions induced by cell-permeable chelators abrogated Ca2+ responses evoked by fertilization and other physiological and pharmacological agonists. We also found that chemically or genetically generated eggs with lower levels of labile Zn2+ displayed reduced IP3R1 sensitivity and diminished ER Ca2+ leak despite the stable content of the stores and IP3R1 mass. Resupplying Zn2+ restarted Ca2+ oscillations, but excessive Zn2+ prevented and terminated them, hindering IP3R1 responsiveness. The findings suggest that a window of Zn2+ concentrations is required for Ca2+ responses and IP3R1 function in eggs, ensuring optimal response to fertilization and egg activation.

Phospholipase C Zeta 1 (PLCZ1): The Function and Potential for Fertility Assessment and In Vitro Embryo Production in Cattle and Horses

Phospholipase C Zeta 1 (PLCZ1) is considered a major sperm-borne oocyte activation factor. After gamete fusion, PLCZ1 triggers calcium oscillations in the oocyte, resulting in oocyte activation. In assisted fertilization, oocyte activation failure is a major cause of low fertility. Most cases of oocyte activation failures in humans related to male infertility are associated with gene mutations and/or altered PLCZ1. Consequently, PLCZ1 evaluation could be an effective diagnostic marker and predictor of sperm fertilizing potential for in vivo and in vitro embryo production. The characterization of PLCZ1 has been principally investigated in men and mice, with less known about the PLCZ1 impact on assisted reproduction in other species, such as cattle and horses. In horses, sperm PLCZ1 varies among stallions, and sperm populations with high PLCZ1 are associated with cleavage after intracytoplasmic sperm injection (ICSI). In contrast, bull sperm is less able to initiate calcium oscillations and undergo nuclear remodeling, resulting in poor cleavage after ICSI. Advantageously, injections of PLCZ1 are able to rescue oocyte failure in mouse oocytes after ICSI, promoting full development and birth. However, further research is needed to optimize PLCZ1 diagnostic tests for consistent association with fertility and to determine whether PLCZ1 as an oocyte-activating treatment is a physiological, efficient, and safe method for improving assisted fertilization in cattle and horses.

Serum Cu, Zn and IL-1β Levels May Predict Fetal Miscarriage Risk After IVF Cycles: A Nested Case-Control Study

To explore the association between serum-related indicators (levels of inflammatory cytokines and essential trace elements) and miscarriage risk among infertile women undergoing assisted reproductive techniques (ART) on the 14th day after embryo transfer, and to develop and establish a multivariable algorithm model that might predict pregnancy outcome. According to a nested case-control study design, a total of 100 miscarriage cases and 100 live birth controls were included in this study, and women in both groups were infertile and have underwent in vitro fertilization (IVF). Pregnancy tests were performed and serum levels of five essential trace elements (vanadium (V), copper (Cu), zinc (Zn), selenium (Se) and molybdenum (Mo)) and five inflammatory cytokines (interleukin-1β (IL-1β), IL-6, IL-8, IL-10 and tumor necrosis factor-α (TNF-α)) of the participants were measured on the 14th day after embryo transfer. The serum levels of five inflammatory cytokines were determined by multiple magnetic bead enzyme immunity analyzer; and the serum concentrations of five elements were determined simultaneously by inductively coupled plasma‒mass spectrometry (ICP ‒ MS). The logistic regression was used to evaluate the relationship between these serum indices and miscarriage risk among women undergoing ART, and a predictive model of pregnancy outcome based on these indices was established. The levels of IL-10, IL-1β and TNF-α of infertile women in the live birth group were significantly higher than those in the miscarriage group (p = 0.009, p < 0.001, p = 0.006), and the levels of V, Cu, Zn and Se of infertile women in the live birth group were also significantly higher than those in the miscarriage group (all p < 0.001). Through logistic regression analyses, we found that serum levels of IL-1β, TNF-α, V, Cu, Zn and Se were significantly and negatively associated with miscarriage risk. Different combination prediction models were generated according to the results of logistic regression analyses, and the combination of IL-1β, Cu and Zn had the best prediction performance. The area under the curve (AUC) was 0.776, the sensitivity of the model was 60% and the specificity was 84%. In conclusion, the serum-related indicators of women undergoing ART on the 14th day after embryo transfer, including the inflammatory cytokines such as IL-1β and TNF-α and the essential trace metal elements such as V, Cu, Zn and Se, were negatively correlated with miscarriage risk. A multivariate algorithm model to predict pregnancy outcome among women undergoing ART was established, which showed that IL-1β, Cu and Zn might synergistically predict pregnancy outcome.

Towards multimodal cellular imaging: optical and X-ray fluorescence

Imaging techniques permit the study of the molecular interactions that underlie health and disease. Each imaging technique collects unique chemical information about the cellular environment. Multimodal imaging, using a single probe that can be detected by multiple imaging modalities, can maximise the information extracted from a single cellular sample by combining the results of different imaging techniques. Of particular interest in biological imaging is the combination of the specificity and sensitivity of optical fluorescence microscopy (OFM) with the quantitative and element-specific nature of X-ray fluorescence microscopy (XFM). Together, these techniques give a greater understanding of how native elements or therapeutics affect the cellular environment. This review focuses on recent studies where both techniques were used in conjunction to study cellular systems, demonstrating the breadth of biological models to which this combination of techniques can be applied and the potential for these techniques to unlock untapped knowledge of disease states.

Zn2+ is Essential for Ca2+ Oscillations in Mouse Eggs

Changes in the intracellular concentration of free calcium (Ca2+) underpin egg activation and initiation of development in animals and plants. In mammals, the Ca2+ release is periodical, known as Ca2+ oscillations, and mediated by the type 1 inositol 1,4,5-trisphosphate receptor (IP3R1). Another divalent cation, zinc (Zn2+), increases exponentially during oocyte maturation and is vital for meiotic transitions, arrests, and polyspermy prevention. It is unknown if these pivotal cations interplay during fertilization. Here, using mouse eggs, we showed that basal concentrations of labile Zn2+ are indispensable for sperm-initiated Ca2+ oscillations because Zn2+-deficient conditions induced by cell-permeable chelators abrogated Ca2+ responses evoked by fertilization and other physiological and pharmacological agonists. We also found that chemically- or genetically generated eggs with lower levels of labile Zn2+ displayed reduced IP3R1 sensitivity and diminished ER Ca2+ leak despite the stable content of the stores and IP3R1 mass. Resupplying Zn2+ restarted Ca2+ oscillations, but excessive Zn2+ prevented and terminated them, hindering IP3R1 responsiveness. The findings suggest that a window of Zn2+ concentrations is required for Ca2+ responses and IP3R1 function in eggs, ensuring optimal response to fertilization and egg activation.

The Role of Thyroid Hormones, Vitamins, and Microelements in Female Infertility

OBJECTIVE

 It is well known that female infertility is multifactorial. Therefore, we aimed to compare the effects of thyroid dysfunction, vitamin deficiency, and microelement deficiency in fertile and infertile patients.

MATERIALS AND METHODS

 Between May 1st, 2017, and April 1st, 2019, we conducted a retrospective case-control study with of 380 infertile and 346 pregnant patients (who normally fertile and able to conceive spontaneously). The fertile patients were selected among those who got pregnant spontaneously without treatment, had a term birth, and did not have systemic or obstetric diseases. The levels of thyroid-stimulating hormone (TSH), triiodothyronine (T3), thyroxine (T4), anti-thyroid peroxidase (anti-TPO), vitamin D, vitamin B12, folic acid, ferritin, and zinc of both groups were compared.

RESULTS

 There was no difference between patients in the infertile and pregnant groups in terms of low normal and high serum T3 and T4 levels (p = 0.938; p > 0.05) respectively, nor in terms of normal and high anti-TPO levels (p = 0.182; p > 0.05) respectively. There was no significant difference regarding patients with low, insufficient, and sufficient vitamin D levels in the infertile and pregnant groups (p = 0.160; p >0.05) respectively. The levels of folic acid, ferritin, and zinc of the infertile group were significantly lower than those of the pregnant group.

CONCLUSION

 The serum levels of folic acid, ferritin, and zinc in infertile patients presenting to our outpatient clinic were lower than those o the fertile patients.

A Responsive Nanorobot Modulates Intracellular Zinc Homeostasis to Amplify Mitochondria-Targeted Phototherapy

Zinc has been proven to interweave with many critical cell death pathways, and not only exhibits potent anticancer activity solely, but sensitizes cancer cells to anticancer treatment, making zinc supplementation ideal for boosting odds against malignancy. Herein, a smart nanorobot (termed as Zinger) is developed, composed of iRGD-functionalized liposome encapsulating black phosphorus nanosheet (BPNs) doped zeolite imidazole framework-8 (BPN@ZIF-8), for advancing zinc-promoted photodynamic therapy (PDT). Zinger exhibits photo-triggered sequential mitochondria-targeting ability, and can induce zinc overload-mediated mitochondrial stress, which consequently sensitized tumor to PDT through synergistically modulating reactive oxygen species (ROS) production and p53 pathway. It is identified that Zinger selectively triggered intracellular zinc overload and photodynamic effect in cancer cells, which together enhanced PDT treatment outcomes. Importantly, Zinger shows high efficacy in overcoming various treatment barriers, allowing for effectively killing cancer cells in the complex circumstances. Particularly, Zinger exhibits good tumor accumulation, penetration, and even cell uptake, and can respond to light stimulation to eliminate tumors while avoiding normal tissues, thereby prolonging survival of tumor-bearing mice. Therefore, the study provides a novel insight in the development of novel zinc-associated therapy for advancing cancer treatment approaches.

Essential role of Mg2+ in mouse preimplantation embryo development revealed by TRPM7 chanzyme-deficient gametes

TRPM7 (transient receptor potential cation channel subfamily M member 7) is a chanzyme with channel and kinase domains essential for embryo development. Using gamete-specific Trpm7-null lines, we report that TRPM7-mediated Mg2+ influx is indispensable for reaching the blastocyst stage. TRPM7 is expressed dynamically from gametes to blastocysts; displays stage-specific localization on the plasma membrane, cytoplasm, and nucleus; and undergoes cleavage that produces C-terminal kinase fragments. TRPM7 underpins Mg2+ homeostasis, and excess Mg2+ but not Zn2+ or Ca2+ overcomes the arrest of Trpm7-null embryos; expressing Trpm7 mRNA restores development, but mutant versions fail or are partially rescued. Transcriptomic analyses of Trpm7-null embryos reveal an abundance of oxidative stress-pathway genes, confirmed by mitochondrial dysfunction, and a reduction in transcription factor networks essential for proliferation; Mg2+ supplementation corrects these defects. Hence, TRPM7 underpins Mg2+ homeostasis in preimplantation embryos, prevents oxidative stress, and promotes gene expression patterns necessary for developmental progression and cell-lineage specification.

ZnSO4 Protects against premature ovarian failure through PI3K/AKT/GSK3β signaling pathway

Zinc (Zn) is an essential trace element with anti-inflammatory and antioxidant effects and plays a crucial role in the female reproductive system. We aimed to investigate the protective effect of ZnSO4 on premature ovarian failure (POF) in SD rats and granulosa cells (GCs) treated with cisplatin. We also explored the underlying mechanisms. In vivo experiments showed that ZnSO4 increased the serum levels of Zn2+, increased estrogen (E2) secretion, and decreased follicle-stimulating hormone (FSH) secretion in rats. ZnSO4 increased ovarian index, protected ovarian tissues and blood vessels, reduced excessive follicular atresia, and maintained follicular development. At the same time, ZnSO4 inhibited apoptosis in the ovaries. In vitro experiments showed that ZnSO4 combination treatment restored the intracellular levels of Zn2+ and inhibited the apoptosis of GCs. ZnSO4 inhibited cisplatin-induced reactive oxygen species (ROS) production and preserved mitochondrial membrane potential (MMP). We also found that ZnSO4 protected against POF by activating the PI3K/AKT/GSK3β signaling pathway and reducing apoptosis of GCs. These data suggest that ZnSO4 may be a potential therapeutic agent for protecting the ovaries and preserving fertility during chemotherapy.

The Implications of Insufficient Zinc on the Generation of Oxidative Stress Leading to Decreased Oocyte Quality

Zinc is a transition metal that displays wide physiological implications ranging from participation in hundreds of enzymes and proteins to normal growth and development. In the reproductive tract of both sexes, zinc maintains a functional role in spermatogenesis, ovulation, fertilization, normal pregnancy, fetal development, and parturition. In this work, we review evidence to date regarding the importance of zinc in oocyte maturation and development, with emphasis on the role of key zinc-binding proteins, as well as examine the effects of zinc and reactive oxygen species (ROS) on oocyte quality and female fertility. We summarize our current knowledge about the participation of zinc in the developing oocyte bound to zinc finger proteins as well as loosely bound zinc ion in the intracellular and extracellular environments. These include aspects related to (1) the impact of zinc deficiency and overwhelming production of ROS under inflammatory conditions on the offset of the physiological antioxidant machinery disturbing biomolecules, proteins, and cellular processes, and their role in contributing to further oxidative stress; (2) the role of ROS in modulating damage to proteins containing zinc, such as zinc finger proteins and nitric oxide synthases (NOS), and expelling the zinc resulting in loss of protein function; and (3) clarify the different role of oxidative stress and zinc deficiency in the pathophysiology of infertility diseases with special emphasis on endometriosis-associated infertility.

Zinc supplementation promotes oocyte maturation and subsequent embryonic development in sheep

Zinc plays a crucial role in the growth and reproductive functions of animals. Despite the positive effects of zinc that have been reported in oocytes of cows, pigs, yaks, and other animals, the influence of zinc on sheep is little known. To investigate the effect of zinc on the in vitro maturation of sheep oocytes and subsequent parthenogenesis-activated embryonic development, we added different concentrations of zinc sulfate to the in vitro maturation (IVM) culture medium. The IVM culture medium with zinc improved the maturation of sheep oocytes and the subsequent blastocyst rate after parthenogenesis activation. Notably, it also enhanced the level of glutathione and mitochondrial activity while reducing levels of reactive oxygen species. Thus, zinc addition to the IVM medium improved the quality of oocytes with a positive effect on the subsequent development of oocytes and embryos.

Attenuating effects of selenium and zinc against hexavalent chromium-induced oxidative stress, hormonal instability, and placenta damage in preimplanted rats

As a toxic metal, hexavalent chromium (CrVI) has effects on both the reproductive and endocrine systems. This study aimed to evaluate the protective effects of selenium (Se) and zinc (Zn) against the toxicity of chromium on the placenta in pregnant Wistar albino rats. Thirty pregnant Wistar rats were divided into control and four treated groups, receiving subcutaneously (s.c) on the 3rd day of pregnancy, K₂Cr₂O₇ (10 mg/kg body weight (bw)) alone, or in association with Se (0.3 mg/kg bw), ZnCl₂ (20 mg/kg bw), or both of them simultaneously. Plasma steroid hormones, placenta histoarchitecture, oxidative stress profile, and developmental parameters were investigated. These results showed that K₂Cr₂O₇ exposure induced a significant increase in the levels of both plasma estradiol (E₂) and placenta malondialdehyde (MDA), the number of fetal resorptions, and percent of post-implantation loss. On the other hand, K₂Cr₂O₇ significantly reduced developmental parameters, maternal body and placenta weight, and plasma progesterone (P) and chorionic gonadotropin hormone (β HCG) levels. However, K₂Cr₂O₇ significantly decreased the placenta activities of superoxide dismutase (SOD), glutathione peroxidase (GPx), reduced glutathione (GSH), and nonprotein sulfhydryl (NPSH). These changes have been reinforced by histopathological evaluation of the placenta. Se and/or ZnCl₂ supplementation provoked a significant improvement in most indices. These results suggest that the co-treatment with Se or ZnCl₂ strongly opposes the placenta cytotoxicity induced by K₂Cr₂O₇ through its antioxidant action.

The Therapeutic and Diagnostic Potential of Phospholipase C Zeta, Oocyte Activation, and Calcium in Treating Human Infertility

Oocyte activation, a fundamental event during mammalian fertilisation, is initiated by concerted intracellular patterns of calcium (Ca2+) release, termed Ca2+ oscillations, predominantly driven by testis-specific phospholipase C zeta (PLCζ). Ca2+ exerts a pivotal role in not just regulating oocyte activation and driving fertilisation, but also in influencing the quality of embryogenesis. In humans, a failure of Ca2+ release, or defects in related mechanisms, have been reported to result in infertility. Furthermore, mutations in the PLCζ gene and abnormalities in sperm PLCζ protein and RNA, have been strongly associated with forms of male infertility where oocyte activation is deficient. Concurrently, specific patterns and profiles of PLCζ in human sperm have been linked to parameters of semen quality, suggesting the potential for PLCζ as a powerful target for both therapeutics and diagnostics of human fertility. However, further to PLCζ and given the strong role played by Ca2+ in fertilisation, targets down- and up-stream of this process may also present a significantly similar level of promise. Herein, we systematically summarise recent advancements and controversies in the field to update expanding clinical associations between Ca2+-release, PLCζ, oocyte activation and human fertility. We discuss how such associations may potentially underlie defective embryogenesis and recurrent implantation failure following fertility treatments, alongside potential diagnostic and therapeutic avenues presented by oocyte activation for the diagnosis and treatment of human infertility.

The role of zinc in follicular development

Follicles consist of specialized somatic cells that encase a single oocyte. Follicle development is a process regulated by a variety of endocrine, paracrine, and secretory factors that work together to select follicles for ovulation. Zinc is an essential nutrient for the human body and is involved in many physiological processes, such as follicle development, immune response, homeostasis, oxidative stress, cell cycle progression, DNA replication, DNA damage repair, apoptosis, and aging. Zinc deficiency can lead to blocked oocyte meiotic process, cumulus expansion, and follicle ovulation. In this mini-review, we summarize the the role of zinc in follicular development.

Cumulus Cell Transcriptome after Cumulus-Oocyte Complex Exposure to Nanomolar Cadmium in an In Vitro Animal Model of Prepubertal and Adult Age

Cadmium (Cd), a highly toxic pollutant, impairs oocyte fertilization, through oxidative damage on cumulus cells (CCs). This study analysed the transcriptomic profile of CCs of cumulus-oocyte complexes (COCs) from adult and prepubertal sheep, exposed to Cd nanomolar concentration during in vitro maturation. In both age-groups, CCs of matured oocytes underwent RNA-seq, data analysis and validation. Differentially expressed genes (DEGs) were identified in adult (n = 99 DEGs) and prepubertal (n = 18 DEGs) CCs upon Cd exposure. Transcriptomes of adult CCs clustered separately between Cd-exposed and control samples, whereas prepubertal ones did not as observed by Principal Component Analysis. The transcriptomic signature of Cd-induced CC toxicity was identified by gene annotation and literature search. Genes associated with previous studies on ovarian functions and/or Cd effects were confirmed and new genes were identified, thus implementing the knowledge on their involvement in such processes. Enrichment and validation analysis showed that, in adult CCs, Cd acted as endocrine disruptor on DEGs involved in hormone biosynthesis, cumulus expansion, regulation of cell signalling, growth and differentiation and oocyte maturation, whereas in prepubertal CCs, Cd affected DEGs involved in CC development and viability and CC-oocyte communications. In conclusion, these DEGs could be used as valuable non-invasive biomarkers for oocyte competence.

Preimplantation Developmental Competence of Bovine and Porcine Oocytes Activated by Zinc Chelation

After sperm-oocyte fusion, intracytoplasmic rises of calcium (Ca) induce the release of zinc (Zn) out of the oocyte (Zn sparks). Both phenomena are known to play an essential role in the oocyte activation process. Our work aimed to explore different protocols for activating bovine and porcine oocytes using the novel zinc chelator 1,10-phenanthroline (PHEN) and to compare developmental rates and quality to bovine IVF and parthenogenetic ionomycin-induced embryos in both species. Different incubation conditions for the zinc chelator were tested, including its combination with ionomycin. Embryo quality was assessed by immunofluorescence of SOX2, SOX17, OCT4, and CDX2 and total cell number at the blastocyst stage. Even though blastocyst development was achieved using a zinc chelator in bovine, bypassing calcium oscillations, developmental rates, and blastocyst quality were compromised compared to embryos generated with sperm-induced or ionomycin calcium rise. On the contrary, zinc chelation is sufficient to trigger oocyte activation in porcine. Additionally, we determined the optimal exposure to PHEN for this species. Zinc chelation and artificial induction of calcium rise combined did not improve developmental competence. Our results contribute to understanding the role of zinc during oocyte activation and preimplantation embryo development across different mammalian species.

Zinc dynamics regulate early ovarian follicle development

Zinc fluctuations regulate key steps in late oocyte and preimplantation embryo development; however, roles for zinc in preceding stages in early ovarian follicle development, when cooperative interactions exist between the oocyte and somatic cells, are unknown. To understand the roles of zinc during early follicle development, we applied single cell X-ray fluorescence microscopy, a radioactive zinc tracer, and a labile zinc probe to measure zinc in individual mouse oocytes and associated somatic cells within early follicles. Here, we report a significant stage-specific increase and compartmental redistribution in oocyte zinc content upon the initiation of early follicle growth. The increase in zinc correlates with the increased expression of specific zinc transporters, including two that are essential in oocyte maturation. While oocytes in follicles exhibit high tolerance to pronounced changes in zinc availability, somatic survival and proliferation are significantly more sensitive to zinc chelation or supplementation. Finally, transcriptomic, proteomic, and zinc loading analyses reveal enrichment of zinc targets in the ubiquitination pathway. Overall, these results demonstrate that distinct cell type-specific zinc regulations are required for follicle growth and indicate that physiological fluctuation in the localization and availability of this inorganic cofactor has fundamental functions in early gamete development.

Zinc's Association with the CmPn/CmP Signaling Network in Breast Cancer Tumorigenesis

It is well-known that serum and cellular concentrations of zinc are altered in breast cancer patients. Specifically, there are notable zinc hyper-aggregates in breast tumor cells when compared to normal mammary epithelial cells. However, the mechanisms responsible for zinc accumulation and the consequences of zinc dysregulation are poorly understood. In this review, we detailed cellular zinc regulation/dysregulation under the influence of varying levels of sex steroids and breast cancer tumorigenesis to try to better understand the intricate relationship between these factors based on our current understanding of the CmPn/CmP signaling network. We also made some efforts to propose a relationship between zinc signaling and the CmPn/CmP signaling network.

An overview of the role of metallic and nonmetallic nanoparticles and their salts during sperm cryopreservation and in vitro embryo manipulation

The cryopreservation of spermatozoa and the in vitro embryo production are valuable tools used in a variety of species, including humans, livestock, fish, and aquatic invertebrates. Sperm cryopreservation has been used to maintain or increase the genetic diversity of threatened species. Reactive oxygen species (ROS) are molecules derived from oxygen, being formed as byproducts of cellular metabolism. During cryopreservation of sperm and other in vitro manipulations of oocytes and embryos, ROS production is dramatically increased. In cells, low, medium, and high levels of ROS lead to different outcomes, apoptosis, auto-phagocytosis, and necrosis, respectively. ROS produced by cells can be neutralized by intracellular antioxidant systems, including enzymes as well as non-enzymatic antioxidants. Free radicals and oxidative stress can be major factors influencing in vitro manipulations. In this review, we discuss the role that metallic and nonmetallic nanoparticles and their salts play in the modulation of oxidative stress during in vitro embryo production and cryopreservation of sperm.

A Post-GWAS Functional Analysis Confirming Effects of Three BTA13 Genes CACNB2, SLC39A12, and ZEB1 on Dairy Cattle Reproduction

In our previous GWAS of Chinese and Nordic dairy cattle, genes CACNB2, SLC39A12, and ZEB1 locating on BTA 13 were suggested as candidate genes for reproduction. In this study, validation of these associations was performed in an independent population with records of nine reproductive traits. More importantly, functions of these genes in the reproductive process were verified by employing the expression data of ovarian follicles. The potential variants within the three genes were firstly detected in 68 Chinese Holstein bulls, and then screened in 1,588 Chinese Holstein cows using the KASP (Kompetitive allele-specific PCR) method. There were nine variants with polymorphisms in CACNB2, five in SLC39A12, and four in ZEB1, respectively, of which one SNP was in the upstream regulatory region, two in exon region, four in downstream regulatory region, and 11 SNPs in intronic regions. Amongst the 18 variants, g.33267056T/G in CACNB2 explained the largest phenotypic variance for age at first calving (0.011%), interval from first to last insemination (0.004%), and calving ease (0.002%), while g.32751518G/A in SLC39A12 contributed the most to stillbirth in heifers (0.038%). Two haplotype blocks were constructed for CACNB2 while one each for SLC39A12 and ZEB1, which were significantly associated with five reproductive traits, including age at the first service, age at the first calving, calving ease in heifers and cows, and the interval from calving to the first insemination. We then studied the profile of gene expression in granulosa cells isolated from four developmental stages of ovarian follicles from eight dairy cows. All three genes were differentially expressed between ovarian follicles with different sizes (p < 0.05), indicating their potential roles in the reproductive process of dairy cows. This study successfully demonstrated the associations of three BTA 13 genes CACNB2, SLC39A12, and ZEB1 with reproduction and further examined their expression levels in ovarian follicles directly. These findings can be beneficial for the ongoing genomic selection program for reproductive traits which have long been considered as traits that are difficult to achieve genetic improvement due to the lack of efficient genetic markers.

Quantitative imaging approaches to understanding biological processing of metal ions

Faster, more sensitive, and higher resolution quantitative instrumentation are aiding a deeper understanding of how inorganic chemistry regulates key biological processes. Researchers can now image and quantify metals with subcellular resolution, leading to a vast array of new discoveries in organismal development, pathology, and disease. Metals have recently been implicated in several diseases such as Parkinson's, Alzheimers, ischemic stroke, and colorectal cancer that would not be possible without these advancements. In this review, instead of focusing on instrumentation we focus on recent applications of label-free elemental imaging and quantification and how these tools can lead to a broader understanding of metals role in systems biology and human pathology.

Zinc transporters ZIPT-2.4 and ZIPT-15 are required for normal C. elegans fecundity

PURPOSE

The requirement of zinc for the development and maturation of germ lines and reproductive systems is deeply conserved across evolution. The nematode Caenorhabditis elegans offers a tractable platform to study the complex system of distributing zinc to the germ line. We investigated several zinc importers to investigate how zinc transporters play a role in the reproductive system in nematodes, as well as establish a platform to study zinc transporter biology in germline and reproductive development.

METHODS

Previous high throughput transcriptional datasets as well as phylogenetic analysis identified several putative zinc transporters that have a function in reproduction in worms. Phenotypic analysis of CRISPR-generated knockouts and tags included characterization of offspring output, gonad development, and protein localization. Light and immunofluorescence microscopy allowed for visualization of physiological and molecular effects of zinc transporter mutations.

RESULTS

Disruption of two zinc transporters, ZIPT-2.4 and ZIPT-15, was shown to lead to defects in reproductive output. A mutation in zipt-2.4 has subtle effects on reproduction, while a mutation in zipt-15 has a clear impact on gonad and germline development that translates into a more pronounced defect in fecundity. Both transporters have germline expression, as well as additional expression in other cell types.

CONCLUSIONS

Two ZIP-family zinc transporter orthologs of human ZIP6/10 and ZIP1/2/3 proteins are important for full reproductive fecundity and participate in development of the gonad. Notably, these zinc transporters are present in gut and reproductive tissues in addition to the germ line, consistent with a complex zinc trafficking network important for reproductive success.

Dynamic zinc fluxes regulate meiotic progression in Caenorhabditis elegans†

Zinc influx and efflux events are essential for meiotic progression in oocytes of several mammalian and amphibian species, but it is less clear whether this evolutionary conservation of zinc signals is also important in late-stage germline development in invertebrates. Using quantitative, single cell elemental mapping methods, we find that Caenorhabditis elegans oocytes undergo significant stage-dependent fluctuations in total zinc content, rising by over sevenfold from Prophase I through the beginning of mitotic divisions in the embryo. Live imaging of the rapid cell cycle progression in C. elegans enables us to follow changes in labile zinc pools across meiosis and mitosis in single embryo. We find a dynamic increase in labile zinc prior to fertilization that then decreases from Anaphase II through pronuclear fusion and relocalizes to the eggshell. Disruption of these zinc fluxes blocks extrusion of the second polar body, leading to a range of mitotic defects. We conclude that spatial temporal zinc fluxes are necessary for meiotic progression in C. elegans and are a conserved feature of germ cell development in a broad cross section of metazoa.

Molecular determinants of the meiotic arrests in mammalian oocytes at different stages of maturation

Mammalian oocytes undergo two rounds of developmental arrest during maturation: at the diplotene of the first meiotic prophase and metaphase of the second meiosis. These arrests are strictly regulated by follicular cells temporally producing the secondary messengers, cAMP and cGMP, and other factors to regulate maturation promoting factor (composed of cyclin B1 and cyclin-dependent kinase 1) levels in the oocytes. Out of these normally appearing developmental arrests, permanent arrests may occur in the oocytes at germinal vesicle (GV), metaphase I (MI), or metaphase II (MII) stage. This issue may arise from absence or altered expression of the oocyte-related genes playing key roles in nuclear and cytoplasmic maturation. Additionally, the assisted reproductive technology (ART) applications such as ovarian stimulation and in vitro culture conditions both of which harbor various types of chemical agents may contribute to forming the permanent arrests. In this review, the molecular determinants of developmental and permanent arrests occurring in the mammalian oocytes are comprehensively evaluated in the light of current knowledge. As number of permanently arrested oocytes at different stages is increasing in ART centers, potential approaches for inducing permanent arrests to obtain competent oocytes are discussed.

Dynamic changes of intracellular zinc ion level during maturation, fertilization, activation, and development in mouse oocytes

Although it is well known that calcium oscillations are required for fertilization in all mammalian species studied to date, recent studies also showed the ejection of zinc into the extracellular milieu in a series of coordinated events, called "zinc spark," during mammalian fertilization. These results led us to the hypothesis that a zinc ion-dependent signal is important for oocyte maturation, fertilization (activation), and further embryonic development. In this study, we evaluated the amounts and localization of intracellular zinc ions during maturation, fertilization, activation, and embryonic development in mouse oocytes. Our results show that abundant zinc ions are present in both immature and mature oocytes. After in vitro fertilization, the amounts of zinc ions were dramatically decreased at the pronuclear (PN) stage. Artificial activation by cycloheximide, SrCl₂ , and TPEN also reduced the amounts of zinc ions in the PN stage. On the other hand, PN embryos derived from sperm injection still showed high level of zinc ions. However, the amounts of zinc ions rapidly increased at the blastocysts regardless of activation method. We showed here that the amounts of zinc ions dramatically changed during maturation, fertilization, activation, and development in mouse oocytes.

Design of novel oocyte activation methods: The role of zinc

Oocyte activation occurs at the time of fertilization and is a series of cellular events initiated by intracellular Ca2+ increases. Consequently, oocytes are alleviated from their arrested state in meiotic metaphase II (MII), allowing for the completion of meiosis. Oocyte activation is also an essential step for somatic cell nuclear transfer (SCNT) and an important tool to overcome clinical infertility. Traditional artificial activation methods aim to mimic the intracellular Ca2+ changes which occur during fertilization. Recent studies emphasize the importance of cytoplasmic Zn2+ on oocyte maturation and the completion of meiosis, thus suggesting artificial oocyte activation approaches that are centered around the concentration of available Zn2+in oocytes. Depletion of intracellular Zn2+ in oocytes with heavy metal chelators leads to successful oocyte activation in the absence of cellular Ca2+ changes, indicating that successful oocyte activation does not always depends on intracellular Ca2+ increases. Current findings lead to new approaches to artificially activate mammalian oocytes by reducing available Zn2+ contents, and the approaches improve the outcome of oocyte activation when combined with existing Ca2+ based oocyte activation methods. Here, we review the important role of Ca2+ and Zn2+ in mammalian oocyte activation and development of novel oocyte activation approaches based on Zn2+ availability.

Comparative transcriptomic analysis of gonadal development and renewal in the ovoviviparous black rockfish (Sebastes schlegelii)

BACKGROUND

The black rockfish (Sebastes schlegelii) has an ovoviviparous reproductive pattern and long-term sperm storage, resulting in asynchronous gonadal development between the sexes. However, the comprehensive understanding of gonadal development in black rockfish has not yet been achieved. Here, we studied gonadal development and germ cell renewal using histology and RNA-seq.

RESULTS

In this study, RNA-seq was performed on testes and ovaries to characterize key pathways and genes that are active during development and gamete maturation in black rockfish. Differentially expressed genes (DEGs) were identified and annotated in 4 comparisons (F_III vs. F_IV, F_IV vs. F_V, M_III vs. M_IV and M_IV vs. M_V). Based on analysis of DEGs enriched in the testis, 11 and 14 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were mapped to the M_III vs. M_IV group and the M_IV vs. M_V group, respectively. DEGs in ovarian development were also classified into 10 groups according to their biological functions. The expression patterns of the selected genes determined by qPCR were significantly correlated with the RNA-Seq results, supporting the reliability and accuracy of the RNA-Seq analysis. E2 levels showed down regulation from previtellogenesis to mature stage in female and T level showed down regulation from spermatogenesis to regressed stage in the male.

CONCLUSIONS

The categories "intercellular interaction and cytoskeleton", "molecule amplification" and "repair in the cell cycle" were revealed to be crucial in testis development and spermatogenesis, as was the biosynthesis of a series of metabolites. Our results provide comprehensive insight into black rockfish gonadal development and provide a basis for further study of reproductive physiology and molecular biology in ovoviviparity teleosts.

Quercetin-treated rat sperm enables refrigerated transport with motility and fertility for five days

Shipment of laboratory rats between animal facilities is frequently performed using special containers. However, the shipment of live animals is associated with potential risks of infectious diseases, escape and death during shipment and animal welfare issues. The transport of cold-stored sperm avoids such risks; however, there have been no reports on cold storage of rat sperm. We previously reported that dimethyl sulfoxide (DMSO) and quercetin maintained the motility and fertilising abilities of cold-stored mouse sperm stored for 10 days. The present study investigated the efficacy of DMSO and quercetin in the cold storage of rat sperm. Quercetin maintained motility and fertility of cold-stored rat sperm stored for 5 days. After in vitro fertilisation using cold-stored sperm, pronuclear and two-cell embryos developed normally to pups following embryo transfer. Therefore, we demonstrated that live pups could be obtained from sperm transported using the cold-storage system. We conclude that cold storage of rat sperm may provide an efficient system for transporting rat resources as an alternative to shipping live animals.

Zn2+ influx activates ERK and Akt signaling pathways

Zinc (Zn²⁺) is an essential metal in biology, and its bioavailability is highly regulated. Many cell types exhibit fluctuations in Zn²⁺ that appear to play an important role in cellular function. However, the detailed molecular mechanisms by which Zn²⁺ dynamics influence cell physiology remain enigmatic. Here, we use a combination of fluorescent biosensors and cell perturbations to define how changes in intracellular Zn²⁺ impact kinase signaling pathways. By simultaneously monitoring Zn²⁺ dynamics and kinase activity in individual cells, we quantify changes in labile Zn²⁺ and directly correlate changes in Zn²⁺ with ERK and Akt activity. Under our experimental conditions, Zn²⁺ fluctuations are not toxic and do not activate stress-dependent kinase signaling. We demonstrate that while Zn²⁺ can nonspecifically inhibit phosphatases leading to sustained kinase activation, ERK and Akt are predominantly activated via upstream signaling and through a common node via Ras. We provide a framework for quantification of Zn²⁺ fluctuations and correlate these fluctuations with signaling events in single cells to shed light on the role that Zn²⁺ dynamics play in healthy cell signaling.

Silica encapsulation of ZnO nanoparticles reduces their toxicity for cumulus cell-oocyte-complex expansion

Background

Metal oxide nanoparticles (NPs) are increasingly used in many industrial and biomedical applications, hence their impact on occupational and public health has become a concern. In recent years, interest on the effect that exposure to NPs may exert on human reproduction has grown, however data are still scant. In the present work, we investigated whether different metal oxide NPs interfere with mouse cumulus cell-oocyte complex (COC) expansion.

Methods

Mouse COCs from pre-ovulatory follicles were cultured in vitro in the presence of various concentrations of two types of TiO₂ NPs (JRC NM-103 and NM-104) and four types of ZnO NPs (JRC NM-110, NM-111, and in-house prepared uncoated and SiO₂-coated NPs) and the organization of a muco-elastic extracellular matrix by cumulus cells during the process named cumulus expansion was investigated.

Results

We show that COC expansion was not affected by the presence of both types of TiO₂ NPs at all tested doses, while ZnO NM-110 and NM-111 induced strong toxicity and inhibited COCs expansion at relatively low concentration. Medium conditioned by these NPs showed lower toxicity, suggesting that, beside ion release, inhibition of COC expansion also depends on NPs per se. To further elucidate this, we compared COC expansion in the presence of uncoated or SiO₂-coated NPs. Differently from the uncoated NPs, SiO₂-coated NPs underwent slower dissolution, were not internalized by the cells, and showed an overall lower toxicity. Gene expression analysis demonstrated that ZnO NPs, but not SiO₂-coated ZnO NPs, affected the expression of genes fundamental for COC expansion. Dosimetry analysis revealed that the delivered-to-cell mass fractions for both NPs was very low.

Conclusions

Altogether, these results suggest that chemical composition, dissolution, and cell internalization are all responsible for the adverse effects of the tested NPs and support the importance of a tailored, safer-by-design production of NPs to reduce toxicity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-021-00424-z.

Metal ion fluxes controlling amphibian fertilization

Mammalian oocytes undergo major changes in zinc content and localization to be fertilized, the most striking being the rapid exocytosis of over 10 billion zinc ions in what are known as zinc sparks. Here, we report that fertilization of amphibian Xenopus laevis eggs also initiates a zinc spark that progresses across the cell surface in coordination with dynamic calcium waves. This zinc exocytosis is accompanied by a newly recognized loss of intracellular manganese. Synchrotron-based X-ray fluorescence and analytical electron microscopy reveal that zinc and manganese are sequestered in a system of cortical granules that are abundant at the animal pole. Through electron-nuclear double-resonance studies, we rule out Mn²⁺ complexation with phosphate or nitrogenous ligands in intact eggs, but the data are consistent with a carboxylate coordination environment. Our observations suggest that zinc and manganese fluxes are a conserved feature of fertilization in vertebrates and that they function as part of a physiological block to polyspermy.

Zinc exocytosis is sensitive to myosin light chain kinase inhibition in mouse and human eggs

Zinc dynamics are essential for oocyte meiotic maturation, egg activation, and preimplantation embryo development. During fertilisation and egg activation, the egg releases billions of zinc atoms (Zn2+) in an exocytotic event termed the 'zinc spark'. We hypothesised that this zinc transport and exocytosis is dependent upon the intracellular trafficking of cortical granules (CG) which requires myosin-actin-dependent motors. Treatment of mature mouse and human eggs with ML-7, a myosin light chain kinase inhibitor (MLCK), resulted in an 80% reduction in zinc spark intensity compared to untreated controls when activated with ionomycin. Moreover, CG migration towards the plasma membrane was significantly decreased in ML-7-treated eggs compared with controls when activated parthenogenetically with ionomycin. In sperm-induced fertilisation via intracytoplasmic sperm injection (ICSI), ML-7-treated mouse eggs exhibited decreased labile zinc intensity and cortical CG staining. Collectively, these data demonstrate that ML-7 treatment impairs zinc release from both murine and human eggs after activation, demonstrating that zinc exocytosis requires myosin light chain kinase activity. Further, these results provide additional support that zinc is likely stored and released from CGs. These data underscore the importance of intracellular zinc trafficking as a crucial component of egg maturation necessary for egg activation and early embryo development.

Role of zinc in female reproduction

Zinc is a critical component in a number of conserved processes that regulate female germ cell growth, fertility, and pregnancy. During follicle development, a sufficient intracellular concentration of zinc in the oocyte maintains meiotic arrest at prophase I until the germ cell is ready to undergo maturation. An adequate supply of zinc is necessary for the oocyte to form a fertilization-competent egg as dietary zinc deficiency or chelation of zinc disrupts maturation and reduces the oocyte quality. Following sperm fusion to the egg to initiate the acrosomal reaction, a quick release of zinc, known as the zinc spark, induces egg activation in addition to facilitating zona pellucida hardening and reducing sperm motility to prevent polyspermy. Symmetric division, proliferation, and differentiation of the preimplantation embryo rely on zinc availability, both during the oocyte development and post-fertilization. Further, the fetal contribution to the placenta, fetal limb growth, and neural tube development are hindered in females challenged with zinc deficiency during pregnancy. In this review, we discuss the role of zinc in germ cell development, fertilization, and pregnancy with a focus on recent studies in mammalian females. We further detail the fundamental zinc-mediated reproductive processes that have only been explored in non-mammalian species and speculate on the role of zinc in similar mechanisms of female mammals. The evidence collected over the last decade highlights the necessity of zinc for normal fertility and healthy pregnancy outcomes, which suggests zinc supplementation should be considered for reproductive age women at risk of zinc deficiency.

Sex- and sexual maturation-related aspects of the element accumulation in soft tissues of the bivalve Mytilus galloprovincialis Lam. collected off coasts of Sevastopol (southwestern Crimea, Black Sea)

Mussels are widely used to monitor trace element pollution, but the role of their sex and sexual maturation in the element accumulation was not comprehensively studied and the number of elements under consideration never exceeded three dozen. In this work, concentrations of 67 elements in different tissues of females and males of the Mediterranean mussel are determined. Statistically significant differences are obtained in the element composition of analogous tissues of mussel males and females and in gonads of the same sex at different sexual maturation stages. The significantly higher concentrations of some elements found in gonads of females (Mn, Zn, As) and males (P) at most of the sexual maturation stages suggest essentiality of these elements in the reproduction. Elements exhibit several accumulation patterns in gonads during the ripening, with the most general one being the accumulation after spawning. Indications of a new phenomenon of circulation of most elements in gonads over the reproductive cycle are obtained, with the element concentrations decreasing at the first two stages and increasing at the posterior stages. Principal component analysis shows that the differences in the element accumulation are mainly due to the element uptake pathways and sexual differentiation. The most important identified factors determining the decrease in concentrations of tissue elements are their redistribution over mussel's body, biomass dilution, sequestration, and release with gametes. Five detected non-overlapping clusters of the non-normalized element concentrations in the pooled mussel tissues are associated with macroelements, two groups of trace elements, and two groups of ultratrace elements.

Simultaneous Zn2+ tracking in multiple organelles using super-resolution morphology-correlated organelle identification in living cells

Zn²⁺ plays important roles in metabolism and signaling regulation. Subcellular Zn²⁺ compartmentalization is essential for organelle functions and cell biology, but there is currently no method to determine Zn²⁺ signaling relationships among more than two different organelles with one probe. Here, we report simultaneous Zn²⁺ tracking in multiple organelles (Zn-STIMO), a method that uses structured illumination microscopy (SIM) and a single Zn²⁺ fluorescent probe, allowing super-resolution morphology-correlated organelle identification in living cells. To guarantee SIM imaging quality for organelle identification, we develop a new turn-on Zn²⁺ fluorescent probe, NapBu-BPEA, by regulating the lipophilicity of naphthalimide-derived Zn²⁺ probes to make it accumulate in multiple organelles except the nucleus. Zn-STIMO with this probe shows that CCCP-induced mitophagy in HeLa cells is associated with labile Zn²⁺ enhancement. Therefore, direct organelle identification supported by SIM imaging makes Zn-STIMO a reliable method to determine labile Zn²⁺ dynamics in various organelles with one probe. Finally, SIM imaging of pluripotent stem cell-derived organoids with NapBu-BPEA demonstrates the potential of super-resolution morphology-correlated organelle identification to track biospecies and events in specific organelles within organoids.

Subcellular Zn²⁺ compartmentalisation is essential for cell biology. Here the authors make a turn-on fluorescent Zn²⁺ probe that localises to multiple organelles, and correlate its location using organelle morphology derived from structured illumination microscopy.

[Transcription Factor MTF-1 Involved in the Cellular Response to Zinc]

Heavy metals, both toxic and essential, have long been an important research focus in life science. To investigate the intracellular actions of heavy metals at the molecular level, I have been exploring protein factors involved in induction of metallothionein (MT) genes by heavy metals that specifically bind to a metal responsive element (MRE) in the region upstream of the human MT-IIA gene. Purification of a zinc-dependent MRE-binding factor, and cloning of its cDNA identified a sequence identical to that of metal-responsive transcription factor-1 (MTF-1). MTF-1, which is characterized by six tandem repeats of the C2H2 type zinc finger motif, is indispensable for induction of MT gene expression by multiple types of heavy metal, but zinc is the only metal that can directly activate MTF-1 binding to the MRE, indicating that other heavy metal signals act through zinc as a second messenger. Functional analysis of various MTF-1 point mutants revealed several cysteine (Cys) residues critical for DNA binding and/or transactivation activity. Interestingly, six finger motifs seem to mediate several MTF-1 functions other than DNA binding. Immunohistochemical analyses of various mouse tissues revealed selective expression of MTF-1 in spermatocytes among the testicular cells, suggesting roles relevant to spermatogenesis. The zinc regulon, under the control of MTF-1, will likely provide good clues to aid in unraveling novel functions of intracellular zinc ions.

General Aspects of Metal Ions as Signaling Agents in Health and Disease

This review focuses on the current knowledge on the involvement of metal ions in signaling processes within the cell, in both physiological and pathological conditions. The first section is devoted to the recent discoveries on magnesium and calcium-dependent signal transduction-the most recognized signaling agents among metals. The following sections then describe signaling pathways where zinc, copper, and iron play a key role. There are many systems in which changes in intra- and extra-cellular zinc and copper concentrations have been linked to important downstream events, especially in nervous signal transduction. Iron signaling is mostly related with its homeostasis. However, it is also involved in a recently discovered type of programmed cell death, ferroptosis. The important differences in metal ion signaling, and its disease-leading alterations, are also discussed.

The zinc transporter ZIP9 (Slc39a9) regulates zinc dynamics essential to egg activation in zebrafish

The zinc transporter ZIP9 (SLC39A9) was recently characterized as a membrane androgen receptor in various teleost and mammalian cell models. ZIP9 shows the highest expression in ovaries of teleosts, a tissue in which both androgen signaling and zinc dynamics have significant roles. To examine the role of ZIP9 in ovarian physiology, we generated a ZIP9-mutant zebrafish strain using a CRISPR/Cas9 system. zip9^-/- females showed significant reductions in fecundity, embryo viability, and growth of their offspring compared to wildtype (WT) fish. Furthermore, a high proportion of zip9^-/- eggs failed to undergo normal chorion elevation during activation. In WT eggs, zinc was detected in cortically-localized vesicles which underwent exocytosis upon activation. zip9^-/- eggs showed abnormal cortical vesicle development and had a significantly depressed activation-induced zinc release compared to WT eggs. Moreover, pharmacologically sustained elevation of zinc in WT eggs prior to activation resulted in abnormal chorion elevation similar to that observed in zip9^-/- eggs. These results indicate that ZIP9 is essential for proper zinc modulation during zebrafish egg activation and presents the first evidence of zinc modulation during egg activation in a non-mammalian species.

Zinc supplementation alleviates endoplasmic reticulum stress during porcine oocyte in vitro maturation by upregulating zinc transporters

Endoplasmic reticulum (ER) stress is a major contributor to embryonic development failure. Mammalian oocytes have a high risk of exposure to cellular stress during in vitro embryo production. We investigated the effects of zinc supplementation during in vitro maturation under ER stress. We evaluated cumulus expansion, embryonic development derived by parthenogenetic activation, reactive oxygen species, protein expression of X-box binding protein 1 (XBP1), and expression of genes related to ER stress. Supplementation with 1 μg/ml zinc significantly increased the nuclear maturation of oocytes, cleavage and blastocyst formation rates, and total blastocyst cell number (p < .05). Under ER stress, zinc significantly reduced protein expression of XBP1, and increased cleavage and blastocyst rates (p < .05). Concomitantly, zinc supplementation upregulated the expression of zinc transporters (SLC39A14 and SLC39A10), PTGS2, and downregulated ER stress-related genes (sXBP1, uXBP1, ATF4, and PTPN1/PTP1B), and caspase 3. These results suggest that zinc supplementation alleviates ER stress by providing essential metal-ion transporters for oocyte maturation and subsequent embryonic development.

Phospholipase Cζ (PLCζ) versus postacrosomal sheath WW domain-binding protein (PAWP): Which molecule will survive as a sperm factor?

During mammalian fertilization, sperm is fused with the oocyte's membrane, triggering the resumption of meiosis from the metaphase II arrest, the extrusion of the second polar body, and the exocytosis of cortical granules; these events are collectively called 'oocyte activation.' In all species studied to date, the transient rise in the cytosolic level of calcium (in particular, the repeated calcium increases called 'calcium oscillations' in mammals) is required for these events. Researchers have focused on identifying the factor(s) that can induce calcium oscillations during fertilization. Sperm‐specific phospholipase C, i.e., PLC zeta (PLCζ), is a strong candidate of the factor(s), and several research groups using different species obtained evidence that PLCζ is a sperm factor that can induce calcium oscillations during fertilization. However, postacrosomal sheath Tryptophan‐Tryptophan (WW)—domain‐binding protein (PAWP) was recently shown to have a pivotal role in inducing calcium oscillations in some species. In this review, we focus on PLCζ and PAWP as sperm factors, and we discuss this controversy: Which of these two molecules survives as a sperm factor?

The Role of Zinc in Selected Female Reproductive System Disorders

Zinc is an essential microelement that plays many important functions in the body. It is crucial for the regulation of cell growth, hormone release, immunological response and reproduction. This review focuses on its importance in the reproductive system of women of reproductive and postmenopausal ages, not including its well described role in pregnancy. Only recently, attention has been drawn to the potential role of zinc in polycystic ovary syndrome (PCOS), dysmenorrhea, or endometriosis. This review is mainly based on 36 randomized, controlled studies on reproductive, pre- and post-menopausal populations of women and on research trying to explain the potential impact of zinc and its supplementation in the etiology of selected female reproductive system disorders. In women with PCOS, zinc supplementation has a positive effect on many parameters, especially those related to insulin resistance and lipid balance. In primary dysmenorrhea, zinc supplementation before and during each menstrual cycle seems to be an important factor reducing the intensity of menstrual pain. On the other hand, little is known of the role of zinc in endometriosis and in postmenopausal women. Therefore, further studies explaining the potential impact of zinc and its supplementation on female reproductive system would be highly advisable and valuable.

Zinc Dynamics during Drosophila Oocyte Maturation and Egg Activation

Temporal fluctuations in zinc concentration are essential signals, including during oogenesis and early embryogenesis. In mammals, zinc accumulation and release are required for oocyte maturation and egg activation, respectively. Here, we demonstrate that zinc flux occurs in Drosophila oocytes and activated eggs, and that zinc is required for female fertility. Our synchrotron-based X-ray fluorescence microscopy reveals zinc as the most abundant transition metal in Drosophila oocytes. Its levels increase during oocyte maturation, accompanied by the appearance of zinc-enriched intracellular granules in the oocyte, which depend on transporters. Subsequently, in egg activation, which mediates the transition from oocyte to embryo, oocyte zinc levels decrease significantly, as does the number of zinc-enriched granules. This pattern of zinc dynamics in Drosophila oocytes follows a similar trajectory to that in mammals, extending the parallels in female gamete processes between Drosophila and mammals and establishing Drosophila as a model for dissecting reproductive roles of zinc.