RAB14 GTPase is essential for actin-based asymmetric division during mouse oocyte maturation

Age-associated accumulation of RAB9 disrupts oocyte meiosis

The critical role of some RAB family members in oocyte meiosis has been extensively studied, but their role in oocyte aging remains poorly understood. Here, we report that the vesicle trafficking regulator, RAB9 GTPase, is essential for oocyte meiosis and aging in humans and mice. RAB9 was mainly located at the meiotic spindle periphery and cortex during oocyte meiosis. In humans and mice, we found that the RAB9 protein level were significantly increased in old oocytes. Age-related accumulation of RAB9 inhibits first polar body extrusion and reduces the developmental potential of oocytes. Further studies showed that increased Rab9 disrupts spindle formation and chromosome alignment. In addition, Rab9 overexpression disrupts the actin cap formation and reduces the cortical actin levels. Mechanically, Rab9-OE increases ROS levels, decreases mitochondrial membrane potential, ATP content and the mtDNA/nDNA ratio. Further studies showed that Rab9-OE activates the PINK1-PARKIN mitophagy pathway. Importantly, we found that reducing RAB9 protein expression in old oocytes could partially improve the rate of old oocyte maturation, ameliorate the accumulation of age-related ROS levels and spindle abnormalities, and partially rescue ATP levels, mtDNA/nDNA ratio, and PINK1 and PARKIN expression. In conclusion, our results suggest that RAB9 is required to maintain the balance between mitochondrial function and meiosis, and that reducing RAB9 expression is a potential strategy to ameliorate age-related deterioration of oocyte quality.

Fbxo28 is essential for spindle migration and morphology during mouse oocyte meiosis I

Spindle migration and assembly regulates asymmetric oocyte division, which is essential for fertility. Fbxo28, as a member of SCF (Skp1-Cul1-F-box) ubiquitin E3 ligases complex, is specifically expressed in oocytes. However, little is known about the functions of Fbxo28 in spindle assembly and migration during oocyte meiosis I. In present study, microinjection with morpholino oligonucleotides and exogenous mRNA for knockdown and rescue experiments, and immunofluorescence staining, western blot, timelapse confocal microscopy and chromosome spreading were utilized to explore the roles of Fbxo28 in asymmetric division during meiotic maturation. Our data suggested that Fbxo28 mainly localized at chromosomes and acentriolar microtubule-organizing centers (aMTOCs). Depletion of Fbxo28 did not affect polar body extrusion but caused defects in spindle morphology and migration, indicative of the failure of asymmetric division. Moreover, absence of Fbxo28 disrupted both cortical and cytoplasmic actin assembly and decreased the expression of ARPC2 and ARP3. These defects could be rescued by exogenous Fbxo28-myc mRNA supplement. Collectively, this study demonstrated that Fbxo28 affects spindle morphology and actin-based spindle migration during mouse oocyte meiotic maturation.

Benzo[a]pyrene exposure disrupts the organelle distribution and function of mouse oocytes

Benzo[a]pyrene (BaP) is a polycyclic aromatic hydrocarbon compound that is generated during combustion processes, and is present in various substances such as foods, tobacco smoke, and burning emissions. BaP is extensively acknowledged as a highly carcinogenic substance to induce multiple forms of cancer, such as lung cancer, skin cancer, and stomach cancer. Recently it is shown to adversely affect the reproductive system. Nevertheless, the potential toxicity of BaP on oocyte quality remains unclear. In this study, we established a BaP exposure model via mouse oral gavage and found that BaP exposure resulted in a notable decrease in the ovarian weight, number of GV oocytes in ovarian, and oocyte maturation competence. BaP exposure caused ribosomal dysfunction, characterized by a decrease in the expression of RPS3 and HPG in oocytes. BaP exposure also caused abnormal distribution of the endoplasmic reticulum (ER) and induced ER stress, as indicated by increased expression of GRP78. Besides, the Golgi apparatus exhibited an abnormal localization pattern, which was confirmed by the GM130 localization. Disruption of vesicle transport processes was observed by the abnormal expression and localization of Rab10. Additionally, an enhanced lysosome and LC3 fluorescence intensity indicated the occurrence of protein degradation in oocytes. In summary, our results suggested that BaP exposure disrupted the distribution and functioning of organelles, consequently affecting the developmental competence of mouse oocytes.

Arf6 GTPase deficiency leads to porcine oocyte quality decline during aging

Arf6 is a member of ADP-ribosylation factor (Arf) family, which is widely implicated in the regulation of multiple physiological processes including endocytic recycling, cytoskeletal organization, and membrane trafficking during mitosis. In this study, we investigated the potential relationship between Arf6 and aging-related oocyte quality, and its roles on organelle rearrangement and cytoskeleton dynamics in porcine oocytes. Arf6 expressed in porcine oocytes throughout meiotic maturation, and it decreased in aged oocytes. Disruption of Arf6 led to the failure of cumulus expansion and polar body extrusion. Further analysis indicated that Arf6 modulated ac-tubulin for meiotic spindle organization and microtubule stability. Besides, Arf6 regulated cofilin phosphorylation and fascin for actin assembly, which further affected spindle migration, indicating the roles of Arf6 on cytoskeleton dynamics. Moreover, the lack of Arf6 activity caused the dysfunction of Golgi and ER for protein synthesis and signal transduction. Mitochondrial dysfunction was also observed in Arf6-deficient porcine oocytes, which was supported by the increased ROS level and abnormal membrane potential. In conclusion, our results reported that insufficient Arf6 was related to aging-induced oocyte quality decline through spindle organization, actin assembly, and organelle rearrangement in porcine oocytes.

Extracellular vesicles secreted by cumulus cells contain microRNAs that are potential regulatory factors of mouse oocyte developmental competence

The role of cumulus cells (CCs) in the acquisition of oocyte developmental competence is not yet fully understood. In a previous study, we matured cumulus-denuded fully-grown mouse oocytes to metaphase II (MII) on a feeder layer of CCs (FL-CCs) isolated from developmentally competent (FL-SN-CCs) or incompetent (FL-NSN-CCs) SN (surrounded nucleolus) or NSN (not surrounding nucleolus) oocytes, respectively. We observed that oocytes cultured on the former could develop into blastocysts, while those matured on the latter arrested at the 2-cell stage. To investigate the CC factors contributing to oocyte developmental competence, here we focused on the CCs' release into the medium of extracellular vesicles (EVs) and on their miRNA content. We found that, during the 15-h transition to MII, both FL-SN-CCs and FL-NSN-CCs release EVs that can be detected, by confocal microscopy, inside the zona pellucida (ZP) or the ooplasm. The majority of EVs are <200 nm in size, which is compatible with their ability to cross the ZP. Next-generation sequencing of the miRNome of FL-SN-CC versus FL-NSN-CC EVs highlighted 74 differentially expressed miRNAs, with 43 up- and 31 down-regulated. Although most of these miRNAs do not have known roles in the ovary, in silico functional analysis showed that seven of these miRNAs regulate 71 target genes with specific roles in meiosis resumption (N = 24), follicle growth (N = 23), fertilization (N = 1), and the acquisition of oocyte developmental competence (N = 23). Overall, our results indicate CC EVs as emerging candidates of the CC-to-oocyte communication axis and uncover a group of miRNAs as potential regulatory factors.

Live birth derived from a markedly large polar body oocyte: a rare case report

Oocytes with excessively large first polar bodies (PB1) often occur in assisted reproductive procedures. Many times these oocytes are discarded without insemination and, as a result, the application of this portion of oocytes has scarcely been reported to date. Few studies have examined large PB1 oocytes in infertile women and have virtually entirely studied genetic variations for large PB1 oocyte abnormalities. Here, we describe an unusual case of a live birth from a remarkably large PB1 oocyte in a frozen embryo transfer (FET) cycle. This is the first instance of a successful live birth resulting from a PB1 oocyte with an extremely large polar body measuring 80 μM × 40 μM in size. The large PB1 oocyte was performed by an early rescue intracytoplasmic sperm injection (r-ICSI) and was formed into a blastocyst on day 5. Following FET, a healthy boy baby weighing 3100 g was finally delivered by caesarean section at 37 weeks and 5 days after conception. Additionally, there were no complications throughout the antenatal period or the perinatal phase of this following full-term delivery. In this study, it is revealed for the first time that a huge PB1 oocyte can be fertilized, resulting in the growth of a blastocyst, a subsequent pregnancy, and a live birth. This new information prompts us to reconsider the use of large PB1 oocytes. More insightful talks should be given attention to prevent the waste of embryos because not all oocytes with aberrant morphology are unavailable.

Impaired erythropoietin-producing hepatocellular B receptors signaling in the prefrontal cortex and hippocampus following maternal immune activation in male rats

An environmental risk factor for schizophrenia (SZ) is maternal infection, which exerts longstanding effects on the neurodevelopment of offspring. Accumulating evidence suggests that synaptic disturbances may contribute to the pathology of the disease, but the underlying molecular mechanisms remain poorly understood. Erythropoietin-producing hepatocellular B (EphB) receptor signaling plays an important role in synaptic plasticity by regulating the formation and maturation of dendritic spines and regulating excitatory neurotransmission. We examined whether EphB receptors and downstream associated proteins are susceptible to environmental risk factors implicated in the etiology of synaptic disturbances in SZ. Using an established rodent model, which closely imitates the characteristics of SZ, we observed the behavioral performance and synaptic structure of male offspring in adolescence and early adulthood. We then analyzed the expression of EphB receptors and associated proteins in the prefrontal cortex and hippocampus. Maternal immune activation offspring showed significantly progressive cognitive impairment and pre-pulse inhibition deficits together with an increase in the expression of EphB2 receptors and NMDA receptor subunits. We also found changes in EphB receptor downstream signaling, in particular, a decrease in phospho-cofilin levels which may explain the reduced dendritic spine density. Besides, we found that the AMPA glutamate, another glutamate ionic receptor associated with cofilin, decreased significantly in maternal immune activation offspring. Thus, alterations in EphB signaling induced by immune activation during pregnancy may underlie disruptions in synaptic plasticity and function in the prefrontal cortex and hippocampus associated with behavioral and cognitive impairment. These findings may provide insight into the mechanisms underlying SZ.

Aflatoxin B1 impairs porcine oocyte quality via disturbing intracellular membrane system and ATP production

Aflatoxin is the most common type of mycotoxins in contaminated corn, peanuts and rice, which affects the livestock and ultimately endangers human health. Aflatoxin is reported to have carcinogenicity, mutation, growth retardation, immunosuppression and reproductive toxicity. In present study we reported the causes for the declined porcine oocyte quality under aflatoxin exposure. We set up an in vitro exposure model and showed that aflatoxin B1 disturbed cumulus cell expansion and oocyte polar body extrusion. We found that aflatoxin B1 exposure disrupted ER distribution and elevated the expression of GRP78, indicating the occurrence of ER stress, and the increased calcium storage also confirmed this. Besides, the structure of cis-Golgi apparatus, another intracellular membrane system was also affected, showing with decreased GM130 expression. The oocytes under aflatoxin B1 exposure showed aberrant lysosome accumulation and higher LAMP2 expression, a marker for lysosome membrane protection, and this might be due to the aberrant mitochondria function with low ATP production and the increase of apoptosis, since we found that BAX expression increased, and ribosomal protein which is also an apoptosis-related factor RPS3 decreased. Taken together, our study revealed that aflatoxin B1 impairs intracellular membrane system ER, Golgi apparatus, lysosome and mitochondria function to affect porcine oocyte maturation quality.

High Temperature Disrupts Organelle Distribution and Functions Affecting Meiotic Maturation in Porcine Oocytes

Heat stress (HS) has been known to cause reproductive failure in animals, especially in summer. HS severely affects the developmental potential of oocytes and leads to low fertility rates. Previous studies have reported that HS compromises embryo development in bovine oocytes, and reduces ovarian development in mice, thereby impairing reproductive function in animals. However, the effect of high temperature (HT) on the organelles of porcine oocytes is unknown. In this study, we reported that exposure to HT for 24 h (41°C) significantly decreased meiotic maturation in porcine oocytes (p < 0.05). Further experiments on organelles found that HT induced mitochondrial dysfunction, increased abnormal mitochondrial distribution, and decreased mitochondrial membrane potential (MMP). We also found that HT induced abnormal endoplasmic reticulum (ER) distribution and higher expression of glucose regulatory protein 78 (GRP78), suggesting that HT exposure induces ER stress. Our results also indicated that exposure to HT induced abnormal distribution and dysfunction of the Golgi apparatus, which resulted from a decrease in the expression of the vesicle transporter, Ras-related protein Rab-11A (RAB11A). In addition, we found that HT exposure led to lysosomal damage by increasing the expression of lysosome-associated membrane protein 2 (LAMP2) and microtubule-associated protein 1A/1B-light chain 3 (LC3). In summary, our study revealed that HT exposure disrupts organelle dynamics, which further leads to the failure of meiotic maturation in porcine oocytes.