Participation of IP 3 R, RyR and L-type Ca 2+ channel in the nuclear maturation of Rhinella arenarum oocytes

Transcriptome-wide N6-methyladenine methylation in granulosa cells of women with decreased ovarian reserve

Background

The emerging epitranscriptome plays an essential role in female fertility. As the most prevalent internal mRNA modification, N6-methyladenine (m6A) methylation regulate mRNA fate and translational efficiency. However, whether m6A methylation was involved in the aging-related ovarian reserve decline has not been investigated. Herein, we performed m6A transcriptome-wide profiling in the ovarian granulosa cells of younger women (younger group) and older women (older group).

Results

m6A methylation distribution was highly conserved and enriched in the CDS and 3’UTR region. Besides, an increased number of m6A methylated genes were identified in the older group. Bioinformatics analysis indicated that m6A methylated genes were enriched in the FoxO signaling pathway, adherens junction, and regulation of actin cytoskeleton. A total of 435 genes were differently expressed in the older group, moreover, 58 of them were modified by m6A. Several specific genes, including BUB1B, PHC2, TOP2A, DDR2, KLF13, and RYR2 which were differently expressed and modified by m6A, were validated using qRT-PCR and might be involved in the decreased ovarian functions in the aging ovary.

Conclusions

Hence, our finding revealed the transcriptional significance of m6A modifications and provide potential therapeutic targets to promote fertility reservation for aging women.

Targeted whole exome sequencing and Drosophila modelling to unveil the molecular basis of primary ovarian insufficiency

STUDY QUESTION

Can a targeted whole exome sequencing (WES) on a cohort of women showing a primary ovarian insufficiency (POI) phenotype at a young age, combined with a study of copy number variations, identify variants in candidate genes confirming their deleterious effect on ovarian function?

SUMMARY ANSWER

This integrated approach has proved effective in identifying novel candidate genes unveiling mechanisms involved in POI pathogenesis.

WHAT IS KNOWN ALREADY

POI, a condition occurring in 1% of women under 40 years of age, affects women’s fertility leading to a premature loss of ovarian reserve. The genetic causes of POI are highly heterogeneous and several determinants contributing to its prominent oligogenic inheritance pattern still need to be elucidated.

STUDY DESIGN, SIZE, DURATION

WES screening for pathogenic variants of 41 Italian women with non-syndromic primary and early secondary amenorrhoea occurring before age 25 was replicated on another 60 POI patients, including 35 French and 25 American women, to reveal statistically significant shared variants.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The Italian POI patients’ DNA were processed by targeted WES including 542 RefSeq genes expressed or functioning during distinct reproductive or ovarian processes (e.g. DNA repair, meiosis, oocyte maturation, folliculogenesis and menopause). Extremely rare variants were filtered and selected by means of a Fisher Exact test using several publicly available datasets. A case-control Burden test was applied to highlight the most significant genes using two ad-hoc control female cohorts. To support the obtained data, the identified genes were screened on a novel cohort of 60 Caucasian POI patients and the same case-control analysis was carried out. Comparative analysis of the human identified genes was performed on mouse and Drosophila melanogaster by analysing the orthologous genes in their ovarian phenotype, and two of the selected genes were fruit fly modelled to explore their role in fertility.

MAIN RESULTS AND THE ROLE OF CHANCE

The filtering steps applied to search for extremely rare pathogenic variants in the Italian cohort revealed 64 validated single-nucleotide variants/Indels in 59 genes in 30 out of 41 screened women. Burden test analysis highlighted 13 ovarian genes as being the most enriched and significant. To validate these findings, filtering steps and Burden analysis on the second cohort of Caucasian patients yielded 11 significantly enriched genes. Among them, AFP, DMRT3, MOV10, FYN and MYC were significant in both patient cohorts and hence were considered strong candidates for POI. Mouse and Drosophila comparative analysis evaluated a conserved role through the evolution of several candidates, and functional studies using a Drosophila model, when applicable, supported the conserved role of the MOV10 armitage and DMRT3 dmrt93B orthologues in female fertility.

LARGE SCALE DATA

The datasets for the Italian cohort generated during the current study are publicly available at ClinVar database (http://www.ncbi.nlm.nih.gov/clinvar/): accession numbers SCV001364312 to SCV001364375.

LIMITATIONS, REASONS FOR CAUTION

This is a targeted WES analysis hunting variants in candidate genes previously identified by different genomic approaches. For most of the investigated sporadic cases, we could not track the parental inheritance, due to unavailability of the parents’ DNA samples; in addition, we might have overlooked additional rare variants in novel candidate POI genes extracted from the exome data. On the contrary, we might have considered some inherited variants whose clinical significance is uncertain and might not be causative for the patients’ phenotype. Additionally, as regards the Drosophila model, it will be extremely important in the future to have more mutants or RNAi strains available for each candidate gene in order to validate their role in POI pathogenesis.

WIDER IMPLICATIONS OF THE FINDINGS

The genomic, statistical, comparative and functional approaches integrated in our study convincingly support the extremely heterogeneous oligogenic nature of POI, and confirm the maintenance across the evolution of some key genes safeguarding fertility and successful reproduction. Two principal classes of genes were identified: (i) genes primarily involved in meiosis, namely in synaptonemal complex formation, asymmetric division and oocyte maturation and (ii) genes safeguarding cell maintenance (piRNA and DNA repair pathways).

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by Italian Ministry of Health grants ‘Ricerca Corrente’ (08C621_2016 and 08C924_2019) provided to IRCCS Istituto Auxologico Italiano, and by ‘Piano Sostegno alla Ricerca’ (PSR2020_FINELLI_LINEA_B) provided by the University of Milan; M.P.B. was supported by Telethon-Italy (grant number GG14181). There are no conflicts of interest.

Prenatal hypoxia attenuated contraction of offspring coronary artery associated with decreased PKCβ Ser660 phosphorylation and intracellular calcium

AIMS

Prenatal hypoxia (PH) could affect peripheral vascular tone of the offspring, thus increasing the risk of cardiovascular diseases in adult. However, it's still unknown whether functions of coronary arteries (COA) in adult offspring would be influenced by PH. The present study aimed at effects of PH on vascular tone of COA and its related mechanisms.

METHODS

Coronary arteries of adult offspring exposed to hypoxic or normoxic circumstances during gestational day 5 to 21 were collected. Wire myograph system, whole-cell patch clamp technique, IonOptix MyoCam system, PCR, and western blot were used to detect vascular function of adult offspring COA.

KEY FINDINGS

PH significantly attenuated serotonin- and phorbol 12, 13-dibutyrate (PDBu)-induced constriction. Iberiotoxin potentiated PDBu-induced constriction and the effect was augmented by PH, however, no significant differences were found in whole-cell BK_Ca channel currents and its protein expression. Nifedipine inhibited PDBu-mediated constriction and the inhibitory effect was reduced in PH group, and whole-cell calcium channel current was decreased in offspring COA. Besides, PH reduced the capability of calcium release from the endoplasmic reticulum in COA. The phosphorylated PKCβ protein expression at Ser⁶⁶⁰ site, not Thr⁶⁴¹ site, was significantly decreased in PH offspring. Chronic hypoxia during pregnancy attenuated PDBu-mediated constriction in offspring COA, presumably through decreased phosphorylated PKCβ at serine⁶⁶⁰ sites and decreased intracellular calcium-related weaker PKC activation.

SIGNIFICANCE

The findings provided new information on the influence of prenatal hypoxia on COA, and suggested potential use of PKCβ-serine⁶⁶⁰ for early prevention of coronary heart diseases in developmental origins.

Effect of Wilforine on the Calcium Signaling Pathway in Mythimna separata Walker Myocytes Using the Calcium Imaging Technique

Although the action site of wilforine is located in the muscle tissue of insects, the insecticidal mechanism of wilforine is not yet clear. This research explored the effects of wilforine on the calcium signaling pathway using the calcium imaging technique to reveal the insecticidal mechanism. It was confirmed that wilforine had strong cytotoxicity to Mythimna separata myocytes with the IC₅₀ values of 25.14 and 19.65 mg/L using CCK-8 and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide methods, respectively. The morphological development of M. separata myocytes was also affected. The calcium imaging technique showed that the intracellular calcium ion concentration ([Ca²⁺]_i) increased by 23.45% of the initial value after being treated with 100 nM wilforine. However, wilforine did not increase [Ca²⁺]_i after the myocytes were preincubated with thapsigargin, and the [Ca²⁺]_i could not be decreased by 50 μM ryanodine after being treated with 100 nM wilforine. These results indicated that the targets of wilforine are located in the sarcoplasmic reticulum, and ryanodine receptor (RyR) is an important action target of wilforine. Furthermore, wilforine can also activate the inositol triphosphate receptor (IP₃R), which was confirmed through the use of 2-aminoethyl diphenylborinate, an inhibitor of IP₃R. Connected with previous research studies, it can be concluded that wilforine affects the calcium signaling pathway by combining with RyR and IP₃R, causing calcium dyshomeostasis, which results in insect paralysis and death.

Role of calcium-sensing receptor in regulating spontaneous activation of postovulatory aging rat oocytes

Mechanisms for postovulatory aging (POA) of oocytes and for spontaneous activation (SA) of rat oocytes are largely unknown. Expression of calcium-sensing receptor (CaSR) in rat oocytes and its role in POA remain unexplored. In this study, expression of CaSR in rat oocytes aging for different times was detected by immunofluorescence microscopy, and western blotting and the role of CaSR in POA was determined by observing the effects of regulating its activity on SA susceptibility and cytoplasmic calcium levels. The results showed that CaSR was expressed in rat oocytes. Oocytes recovered 19 h post human chorionic gonadotropin (hCG) injection were more susceptible to SA and expressed more functional CaSR than oocytes recovered 13 h after hCG injection, although both expressed the same level of total CaSR protein. Treatment with CaSR antagonist significantly suppressed cytoplasmic calcium elevation and SA of oocytes. Activation of Na-Ca2+ exchanger with NaCl inhibited SA to a greater extent than suppression of CaSR with NPS-2143, suggesting that calcium sources other than CaSR-controlled channels contributed to the elevation of cytoplasmic calcium. Treatment with T- or L-type calcium channel blockers significantly reduced SA. Suppression of all calcium channels tested reduced SA to minimum. It is concluded that the level of CaSR functional dimer protein, but not that of the total CaSR protein, was positively correlated with the SA susceptibility during POA of rat oocytes confirming that CaSR is involved in POA regulation. Blocking multiple calcium channels might be a better choice for efficient control of SA in rat oocytes.

Chemical activation in Rhinella arenarum oocytes: effect of dehydroleucodine (DhL) and its hydrogenated derivative (2H-DhL)

Mature oocytes are arrested in metaphase II due to the presence of high levels of active maturation promoting factor (MPF). After fertilization, active MPF levels decline abruptly, enabling oocytes to complete meiosis II. One of the first and universal events of oocyte activation is an increase in cytosolic Ca2+ that would be responsible for MPF inactivation. Mature oocytes can also be activated by parthenogenetic activation. The aims of this work are to test the ability of dehydroleucodine (DhL) and its hydrogenated derivative 11,13-dihydro-dehydroleucodine (2H-DhL) to induce chemical activation in amphibian oocytes and to study the participation of calcium in the process. Results indicated that DhL and 2H-DhL induced oocyte activation in a dose-dependent manner. After 90 min of treatment, DhL 36 μM was able to induce 95% activation, while 2H-DhL 36 μM was less active, with only 40% activation. Our results suggest that DhL induced the inhibition of MPF activity, probably by an increase in intracellular Ca2+ concentration. Extracellular Ca2+ would not be significant, although Ca2+ release from intracellular stores is critical. In this sense, IP3Rs and RyRs were involved in the Ca2+ transient induced by lactones. In this species, RyRs appears to be the largest contributor to Ca2+ release in DhL-induced activation. Although more studies are needed on the mechanism of action through which these lactones induce oocyte activation in Rhinella arenarum, the results of this research provide interesting perspectives for the use of these lactones as chemical activators in in vitro fertilization and cloning.

RyR channel-mediated increase of cytosolic free calcium level signals cyclin B1 degradation during abortive spontaneous egg activation in rat

In few mammalian species including rat, post-ovulatory aging induces abortive spontaneous egg activation (SEA), which is morphologically characterized by exit from metaphase-II (M-II) arrest. A possibility exists that the RyR channel-mediated insufficient increase of cytosolic free Ca(2+) level could be one of the causes for post-ovulatory aging-induced abortive SEA. To test this possibility, eggs collected after 17 h post-hCG surge were cultured with or without various concentrations of nifedipine (NF), ruthenium red (RR), and KN-93 for 3 h in vitro. Morphological changes characteristic of abortive SEA, cytosolic free Ca(2+) level, cyclin B1 level, and meiotic status were analyzed. Data of the present study indicate that NF and RR inhibited post-ovulatory aging-induced abortive SEA in a concentration-dependent manner. Further, RR protected against RyR channel as well as caffeine-mediated increase of cytosolic free Ca(2+) level. In addition, KN-93 inhibited post-ovulatory aging-induced abortive SEA in a concentration-dependent manner. An increase of cytosolic free Ca(2+) level was associated with a reduction of cyclin B1 level during post-ovulatory aging-induced abortive SEA. These data indirectly suggest the involvement of RyR channels in the increase of cytosolic free Ca(2+) level. The increased cytosolic free Ca(2+) level triggers cyclin B1 degradation possibly through CaMK-II activity during post-ovulatory aging-induced abortive SEA in rat eggs cultured in vitro.

Expression of G protein estrogen receptor (GPER) on membrane of mouse oocytes during maturation

PURPOSE

To determine expression of G-protein estrogen receptor (GPER) in mouse oocyte membrane during maturation.

METHODS

The expression of GPER from different maturation stages of oocytes, in vivo and in vitro matured oocytes as well as aging oocytes was examined by immune-fluorescence GPR30 antibody and the images were analyzed by laser scanning confocal microscope. Further confirmation was performed by Western blots for cell fractionation.

RESULTS

Significant fluorescent signal was observed on the surface of mouse oocytes. The image expression was lower in germinal vesicle (GV) stage than mature metaphase-II (M-II) stage oocytes. There was high expression in in-vivo matured oocytes compared to in vitro matured oocytes. The highest expression was observed in aging oocytes compared with other oocytes.

CONCLUSIONS

The changes of expression of GPER on mouse oocytes plasma membrane confirm oocyte membrane maturation, suggesting that those changes of GPER may be related to the functional role of oocyte maturation.