The present study investigated the subcellular localization of inducible nitric oxide synthase (iNOS) during mouse oocyte meiotic maturation and fertilization using confocal microscopy, and further studied the roles of iNOS-derived NO in oocyte maturation by using an iNOS-specific inhibitor aminoguanidine (AG) and iNOS antibody microinjection. In germinal vesicle-stage oocytes, iNOS immunoreactivity was mainly localized in the germinal vesicle. Shortly after germinal vesicle breakdown, the iNOS immunoreactivity accumulated around the condensed chromosomes. At metaphase I and metaphase II, with the organization of chromosomes to the equatorial plate, iNOS immunoreactivity was concentrated around the aligned chromosomes, putatively the position of the metaphase spindle. The accumulation of iNOS immunoreactivity could not be detected at anaphase I and anaphase II. However, at telophase I and telophase II, the staining of iNOS was concentrated in the region between the separating chromosomes/chromatids. Furthermore, the staining of iNOS also accumulated in the male and female pronuclei in fertilized eggs. Germinal vesicle breakdown and the first polar body emission of the oocytes were significantly blocked by the iNOS-specific inhibitor AG in a dose-dependent manner. The germinal vesicle breakdown in oocytes injected with iNOS antibody was also inhibited. We found that the phosphorylation of mitogen-activated protein kinase in oocytes after germinal vesicle breakdown was inhibited by AG treatment. The control oocytes extruded a normal first polar body, while the AG-treated oocytes exhibited an elongated protrusion or no elongated protrusion. The results of confocal microscopy showed that the AG-treated oocytes were arrested at anaphase I–telophase I. Our results suggest that the iNOS-derived NO pathway plays important roles in mouse oocyte meiotic maturation, especially in germinal vesicle breakdown and the anaphase–telophase transition.
Li-Jun Huo, Cheng-Guang Liang, Ling-Zhu Yu, Zhi-Sheng Zhong, Zeng-Ming Yang, Heng-Yu Fan, Da-Yuan Chen and Qing-Yuan Sun
Shuai Lin, Yu-Yuan Zhu, Wei Hu, Yan Yang, Jia-Mei Luo, Shi-Jun Hu and Zeng-Ming Yang
Decidualization is required for the successful establishment of pregnancy in rodents and primates. Fatty acid desaturase 3 (Fads3) belongs to the fatty acid desaturase family, which is a crucial enzyme for highly unsaturated fatty acid biosynthesis. However, the expression, regulation and function of Fads3 during early pregnancy in mice are still unknown. In this study, we examined Fads3 expression, regulation and function during mouse decidualization. The expression of Fads3 is detected in the subluminal stromal cells at implantation site on day 5 of pregnancy, but not at inter-implantation site and in day 5 pseudopregnant uteri. Compared to delayed implantation, Fads3 is strongly expressed after delayed implantation is activated by estrogen treatment. From days 6 to 8, Fads3 mRNA signals are significantly detected in the decidua. In ovariectomized mice, estrogen significantly stimulates Fads3 expression. However, estrogen has no effect on Fads3 expression in ovariectomized ERα-deficient mice, suggesting that estrogen regulation on Fads3 expression is ERα dependent. When ovariectomized mice were treated with progesterone, Fads3 expression is significantly increased by progesterone. Progesterone stimulation on Fads3 expression is also detected in cultured stromal cells, which is abrogated by RU486 treatment. These data indicate that progesterone upregulation on Fads3 expression is progesterone receptor-dependent. Fads3 knockdown by siRNA reduces in vitro decidualization of mouse stromal cells. Taken together, Fads3 may play an important role during mouse decidualization.
Dong Zhang, Shen Yin, Man-Xi Jiang, Wei Ma, Yi Hou, Cheng-Guang Liang, Ling-Zhu Yu, Wei-Hua Wang and Qing-Yuan Sun
The present study was designed to investigate the localization and function of cytoplasmic dynein (dynein) during mouse oocyte meiosis and its relationship with two major spindle checkpoint proteins, mitotic arrest-deficient (Mad) 1 and Mad2. Oocytes at various stages during the first meiosis were fixed and immunostained for dynein, Mad1, Mad2, kinetochores, microtubules, and chromosomes. Some oocytes were treated with nocodazole before examination. Anti-dynein antibody was injected into the oocytes at germinal vesicle (GV) stage before the examination of its effects on meiotic progression or Mad1 and Mad2 localization. Results showed that dynein was present in the oocytes at various stages from GV to metaphase II and the locations of Mad1 and Mad2 were associated with dynein’s movement. Both Mad1 and Mad2 had two existing states: one existed in the cytoplasm (cytoplasmic Mad1 or cytoplasmic Mad2), which did not bind to kinetochores, while the other bound to kinetochores (kinetochore Mad1 or kinetochore Mad2). The equilibrium between the two states varied during meiosis and/or in response to the changes of the connection between microtubules and kinetochores. Cytoplasmic Mad1 and Mad2 recruited to chromosomes when the connection between microtubules and chromosomes was destroyed. Inhibition of dynein interferes with cytoplasmic Mad1 and Mad2 transportation from chromosomes to spindle poles, thus inhibits checkpoint silence and delays anaphase onset. These results indicate that dynein may play a role in spindle checkpoint inactivation.
Li-Ying Yan, Jun-Cheng Huang, Zi-Yu Zhu, Zi-Li Lei, Li-Hong Shi, Chang-Long Nan, Zhen-Jun Zhao, Ying-Chun OuYang, Xiang-Fen Song, Qing-Yuan Sun and Da-Yuan Chen
The assembly of microtubules and the distribution of NuMA were analyzed in rabbit oocytes and early cloned embryos. α-Tubulin was localized around the periphery of the germinal vesicle (GV). After germinal vesicle breakdown (GVBD), multi-arrayed microtubules were found tightly associated with the condensed chromosomes and assembled into spindles. After the enucleated oocyte was fused with a fibroblast, microtubules were observed around the introduced nucleus in most reconstructed embryos and formed a transient spindle 2–4 h post-fusion (hpf). A mass of microtubules surrounded the swollen pseudo-pronucleus 5 hpf and a normal spindle was formed 13 hpf in cloned embryos. NuMAwas detected in the nucleus in germinal vesicle-stage oocytes, and it was concentrated at the spindle poles in both meiotic and mitotic metaphase. In both donor cell nucleus and enucleated oocyte cytoplasm, NuMA was not detected, while NuMA reappeared in pseudo-pronucleus as reconstructed embryo development proceeded. However, no evident NuMA staining was observed in the poles of transient spindle and first mitotic spindle in nuclear transfer eggs. These results indicate that NuMA localization and its spindle pole tethering function are different during rabbit oocyte meiosis and cloned embryo mitosis.