The mechanisms underlying postovulatory oocyte aging (POA) remain largely unknown. The expression of the calcium-sensing receptor (CaSR) in mouse oocytes and its role in POA need to be explored. Our objective was to observe CaSR expression and its role in the susceptibility to activating stimuli (STAS) in POA mouse oocytes. The results showed that, although none of the newly ovulated oocytes were activated, 40% and 94% of the oocytes recovered 19 and 25 h after human chorionic gonadotropin (hCG) injection were activated, respectively, after ethanol treatment. The level of the CaSR functional dimer protein in oocytes increased significantly from 13 to 25 h post hCG. Thus, the CaSR functional dimer level was positively correlated with the STAS of POA oocytes. Aging in vitro with a CaSR antagonist suppressed the elevation of STAS, and cytoplasmic calcium in oocytes recovered 19 h post hCG, whereas aging with a CaSR agonist increased STAS, and cytoplasmic calcium of oocytes recovered 13 h post hCG. Furthermore, the CaSR was more important than the Na-Ca²⁺ exchanger in regulating oocyte STAS, and T- and L-type calcium channels were inactive in aging oocytes. We conclude that the CaSR is involved in regulating STAS in POA mouse oocytes, and that it is more important than the other calcium channels tested in this connection.

View full abstract

In this study, we evaluated the effects of pre-maturational culture (pre-IVM) on the developmental competence of bovine oocytes derived from an 8-day in vitro growth (IVG) culture system. IVG oocytes were subjected to 5 h pre-IVM before in vitro maturation, followed by in vitro fertilization (IVF). The proportion of oocytes that progressed to the germinal vesicle breakdown stage was similar between groups with and without pre-IVM. Although metaphase II oocytes and cleavage rates after IVF were similar regardless of pre-IVM culture, the blastocyst rate was significantly higher in the group with pre-IVM (22.5%) than without pre-IVM (11.0%, P < 0.05). In conclusion, pre-IVM culture improved the developmental competence of bovine oocytes derived from an 8-day IVG system.

View full abstract

MicroRNA (miR)-145 is enriched in the follicular granulosa cells (GCs) of 3-week-old mice. Downregulating miR-145 inhibits the proliferation and differentiation of GCs and induces evident changes in their cytoskeleton. In this study, we examined how miR-145 induces cytoskeletal changes in mouse GCs and its potential mechanism in regulating GC steroidogenesis. We found that actin related protein 2/3 complex subunit 5 (Arpc5) is a target of miR-145. The miR-145 antagomir increased ARPC5 expression but not β-ACTIN, β-TUBULIN, and PAXILLIN expression. Arpc5 overexpression inhibited GC proliferation, differentiation, and progesterone synthesis. Furthermore, the expression of progesterone synthesis-associated enzymes was downregulated in the Arpc5 overexpression group, and the GC cytoskeleton exhibited evident changes. We conclude that Arpc5, a new target of miR-145, regulates primary GC proliferation and progesterone production by regulating the cytoskeleton remodeling.

View full abstract

This study aimed to characterize calyculin A (CL-A)-induced and thimerosal-induced hyperactivation of cryopreserved bovine spermatozoa. Hyperactivation was effectively induced by treating with 10 nM CL-A for 60 min in the presence of cyclic AMP analogs, extracellular Ca²⁺, and albumin or with 12.5 µM thimerosal briefly in the absence of these capacitation-supporting factors. Majority of the spermatozoa exhibiting CL-A-induced hyperactivation were characterized by the 3-dimensional helical movement with head rotation, higher degree of flagellar curvature, and faster beating of the flagella than those exhibiting thimerosal-induced hyperactivation of the 2-dimensional planar movement without head rotation. The CL-A-induced hyperactivation was linked to the activation of cAMP/protein phosphorylation-dependent signaling cascades and to the decreased activity of glycogen synthase kinase-3α (GSK-3α). In contrast, the thimerosal-induced hyperactivation was suppressed by pretreatment with CL-A and cyclic AMP analogs in the absence of CaCl₂ to activate cAMP/protein phosphorylation-dependent signaling cascades. Additionally, the intracellular Ca²⁺ level in live sperm flagella was significantly higher in the CL-A-treated samples than in the thimerosal-treated samples. These results indicate that CL-A-induced hyperactivation of cryopreserved bovine spermatozoa is an extracellular Ca²⁺-dependent type with the 3-dimensional helical movement, which can be regulated not only by the activation of cAMP/protein phosphorylation-dependent signaling cascades, leading to a large enhancement of the intracellular Ca²⁺ level, but also by the reduction in GSK-3α activity. Considering the different characteristics of thimerosal-induced hyperactivation, our results suggest that the diversity of sperm hyperactivation arises from different combinations of flagellar bending and head rotation.

View full abstract

Linker histone variants regulate higher-order chromatin structure and various cellular processes. It has been suggested that linker histone variant H1a loosens chromatin structure and activates transcription. However, its role in early mouse development remains to be elucidated. We investigated the functions of H1a during preimplantation development using H1a gene-deleted mice. Although H1a homozygous knockout (KO) mice were born without any abnormalities, the number of offspring were reduced when the mothers but not fathers were homozygous KO animals. Maternal H1a KO compromised development during the morula and blastocyst stages, but not differentiation of the inner cell mass or trophectoderm. Thus, maternal linker histone H1a is important in early development.

View full abstract

Lysophosphatidic acid (LPA) has been implicated in the uterine endometrial functions of implantation and decidualization; however, not much is known about its myometrial contractile function. Herein we characterized the uterotonic effects of LPA in non-pregnant (estrus) and peri-parturient rats in vitro. LPA dose-dependently (0.01–10 μM) stimulated the amplitude and integral, but not the frequency, of the uterine strip contraction of estrous rats. The stimulatory effect of LPA was enhanced 1 day before parturition but was lost 1 day postpartum. LPA did not cause the de novo synthesis of prostaglandin (PG) F₂α but stimulated contractions cooperatively with the PG. LPA-induced contractions were significantly inhibited by an LPA1/2/3 antagonist in the uteri of estrous rats but not in term rats. In this study we characterized the uterotonic effect of a natural LPA that occurs at physiological concentrations, changes with reproductive states, and is independent of mediation by the newly synthesized PG.

View full abstract

Progesterone (P) enhances spermatozoal hyperactivation, a capacitation event. Hyperactivation is associated with successful in vitro fertilization (IVF). In this study, we examined the effects of P on hyperactivation and IVF in mice. P enhanced spermatozoal hyperactivation and increased IVF success rate in a dose-dependent manner. Moreover, P affected spermatozoal hyperactivation and IVF through the membrane progesterone receptor of the spermatozoal head. These results show that P regulates spermatozoal capacitation and fertilization in mice. The concentration of P changes during the estrous cycle, indicating that spermatozoa are capacitated in response to the oviductal environment and subsequently fertilize the oocyte.

View full abstract

In mouse fetal gonads, germ cell development is accompanied by changes in cell cycle mode in response to external signals and intrinsic mechanisms of cells. During fetal development, male germ cells undergo G0/G1 arrest, while female germ cells exit the mitotic cell cycle and enter meiosis. In fetal testes, NANOS2 and CYP26B1 force germ cells to stay in G0/G1 arrest phase, preventing them from entering the meiotic cell cycle. In the fetal ovary, external signals, such as RA, BMP, and WNT, promote the competency of female germ cells to enter the meiotic cell cycle. MEIOSIN and STRA8 ensure the establishment of the meiotic cell cycle by activating meiotic genes, such that meiotic entry coincides with the S phase. This review discusses germ cell development from the viewpoint of cell cycle regulation and highlights the mechanism of the entry of germ cells into meiosis.

View full abstract

Somatic cell nuclear transfer (SCNT) is the only reproductive technology used to produce individuals from somatic cells by transferring them to enucleated oocytes. Although more than 25 years have passed since the first mammalian SCNT was reported in sheep, problems such as low birth rates and morphological abnormalities have persisted and limited its practical applications. The mouse is the ideal laboratory animal to unveil these questions due to its established reproductive technologies and extensive knowledge base of its genome and various strains. We investigated the causes of incomplete reprogramming after nuclear transfer of donor somatic cells and found that the loss of imprint in some placenta-specific imprinted genes could induce non-random SCNT abnormalities. By ameliorating aberrantly expressed imprinted genes, we succeeded in increasing the low birth rate and improving morphological abnormalities observed in SCNT fetuses. Furthermore, we sought appropriate mouse strains and cell types as nuclear donors to increase their developmental efficiencies and expand their applications in various fields. Peripheral blood cells are useful as ethical and economical cell species because they can be collected easily, even though SCNT embryos derived from hematopoietic cells show poor developmental abilities after reconstruction. Additionally, it is possible to obtain mice that are reactive to specific antigens of interest by using lymphocytes. Although there are still many limitations to the practical use of SCNT, its utilization is steadily expanding.

View full abstract

This article released online on March 5, 2019 as advance publication was withdrawn from consideration for publication in Journal of Reproduction and Development at author’s request.

View full abstract

This article released online on January 18, 2019 as advance publication was withdrawn from consideration for publication in The Journal of Reproduction and Development at author’s request.

View full abstract

This article released online on March 5, 2019 as advance publication was withdrawn from consideration for publication in Journal of Reproduction and Development at author’s request.

View full abstract

This article released online on January 18, 2019 as advance publication was withdrawn from consideration for publication in The Journal of Reproduction and Development at author’s request.

View full abstract

This article was retracted. See the Notification.

View full abstract