Zebrafish cyp11c1 Knockout Reveals the Roles of 11-ketotestosterone and Cortisol in Sexual Development and Reproduction

Endocrinology ◽  
2020 ◽  
Vol 161 (6) ◽  
Author(s):  
Qifeng Zhang ◽  
Ding Ye ◽  
Houpeng Wang ◽  
Yaqing Wang ◽  
Wei Hu ◽  
...  
Keyword(s):  
Sexual Development ◽  
Leydig Cells ◽  
Sex Differentiation ◽  
Germinal Vesicle ◽  
Genital Papilla ◽  
Germinal Vesicle Breakdown ◽  
And Function ◽  
Defective Spermatogenesis

Abstract Androgen is essential for male development and cortisol is involved in reproduction in fishes. However, the in vivo roles of cortisol and specific androgens such as 11-ketotestosterone (11-KT) in reproductive development need to be described with genetic models. Zebrafish cyp11c1 encodes 11β-hydroxylase, which is essential for the biosynthesis of 11-KT and cortisol. In this study, we generated a zebrafish mutant of cyp11c1 (cyp11c1-/-) and utilized it to clarify the roles of 11-KT and cortisol in sexual development and reproduction. The cyp11c1-/- fish had smaller genital papilla and exhibited defective natural mating but possessed mature gametes and were found at a sex ratio comparable to the wildtype control. The cyp11c1-/- males showed delayed and prolonged juvenile ovary-to-testis transition and displayed defective spermatogenesis at adult stage, which could be rescued by treatment with 11-ketoandrostenedione (11-KA) at certain stages. Specifically, during testis development of cyp11c1-/- males, the expression of insl3, cyp17a1, and amh was significantly decreased, suggesting that 11-KT is essential for the development and function of Leydig cells and Sertoli cells. Further, spermatogenesis-related dmrt1 was subsequently downregulated, leading to insufficient spermatogenesis. The cyp11c1-/- females showed a reduction in egg spawning and a failure of in vitro germinal vesicle breakdown, which could be partially rescued by cortisol treatment. Taken together, our study reveals that zebrafish Cyp11c1 is not required for definite sex differentiation but is essential for juvenile ovary-to-testis transition, Leydig cell development, and spermatogenesis in males through 11-KT, and it is also involved in oocyte maturation and ovulation in females through cortisol.

scholarly journals Effects of gonadotrophin in vivo and 2-hydroxyoestradiol-17β in vitro on follicular steroid hormone profile associated with oocyte maturation in the catfish Heteropneustes fossilis

2006 ◽  
Vol 189 (2) ◽  
pp. 341-353 ◽  
Author(s):  
A Mishra ◽  
K P Joy
Keyword(s):  
Oocyte Maturation ◽  
Germinal Vesicle ◽  
Hplc Method ◽  
Heteropneustes Fossilis ◽  
Germinal Vesicle Breakdown ◽  
Steroid Profile ◽  
17 Hydroxyprogesterone ◽  
Envelope Layer

An HPLC method was used to tentatively identify progesterone (P4) and its metabolites (17-hydroxyprogesterone (17-P4) and 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P)), corticosteroids (cortisol and corticosterone) and testosterone in ovary/follicular preparations of the catfish Heteropneustes fossilis associated with in vivo or in vitro oocyte maturation/ovulation. A single i.p. injection of human chorionic gonadotrophin (100 IU/fish, sampled at 0, 8 and 16 h) induced oocyte maturation and ovulation, which coincided with significant and progressive increases in 17,20β-P, and P4 and 17-P4, the precursors of the former. Both cortisol and corticosterone also increased significantly. Conversely, testosterone decreased significantly and progressively over time. Under in vitro conditions, incubation of post-vitellogenic (intact) follicles or follicular envelope (layer) with 2-hydroxyoestradiol (2-OHE2, 5 μM for 0, 6 and 24 h) elicited a sharp significant increase in 17,20β-P, the increase being higher in the follicular envelope incubate. P4 and 17-P4 also registered significant increases over the time with the peak values at 24 h. Cortisol and corticosterone increased significantly in the intact follicle, but not in the follicular envelope incubate. Testosterone decreased significantly in the intact follicle, but increased significantly (24 h) in the follicular envelope incubate. Coincident with these changes, the percentage of germinal vesicle breakdown (GVBD) increased over the time in the intact follicle incubate (48.9% at 6 h and 79.8% at 24 h). Denuded oocytes on incubation with 2-OHE2 (5 μM) did not produce any significant change in the percentage of GVBD or in the steroid profile. While corticosterone and 17,20β-P were undetected, P4, 17-P4, cortisol and testosterone were detected in low amounts. The results show that the 2-OHE2-induced GVBD response seems to be mediated through the production of 17,20β-P and corticosteroids. It is suggested that hydroxyoestrogens seem to be a component in the gonadotrophin cascade of regulation of oocyte maturation/ovulation in the catfish.

scholarly journals Releasing prophase arrest in zebrafish oocyte: synergism between maturational steroid and Igf1

Reproduction ◽  
2016 ◽  
Vol 151 (1) ◽  
pp. 59-72 ◽  
Author(s):  
Debabrata Das ◽  
Soumojit Pal ◽  
Sudipta Maitra
Keyword(s):  
Growth Factor Receptor ◽  
Germinal Vesicle ◽  
Germinal Vesicle Breakdown ◽  
Akt Phosphorylation ◽  
Physiological Relevance ◽  
17Β Estradiol ◽  
Epidermal Growth ◽  
Membrane Progestin Receptor

Binding of 17β-estradiol (E2) to novel G-protein coupled receptor, Gper1, promotes intra-oocyte adenylyl cyclase activity and transactivates epidermal growth factor receptor to ensure prophase-I arrest. Although involvement of either membrane progestin receptor (mPR) or Igf system has been implicated in regulation of meiosis resumption, possibility of concurrent activation and potential synergism between 17α,20β-dihydroxy-4-pregnen-3-one (DHP)- and Igf-mediated signalling cascades in alleviating E2 inhibition of oocyte maturation (OM) has not been investigated. Here using zebrafish (Danio rerio) defolliculated oocytes, we examined the effect of DHP and Igf1, either alone or in combination, in presence or absence of E2, on OM in vitro. While priming of denuded oocytes with E2 blocked spontaneous maturation, co-treatment with DHP (3 nM) and Igf1 (10 nM), but not alone, reversed E2 inhibition and promoted a robust increase in germinal vesicle breakdown (GVBD). Although stimulation with either Igf1 or DHP promoted Akt phosphorylation, pharmacological inhibition of PI3K/Akt signalling prevented Igf1-induced GVBD but delayed DHP action till 4–5 h of incubation. Moreover, high intra-oocyte cAMP attenuates both DHP and Igf1-mediated OM and co-stimulation with DHP and Igf1 could effectively reverse E2 action on PKA phosphorylation. Interestingly, data from in vivo studies reveal that heightened expression of igf1, igf3 transcripts in intact follicles corresponded well with elevated phosphorylation of Igf1r and Akt, mPRa immunoreactivity, PKA inhibition and accelerated GVBD response just prior to ovulation. This indicates potential synergism between maturational steroid and Igf1 which might have physiological relevance in overcoming E2 inhibition of meiosis resumption in zebrafish oocytes.

Antiandrogens as environmental endocrine disruptors¤

1998 ◽  
Vol 10 (1) ◽  
pp. 105 ◽  
Author(s):  
W. R. Kelce ◽  
L. E. Gray ◽  
E. M. Wilson
Keyword(s):  
Androgen Receptor ◽  
Hormone Receptors ◽  
Steroid Hormone ◽  
Sex Differentiation ◽  
Environmental Chemicals ◽  
Steroid Hormone Receptors ◽  
Environmental Endocrine Disruptors ◽  
And Function

Steroid hormone receptors control fundamental events in embryonic development and sex differentiation through their function as ligand-inducible transcription factors. The consequences of disrupting these processes can be especially profound during development due to the crucial role hormones play in controlling transient and irreversible developmental processes. Several environmental chemicals, including metabolites of the fungicide vinclozolin and the pesticide DDT, disrupt male reproductive development and function by inhibiting androgen receptor mediated events. A variety of in vitro and in vivo approaches have been used to determine the molecular basis of environmental antiandrogen toxicity. These chemicals commonly bind androgen receptor with moderate affinity and act as antagonists by inhibiting transcription of androgen dependent genes.

171 IN VIVO AND IN VITRO MATURATION OF WOOD BISON (BISON BISON ATHABASCAE) CUMULUS–OOCYTE COMPLEXES DURING THE OVULATORY SEASON

2014 ◽  
Vol 26 (1) ◽  
pp. 199
Author(s):  
M. P. Cervantes ◽  
M. Anzar ◽  
R. J. Mapletoft ◽  
J. M. Palomino ◽  
G. P. Adams
Keyword(s):  
In Vitro Maturation ◽  
Calf Serum ◽  
Germinal Vesicle ◽  
Bison Bison ◽  
Germinal Vesicle Breakdown ◽  
Cumulus Expansion ◽  
Nuclear Maturation ◽  
Wood Bison

Technologies are being developed to conserve the genetic diversity of wood bison. Knowledge of the characteristics of in vivo and in vitro maturation of the cumulus–oocyte complex (COC) are needed in wood bison to design efficient in vitro embryo production protocols. The objectives were to (1) determine the optimal interval after hCG treatment for in vivo maturation of COC in superstimulated wood bison, and (2) compare the characteristics of COC after in vitro and in vivo maturation. Ovarian synchronization was induced in 25 bison during October and November by giving a luteolytic dose of prostaglandin followed 8 days later by follicular ablation (Day –1). Ovarian superstimulation was induced with FSH (Folltropin-V) given i.m. on Day 0 (300 mg) and Day 2 (100 mg). A second luteolytic dose of prostaglandin was given on Day 3. Bison were assigned randomly to 5 groups (n = 5/group). The COC were collected by transvaginal follicle aspiration on Day 4 and were either assessed immediately (0 h, control), or matured in vitro for 24 or 30 h (in vitro maturation), or collected on Day 5 (in vivo maturation), 24 or 30 h after bison were given 2000 IU of hCG i.m. on Day 4. In vitro maturation was done in TCM-199 with 5% calf serum, 5 μg mL–1 LH, 0.5 μg mL–1 FSH, and 0.05 μg mL–1 gentamicin, at 38.5°C and in a 5% CO2 humidified atmosphere. Nuclear maturation was classified as germinal vesicle (GV), germinal vesicle breakdown (GVBD), metaphase I (MI), or metaphase II (MII) with anti-lamin AC/DAPI staining. Groups were compared by analysis of variance and Fisher's exact test (Table 1). A mean (±s.e.m.) of 7.3 ± 1.7 COC were collected per bison, with no difference among groups. The COC in the control (0 h) group were at the nonexpanded GV stage. Cumulus cells were more expanded after in vivo than in vitro maturation, and the percentage of fully expanded COC was the highest in the 30-h in vivo maturation group (87%; P < 0.05). The greatest number of oocytes reached MII stage after 24 h of in vitro maturation, and 30 h of in vivo maturation. In conclusion, nuclear maturation occurred more quickly in vitro compared with in vivo, but the degree and incidence of cumulus expansion was greater after in vivo maturation. The competence of oocytes to undergo fertilization and develop into embryos remains to be investigated. Table 1.Cumulus expansion and nuclear maturation of wood bison oocytes

Role of follicle wall in meiosis reinitiation induced by insulin in Rana pipiens oocytes

1981 ◽  
Vol 241 (1) ◽  
pp. E51-E56 ◽  
Author(s):  
C. A. Lessman ◽  
A. W. Schuetz
Keyword(s):  
Oocyte Maturation ◽  
Rana Pipiens ◽  
Ovarian Follicle ◽  
Insulin Dose ◽  
Germinal Vesicle ◽  
Complete Removal ◽  
Germinal Vesicle Breakdown ◽  
Maturation In Vitro

The involvement of the ovarian follicle wall in insulin induction of Rana pipiens oocyte maturation in vitro was examined. Complete removal of the follicle wall significantly decreased, but did not obliterate, oocyte maturation (i.e., germinal vesicle breakdown, GVBD) induced by insulin. Dose-response studies of GVBD induction revealed that oocytes within intact follicles were at least 100 times more sensitive to insulin than denuded oocytes. Addition of cyanoketone, a steroid biosynthesis inhibitor, to intact follicles also suppressed insulin-induced GVBD. Inhibitory effects of either follicle wall removal or cyanoketone were not observed when denuded oocytes were treated with progesterone. Addition of either progesterone or pregnenolone to insulin-treated denuded oocytes augmented the oocyte GVBD response compared to either steroid alone and essentially replaced the effect of the follicle wall. In summary, steroidogenesis in the follicle wall appears to be a major factor contributing to the ability of insulin to induce GVBD. However, whether insulin stimulates follicle wall steroidogenesis or simply augments the biological activity of endogenous basal steroid levels is unresolved. The in vitro results show that oocyte maturation can be modulated by the combined actions of several hormones. Such steroid-insulin interactions may also be relevant to understanding the control of oocyte maturation in amphibians and other vertebrates, including mammals, under physiological conditions in vivo.

Effects of follicle-stimulating hormone, bovine somototrophin and okadaic acid on cumulus expansion and nuclear maturation of Blue fox (Alopex lagopus) oocytes in vitro

Zygote ◽  
1998 ◽  
Vol 6 (4) ◽  
pp. 299-309 ◽  
Author(s):  
Vlastimil Sršeň ◽  
Jaroslav Kalous ◽  
Eva Nagyova ◽  
Peter šutovský ◽  
W. Allan King ◽  
...  
Keyword(s):  
Gap Junctions ◽  
Okadaic Acid ◽  
Germinal Vesicle ◽  
Alopex Lagopus ◽  
Germinal Vesicle Breakdown ◽  
Cumulus Expansion ◽  
Corona Radiata ◽  
Blue Fox

The meiotic competence and meiosis resumption of Blue fox (Alopex lagopus) oocytes from anoestrous animals were followed. Oocyte–cumulus complexes (OCC) were cultured in modified TC 199 medium with or without FSH, recombinant bovine somatotrophin (bST) and okadaic acid (OA). The results showed that oocytes less than 100 μm in diameter did not achieve germinal vesicle breakdown (GFBD) by 72 h of culture, which indicates their meiotic incompetence. Oocytes larger than 100 µm in diameter underwent GVBD after 48 h of culture (27%) and reached metaphase II (MII) after 72 and 96 h (20% and 27%) in control medium. Both bST and OA accelerated resumption of meiosis (bST: 55% GVBD and 42% MII after 48 h; OA: 66% GVBD after 18 h). In contrast, FSH significantly reduced meiosis resumption (only 3% GVBD and MII after 72 h) and induced changes in the shape of cumulus granulosa (CG) cells and F-actin assembly typical for cumulus expansion. However, the innermost layers of CG cells (corona radiata) remained connected with the oocyte via gap junctions until the end of culture. Cumuli of oocytes cultured in control, bST-supplemented or OA-supplemented medium did not expand (changes in cell shape and F-actin redistribution did not occur). Moreover, especially in media with bST and OA an increased detachment and rapid disconnection of their gap junctions with the oocyte were observed. These results suggest that under in vitro conditions FSH stimulates expansion of the CG cells and the attached membrana granulosa cells but in contrast it secures heterologous gap junctions between cytoplasmic processes of the corona radiata cells and oolemma during 3 days of culture. Thus, in agreement with the in vivo situation in which Canidae oocytes are ovulated in the GV stage, the cumulus, mainly corona radiata cells, controls resumption of meiosis in Blue fox oocytes under in vitro conditions also.

scholarly journals Host cell factors controlling vimentin organization in the Xenopus oocyte.

1992 ◽  
Vol 119 (4) ◽  
pp. 855-866 ◽  
Author(s):  
J A Dent ◽  
R B Cary ◽  
J B Bachant ◽  
A Domingo ◽  
M W Klymkowsky
Keyword(s):  
Direct Interaction ◽  
Germinal Vesicle ◽  
Germinal Vesicle Breakdown ◽  
Head Domain ◽  
M Phase ◽  
Filament Bundles ◽  
Keratin Filament ◽  
Vimentin Filaments

To study vimentin filament organization in vivo we injected Xenopus oocytes, which have no significant vimentin system of their own, with in vitro-synthesized RNAs encoding Xenopus vimentins. Exogenous vimentins were localized primarily to the cytoplasmic surface of the nucleus and to the subplasma membrane "cortex." In the cortex of the animal hemisphere, wild-type vimentin forms punctate structures and short filaments. In contrast, long anastomosing vimentin filaments are formed in the vegetal hemisphere cortex. This asymmetry in the organization of exogenous vimentin is similar to that of the endogenous keratin system (Klymkowsky, M. W., L. A. Maynell, and A. G. Polson. 1987. Development (Camb.). 100:543-557), which suggests that the same cellular factors are responsible for both. Before germinal vesicle breakdown, in the initial stage of oocyte maturation, large vimentin and keratin filament bundles appear in the animal hemisphere. As maturation proceeds, keratin filaments fragment into soluble oligomers (Klymkowsky, M. W., L. A. Maynell, and C. Nislow. 1991. J. Cell Biol. 114:787-797), while vimentin filaments remain intact and vimentin is hyperphosphorylated. To examine the role of MPF kinase in the M-phase reorganization of vimentin we deleted the conserved proline of vimentin's single MPF-kinase site; this mutation had no apparent effect on the prophase or M-phase behavior of vimentin. In contrast, deletion of amino acids 19-68 or 18-61 of the NH2-terminal "head" domain produced proteins that formed extended filaments in the animal hemisphere of the prophase oocyte. We suggest that the animal hemisphere cortex of the prophase oocyte contains a factor that actively suppresses the formation of extended vimentin filaments through a direct interaction with vimentin's head domain. During maturation this "suppressor of extended filaments" appears to be inactivated, leading to the formation of an extended vimentin filament system.

scholarly journals Molecular cloning of an amphibian insulin receptor substrate 1-like cDNA and involvement of phosphatidylinositol 3-kinase in insulin-induced Xenopus oocyte maturation.

1995 ◽  
Vol 15 (7) ◽  
pp. 3563-3570 ◽  
Author(s):  
X J Liu ◽  
A Sorisky ◽  
L Zhu ◽  
T Pawson
Keyword(s):  
Insulin Receptor ◽  
Oocyte Maturation ◽  
Xenopus Oocytes ◽  
Germinal Vesicle ◽  
Insulin Receptor Substrate ◽  
Phosphorylation Sites ◽  
Glutathione S Transferase ◽  
Germinal Vesicle Breakdown

An insulin receptor substrate 1 (IRS-1)-like cDNA was isolated from a Xenopus ovary cDNA library by low-stringency hybridization using rat IRS-1 cDNA as a probe. The deduced amino acid sequence encoded by this cDNA (termed XIRS-L) is 67% identical (77% similar) to that of rat IRS-1. Significantly, all the insulin-induced tyrosine phosphorylation sites identified in rat IRS-1, including those responsible for binding to the Src homology domains of phosphatidylinositol (PI) 3-kinase, Syp and Grb2, are conserved in XIRS-L. Both mRNA and protein corresponding to the cloned XIRS-L can be detected in immature Xenopus oocytes. Recombinant XIRS-L protein produced in insect cells or a bacterial glutathione S-transferase fusion protein containing the putative PI 3-kinase binding site can be phosphorylated in vitro by purified insulin receptor kinase (IRK) domain, and the IRK-catalyzed phosphorylation renders both proteins capable of binding PI 3-kinase in Xenopus oocyte lysates. Another glutathione S-transferase fusion protein containing the C terminus of XIRS-L and including several putative tyrosine phosphorylation sites is also phosphorylated by IRK in vitro, but it failed to bind PI 3-kinase. Insulin stimulation of immature Xenopus oocytes activates PI 3-kinase in vivo [as indicated by an elevation of PI(3,4)P2 and PI(3,4,5)P3] as well as oocyte maturation (as indicated by germinal vesicle breakdown). Pretreatment of these oocytes with wortmannin inhibited insulin-induced activation of PI 3-kinase in vivo. The same treatment also abolished insulin-induced, but not progesterone-induced, germinal vesicle breakdown. These results (i) identify an IRS-1-like molecule in immature Xenopus oocytes, suggesting that the use of IRS-1-like Scr homology 2 domain-docking proteins in signal transduction is conserved in vertebrates, and (ii) strongly implicate PI 3-kinase as an essential effector of insulin-induced oocyte maturation.

scholarly journals The capability of reprogramming the male chromatin after fertilization is dependent on the quality of oocyte maturation

Reproduction ◽  
2005 ◽  
Vol 130 (1) ◽  
pp. 29-39 ◽  
Author(s):  
Luisa Gioia ◽  
Barbara Barboni ◽  
Maura Turriani ◽  
Giulia Capacchietti ◽  
Maria Gabriella Pistilli ◽  
...  
Keyword(s):  
Dna Methylation ◽  
Histone Acetylation ◽  
Hdac Inhibitors ◽  
Germinal Vesicle ◽  
Fertilization Rate ◽  
Sperm Nucleus ◽  
Sperm Chromatin ◽  
Germinal Vesicle Breakdown

The present experiments compared the ability of pig oocytes matured eitherin vivoorin vitroto structurally reorganize the penetrated sperm chromatin into male pronucleus (PN) and to carry out, in parallel, the epigenetic processes of global chromatin methylation and acetylation, 12–14 h afterin vitrofertilization (IVF). In addition, PN distribution of histone deacetylase (HDAC), a major enzyme interfacing DNA methylation and histone acetylation, was investigated. The ability of the oocyte to operate an efficient block to polyspermy was markedly affected by maturation. The monospermic fertilization rate was significantly higher forin vivothan forin vitromatured (IVM) oocytes(P< 0.01) which, furthermore, showed a reduced ability to transform the chromatin of penetrated sperm into male PN(P< 0.01). Indirect immunofluorescence analysis of global DNA methylation, histone acetylation and HDAC distribution (HDAC-1, -2 and -3), carried out in monospermic zygotes that reached the late PN stage, showed that IVM oocytes also had a reduced epigenetic competence. In fact, while in about 80% ofin vivomatured and IVF oocytes the male PN underwent a process of active demethylation and showed a condition of histone H4 hyperacetylation, only 40% of IVM/IVF zygotes displayed a similar PN remodelling asymmetry. Oocytes that carried out the first part of maturationin vivo(up to germinal vesicle breakdown; GVBD) and then completed the processin vitro, displayed the same PN asymmetry as oocytes matured entirelyin vivo. A crucial role of HDAC in the establishment of PN acetylation asymmetry seems to be confirmed by the use of HDAC inhibitors as well as by the abnormal distribution of the enzyme between the two PN in IVM zygotes. Collectively, these data demonstrated that some pig IVM oocytes fail to acquire full remodelling competence which is independent from their ooplasmic ability to morphologically reorganize the sperm nucleus into PN.

Cortical granules of the sea urchin translocate early in oocyte maturation

Development ◽  
1997 ◽  
Vol 124 (9) ◽  
pp. 1845-1850
Author(s):  
L.K. Berg ◽  
G.M. Wessel
Keyword(s):  
Cell Surface ◽  
Sea Urchin ◽  
Oocyte Maturation ◽  
Germinal Vesicle ◽  
Cortical Granule ◽  
Ionophore A23187 ◽  
Cortical Granules ◽  
Germinal Vesicle Breakdown

Cortical granules are secretory vesicles poised at the cortex of an egg that, upon stimulation by sperm contact at fertilization, secrete their contents. These contents modify the extracellular environment and block additional sperm from reaching the egg. The role of cortical granules in blocking polyspermy is conserved throughout much of phylogeny. In the sea urchin, cortical granules accumulate throughout the cytoplasm during oogenesis, but in mature eggs the cortical granules are attached to the plasma membrane, having translocated to the cortex at some earlier time. To study the process of cortical granule translocation to the cell surface we have devised a procedure for maturation of sea urchin oocytes in vitro. Using this procedure, we examined the rate of oocyte maturation by observing the movement and breakdown of the germinal vesicle, the formation of polar bodies and the formation of the egg pronucleus. We find that oocyte maturation takes approximately 9 hours in the species used here (Lytechinus variegatus), from the earliest indication of maturation (germinal vesicle movement) to formation of a distinct pronucleus. We then observed the translocation of cortical granules in these cells by immunolocalization using a monoclonal antibody to hyalin, a protein packaged specifically in cortical granules. We found that the translocation of cortical granules in in vitro-matured oocytes begins with the movement of the germinal vesicle to the oocyte cell surface, and is 50% complete 1 hour after germinal vesicle breakdown. In the in vitro-matured egg, 99% of the cortical granules are at the cortex, indistinguishable from translocation in oocytes that mature in vivo. We have also found that eggs that mature in vitro are functionally identical to eggs that mature in vivo by four criteria. (1) The matured cells undergo a selective turnover of mRNA encoding cortical granule contents. (2) The newly formed pronucleus begins transcription of histone messages. (3) Cortical granules that translocate in vitro are capable of exocytosis upon activation by the calcium ionophore, A23187. (4) The mature egg is fertilizable and undergoes normal cleavage and development. In vitro oocyte maturation enables us to examine the mechanism of cortical granule translocation and other processes that had previously only been observed in static sections of fixed ovaries.

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