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1.

Background

Mater and Padi6 are maternal effect genes that are first expressed during oocyte growth and are required for embryonic development beyond the two-cell stage in the mouse. We have recently found that PADI6 localizes to, and is required for the formation of, abundant fibrillar Triton X-100 (Triton) insoluble structures termed the oocyte cytoplasmic lattices (CPLs). Given their similar expression profiles and mutant mouse phenotypes, we have been testing the hypothesis that MATER also plays a role in CPL formation and/or function.

Methodology/Findings

Herein, we show that PADI6 and MATER co-localize throughout the oocyte cytoplasm following Triton extraction, suggesting that MATER co-localizes with PADI6 at the CPLs. Additionally, the solubility of PADI6 was dramatically increased in Matertm/tm oocytes following Triton extraction, suggesting that MATER is involved in CPL nucleation. This prediction is supported by transmission electron microscopic analysis of Mater+/+ and Matertm/tm germinal vesicle stage oocytes which illustrated that volume fraction of CPLs was reduced by 90% in Matertm/tm oocytes compared to Mater+/+ oocytes.

Conclusions

Taken together, these results suggest that, similar to PADI6, MATER is also required for CPL formation. Given that PADI6 and MATER are essential for female fertility, these results not only strengthen the hypothesis that the lattices play a critical role in mediating events during the oocyte-to-embryo transition but also increase our understanding of the molecular nature of the CPLs.  相似文献   

2.

Background

At fertilisation, mammalian oocytes are activated by oscillations of intracellular Ca2+ ([Ca2+]i). Phospholipase Cζ, which is introduced by fertilising spermatozoon, triggers [Ca2+]i oscillations through the generation of inositol 1,4,5-triphosphate (IP3), which causes Ca2+ release by binding to IP3 receptors located on the endoplasmic reticulum (ER) of the oocyte. Ability to respond to this activating stimulus develops during meiotic maturation of the oocyte. Here we examine how the development of this ability is perturbed when a single spermatozoon is introduced into the oocyte prematurely, i.e. during oocyte maturation.

Results

Mouse oocytes during maturation in vitro were fertilised by ICSI (intracytoplasmic sperm injection) 1 – 4 h after germinal vesicle break-down (GVBD) and were subsequently cultured until they reached metaphase II (MII) stage. At MII stage they were fertilised in vitro for the second time (refertilisation). We observed that refertilised oocytes underwent activation with similar frequency as control oocytes, which also went through maturation in vitro, but were fertilised only once at MII stage (87% and 93%, respectively). Refertilised MII oocytes were able to develop [Ca2+]i oscillations in response to penetration by spermatozoa. We found however, that they generated a lower number of transients than control oocytes. We also showed that the oocytes, which were fertilised during maturation had a similar level of MPF activity as control oocytes, which were not subjected to ICSI during maturation, but had reduced level of IP3 receptors.

Conclusion

Mouse oocytes, which were experimentally fertilised during maturation retain the ability to generate repetitive [Ca2+]i transients, and to be activated after completion of maturation.  相似文献   

3.
Mouse oocytes develop sensitivity to inositol 1,4,5-trisphosphate (IP3) during oocyte maturation. We recently reported that a change in the organization of the endoplasmic reticulum (ER) during oocyte maturation may contribute to this enhanced sensitivity (Mehlmannet al.,1995,Dev. Biol.170, 607–615). Here, we investigated whether there is an increase in the number of available IP3receptors after maturation and whether there is a redistribution of IP3receptors similar to the redistribution of the ER that occurs during maturation. Western blot analysis of the IP3receptor in oocytes and eggs demonstrated a 1.8-fold increase in immunoreactive mass of the IP3receptor following oocyte maturation. Microinjection of the function-blocking monoclonal antibody 18A10 inhibited IP3-induced Ca2+release in a concentration-dependent manner in both eggs and oocytes. More antibody was required to inhibit Ca2+release to the same extent in eggs compared to oocytes when both were injected with the same concentration of IP3, suggesting that eggs contain a greater number of functional IP3receptors. Immunolocalization of the IP3receptor revealed that receptors were present in large clusters, 1–2 μm in diameter, in the cortex of the mature egg except in a ring-shaped band of cortex adjacent to the meiotic spindle. In contrast, receptor clusters were located around the entire cortex of the immature oocyte and were much smaller (<1 μm); larger patches were sometimes seen, but they did not display the same spherical organization as those in eggs. These results suggest that the number of cortical IP3receptors increases during mouse oocyte maturation and that this increase may contribute to enhanced Ca2+release at fertilization.  相似文献   

4.
Oocyte is arrested at metaphase of the second meiosis until fertilization switching on [Ca2+]i oscillations. Oocyte activation inefficiency is the most challenging problem for failed fertilization and embryonic development. Mitochondrial function and intracellular [Ca2+]i oscillations are two critical factors for the oocyte’s developmental potential. We aimed to understand the possible correlation between mitochondrial function and [Ca2+]i oscillations in oocytes. To this end, mitochondrial uncoupler CCCP which damages mitochondrial function and two small molecule mitochondrial agonists, L-carnitine (LC) and BGP-15, were used to examine the regulation of [Ca2+]i by mitochondrial functions. With increasing CCCP concentrations, [Ca2+]i oscillations were gradually diminished and high concentrations of CCCP led to oocyte death. LC enhanced mitochondrial membrane potential and [Ca2+]i oscillations and even improved the damage induced by CCCP, however, BGP-15 had no beneficial effect on oocyte activation. We have found that mitochondrial function plays a vital role in the generation of [Ca2+]i oscillations in oocytes, and thus mitochondria may interact with the ER to generate [Ca2+]i oscillations during oocyte activation. Improvement of mitochondrial functions with small molecules can be expected to improve oocyte activation and embryonic development in infertile patients without invasive micromanipulation.  相似文献   

5.
Repetitive oscillations in cytoplasmic Ca2+ due to periodic Ca2+ release from the endoplasmic reticulum (ER) drive mammalian embryo development following fertilization. Influx of extracellular Ca2+ to support the refilling of ER stores is required for sustained Ca2+ oscillations, but the mechanisms underlying this Ca2+ influx are controversial. Although store-operated Ca2+ entry (SOCE) is an appealing candidate mechanism, several groups have arrived at contradictory conclusions regarding the importance of SOCE in oocytes and eggs. To definitively address this question, Ca2+ influx was assessed in oocytes and eggs lacking the major components of SOCE, the ER Ca2+ sensor STIM proteins, and the plasma membrane Ca2+ channel ORAI1. We generated oocyte-specific conditional knockout (cKO) mice for Stim1 and Stim2, and also generated Stim1/2 double cKO mice. Females lacking one or both STIM proteins were fertile and their ovulated eggs displayed normal patterns of Ca2+ oscillations following fertilization. In addition, no impairment was observed in ER Ca2+ stores or Ca2+ influx following store depletion. Similar studies were performed on eggs from mice globally lacking ORAI1; no abnormalities were observed. Furthermore, spontaneous Ca2+ influx was normal in oocytes from Stim1/2 cKO and ORAI1-null mice. Finally, we tested if TRPM7-like channels could support spontaneous Ca2+ influx, and found that it was largely prevented by NS8593, a TRPM7-specific inhibitor. Fertilization-induced Ca2+ oscillations were also impaired by NS8593. Combined, these data robustly show that SOCE is not required to support appropriate Ca2+ signaling in mouse oocytes and eggs, and that TRPM7-like channels may contribute to Ca2+ influx that was previously attributed to SOCE.  相似文献   

6.
In this study we evaluated nuclear and ooplasmic maturation of prepuberal calf oocytes to determine a possible cause for their low developmental competency. Calf oocytes resumed meiosis and arrested at the MII stage at rates similar to that of adult animals; however, zygotes derived from calf oocytes cleaved and developed at significantly lower rates. Ooplasmic maturation was assessed during oocyte maturation and fertilization. Transmission electron microscopy revealed that a majority of calf oocytes exhibited some delay in organelle migration and redistribution following maturation. Immunofluorescence microscopy showed that following IVF, a higher percentage of calf oocytes had abnormal chromatin and microtubule configurations than those of adult cattle. These anomalies were characterized by delayed formation of sperm aster and asynchronous pronuclear formation. Microfluorometry was used to characterize the Ca2+ responses of calf oocytes to the addition of agonists or after IVF. The addition of thimerosal demonstrated the presence of Ca2+ stores in calf oocytes. Injection of near threshold concentrations of inositol 1,4,5-trisphosphate (InsP3), used to test the sensitivity of the InsP3R, released significantly less Ca2+ in calf than in cow oocytes, whereas higher concentrations of InsP3 (500 μM) released maximal [Ca2+]i in both oocytes. These results suggested that the Ca2+ content of intracellular stores was similar, but the sensitivity of the InsP3R may be different. Following insemination, calf oocytes exhibiting [Ca2+]i oscillations displayed comparable amplitude and intervals to cow oocytes; however, a significantly higher number of fertilized calf oocytes failed to show oscillations. Our findings suggest that the low developmental competence of calf oocytes can be attributed, at least in part, to incomplete or delayed ooplasmic maturation. © 1996 Wiley-Liss, Inc.  相似文献   

7.
Aging of oocytes, being not fertilized after ovulation for a prolonged time, considerably affects normal development of the fertilized oocyte. We examined effects of the aging on a series of highly repetitive Ca2+ transients commonly seen in fertilized mouse oocytes (Ca2+ oscillations). Frequency of Ca2+ oscillations in the aged oocyte [20 hrs after induction of superovulation by i.p. human chorionic gonadotropin (hCG)] was significantly higher (34.1 ± 5.8 1/hr) than the fresh oocyte (14 hr post-hCG, 21.8 ± 7.9 1/hr). Rates of rise and fall of individual Ca2+ transient in the aged oocyte were significantly slower than the fresh oocyte, whereas durations of individual Ca2+ transients were similar. When extracellular Ca2+ was raised from 2.04 mM to 5.00 mM, aged oocytes showed significant prolongation of the duration of individual Ca2+ transient, that resulted in a sustained elevation of intracellular Ca2+ ([Ca2+]i) in 33% of the aged oocyte. Transient increase in [Ca2+]i by photolysis of a caged Ca2+, Nitr-5, injected into cytoplasm was completely restored in the fresh oocyte [fluorescence intensity of [Ca2+]i indicator dye Fluo-3 (F480) returned to 97 ± 2% of the control level, time constant = 37 ± 9 sec]. In contrast, in the aged oocyte, restoration of F480 following Nitr-5 photolysis was incomplete (115 ± 12% of the control) and slow (time constant = 64 ± 23 sec). Because inhibition of the Ca2+ pump of the endoplasmic reticulum (ER) by 5 μM thapsigargin almost completely inhibited restoration of F480 following Nitr-5 photolysis in the fresh oocyte, we conclude that the aging-related changes in Ca2+ oscillations may be accounted for by dysfunction of intracellular Ca2+ regulation, presumably of the Ca2+ pump of the ER. Mol. Reprod. Dev. 48:383–390, 1997. © 1997 Wiley-Liss, Inc.  相似文献   

8.
9.
Epidermal growth factor (EGF) has received much attention recently for its positive effects on mammalian oocyte maturation and embryo development and its potential importance in cytoplasmic maturation of oocytes. Calcium (Ca2+) homeostasis in germinal vesicle stage oocytes has also been suggested to play a role in cytoplasmic maturation. This study examined the effects of EGF on Ca2+ mobilization as measured by its efflux from mouse oocytes at three time periods throughout maturation (0–4 hr, 4–8 hr, and 12 hr). Immature cumulus oocyte complexes (COCs) removed from the ovary for less than 4 hr exhibit oscillations in Ca2+ efflux that initiated 5–30 min following EGF stimulation. This response was not observed in COCs matured for 4–8 hr or 12 hr or in unstimulated 0–4 hr COCs. Denuded oocytes and cumulus cells did not show the same response to EGF (8.2 nM and 16.4 nM). Immunohistochemistry for detection of the EGF receptor along with EGF internalization studies showed that receptors are present both on cumulus cells and the oocyte but EGF appears to be internalized mainly by the cumulus cells. These data demonstrate that EGF induces oscillations in Ca2+ efflux in COCs 0–4 hr old and this response is mediated by the cumulus cells. Mol. Reprod. Dev. 53:244–253, 1999. © 1999 Wiley‐Liss, Inc.  相似文献   

10.
Prior to maturation, mouse oocytes are arrested at the germinal vesicle (GV) stage during which they experience constitutive calcium (Ca2+) influx and spontaneous Ca2+ oscillations. The oscillations cease during maturation but Ca2+ influx continues, as the oocytes’ internal stores attain maximal content at the culmination of maturation, the metaphase II stage. The identity of the channel(s) that underlie this Ca2+ influx has not been completely determined. GV and matured oocytes are known to express three Ca2+ channels, CaV3.2, TRPV3 and TRPM7, but females null for each of these channels are fertile and their oocytes display minor modifications in Ca2+ homeostasis, suggesting a complex regulation of Ca2+ influx. To define the contribution of these channels at the GV stage, we used different divalent cations, pharmacological inhibitors and genetic models. We found that the three channels are active at this stage. CaV3.2 and TRPM7 channels contributed the majority of Ca2+ influx, as inhibitors and oocytes from homologous knockout (KO) lines showed severely reduced Ca2+ entry. Sr2+ influx was promoted by CaV3.2 channels, as Sr2+ oscillations were negligible in CaV3.2-KO oocytes but robust in control and Trpv3-KO GV oocytes. Mn2+ entry relied on expression of CaV3.2 and TRPM7 channels, but Ni2+ entry depended on the latter. CaV3.2 and TRPV3 channels combined to fill the Ca2+ stores, although CaV3.2 was the most impactful. Studies with pharmacological inhibitors effectively blocked the influx of divalent cations, but displayed off-target effects, and occasionally agonist-like properties. In conclusion, GV oocytes express channels mediating Ca2+ and other divalent cation influx that are pivotal for fertilization and early development. These channels may serve as targets for intervention to improve the success of assisted reproductive technologies.  相似文献   

11.
Intracellular free calcium ([Ca2+]i) is essential for oocyte maturation and early embryonic development. Here, we investigated the role of [Ca2+]i in oocytes from cumulus‐oocyte complexes (COCs) with respect to maturation and early embryonic development, using the calcium‐buffering agent BAPTA‐AM (1,2‐bis[2‐aminophenoxy]ethane‐N,N,N′,N′‐tetraacetic acid tetrakis [acetoxymethyl ester]). COCs were graded based on compactness of the cumulus mass and appearance of the cytoplasm, with Grade 1 indicating higher quality and developmental potential than Grade 3. Results showed that: (i) [Ca2+]i in metaphase‐II (MII) oocytes from Grade‐3 COCs was significantly higher than those from Grade‐1 COCs, and was significantly reduced by BAPTA‐AM; (ii) nuclear maturation of oocytes from Grade‐3 COCs treated with BAPTA‐AM was enhanced compared to untreated COCs; (iii) protein abundance of Cyclin B and oocyte‐specific Histone 1 (H1FOO) was improved in MII oocytes from Grade‐3 COCs treated with BAPTA‐AM; (iv) Ca2+ transients were triggered in each group upon fertilization, and the amplitude of [Ca2+]i oscillations increased in the Grade‐3 group upon treatment with BAPTA‐AM, with the magnitude approaching that of the Grade‐1 group; and (v) cleavage rates and blastocyst‐formation rates were improved in the Grade‐3 group treated with BAPTA‐AM compared to untreated controls following in vitro fertilization and parthenogenetic activation. Therefore, BAPTA‐AM dramatically improved oocyte maturation, oocyte quality, and embryonic development of oocytes from Grade‐3 COCs.  相似文献   

12.
Mammalian reproduction is one of the most complex and fascinating biological phenomenon, which aims to transfer maternal and paternal genetic material to the next generation. At the end of oogenesis and spermatogenesis, both haploid gametes contain a single set of chromosomes ready to form the zygote, the first cell of the newly developing individual. The mature oocyte and spermatozoa remain in a quiescent state, during which the oocyte is characterized by nuclear and cytoplasmic arrest, while the spermatozoa necessitates further maturation within the epididymis and female reproductive track prior to egg fertilization. Either in vivo or in vitro, the sperm initiates a series of irreversible biochemical and physiological modifications in the oocyte. The earliest detected signal after fertilization is cytosolic Ca2+ oscillations, a prerequisite step for embryo development. These oscillations trigger the release of the oocyte from the second meiosis arrest towards embryogenesis, also known as “oocyte activation”. Phospholipase C zeta (PLCζ) is a unique sperm-soluble protein responsible for triggering the InsP3/Ca2+ pathway within the oocyte, leading to Ca2+ oscillations and consequently to embryo development. The specific structure of PLCζ (compared to other PLCs) enables its specialized activity via the preserved X and Y catalytic domains, as well as distinct features such as rapid onset, high sensitivity to Ca2+ and cession of oscillations upon zygote formation. The emerging discoveries of PLCζ have stimulated studies focusing on the possible clinical applications of this protein in male infertility evaluation and management during IVF/ICSI. Fertilization failure is attributed to lack of oocyte second meiosis resumption, suggesting that ICSI failure may be related to impaired PLCζ activity. Microinjection of recombinant human PLCζ to human oocytes after ICSI fertilization failure may trigger Ca2+ oscillations and achieve successful fertilization, offering new hope for couples traditionally referred to sperm donation. However, more studies are still required prior to the routine implementation of this approach in the clinic. Directions for future studies are discussed.  相似文献   

13.
《Theriogenology》2015,84(9):1493-1501
Oocyte aging due to delayed fertilization is associated with declining quality and developmental potential. Intracellular calcium (Ca2+) concentration ([Ca2+]i) regulates oocyte growth, maturation, and fertilization and has also been implicated in aging. Using bovine oocytes, we tested the hypothesis that oocyte aging could be delayed by reducing [Ca2+]i via blocking the influx of extracellular Ca2+ or chelating ooplasmic free Ca2+. After IVM, cumulus–oocyte complexes or denuded oocytes were cultured in medium supplemented with 1-octanol, phorbol 12-myristate 13-acetate, or 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid tetrakis-acetoxymethyl ester (BAPTA-AM) to manipulate [Ca2+]i. Addition of 1-mM 1-octanol increased blastocyst development rates in the cumulus–oocyte complexes aged for 6 hours by IVF and for 6, 12, and 24 hours by parthenoactivation, and this effect was independent of the presence of cumulus cells. The intracellular levels of ATP, Glutathione, and Glutathione disulfide were not affected by 1-octanol, but [Ca2+]i was significantly decreased. When oocytes were cultured in Ca2+-free medium for 12 hours, the blastocyst development rate was greater and the beneficial effects of 1-octanol on oocyte aging were abolished. However, when the medium was supplemented with phorbol 12-myristate 13-acetate, [Ca2+]i increased and the blastocyst development rate decreased. Moreover, BAPTA-AM reduced [Ca2+]i and increased blastocyst development rates after IVF or parthenoactivation. We conclude that the age-associated developmental potency decline was delayed by blocking the influx of extracellular Ca2+ or reducing ooplasmic free Ca2+. 1-Octanol, BAPTA-AM, or Ca2+-free medium could be used to lengthen the fertilization windows of aged bovine oocytes.  相似文献   

14.
 By monitoring 45Ca2+ influx and efflux from oocytes a transient increase followed by a transient decrease in the Ca2+-content of progesterone-treated oocytes was observed. Chelation of intracellular Ca2+ with EGTA or BAPTA-type buffers inhibited progesterone-induced GVBD. Buffers with a mid-range Kd (∼1.5 μm) were most effective in inhibiting GVBD whereas buffers with a Kd above or below this value were less effective. These observations indicate that intracellular Ca2+, probably in the form of a localized release, is required for progesterone-induced oocyte maturation. However, Ca2+ alone was insufficient to induce GVBD. When the effects of nocodazole and taxol upon this Ca2+-requirement were tested, we observed that taxol-induced microtubule polymerization not only delayed progesterone-induced GVBD but also completely inhibited it in combination with BAPTA-AM. Conversely, nocodazole-induced microtubule depolymerization in combination with ionophore A23187 not only accelerated progesterone-induced GVBD, but also induced GVBD in the absence of progesterone. The combined treatment of oocytes with nocodazole and InsP3, or with cold treatment and ionophore A23187 also induced GVBD in the absence of progesterone. Thus, Ca2+ and microtubule depolymerization synergistically promote GVBD. In both nocodazole- and cold-treated oocytes, the GV was displaced to the periphery of the oocyte and underwent GVBD when treated with A23187. However, when the GV was displaced to the cortex by a centrifugal force under conditions that would not cause microtubule depolymerization and the oocyte was treated with A23187, oocytes did not undergo GVBD. Received: 19 January 1996 / Accepted: 21 May 1996  相似文献   

15.
A transient increase in intracellular Ca2+ is the universal signal for egg activation at fertilization. Eggs acquire the ability to mount the specialized fertilization-specific Ca2+ signal during oocyte maturation. The first Ca2+ transient following sperm entry in vertebrate eggs has a slow rising phase followed by a sustained plateau. The molecular determinants of the sustained plateau are poorly understood. We have recently shown that a critical determinant of Ca2+ signaling differentiation during oocyte maturation is internalization of the plasma membrane calcium ATPase (PMCA). PMCA internalization is representative of endocytosis of several integral membrane proteins during oocyte maturation, a requisite process for early embryogenesis. Here we investigate the mechanisms regulating PMCA internalization. To track PMCA trafficking in live cells we cloned a full-length cDNA of Xenopus PMCA1, and show that GFP-tagged PMCA traffics in a similar fashion to endogenous PMCA. Functional data show that MPF activation during oocyte maturation is required for full PMCA internalization. Pharmacological and co-localization studies argue that PMCA is internalized through a lipid raft endocytic pathway. Deletion analysis reveal a requirement for the N-terminal cytoplasmic domain for efficient internalization. Together these studies define the mechanistic requirements for PMCA internalization during oocyte maturation.  相似文献   

16.
Although oocytes from prepubertal animals are found less competent than oocytes from adults, the underlying mechanisms are poorly understood. Using the mouse oocyte model, this paper has tested the hypothesis that the developmental potential of prepubertal oocytes is compromised due mainly to their impaired potential for glutathione synthesis. Oocytes from prepubertal and adult mice, primed with or without eCG, were matured in vitro and assessed for glutathione synthesis potential, oxidative stress, Ca2+ reserves, fertilization and in vitro development potential. In unprimed mice, abilities for glutathione synthesis, activation, male pronuclear formation, blastocyst formation, cortical granule migration and polyspermic block were all compromised significantly in prepubertal compared to adult oocytes. Cysteamine and cystine supplementation to maturation medium significantly promoted oocyte glutathione synthesis and blastocyst development but difference due to maternal age remained. Whereas reactive oxygen species (ROS) levels increased, Ca2+ storage decreased significantly in prepubertal oocytes. Levels of both catalytic and modifier subunits of the γ-glutamylcysteine ligase were significantly lower in prepubertal than in adult oocytes. Maternal eCG priming improved all the parameters and eliminated the age difference. Together, the results have confirmed our hypothesis by showing that prepubertal oocytes have a decreased ability to synthesize glutathione leading to an impaired potential to reduce ROS and to form male pronuclei and blastocysts. The resulting oxidative stress decreases the intracellular Ca2+ store resulting in impaired activation at fertilization, and damages the microfilament network, which affects cortical granule redistribution leading to polyspermy.  相似文献   

17.
Ca2+-sensitive electrodes and the photoproteins obelin and aequorin were used with the oocytes of the anuran Xenopus laevis and the urodeles Ambystoma mexicanum and Pleurodeles waltlii in order to detect any changes in internal free Ca2+ which might result from progesterone or agonist stimulation. A dramatic Ca2+ surge was recorded: from 0.7 × 10?6M in the unstimulated oocyte to 7 × 10?6M after stimulation but before germinal vesicle breakdown (GVBD). Ca2+ efflux was also measured, but it accounted for less than 0.2% of the internal Ca2+ transient; this efflux did not take place in the absence of external calcium. The Ca2+ surge and maturation in response to progesterone, p-hydroxymethylenesulfonate (PHMPS), or Mn2+ occurred normally even when divalent cations were absent from the external medium. In contrast, external divalent cations were necessary for the induction of meiosis and a Ca2+ transient by the K+ ionophore valinomycin. HCO3? also triggers meiosis and causes Ca2+ release, but the release occurs with quite different kinetics. Incompletely grown or seasonally dormant oocytes as well as 10 mM theophilline- or procaine-treated oocytes neither release Ca2+ nor respond to the hormone. We conclude that intracellular released Ca2+ is likely to be the major “second messenger” following hormone stimulation in amphibian oocytes as in starfish.  相似文献   

18.
1-Methyladenine, which has been previously shown to be the hormone responsible for meiosis reinitiation in starfish oocytes, triggers parthenogenetic activation when applied to matured starfish oocytes after emission of the second polar body and formation of the pronucleus. In Marthasterias glacialis and Asterias rubens oocytes parthenogenetic activation includes elevation of a fertilization membrane, cleavage and the formation of normal bipinnaria larvae. Activation is likely to result from 1-methyladenine interaction with the category of stereospecific membrane receptors involved in meiosis reinitiation, since structural requirements of this compound are identical for both biological responses. Appearance of oocyte responsiveness to 1-MeAde after, but not before emission of the second polar body cannot be accounted for by their increased sensitivity to intracellular Ca2+ at that time, although it is shown that Ca2+ mediates hormone effect in inducing parthenogenetic activation. Pretreatment of immature oocytes with the free hormone in excess strongly inhibits the 1-methyladenine-induced parthenogenetic activation of the oocytes when they have completed maturation.It is suggested that reappearance of 1-MeAde sensitivity when oocytes form a pronucleus depends either upon recruitment or new receptor units or on the reactivation of pre-existing inactivated receptors at this stage of oocyte maturation.  相似文献   

19.
The germinal vesicle of mechanically released Chaetopterus oocytes disintegrates in natural sea water (NSW), but not in artificial sea water of normal composition (ASW), calcium-free sea water (CaFSW), magnesium-free sea water (MgFSW) or calcium and magnesium-free sea water (CaMgFSW). Several methods of inducing oocyte maturation using chemically well-defined medium have been established. (1) Germinal vesicle breakdown was induced by the treatment of immature oocytes with KCl (60 mM) in ASW or MgFSW. The presence of Ca2+ is necessary for inducing oocyte maturation with high potassium concentration. “Differentiation without cleavage” was observed after this treatment. (2) Trypsin (0.3%) induced oocyte maturation in ASW, but not in CaFSW. Oocytes matured in this manner developed to trochophores upon insemination. (3) Immature oocytes, treated with isotonic CaCl2 for less than 1 min and then transferred to ASW, underwent germinal vesicle breakdown. The oocytes were arrested at the first meiotic metaphase and upon insemination developed to trochophore larvae. (4) Tetracaine (0.4 mM) induced oocyte maturation in the absence of Ca2+ in the medium. In ASW, CaFSW or CaMgFSW containing the drug, oocytes were arrested at the first meiotic metaphase, while in MgFSW with tetracaine they developed parthenogenetically up to the 4- and 8-cell stages. The role of calcium in oocyte maturation was established and its importance was discussed based on the results obtained with the different ways of inducing oocyte maturation.  相似文献   

20.
Summary Externally applied membrane permeable cAMP derivatives and the injection of cAMP induce oocyte maturation in several species of hydrozoans. This technique for inducing oocyte maturation has been used to study ion permeability changes, maturation promoting factor activity and surface tension changes during maturation. Oocyte membrane potential remains constant during maturation. Cyclic AMP induced maturation proceeds in the absence of external Ca2+, K, Mg2+ or Na+. Cytoplasm from maturing oocytes that induces oocyte maturation when it is injected into untreated oocytes is produced during cAMP induced maturation. Surface tension, as measured by the application of a standardized force that mechanically deforms individual oocytes, declines during the first part of maturation. This is followed by a sharp rise and fall of surface tension at first and second polar body formation that accompanies a slow rise in the resistance of oocytes to deformation during the last part of maturation. The production of maturation promoting factor activity and some of the changes in surface tension during maturation can occur in the absence of germinal vesicle material. Two early developmental events that follow oocyte maturation are the production of sperm chemoattractant and calcium channel function. Neither of these events occurs in eggs that have undergone maturation in the absence of germinal vesicle material. The addition of germinal vesicle contents from oocytes to eggs that have undergone maturation in the absence of germinal vesicle material initiates calcium channel function. This experiment indicates that the germinal vesicle contains factors that are necessary for post-maturation developmental events.  相似文献   

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