Rab3A, a possible marker of cortical granules, participates in cortical granule exocytosis in mouse eggs

The light chain of tetanus toxin bound to arginine-rich cell-penetrating peptide inhibits cortical reaction in mouse oocytes

Introduction: Cortical reaction is a secretory process that occurs after a spermatozoon fuses with the oocyte, avoiding the fusion of additional sperm. During this exocytic event, the cortical granule membrane fuses with the oocyte plasma membrane. We have identified several molecular components involved in this process and confirmed that SNARE proteins regulate membrane fusion during cortical reaction in mouse oocytes. In those studies, we microinjected different nonpermeable reagents to demonstrate the participation of a specific protein in the cortical reaction. However, the microinjection technique has several limitations. In this work, we aimed to assess the potential of cell-penetrating peptides (CPP) as biotechnological tools for delivering molecules into oocytes, and to evaluate the functionality of the permeable tetanus toxin (bound to CPP sequence) during cortical reaction. Methods: Arginine-rich cell-penetrating peptides have demonstrated the optimal internalization of small molecules in mammalian cells. Two arginine-rich CPP were used in the present study. One, labeled with 5-carboxyfluorescein, to characterize the factors that can modulate its internalization, and the other, the permeable light chain of tetanus toxin, that cleaves the SNAREs VAMP1 and VAMP3 expressed in mouse oocytes. Results: Results showed that fluorescent CPP was internalized into the oocyte cytoplasm and that internalization was dependent on the concentration, time, temperature, and maturation stage of the oocyte. Using our functional assay to study cortical reaction, the light chain of tetanus toxin bound to arginine-rich cell-penetrating peptide inhibited cortical granules exocytosis. Discussion: Results obtained from the use of permeable peptides demonstrate that this CPP is a promising biotechnological tool to study functional macromolecules in mouse oocytes.

Sialylation: fate decision of mammalian sperm development, fertilization, and male fertility†

Sperm development, maturation, and successful fertilization within the female reproductive tract are intricate and orderly processes that involve protein translation and post-translational modifications. Among these modifications, sialylation plays a crucial role. Any disruptions occurring throughout the sperm's life cycle can result in male infertility, yet our current understanding of this process remains limited. Conventional semen analysis often fails to diagnose some infertility cases associated with sperm sialylation, emphasizing the need to comprehend and investigate the characteristics of sperm sialylation. This review reanalyzes the significance of sialylation in sperm development and fertilization and evaluates the impact of sialylation damage on male fertility under pathological conditions. Sialylation serves a vital role in the life journey of sperm, providing a negatively charged glycocalyx and enriching the molecular structure of the sperm surface, which is beneficial to sperm reversible recognition and immune interaction. These characteristics are particularly crucial during sperm maturation and fertilization within the female reproductive tract. Moreover, enhancing the understanding of the mechanism underlying sperm sialylation can promote the development of relevant clinical indicators for infertility detection and treatment.

Tannin Reduces the Incidence of Polyspermic Penetration in Porcine Oocytes

Tannin (TA) improves porcine oocyte cytoplasmic maturation and subsequent embryonic development after in vitro fertilization (IVF). However, the mechanism through which TA blocks polyspermy after IVF remains unclear. Hence, the biological function of organelles (cortical granule [CG], Golgi apparatus, endoplasmic reticulum [ER], and mitochondria) and the incidence of polyspermic penetration were examined. We found no significant difference in oocyte nuclear maturation among the 1 µg/mL, 10 µg/mL TA, and control groups. Moreover, 100 μg/mL TA significantly reduced 1st polar body formation rate compared to the other groups. Additionally, 1 and 10 μg/mL TA significantly increased the protein levels of GDF9, BMP15, and CDK1 compared to the control and 100 μg/mL TA groups. Interestingly, 1 and 10 μg/mL TA improved the normal distribution of CGs, Golgi, ER, and mitochondria by upregulating organelle-related gene expression and downregulating ER stress (CHOP) gene expression. Simultaneously, 1 and 10 μg/mL TA significantly increased the proportion of normal fertilized oocytes (2 pronuclei; 2 PN) and blastocyst formation rate compared to the control, as well as that of 100 μg/mL TA after IVF by upregulating polyspermy-related genes. In conclusion, TA during IVM enhances 2PN and blastocyst formation rates by regulating organelles’ functions and activities.

Phototherapeutic effect of transformable peptides containing pheophorbide a on colorectal cancer

Photodynamic therapy (PDT) and photothermal therapy (PTT) have attracted research interest for their noninvasive nature and selective treatment of tumor tissues. They are effective through the generation of reactive oxygen species (ROS) or heat. Nevertheless, several problems, including low bioavailability and long-lasting cutaneous photosensitivity, have limited their clinical application. In this study, we reported an in situ self-assembly strategy that could improve various biological properties of the photosensitizer in vivo. A photosensitizer connected to a receptor-mediated smart peptide can self-assemble into nanoparticles (NPs) under the force of hydrophobic interaction and then transform into a nanofibrillar network after attaching to the tumor cell surface with the help of the β-sheet-forming peptide KLVFF. The supramolecular structural changes deeply affected the PDT and PTT properties of the photosensitizer on tumors. After being aggregated into the nanostructure, the water solubility and targeting ability of the photosensitizer was ameliorated. Moreover, the improvement of the photothermal conversion efficiency, ROS generation, and tumor retention followed the formation of nanofibrils (NFs). This self-assembly strategy showed the ability of supramolecular nanofibrils to improve the bioavailability of photosensitizers, which provides a new potential treatment avenue for various cancer therapies.

Rab3a, a small GTP-binding protein, is required for the stabilization of the murine leukaemia virus Gag protein

We recently identified a CD63-interacting protein to understand the role of CD63 in virion production of the human immunodeficiency virus type 1, and we have found that Rab3a forms a complex with CD63. In this study, we analysed the effect of Rab3a on virion production of the murine leukaemia virus (MLV), which is another member of the retrovirus family. We found that Rab3a silencing induced lysosomal degradation of the MLV Gag protein, and recovery of the Rab3a expression restored the level of the Gag protein through a complex formation of MLV Gag and Rab3a, indicating that Rab3a is required for MLV Gag protein expression. In contrast, CD63 silencing decreased the infectivity of released virions but had no effect on virion production, indicating that CD63 facilitates the infectivity of released MLV particles. Although Rab3a induced CD63 degradation in uninfected cells, the complex of MLV Gag and Rab3a suppressed the Rab3a-mediated CD63 degradation in MLV-infected cells. Finally, we found that the MLV Gag protein interacts with Rab3a to stabilize its own protein and CD63 that facilitates the infectivity of released MLV particles. Considering the involvement of Rab3a in lysosome trafficking to the plasma membrane, it may also induce cell surface transport of the MLV Gag protein.

Knockin' on Egg's Door: Maternal Control of Egg Activation That Influences Cortical Granule Exocytosis in Animal Species

Fertilization by multiple sperm leads to lethal chromosomal number abnormalities, failed embryo development, and miscarriage. In some vertebrate and invertebrate eggs, the so-called cortical reaction contributes to their activation and prevents polyspermy during fertilization. This process involves biogenesis, redistribution, and subsequent accumulation of cortical granules (CGs) at the female gamete cortex during oogenesis. CGs are oocyte- and egg-specific secretory vesicles whose content is discharged during fertilization to block polyspermy. Here, we summarize the molecular mechanisms controlling critical aspects of CG biology prior to and after the gametes interaction. This allows to block polyspermy and provide protection to the developing embryo. We also examine how CGs form and are spatially redistributed during oogenesis. During egg activation, CG exocytosis (CGE) and content release are triggered by increases in intracellular calcium and relies on the function of maternally-loaded proteins. We also discuss how mutations in these factors impact CG dynamics, providing unprecedented models to investigate the genetic program executing fertilization. We further explore the phylogenetic distribution of maternal proteins and signaling pathways contributing to CGE and egg activation. We conclude that many important biological questions and genotype–phenotype relationships during fertilization remain unresolved, and therefore, novel molecular players of CG biology need to be discovered. Future functional and image-based studies are expected to elucidate the identity of genetic candidates and components of the molecular machinery involved in the egg activation. This, will open new therapeutic avenues for treating infertility in humans.

VAMPs sensitive to tetanus toxin are required for cortical granule exocytosis in mouse oocytes

Fusion of cortical granules with oocyte plasma membrane is one of the most significant secretory events to prevent polyspermy during oocyte activation. Cortical granule exocytosis (CGE) is distinct from most other exocytosis because cortical granules are not renewed after secretion. However, it is thought to be mediated by SNARE complex, which mediates membrane fusion in other exocytoses. SNAREs proteins are divided into Q (glutamine)- and R (arginine)-SNAREs. Q-SNAREs include Syntaxins and SNAP25 family, and R-SNAREs include VAMPs family. In mouse oocytes, Syntaxin4 and SNAP23 have been involved in CGE; nevertheless, it is unknown if VAMP is required. Here, we demonstrated by RT-PCR and immunoblotting that VAMP1 and VAMP3 are expressed in mouse oocyte, and they localized in the cortical region of this cell. Using a functional assay to quantify CGE, we showed that tetanus toxin -which specifically cleavages VAMP1, VAMP2 or VAMP3- inhibited CGE suggesting that at least one VAMP was necessary. Function blocking assays demonstrated that only the microinjection of anti-VAMP1 or anti-VAMP3 antibodies abolished CGE in activated oocytes. These findings demonstrate that R-SNAREs sensitive to tetanus toxin, VAMP1 and VAMP3 -but not VAMP2-, are required for CGE and demonstrate that CGE is mediated by the SNARE complex.

Ocean acidification increases polyspermy of a broadcast spawning bivalve species by hampering membrane depolarization and cortical granule exocytosis

Ensuring that oocytes are fertilized by a single sperm during broadcast spawning is crucial for the fertilization success of many marine invertebrates. Although the adverse impacts of ocean acidification (OA) on various marine species have been revealed in recent years, its impact on polyspermy and the underlying mechanisms involved remain largely unknown. Therefore, in the present study, the effect of OA on polyspermy risk was assessed in a broadcast spawning bivalve, Tegillarca granosa. In addition, the impacts of OA on the two polyspermy blocking processes, the fast block (membrane depolarization) and the permanent block (cortical reaction), were investigated. The results show that the exposure of oocytes to two future OA scenarios (pH 7.8 and pH 7.4) leads to significant increases in polyspermy risk, about 1.70 and 2.38 times higher than the control, respectively. The maximum change in the membrane potential during oocyte membrane depolarization markedly decreased to 15.79 % (pH 7.8) and 34.06 % (pH 7.4) of the control value. Moreover, the duration of oocyte membrane depolarization was significantly reduced to approximately 63.38 % (pH 7.8) and 21.91 % (pH 7.4) of the control. In addition, cortical granule exocytosis, as well as microfilament migration, were significantly arrested by OA treatment. Exposure to future OA scenarios also led to significant reductions in the ATP and Ca²⁺ content of the oocytes, which may explain the hampered polyspermy blocking. Overall, the present study suggests that OA may significantly increase polyspermy risk in T. granosa by inhibiting membrane depolarization and arresting cortical granule exocytosis.

SNAP23 is required for constitutive and regulated exocytosis in mouse oocytes†

Mammalian oocytes are stored in the ovary for prolonged periods, and arrested in meiotic prophase. During this period, their plasma membranes are constantly being recycled by endocytosis and exocytosis. However, the function of this membrane turnover is unknown. Here, we investigated the requirement for exocytosis in the maintenance of meiotic arrest. Using Trim-away, a newly developed method for rapidly and specifically depleting proteins in oocytes, we have identified the SNARE protein, SNAP23, to be required for meiotic arrest. Degradation of SNAP23 causes premature meiotic resumption in follicle-enclosed oocytes. The reduction in SNAP23 is associated with loss of gap junction communication between the oocyte and surrounding follicle cells. Reduction of SNAP23 protein also inhibits regulated exocytosis in response to a Ca2+ stimulus (cortical granule exocytosis), as measured by lectin staining and cleavage of ZP2. Our results show an essential role for SNAP23 in two key processes that occur in mouse oocytes and eggs.

Modulation of P2Y2 receptors in bovine cumulus oocyte complexes: effects on intracellular calcium, zona hardening and developmental competence

The improvement of cryopreserved oocyte survival is imperative for the preservation of female fertility. In this study, we investigate whether P2Y2 receptors (P2Y2R) can be directly implicated in calcium (Ca²⁺) homeostasis misbalances observed during the cryopreservation process of cumulus oocyte complexes (COC). Firstly, RNA was extracted from bovine immature and mature oocytes and cumulus cells and real-time PCR performed to identify P2Y2R transcripts (experiment 1). Changes in intracellular calcium concentration [Ca2+]i of mature COC and oocytes (experiment 2) were measured upon exposure to cryoprotectants (CPA), UTP (P2Y2R stimulator, 100 μM), and/or suramin (P2Y2R inhibitor, 100 and 300 μM). The functional role of P2Y2R was investigated by analyzing the effect on oocyte viability of its modulation prior and during oocyte exposure to CPA (experiment 3). Mature COC were randomly divided into groups, and exposed to CPA and different P2Y2 modulators. Oocytes' viability, cortical granules location, and competence for development were assessed. Results showed that P2Y2R mRNAs are expressed in both oocytes and cumulus cells. Stimulation with UTP and CPA led to [Ca2+]i increase, and this effect was totally or partially blocked by suramin (P2Y2R inhibitor). Oocyte exposure to CPA and UTP reduced embryo rates compared with control and suramin100μM (P ≤ 0.04). The observed enhanced premature zona hardening in oocytes exposed to CPA (P = 0.04) and UTP (P = 0.005) stimulus was inhibited by suramin 100 μM. In conclusion, inhibition of P2Y2R during cryoprotectant exposure reduces premature intracellular Ca²⁺ release and significantly improves the developmental competence of exposed bovine oocytes.

Pleiotropic effects of alpha-SNAP M105I mutation on oocyte biology: ultrastructural and cellular changes that adversely affect female fertility in mice

After sperm-oocyte fusion, cortical granules (CGs) located in oocyte cortex undergo exocytosis and their content is released into the perivitelline space to avoid polyspermy. Thus, cortical granule exocytosis (CGE) is a key process for fertilization success. We have demonstrated that alpha-SNAP -and its functional partner NSF- mediate fusion of CGs with the plasma membrane in mouse oocytes. Here, we examined at cellular and ultrastructural level oocytes from hyh (hydrocephalus with hop gait) mice, which present a missense mutation in the Napa gene that results in the substitution of methionine for isoleucine at position 105 (M105I) of alpha-SNAP. Mutated alpha-SNAP was mislocalized in hyh oocytes while NSF expression increased during oocyte maturation. Staining of CGs showed that 9.8% of hyh oocytes had abnormal localization of CGs and oval shape. Functional tests showed that CGE was impaired in hyh oocytes. Interestingly, in vitro fertilization assays showed a decreased fertilization rate for hyh oocytes. Furthermore, fertilized hyh oocytes presented an increased polyspermy rate compared to wild type ones. At ultrastructural level, hyh oocytes showed small mitochondria and a striking accumulation and secretion of degradative structures. Our findings demonstrate the negative effects of alpha-SNAP M105 mutation on oocyte biology and further confirm the relevance of alpha-SNAP in female fertility.

Live imaging of cortical granule exocytosis reveals that in vitro matured mouse oocytes are not fully competent to secrete their content

Oocyte in vitro maturation does not entirely support all the nuclear and cytoplasmic changes that occur physiologically, and it is poorly understood whether in vitro maturation affects the competence of cortical granules to secrete their content during cortical reaction. Here, we characterize cortical granule exocytosis (CGE) in live mouse oocytes activated by strontium chloride using the fluorescent lectin FITC-LCA. We compared the kinetic of CGE between ovulated (in vivo matured, IVO) and in vitro matured (IVM) mouse oocytes. Results show that: (1) IVM oocytes have a severely reduced response to strontium chloride; (2) the low response was confirmed by quantification of remnant cortical granules in permeabilized cells and by a novel method to quantify the exudate in non-permeabilized cells; (3) the kinetic of CGE in IVO oocytes was rapid and synchronous; (4) the kinetic of CGE in IVM oocytes was delayed and asynchronous; (5) cortical granules in IVM oocytes show an irregular limit in regards to the cortical granule free domain. We propose the analysis of CGE in live oocytes as a biological test to evaluate the competence of IVM mouse oocytes.This article has an associated First Person interview with the first author of the paper.

Lower blastocyst quality after conventional vs. Piezo ICSI in the horse reflects delayed sperm component remodeling and oocyte activation

PURPOSE

The aim of this study was to evaluate the differential effects of conventional and Piezo-driven ICSI on blastocyst development, and on sperm component remodeling and oocyte activation, in an equine model.

METHODS

In vitro-matured equine oocytes underwent conventional (Conv) or Piezo ICSI, the latter utilizing fluorocarbon ballast. Blastocyst development was compared between treatments to validate the model. Then, oocytes were fixed at 0, 6, or 18 h after injection, and stained for the sperm tail, acrosome, oocyte cortical granules, and chromatin. These parameters were compared between injection techniques and between sham-injected and sperm-injected oocytes among time periods.

RESULTS

Blastocyst rates were 39 and 40%. The nucleus number was lower, and the nuclear fragmentation rate was higher, in blastocysts produced by Conv. Cortical granule loss started at 0H after both sperm and sham injection. The acrosome was present at 0H in both ICSI treatments, and persisted to 18H in significantly more Conv than Piezo oocytes (72 vs. 21%). Sperm head area was unchanged at 6H in Conv but significantly increased at this time in Piezo; correspondingly, at 6H significantly more Conv than Piezo oocytes remained at MII (80 vs. 9.5%). Sham injection did not induce significant meiotic resumption.

CONCLUSIONS

These data show that Piezo ICSI is associated with more rapid sperm component remodeling and oocyte meiotic resumption after sperm injection than is conventional ICSI, and with higher embryo quality at the blastocyst stage. This suggests that there is value in exploring the Piezo technique, utilized with a non-toxic fluorocarbon ballast, for use in clinical human ICSI.