1,721,036 research outputs found
Characteristics of receptors for prostaglandin F-2 alpha in bovine and equine corpora lutea.
No full textMATERNAL CHROMATIN REMODELLING DURING MATURATION AND AFTER FERTILIZATION IN MOUSE OOCYTES
No full textImmunofluorescence staining with antibodies against acetylated histone H4 and 5-methylcytosine was carried out to investigate female chromatin remodelling throughout oocyte maturation and chromatin rearrangement involving both male and female genomes after fertilization. Oocyte cytoplasm remodels female chromatin in preparation of the fertilizing event and the subsequent chromatin rearrangement. Histone H4 are in fact progressively deacetylated whereas demethylating enzymes do not seem to be active over this period. The acetylase/deacetylase balance seems to be cell cycle dependent as female chromatin is deacetylated during maturation and reacetylated at telophase II stage both after fertilization and activation. On the contrary, DNA demethylation seems to be strictly selective. It is in fact confined to the remodelling of paternal genome after fertilization of mature oocytes as the ooplasm is not effective in demethylating either paternal chromatin in GVBD fertilized oocytes or maternal genome of partenogenetically activated oocytes. Surprisingly we induced maternal chromatin demethylation after fertilization by treating oocytes with a combination of a methyltransferase inhibitor, 5-Azacytidine (5-AzaC), and a reversible and specific inhibitor of histone deacetylase, Trichostatin A (TSA). This treatment likely induces a hyperacetylation of histones (thus favouring the access to demethylating enzymes by opening female chromatin structure) associated with a block of reparative methylation by inhibiting methytransferases. This manipulation of chromatin remodelling may have applications regarding the biological significance of aberrant DNA methylation.[...
Effect of follicle somatic cells during pig oocyte maturation on egg penetrability and male pronucleus formation
No full textInfluence of progesterone on boar sperm capacitation
No full textThis research investigates the effect of progesterone (P-4) on boar sperm capacitation. Ejaculated spermatozoa were washed and incubated under capacitating conditions with or without P-4. At different times of incubation samples of sperm were exposed to solubilized zonae pellucidae (ZP) and the degree of capacitation was evaluated by the incidence of zona-induced acrosome reaction (AR). The status of the acrosome was studied by using an FITC-conjugated lectin (Pisum sativum agglutinin; FITC-PSA). The effect of P-4 on the fertilizing ability of semen was then evaluated in an in vitro fertilization system by exposing in vitro matured oocytes to sperm preincubated for 2 or 4 h with or without P-4, under capacitating conditions. PSA staining showed that P-4 does not affect the incidence of spontaneous AR. By contrast, spermatozoa incubated with P-4 showed a higher percentage of AR than controls after the exposure to solubilized ZP. This enhanced reactivity to ZP suggests a direct effect of P-4 on sperm capacitation. The in vitro fertilization assay was consistent with these results demonstrating a higher fertilizing ability in sperm preincubated with P-4 than in controls while the steroid was without effect when added only during the fertilization step. These results demonstrate that P-4 improves the fertilizing ability of boar semen essentially by facilitating the process of capacitation.[...
Luteinizing hormone inhibits potassium outward currents in swine granulosa cells by intracellular calcium mobilization
No full textPotassium currents of swine granulosa cells were studied using the patch clamp technique in the whole cell configuration. Granulosa cells stepped to positive potentials (+60 mV) from -40 mV holding potential exhibit a slowly activating, noninactivating outward potassium current. Tail current reverse potential (between -90 and -100 mV) and the current inhibition brought about by the replacement of KCl with CsCl in the pipette solution indicate that this current is carried by K ions. LH was found to significantly reduce the amplitude of this current. The effect was dose and time dependent. Similar inhibition (20-30% of the initial current) was reached with doses of 1-50-mu-g/ml, but in times proportionally shorter as the dose increased (50% inhibition was reached in 170-180 and 30-40 sec with 1 and 50-mu-g LH/ml, respectively). Much longer and variable times (3-10 min) were required with lower doses (0.2-mu-g/ml). The effect of LH was independent of extracellular Ca, while preexposure of cells to TMB-8, an inhibitor of intracellular Ca mobilization, completely prevented the effect of LH. Outward currents after LH treatment could be completely restored by perfusing the cells with ionomycin in Ca-free medium to facilitate calcium efflux from the cells. The present studies indicate that LH modifies the bioelectrical properties of swine granulosa cells. This effect is mediated by an elevation of intracellular calcium, probably mobilized from intracellular stores. The induced changes in K conductance may play a specific role in the transduction mechanisms for LH.[...
Follicular factors influence oocyte fertilizability by modulating the intercellular cooperation between cumulus cells and oocyte
No full textMaturation of pig oocytes: observations on membrane potential.
No full textThe membrane-potential changes of pig oocytes during maturation are described. Cumulus-enclosed oocytes have a restingpotential of -41.81 ± 0.60 my; the removal of cumulus cells caused this potential to drop to -30.95 ± 0A3 my. Adding LHto the culture medium did not influence the potential of denuded oocytes but depolarized the potential of cumulus-enclosedoocytes to -32.90 ± 0.43 mY. FSH did not affect the membrane potential of denuded or cumulus-enclosed oocytes, but significantly reduced the amplitude of the depolarization induced by LH. The effect of gonadotropins on cultured granulosa cells wasalso investigated. Plated granulosa cells have a resting potential of -45.21 ± 0.72 mV, similar to that of cumulus-enclosed oocytes.As recorded in cumulus-enclosed oocytes, LII depolarized granulosa cell membrane potential (-30.33 ± 0.69 mY) and FSHreduced this effect. To evaluate if oocyte maturation in vivo is accompanied by membrane-potential depolarization, folliculargrowth and oocyte maturation were induced in 6 prepubertal gilts by using an eCG-hCG treatment. Twenty hours after thebeginning of oocyte maturation in vivo (induced by hCG), the membrane potential of the oocyte was depolarized to -28.84 ±1.01 mV, a value similar to that observed in vitro.These data indicate that both LB and FSH can influence the membrane potential of fofficular somatic cells and, consequently,that of the oocyte. The electrical coupling between somatic cell and oocyteoocyte. The electrical coupling between somatic cell and oocyte may represent a means by which the gonadotropinmessage is passed to the genninal cell by the somatic compartment.[...
Concentration of cyclic AMP during the maturation of pig oocytes in vivo and in vitro
No full textIntracellular concentrations of cyclic AMP (cAMP) were measured in pig oocytes maturing in vivo or in vitro. Maturation in vivo was induced with 500 iu hCG administered to gilts treated with pregnant mares' serum gonadotrophin (PMSG). Although PMSG did not affect cAMP concentrations (basal values, 1.69 +/- 0.28 fmol per oocyte), hCG induced a transient rise (8.86 +/- 1.15 fmol per oocyte 12 h after hCG injection). Similarly, the cAMP concentration rose in oocytes maturing in vitro if the oocytes (surrounded or not by cumulus cells) were co-cultured with the follicle wall in the presence of LH. The same increase in cAMP was obtained when denuded oocytes were co-cultured with mural granulosa cells. Theca cells exhibited only a moderate activity, while cumulus cells were totally ineffective. Granulosa cells exposed to LH lost their stimulating influence after 24 h of culture. In the presence of FSH, cAMP production by the oocyte was unaffected by any type of follicle cell. The role of cAMP in the control of oocyte maturation was investigated using dibutyryl cAMP. The presence of dibutyryl cAMP prevented the resumption of meiosis in a dose-dependent manner, but when it was present during the first 12 h of culture only, meiotic progression was accelerated (0 versus 47% of oocytes had germinal vesicles in groups treated with dibutyryl cAMP and control groups, respectively, after 24 h of culture). The results demonstrate that: (i) cAMP concentrations increase transiently in oocytes before the resumption of meiosis; (ii) increased concentrations of cAMP depend on the stimulation of oocyte adenylyl cyclase, possibly by a soluble factor produced by follicle cells exposed to LH; (iii) the increase in cAMP is probably confined to the first 10-20 h of maturation owing to the progressive reduction of the stimulating influence of LH-treated somatic cells; and (iv) a high concentration of cAMP throughout maturation maintains meiotic arrest and a transient increase may facilitate meiosis.[...
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