In order to examine the effects of four different light spectra (i.e., white, red, green, blue) on the oocyte maturation in grass puffer, the change of reproductive parameters via brain-pituitary-gonad (BPG) axis were investigated in this study. After exposure to four different light spectra for 7 weeks, the abundance of gonadotropin-releasing hormone (GnRH) mRNA which is a type of seabream (sbGnRH) and two different of subunit of gonadotropin hormones mRNAs, follicle-stimulating hormone (fshβ) mRNA and luteinizing hormone (lhβ) mRNA, were analyzed in the brain and pituitary. Gonadosomatic index (GSI) and oocyte developmental stage were also investigated in the gonad based on anatomical- and histological observations. GSI value was significantly increased in the green spectrum-exposed group when compared to that of the other light-exposed groups (i.e., white, red, blue), with the presence of yolk stage oocytes (p˂0.05). The abundances of sbGnRHmRNA and fshβ mRNA in the green spectrum-exposed group were also significant higher than those of the other light spectra-exposed groups(p˂0.05). However, there was no significant difference between the abundances of lhβmRNA in all light spectra-exposed groups. These results indicate that the maturation of oocyte in grass puffercan be accelerated by exposure to the spectrum of green. The sbGnRHmRNA and fshβ mRNA may play an important reproductive parameters role in the initiation of maturation of oocyte. To better understand the molecular mechanism for the maturation of oocytein grass puffer, further study examining the relationship between oocyte development and its related genes (e.g., sbGnRHmRNA and fshβmRNA) is required.

The aim of this study was to determine the effect of additional alpha-linolenic acid (ALA) supplementation during in vitro maturation (IVM) and culture (IVC) on nucleic maturation and embryo development of pigs. Cumulus-oocyte complexes (COCs) were incubated in IVM medium containing different concentration of ALA (25, 50 and 100 μM) for 44 h. After in vitro maturation, nuclear maturation of oocytes were evaluated by aceto-orcein stain. Mature oocytes with 50 μM ALA were fertilized and cultured in IVC medium with ALA (25, 50 and 100 μM) during early-embryogenesis (48 hours after fertilization). Then, embryos were cultured with 25 μM ALA during early embryogenesis and/or late embryogenesis (120 hours after early-embryogenesis). In results, oocyte maturation were significantly increased by 50 μM ALA treatment groups compared with control groups (p<0.05). Treatment of 25 μM ALA during early-embryogenesis enhanced cleavage rate of embryo compared with other groups (p<0.05), whereas formation and total cell number of blastocyst had no significant difference. Similarly, cleavage rate of embryos were increased by 25 μM ALA supplement during early- or late-embryogenesis than ALA treatment both stage of embryogenesis (p<0.05), but did not influence to blastocyst formation. Interestingly, total cell number of blastocyst were enhanced in ALA treatment group during early-embryogenesis. These findings indicated that ALA supplement enhance the nuclear maturation of oocyte and embryo development, however, excessive ALA could negatively influence. Therefore, we suggest that ALA is used for improvement of in vitro production of mammalian embryo and further study regarding with functional mechanism of ALA is needed.

Intact germinal vesicle (GV) arrest and release are essential for maintaining the fertility of mammals inducing human. Intact germinal vesicle release, maturation of oocytes is maintained by very complex procedures along with folliculogenesis and is a critical step for embryonic development. Cyclic guanosine monophosphate (cGMP) has been suggested a key factor for meiotic arrest but so far its mechanisms are controversy. In this study we examine the effects of cGMP on germinal vesicle breakdown in cumulus-enclosed oocytes and denuded oocytes. Spontaneous maturation was inhibited by a cGMP agonist, 8-Br-cGMP with concentration dependent manners both in cumulus-enclosed oocytes and denuded oocytes. The inhibitory effect was more severe in denuded oocytes than cumulus-enclosed oocytes. The Rp-8-Br-cGMP and Rp-pCPT- 8-Br-cGMP did not severely block GVB compared to 8-Br-cGMP. The spontaneous GVB inhibitory effects were different by the existence of cumulus. Based on them it is suggested that the cumulus modulates the role of cGMP in GV arrest.

Ultrastructural studies on oocyte development and vitellogenesis in oocytes, and the functions of follicle cells during oogenesis and oocyte degeneration were investigated to clarifyb the reproductive mechanism on vitellogenesis of Scapharca subcrenata using electron microscope observations. In this study, vitellogenesis during oogenesis in the oocytes occured by way of autosynthesis and heterosynthesis. Of two processes of vitellogenesis during oogenesis, the process of endogenous autosynthesis involved the combined activity of the Golgi complex, mitochondria and rough endoplasmic reticulum. However, the process of exogenous heterosynthesis involved endocytotic incorporation of extraovarian precursors at the basal region of the oolema of the early vitellogenic oocytes before the formation of the vitelline coat. In this study, follicle cells, which attached to the previtellogenic and vitellogenic oocytes, were easily found. In particular, the follicle cells were involved in the development of previtellogenic oocytes by the supply of nutrients, and vitellogenesis in the early and late vitellogenic oocytes by endocytosis of yolk precursors. Based on observations of follicle cells attached to degenerating oocytes after spawning, follicles of this species are involved in lysosomal induction of oocyte degeneration for the resorption phagosomes (phagolysosomes) in the cytoplasm for nutrient storage, as seen in other bivalves. In this study, the functions of follicle cells can accumulate reserves of lipid granules and glycogen particles for vitellogenesis from degenerating oocytes after spawning.

Purine metabolism is known factor for nuclear maturation of oocytes through both follicle cells and oocyte itself. However, it is largely unknown the roles of purine metabolism in the oocyte competence for fertilization and early development. In this study, the effects of adenosine in oocyte competence for development were examined using adenosine and its synthetic inhibitors. Adenosine treatment from GV intact stage for 18 hr (fGV) caused of decrease the fertilization rate but of increase the cleavage rate compared from the other stage treatment groups. Hadacidin did not effect on fertilization rate but increased cleavage rate without stage specificity. Adenosine did not block the effects of hadacidin with the exception of fGV group. By the inhibition of purine synthetic pathways the fertilization rate was decreased in the fGV and fGVB groups but increased in the fMII group. Exogenous adenosine caused of decrease fertilization rate in the fGVB group but increase in the fMII group. Cleavage rate was dramatically increased in the adenosine treatment with synthetic inhibitors. It means that the metabolism of purine has stage specific effects on fertilization and cleavage. Exogenous adenosine had only can improve oocyte developmental competence when it treated at GV intact stage. On the other hand, endogenous synthesis in all maturation stage caused of increase the cleavage rate without effects on fertilization. These data suggest that adenosine at GV stage as a paracrine fashion and inhibitions of endogenous adenosine in all stage improve oocyte developmental competence..

Cytokinesis is the final event in the cell division. After cytokinesis, one parent cell divided into two symmetric daughter cells. Unlike somatic cell which is symmetrically divided, oocyte meiotic maturation is highly asymmetric division, producing mature ovum and polar body. Class III phosphoinositide 3-kinase (PI3K) has been known as a key molecular component that regulates cell cycle progression, autophagy and endosomal trafficking. However, emerging evidences suggest that class III PI3K and its interactors are involved in midbody abscission during cytokinesis. Here we showed that beclin-1, a key component of PI3K is required to regulate midbody abscission during oocyte asymmetric division. Beclin-1 was widely distributed during meiotic maturation forming small vesicles. However, these vesicles were not colocalized with autophagosomal marker LC3. Instead, beclin-1 was detectable at the midbody ring during cytokinesis. Depletion of beclin-1 showed various defects including the failure of cytokinetic abscission, spindle separation and chromosome decondensation. Similar phenotype was observed when class III PI3K activity was inhibited. Therefore, our results demonstrate that PI3K is essential for cytokinesis but not autophagy during oocyte meiosis.

Primary oocytes that are arrested in first meiotic prophase for years enter maturation process to meet a critical precondition for successful fertilization. During maturation, oocyte finishes meiosis I and progresses to the metaphase II stage, achieving meiotic maturity. Although importance of oocyte maturation for oocyte quality has been recognized, it is not fully understood for molecular mechanisms underlying oocyte maturation. Here, we found that dexamethasone-induced Ras-related protein 1 (RASD1), a member of RAS superfamily of small GTPases, was expressed in the mouse ovary. Immunohistochemical analysis revealed that Rasd1 expression was dominant in oocyte cytoplasm. Real-time PCR and RT-PCR analyses showed that Rasd1 mRNA was steadily expressed in germinal vesicle (GV), germinal vesicle break down (GVBD), metaphase I (MI) oocytes, but decreased in metaphase II(MII) oocytes during oocyte maturation. Konckdown of Rasd1 using RNAi system in the GV oocytes suppressed oocyte maturation through disruption of meiotic spindle and formation of misarranged chromosomes. Taken together, Rasd1 is a critical factor for MI-MII transition of oocyte and is involved in the regulation of spindle formation during oocyte maturation. Further study is needed to examine relationship between Rasd1 and spindle formation in MI-MII transition.

Cryopreservation has become a powerful method of the assisted reproduction technology and supports fertility preservation of cancer and other indication patients. After controlled ovarian hyperstimulation, surplus oocytes and embryos were recommended to store using cryopreservation. Recently, vitrification is replaced with traditional slow freezing protocol, because of improved survival rates and clinical outcomes. Vitrification requires a high concentration of CPAs that may induce significant osmotic and metabolic damage to cells including oocytes even in a short exposure of a few minutes. Generally, MPF plays a crucial role in the cell cycle regulation and maintaining the meiotic arrest of oocytes. In fact, it has been observed to decline in MII ovine oocytes after vitrification and would be suggested that one of the main causes of low fertilization rate and developmental competence derived from cryoinjury during vitrification. Therefore, the aim of this study was to evaluate the effect of caffeine treatment on the activity of MPF, MAPK level in vitrified/warmed mouse mature eggs. Caffeine, Phosphataseinhibitor, may maintain active form of MPF. We evaluated their survival after warming procedure, fertilization, cleavage, and developmental rates. Ovulated MII eggs were retrieved from 6 weeks old B6D2F1 female mouse at 14hr post hCG injection. Collected MII eggs were maintained in HTF medium containing 10% KSR with or without caffeine for 1hr. Eggs were vitrified in 7.5%EG +7.5%DMSO equilibrium solution, 15%EG + 15%DMSO + 0.5M sucrose vitrification solution with or without caffeine. Also warming solution contained sucrose (0.5M, 0.25M, 0.125M, and 0M) with or without caffeine. After warming, eggs were cultured in HTF medium with or without caffeine for 2 hr then fertilized with epididymal sperm in vitro and cultured in KSOM for 5 days to analyze embryonic development. Survival rates were similar in all experimental groups. However, fertilization rate was higher in with caffeine group compare to without caffeine significantly (80% vs. 85%, p<0.05). 2-cell and blastocyst formation were increased in caffeine group (p<0.05). MPF activity and MAP kinase activity were recovered in with caffeine group after vitrification/warming process. In conclusion, Caffeine may maintain MPF and MAPK level in vitrified/warmed MII eggs, and enhance fertilization and further embryonic development.

Dynamic reorganization of actin filaments is essential for various stages of mammalian oocyte maturation, including spindle migration, actin cap formation, polar body extrusion, and cytokinesis. Various actin binding proteins (ABPs) have been known to be involved in the regulation of actin filament remodeling. We elucidate roles of three different actin binding proteins in mouse oocyte maturation. The heterodimeric actin-capping protein (CP) binds to the fast-growing(barbed) ends of actin filaments and plays essential roles in various actin-mediated cellular processes. When CP is knockdowned or inhibitory component was overexpressed, asymmetric division of oocyte have been compromised. It turns out that knockdown or inhibition of CP deplete cytoplasmic actin mesh level, which have been known to be essential for maintain cytoplasmic actin mesh. Another actin binding proteins, tropomodulin 3 (Tmod3), binds to the slow-growing end of actin filaments and knockdown or expression deletion mutant of Tmod3 also decrease actin mesh level in maturing oocyte and it severely ablated asymmetric division of oocyte. Finally, tropomyosin 3, actin filament binding proteins protect actin filament from depolymerization, is also important to maintain cortex integrity in maturing oocyte. Taken together, these finding showed the essential roles of actin binding proteins in remodeling of actin filaments in mammalian oocyte development.

Accurate chromosome segregation is critical to ensure genomic integrity during cell division. This process is facilitated by the kinetochore, a multiprotein structure that is assembled on centromeric regions of chromosomes. The kinetochore establishes a mechanical link between the chromosomes and spindle microtubules and modulates cell cycle progression by regulating spindle assembly checkpoint (SAC). Defects in this process result in an aneuploidy, leading to miscarriages, infertility and various genetic disorder such as Down’s syndrome. Although the numerous kinetochore proteins have been identified and studied, the mechanisms that engaged in kinetochore assembly and chromosome segregation are poorly understood. Here we investigated the function of kinetochore protein Zwint-1 on homologous chromosome segregation during oocyte meiotic maturation. We found that Zwint-1 was localized at the kinetochore during meiotic maturation. Knockdown of Zwint-1 caused premature polar body extrusion, indicating acceleration of meiosis I. Interestingly, Zwint-1 knockdown impaired the recruitment of Mad2 at the kinetochores. However, BubR1 localization at the kinetochores was not affected by Zwint-1 knockdown, suggesting that Zwint-1 selectively regulates the recruitment of SAC components into the kinetochores. We also found that Zwint-1 knockdown abrogated chromosome alignment and segregation, thereby resulting in a high incidence of aneuploidy. These chromosomal defects were mostly due to the abnormal kinetochore-microtubule (kMT) attachments. Intriguingly, chromosome misalignment mediated by SAC inactivation was repaired, when anaphase onset was delayed by treating oocytes with proteasome inhibitor MG132. However, surprisingly, chromosomal defects following Zwint-1 knockdown were not restored by delaying anaphase onset. This result suggests that chromosomal defects induced by Zwint-1 knockdown are less likely associated with the failure of SAC activation. In addition, we observed that Aurora B/C kinase activity was not affected by Zwint-1 knockdown. Nevertheless, the meiotic defects induced by Zwint-1 knockdown were similar to those observed in Aurora B/C inhibition, suggesting that Zwint-1 is a downstream effector of Aurora B/C kinase during meiosis. Consistent with this, in Zwint-1 knockdown oocytes chromosomal defects following Aurora B/C inhibition were not restored when Aurora B/C inhibitor was removed, whereas the defects were well rescued in control oocytes after removing Aurora B/C inhibitor. This result suggests that the role of Aurora B/C kinases that correct erroneous kMT attachment is primarily regulated by Zwint-1. Collectively, our results demonstrated for the first time that Zwint-1 is an essential downstream effector of Aurora B/C kinase that corrects erroneous kMT attachment and regulates SAC activity, which ensures accurate homologous chromosome segregation during oocyte meiosis.

Ultrastructural studies of oocyte degeneration in the oocyte, and the functions of follicle cells during oocyte degeneration are described to clarify the reproductive mechanism on oocyte degeneration of Mactra chinensis using cytological methods. Commonly, the follicle cells are attached to the oocyte. Follicle cells play an important role in oocyte degeneration. In particular, the functions of follicle cells during oocyte degeneration are associated with phagocytosis and the intracellular digestion of products. In this study, morphologically similar degenerated phagosomes (various lysosomes), which were observed in the degenerated oocytes, appeared in the follicle cells. After the spawning of the oocytes, the follicle cells were involved in oocyte degeneration through phagocytosis by phagolysosomes. Therefore, it can be assumed that follicle cells reabsorb phagosomes from degenerated oocytes. In this study, the presence of lipid granules, which occurred from degenerating yolk granules, gradually increased in degenerating oocytes. The function of follicle cells can accumulate reserves of lipid granules and glycogen in the cytoplasm, which can be employed by the vitellogenic oocyte. Based on observations of follicle cells attached to degenerating oocytes after spawning, the follicle cells of this species are involved in the lysosomal induction of oocyte degeneration for the reabsorption of phagosomes (phagolysosomes) in the cytoplasm for nutrient storage, as seen in other bivalves.

Rearing experiments were conducted using several regimes combined with different photoperiods and water temperatures to investigate the role of temperature and photoperiod as environmental cues regulating reproduction in red marbled rockfish, Sebastiscus tertius. The initial gonadosomatic index (GSI) was 1.62±0.32% and that in the 15˚C control was 7.01±0.46% at the end of the experiment. The highest GSI was 9.10±0.35% in the 12L:12D photoperiod-treated fish. The highest GSI at 19˚C was 15.03±0.86% in the 12L:12D photoperiod treatment. The initial hepatosomatic index (HSI) was 3.09±0.72% and that in the 15˚C control was 3.88±0.45%. The highest HSI was 4.00±0.56% in the 15L:9D treated fish. The highest HSI at 19˚C was 4.05±0.63% in the 12L:12D treated fish.

The aim of this study was to analyze the effect of antifreeze proteins (AFPs) on vitrification of mouse mature (MII) oocytes. We studied about 3 types of AFPs from different origins (FfIBP, LeIBPand Type III AFP). The MII oocytes were obtained from 4-week-old BD-F1 mice. Vitrification of oocyte was performed by 2 steps using the Cryotop (equilibration: 7.5% EG + 7.5% PROH for 5 min, vitrification: 15% EG + 15% PROH + 0.5M sucrose for 1 min). The concentrations of AFPs added to these solutions were 0.05 mg/ml for FfIBP and 0.1 mg/ml for LeIBP and Type III AFP. After fertilization, embryo development was assessed up to 5 days. Through immunostaining of vitrified-warmed oocytes, we assessed the normal meiotic spindle. Also, intracellular ROS and mitochondrial activity was analyzed. In the developmental stages, FfIBP and LeIBP groups showed significantly higher survival rates. In the blastocyst and apoptotic blastomere rates were significant differences in AFPs treated groups. AFPs treated groups were significantly higher in blastocyst cell numbers than control group. Among the AFPs treated groups, FfIBP, LeIBP groups were significantly higher rates. And, in cleavage rates, FfIBP group was significantly higher rates than the other groups. In vitrified-warmed MII oocytes, the normal meiotic spindle organization and chromosome alignment rate was significantly higher in FfIBP and LeIBP groups. And in intracellular ROS levels, control group was significantly increased than AFPs treated groups. However, in the mitochondrial activity, LeIBP group was significantly higher than control, FfIBP and LeIBP groups. AFPs treated groups were significant differences in development, meiotic spindle organization and intracellular ROS levels. And in the AFPs treated groups, FfIBP and LeIBP groups were significantly higher rates in normal meiotic spindle and mitochondrial activity than Type III AFP group respectively. In conclusion, FfIBP and LeIBP can be thought to improve oocyte cryopreservation efficiency.

Throughout their meiotic maturation in most mammals, oocytes are arrested twice, prophase I and metaphase II. Being released from these arrests, transient or oscillation of intracellular Ca2+ concentration is observed in the ooplasm, which is not answered in relation to the specific role in the resumption of meiotic arrest. Recently, Ca2+/calmodulin-dependent protein kinase II (CaM KII) has been known as a Ca2+ oscillation decoder from the in vitro experiment. CaM KII is multifunctional serine/threonine kinase observed in most cells. Present studies were performed to investigate the role of CaM KII during resumption of meiotic arrest and activation in vitro of mouse oocytes. It was questioned whether CaM KII might be involved in the meiotic resumption of mouse oocytes. Compared to the control, both of CaM KII inhibitors, KN-93 and KN-62, significantly inhibited germinal vesicle breakdown (GVBD) of mouse oocytes in a dose-dependent manner. As the concentration of KN-93 increased, concomitant decrease of intracellular Ca2+ concentration ([Ca2+]i) was also observed using confocal laser scanning microscope (CLSM) and an intracellular Ca2+ indicator, fluo 3-AM. When GVBD oocytes were treated with 6% ethanol, small [Ca2+]i transient was observed in oocytes bathed with Ca2+-free medium and large increase was observed in oocytes bathed with Ca2+-containing medium, suggesting that [Ca2+]i transient could happen from intracellular Ca2+ store as well as Ca2+ influx through Ca2+-channel on the oolemma. However, KN-93 inhibited the [Ca2+]i transient of GVBD oocytes in both cases. Using monoclonal antibodies against α-subunit of CaM KII, tubulin and microtubule-assocaited proteins (MAPs), CaM KII has been colocalized on the spindle with tubulin and MAPs. The present study also demonstrated the presence of α-subunit of CaM KII in heart, kidney, testes, ovary as well as in brain of the mouse. In ovarian follicles, CaM KII was expressed in granulosa cells and oocytes. Based on overall the above results, followings are suggested. First, CaM KII might be involved in the regulatory mechanism of meiotic resumption. Second, CaM KII might play a regulatory role in the stabilization of microtubule.

In this study, oocyte steroidogenesis are investigated in relation to oocyte development in the starry flounder, Platichthys stellatus, a marine multiple spawner. Vitellogenic (0.52 and 0.55 mm oocyte diameter) and mature oocytes (0.63, 0.66 and 0.71 mm oocyte diameter) were incubated in vitro in the presence of [3H]17α-hydroxyprogesterone ([3H]17α- OHP) as a precursor. Steroid metabolites were extracted from the incubated media and oocytes, the extracts were separated and identified by thin-layer chromatography (TLC), high performance liquid chromatography (HPLC) and gas chromatographymass spectrometry (GC-MS). The major metabolites produced from [3H]17α-OHP were androgens [androstenedione (A4) and testosterone (T)] and estrogens [17β-estradiol (E2) and estrone (E1)] and progestins [17α,20α-dihydroxy-4-pregnen- 3-one (17α20αP) and 17α,20β-dihydroxy-4-pregnen-3-one (17α20βP)] in vitellogenic and mature oocytes. The results from this study suggest the potential roles of E1 in the oocytes with diameter 0.52-0.71 mm, 17α20αP and 17α20βP at the oocytes of 0.63, 0.66 and 0.71 mm.

In oocytes from different species, MPF, a complex of Cdk1 and cyclin B, is the master regulator of cell cycle. The activity of MPF is regulated by the phosphorylations mediated by Wee1B kinase and Cdc25B phosphatase. Although a regulation of MPF activity by these inhibitory phosphorylations are well established, a dogma in the cell cycle is that MPF activity is regulated by the dynamics of cyclin B during the metaphase II (MII) arrest (also known as CSF arrest). However, growing evidences suggest that Wee1B-mediated Cdk1 phosphorylation is also critical to trigger the progression of cell cycle during the onset of anaphase. Therefore, in the present study, we investigated the role of Cdc25B phosphatase during MII arrest. Cdc25B is present in MII arrested oocytes as a hyperphosphorylated form and disruption of its function either by antibody or siRNA injection induces the progression of cell cycle to interphase. Moreover, the hyperphosphorylated form, which has been known as an active form of Cdc25B, is dephosphorylated during the anaphase onset. Interestingly, this dephosphrylation occurred ahead of cyclin B degradation. Conversely, overexpression of Cdc25B prevents metaphase to anaphase transition induced by calcium stimulation. Therefore, our findings provide novel paradigm in cell cycle that MPF activity during metaphase arrest is regulated by the balance between Cdk1 inhibitory kinases, Wee1, and the counteracting phosphatases, Cdc25. When cells exit from metaphase, Cdc25 is inactivated and Wee1 is reactivated and thereby Cdk1 kinase activity is rapidly and transiently decreased. This initial decrease of Cdk1 activity is further promoted by the proteolytic degradation of cyclin B, which ensures irreversible progression of cell cycle to interphase. Thus, the concerted effort of phosphorylation/dephosphorylation of Cdk1 and synthesis/degradation of cyclin B play roles in fine-tuning the activity of Cdk1 during metaphase to anaphase transition.

Recently, we reported growth arrest-specific gene 6 (Gas6) as a new maternal effect gene (MEG), that expressed in the oocytes but functioned principally during embryogenesis. Gas6 RNAi-treated oocytes developed to metaphase II (MII) stage but they have affected M-phase promoting factor (MPF) activity and incurred abnormal pronuclear (PN) formation during fertilization. Gas6 is a ligand of TAM family members (Tyro3, Axl and Mertk) of receptor tyrosine kinase (RTK). Purpose of the present study was to evaluate the expression of Tyro3, Axl and Mertk transcripts in oocytes and early embryos. Expression of Gas6 and Mertk mRNA was detectable in oocytes and follicular cells, while Tyro3 and Axl mRNA was expressed only in follicular cells. Expression of Mertk mRNA was relatively constant during oocytes maturation and embryogenesis, but the other receptors, Tyro3 and Axl, were not expressed in oocytes and PN stage of embryos at all. Knockdown of Mertk mRNA and protein by using sequence-specific Mertk double strand RNA (dsRNA) did not affect oocytes maturation. In this case, however, contrary to the ligand Gas6 RNA interference (RNAi), MPF activity had not been changed by Mertk RNAi. Therefore, we concluded that the Gas6-Mertk signaling is not directly related to the oocyte maturation. It is still required to study further regarding the function of Mertk as the receptor of Gas6 during preimplantational early embryogenesis.

To evaluate the effects of benzo[a]pyrene (B[a]P), one of polycyclic aromatic hydrocarbons (PAHs), on in vitro oocyte maturation (GVBD) and sex steroid hormone production, maturing oocytes (oocyte diameters=0.74, 0.88 and 0.93 mm) of the longchin goby, Chasmichthys dolichognathus were incubated with B[a]P (1, 10 and 100 ng/mL) for 24 hours. After incubation, the oocytes were fixed with clearing solution (ethanol:formalin:glacial acrtic acid=6:3:1). The location of the germinal vesicle was observed under low-power magnification using a dissecting microscope. Steroids in aliquots of the incubation media were extracted twice using five volumes of ethylacetate:cyclohexane (1:1). Then, the T, E2 and 17α20βP levels were measured by RIA. In oocytes 0.74 mm diameter (vitellogenic oocytes), B[a]P had no significant effect on GVBD at the concentrations tested. In oocytes 0.88 mm diameter (fully vitellogenic oocytes), B[a]P inhibited GVBD significantly at 1 and 100 ng/mL. T production was decreased and the ratio of E2/T was increased significantly at 1 and 10 ng/mL compared with control. In 0.93 mm diameter oocytes (germinal vesicle located near the center of oocytes), B[a]P induced GVBD significantly at 10 and 100 ng/mL and decreased the ratio of E2/T significantly at 1 and 10 ng/mL compared with control. These findings suggest that B[a]P has different sensitivity to the oocyte maturation according to the oocyte diameters.