Telomerase, an enzyme complex that binds the chromosome ends (telomeres) and maintains telomere length and integrity, is present in germ cells, proliferative granulosa cells, germline stem cells, and neoplastic cells in the ovary, but it is absent in differentiated or aged cells. Activation of telomerase in the ovary underpins both benign and malignant cell proliferation in several compartments, including the germ cells, membrana granulosa, and the ovarian surface epithelium. The difference in telomerase operation between normal and abnormal cell proliferations may lie in the mechanisms of telomerase activation in a deregulated manner. Recent studies have implicated telomerase activity in ovarian cancer as well as oogenesis and fertility. Inhibition of telomerase and the shortening of telomeres are seen in occult ovarian insufficiency. Studies of how telomerase operates and regulates ovary development may provide insight into the development of both germ cells for ovarian reproductive function and neoplastic cells in ovarian cancer. The current review summarizes the roles of telomerase in the development of oocytes and proliferation of granulosa cells during folliculogenesis and in the process of tumorigenesis. It also describes the regulation of telomerase by estrogen in the ovary.
Jun-Ping Liu and He Li
Na Liu, Yan-Guang Wu, Guo-Cheng Lan, Hong-Shu Sui, Li Ge, Jun-Zuo Wang, Yong Liu, Tian-Wu Qiao and Jing-He Tan
Inhibiting oocyte aging is important not only for healthy reproduction but also for the success of assisted reproduction techniques. Although our previous studies showed that cumulus cells accelerated aging of mouse oocytes, the underlying mechanism is unknown. The objective of this paper was to study the effects of pyruvate and cumulus cells on mouse oocyte aging. Freshly ovulated mouse cumulus–oocyte complexes (COCs) or cumulus-denuded oocytes (DOs) were cultured in Chatot-Ziomek-Bavister (CZB) medium or COC-conditioned CZB medium supplemented with different concentrations of pyruvate before being examined for aging signs and developmental potential. Pyruvate supplementation to CZB medium decreased rates of ethanol-induced activation in both COCs and DOs by maintaining their maturation-promoting factor activities, but more pyruvate was needed for COCs than for DOs. Addition of pyruvate to the COC-conditioned CZB also alleviated aging of DOs. Observations on cortical granules, level of BCL2 proteins, histone acetylation, intracellular concentration of glutathione, and embryo development all confirmed that pyruvate supplementation inhibited aging of mouse oocytes. It is concluded that the aging of mouse oocytes, facilitated by culture in COCs, can be partially prevented by the addition of pyruvate to the culture medium.
Xiaoxiao Hou, Jun Liu, Zhiren Zhang, Yanhui Zhai, Yutian Wang, Zhengzhu Wang, Bo Tang, Xueming Zhang, Liguang Sun and Ziyi Li
DNA methylation and histone modification play important roles in the development of mammalian embryos. Cytochalasin B (CB) is an actin polymerization inhibitor that can significantly affect cell activity and is often used in studies concerning cytology. In recent years, CB is also commonly being used in in vitro experiments on mammalian embryos, but few studies have addressed the effect of CB on the epigenetic modification of embryonic development, and the mechanism underlying this process is also unknown. This study was conducted to investigate the effects of CB on DNA methylation and histone modification in the development of parthenogenetically activated porcine embryos. Treatment with 5 μg/mL CB for 4 h significantly increased the cleavage rate, blastocyst rate and total cell number of blastocysts. However, the percentage of apoptotic cells and the expression levels of the apoptosis-related genes BCL-XL, BAX and CASP3 were significantly decreased. Treatment with CB significantly decreased the expression levels of DNMT1, DNMT3a, DNMT3b, HAT1 and HDAC1 at the pronuclear stage and promoted the conversion of 5-methylcytosine (5mC) into 5-hydroxymethylcytosine (5hmC). After CB treatment, the level of AcH3K9 was upregulated and the level of H3K9me3 was downregulated. When combined with Scriptaid and 5-Aza-Cdr, CB further improved the embryonic development competence and decreased the expression of BCL-XL, BAX and CASP3. In conclusion, these results suggest that CB could improve embryonic development and the quality of the blastocyst by improving the epigenetic modification during the development of parthenogenetically activated embryos.
Jun-Zuo Wang, Hong-Shu Sui, De-Qiang Miao, Na Liu, Ping Zhou, Li Ge and Jing-He Tan
The objectives of this study were to investigate the effect of heat stress during in vitro maturation on the developmental potential of mouse oocytes and to determine whether the deleterious effect was on the nuclear or cytoplasmic component. While rates of oocyte nuclear maturation (development to the metaphase II stage) did not differ from 37 to 40 °C, rates for blastocyst formation decreased significantly as maturation temperature increased from 38.5 to 39 °C. Chromosome spindle exchange showed that while blastocyst formation did not differ when spindles matured in vivo or in vitro at 37, 40 or 40.7 °C were transplanted into in vivo matured cytoplasts, no blastocyst formation was observed when in vivo spindles were transferred into the 40 °C cytoplasts. While oocytes reconstructed between 37 °C ooplasts and 37 or 40 °C karyoplasts developed into 4-cell embryos at a similar rate, no oocytes reconstituted between 40 °C ooplasts and 37 °C spindles developed to the 4-cell stage. Immunofluorescence microscopy revealed impaired migration of cortical granules and mitochondria in oocytes matured at 40 °C compared with oocytes matured at 37 °C. A decreased glutathione/GSSG ratio was also observed in oocytes matured at 40 °C. While spindle assembling was normal and no MAD2 was activated in oocytes matured at 37 or 40 °C, spindle assembling was affected and MAD2 was activated in some of the oocytes matured at 40.7 °C. It is concluded that 1) oocyte cytoplasmic maturation is more susceptible to heat stress than nuclear maturation, and 2) cytoplasmic rather than nuclear components determine the pre-implantation developmental capacity of an oocyte.
Xuan-Tong Liu, Hui-Ting Sun, Zhong-Fang Zhang, Ru-Xia Shi, Li-Bing Liu, Jia-Jun Yu, Wen-Jie Zhou, Chun-Jie Gu, Shao-Liang Yang, Yu-Kai Liu, Hui-Li Yang, Feng-Xuan Xu and Ming-Qing Li
It has been reported that the impaired cytotoxicity of natural killer (NK) cells and abnormal cytokines that are changed by the interaction between ectopic endometrial cells and immune cells is indispensable for the initiation and development of endometriosis (EMS). However, the mechanism of NK cells dysfunction in EMS remains largely unclear. Here, we found that NK cells in peritoneal fluid from women with EMS highly expressed indoleamine 2,3-dioxygenase (IDO). Furthermore, IDO+NK cells possessed lower NKp46 and NKG2D but higher IL-10 than that of IDO-NK. Co-culture with endometrial stromal cells (nESCs) from healthy control or ectopic ESCs (eESCs) from women with EMS led to a significant increase in the IDO level in NK cells from peripheral blood, particularly eESCs, and an anti-TGF-β neutralizing antibody suppressed these effects in vitro. NK cells co-cultured with ESC more preferentially inhibited the viability of nESCs than eESCs did, and pretreating with 1-methyl-tryptophan (1-MT), an IDO inhibitor, reversed the inhibitory effect of NK cells on eESC viability. These data suggest that ESCs induce IDO+NK cells differentiation partly by TGF-β and that IDO further restricts the cytotoxicity of NK cells in response to eESCs, which provides a potential therapeutic strategy for EMS patients, particularly those with a high number of impaired cytotoxic IDO+NK cells.
Jia-Jun Yu, Hui-Ting Sun, Zhong-Fang Zhang, Ru-Xia Shi, Li-Bing Liu, Wen-Qing Shang, Chun-Yan Wei, Kai-Kai Chang, Jun Shao, Ming-Yan Wang and Ming-Qing Li
Endometriosis (EMS) is associated with an abnormal immune response to endometrial cells, which can facilitate the implantation and proliferation of ectopic endometrial tissues. It has been reported that human endometrial stromal cells (ESCs) express interleukin (IL)15. The aim of our study was to elucidate whether or not IL15 regulates the cross talk between ESCs and natural killer (NK) cells in the endometriotic milieu and, if so, how this regulation occurs. The ESC behaviors in vitro were verified by Cell Counting Kit-8 (CCK-8), Annexin/PI, and Matrigel invasion assays, respectively. To imitate the local immune microenvironment, the co-culture system between ESCs and NK cells was constructed. The effect of IL15 on NK cells in the co-culture unit was investigated by flow cytometry (FCM). In this study, we found that ectopic endometrium from patients with EMS highly expressed IL15. Rapamycin, an autophagy inducer, decreased the level of IL15 receptors (i.e. IL15Rα and IL2Rβ). IL15 inhibits apoptosis and promotes the invasiveness, viability, and proliferation of ESCs. Meanwhile, a co-culture with ESCs led to a decrease in CD16 on NK cells. In the co-culture system, IL15 treatment downregulated the levels of Granzyme B and IFN-γ in CD16+NK cells, NKG2D in CD56dimCD16-NK cells, and NKP44 in CD56brightCD16-NK cells. On the one hand, these results indicated that IL15 derived from ESCs directly stimulates the growth and invasion of ESCs. On the other hand, IL15 may help the immune escape of ESCs by suppressing the cytotoxic activity of NK cells in the ectopic milieu, thereby facilitating the progression of EMS.
Ruizhi Deng, Chengquan Han, Lu Zhao, Qing Zhang, Beifen Yan, Rui Cheng, Biao Wei, Peng Meng, Tingchao Mao, Yong Zhang and Jun Liu
Endogenous retroviruses (ERVs), which are abundant in mammalian genomes, can modulate the expression of nearby genes, and their expression is dynamic and stage-specific during early embryonic development in mice and humans. However, the functions and mechanisms of ERV elements in regulating embryonic development remain unclear. Here, we utilized several methods to determine the contribution of ERVs to the makeup and regulation of transcripts during embryonic genome activation (EGA). We constructed an ERV library and embryo RNA-seq library (IVF_2c and IVF_8c) of goat to serve as our research basis. The GO and KEGG analysis of nearby ERV genes revealed that some ERV elements may be associated with embryonic development. RNA-seq results were consistent with the features of EGA. To obtain the transcripts derived from the ERV sequences, we blasted the ERV sequences with embryonic transcripts and identified three lncRNAs and one mRNA that were highly expressed in IVF-8c rather than in IVF-2c (q-value <0.05). Then, we validated the expression patterns of nine ERV-related transcripts during early developmental stages and knocked down three high-expression transcripts in EGA. The knockdown of lncRNA TCONS_00460156 or mRNA HSD17B11 significantly decreased the developmental rate of IVF embryos. Our findings suggested that some transcripts from ERVs are essential for the early embryonic development of goat, and analyzing the ERV expression profile during goat EGA may help elucidate the molecular mechanisms of ERV in regulating embryonic development.
Yue-Mao Zheng, Hui-Ying Zhao, Xiao-E Zhao, Fu-Sheng Quan, Song Hua, Xiao-Ying He, Jun Liu, Xiao-Ning He and Hui Lin
We assessed the developmental ability of embryos cloned from porcine neural stem (NS) cells, amniotic fluid-derived stem (AFS) cells, fetal fibroblast cells, adult fibroblast, and mammary gland epithelial cells. The five cell lines were transfected with enhanced green fluorescence protein gene respectively using lipofection. NS and AFS cells were induced to differentiate in vitro. Stem cells and their differentiated cells were harvested for analysis of the markers using RT-PCR. The five cell lines were used for nuclear transfer. The two-cell stage-cloned embryos derived from each cell line were transferred into the oviducts of surrogate mothers. The results showed that both NS and AFS cells expressed POU5F1, THY1 and SOX2, and they were both induced to differentiate into astrocyte (GFAP+), oligodendrocyte (GalC+), neuron (NF+, ENO2+, and MAP2+), adipocyte (LPL+ and PPARG-D+), osteoblast (osteonectin+ and osteocalcin+), myocyte (MYF6+ and MYOD+), and endothelium (PECAM1+, CD34+, CDH5+, and NOS3+) respectively. Seven cloned fetuses (28 days and 32 days) derived from stem cells were obtained. The in vitro developmental ability (morula–blastocyst rate was 28.26–30.07%) and in vivo developmental ability (pregnancy rate were 1.67–2.17%) of the embryos cloned from stem cells were higher (P<0.05) than that of the embryos cloned from somatic cells (morula–blastocyst rate was 16.27–19.28% and pregnancy rate was 0.00%), which suggests that the undifferentiated state of the donor cells increases cloning efficiency.
Shu-Fang Wang, Xi-Hua Chen, Bin He, De-Dong Yin, Hai-Jun Gao, Hao-Qi Zhao, Nan Nan, Shi-Ge Guo, Jian-Bing Liu, Bin Wu and Xiang-Bo Xu
Stress impacts the reproductive axis at the level of the hypothalamus and the pituitary gland, which exert an effect on the ovary. Menstruation is regulated by the hypothalamic–pituitary–ovary (HPO) axis. However, the role of stress in menstruation remains unclear. The objective of this study was to explore the role of stress in endometrial breakdown and shedding, using the pseudopregnant mouse menstrual-like model. Female mice were mated with vasectomized males and labeled day 0.5, upon observation of a vaginal seminal plug. On day 3.5, decidualization was induced in pseudopregnant mice using arachis oil. On day 5.5, pseudopregnant mice with artificial decidualization were placed in restraint tubes for 3 h. The findings indicated that acute restraint stress resulted in the disintegration of the endometrium. While corticosterone concentration in the serum increased significantly due to restraint stress, follicle-stimulating hormone (FSH), luteinizing hormone (LH) and progesterone (P4) levels in the serum decreased significantly. An endometrial histology examination indicated that progesterone implants may rescue P4 decline caused by acute stress and block endometrium breakdown and shedding. In addition, mice were treated with metyrapone, an inhibitor of corticosterone synthesis, 1 h prior to being subjected to restraint stress. Interestingly, metyrapone not only inhibited stress-induced endometrium breakdown and shedding, but also prevented stress-induced reduction of P4, LH and FSH. Furthermore, real-time PCR and western blot showed that mRNA and protein expression of CYP11A1 (cytochrome P450, family 11, subfamily A, polypeptide 1) and steroidogenic acute regulatory protein (StAR), the two rate-limiting enzymes for progesterone synthesis in the ovary, decreased following acute stress. But metyrapone prevented the reduction of StAR expression induced by restraint stress. Overall, this study revealed that acute stress results in an increase in corticosterone, which may inhibit LH and FSH release in the serum and CYP11A1 and StAR expression in the ovary, which finally leads to the breakdown and shedding of the endometrium. These experimental findings, based on the mouse model, may enable further understanding of the effects of stress on menstruation regulation and determine the potential factors affecting stress-associated menstrual disorders.
Wen-Min Cheng, Lei An, Zhong-Hong Wu, Yu-Bo Zhu, Jing-Hao Liu, Hong-Mei Gao, Xi-He Li, Shi-Jun Zheng, Dong-Bao Chen and Jian-Hui Tian
We recently reported that electrical activation followed by secondary chemical activation greatly enhanced the developmental competence of in vitro matured porcine oocytes fertilized by intracytoplasmic sperm injection (ICSI). We hypothesized that sperm treatment with disulfide bond reducing agents will enhance the development competence of porcine embryos produced by this ICSI procedure. We examined the effects of glutathione (GSH), dithiothreitol (DTT), GSH or DTT in combination with heparin on sperm DNA structure, paternal chromosomal integrity, pronuclear formation, and developmental competence of in vitro matured porcine oocytes after ICSI. Acridine orange staining and flow cytometry based sperm chromatin structure assay were used to determine sperm DNA integrity by calculating the cells outside the main population (COMP αT). No differences were observed in COMP αT values among GSH-treated and control groups. COMP αT values in GSH-treated groups were significantly lower than that in DTT-treated groups. Following ICSI, GSH treatments did not significantly alter paternal chromosomal integrity. Paternal chromosomal integrity in sperm treated with DTT plus or minus heparin was also the lowest among all groups. GSH-treated sperm yielded the highest rates of normal fertilization and blastocyst formation, which were significantly higher than that of control and DTT-treated groups. The majority of blastocysts derived from control and GSH-treated spermatozoa were diploid, whereas blastocysts derived from DTT-treated spermatozoa were haploid. In conclusion, sperm treatment with GSH enhanced the developmental capacity of porcine embryos produced by our optimized ICSI procedure.