Epigenetic regulation of folate receptor-α (FOLR1) in human placenta of preterm newborns

INTRODUCTION

Folates are essential nutrients for fetal development and pregnancy outcomes; they are transported to the fetus during gestation through specific folate transporters located in the placenta. In preterm newborns, we previously showed a lower placental mRNA expression of FOLR1 along with higher folate and lower vitamin B12 cord blood levels. Thereby we aimed to explore FOLR1 methylation in placentas of preterm newborns and hypothesized an increased FOLR1 methylation associated with cord blood folates and vitamin B12 concentrations.

METHODS

FOLR1 methylation and mRNA were determined by methylation sensitive - high resolution melting (MS-HRM) and by real-time PCR respectively, in two placental sides of placental tissues: maternal (basal, BP) and fetal plates (chorionic, CP) of moderate preterm infants (32-36 gestational age) and term birth (37-41 gestational weeks). Folates and vitamin B12 were determined by electrochemiluminescence in umbilical cord blood samples from term and preterm newborns.

RESULTS

We found that in preterm newborns, FOLR1 mRNA was lower in both plates of placenta compared with term newborns (p < 0,05) and was negatively associated with methylation of FOLR1 in CP. Preterm newborns presented higher folate and lower vitB12 concentrations in cord blood which correlated with increased placental FOLR1 methylation.

DISCUSSION

In preterm newborns, placental FOLR1 expression is regulated by epigenetic mechanisms and presumably by maternal concentrations of folate and vitamin B12.

Cadmium exposure during pregnancy reduces birth weight and increases maternal and foetal glucocorticoids

Cadmium exposure induces low birth weight through unknown mechanisms. Since low birth weight is associated to foetal exposure to high glucocorticoids (GC) concentrations, we hypothesized that low birth weight induced by prenatal exposure to Cd(2+) is, at least in part, mediated by higher foetal exposure to GC, specifically corticosterone, the main active GC in rodents. Pregnant rats were exposed to different dose of CdCl(2) administered in drinking water during the whole pregnancy period. At term, corticosterone was measured by enzyme immunoassay in maternal and foetal blood and in placental tissues. Cadmium was determined in placentas, maternal tissues (liver and kidney) and foetuses by inductively coupled plasma-mass spectrometry (ICP-MS). Placental 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) activity and expression were determined by a radiometric conversion assay and quantitative RT-PCR respectively. Results demonstrated that 50 ppm of Cd(2+), which was accumulated in different maternal tissues but not in the foetus, reduced pup birth weights and increased plasma corticosterone concentrations, both in mother and foetus. Placental 11beta-HSD2 activity and expression did not change by the treatment. We conclude that 50 ppm of Cd(2+) administered during pregnancy, increase foetal corticosterone concentrations due, probably, to alterations of the regulatory mechanisms of placental barrier to GC causing a mild but significant reduced birth weight.

Arachidonic acid release from rat Leydig cells: the involvement of G protein, phospholipase A2 and regulation of cAMP production

We have previously demonstrated that the release of arachidonic acid (AA) from human chorionic gonadotropin (hCG)-stimulated Leydig cells occurs in a dose- and time-dependent manner. In addition, the amount of AA released was dependent on the hormone-receptor interaction and the concentration of LH-hCG binding sites on the cell surface. The present study was conducted to evaluate the involvement of phospholipase A(2) (PLA(2)) and G proteins in AA release from hormonally stimulated rat Leydig cells, and the possible role of this fatty acid in cAMP production. Cells were first prelabelled with [(14)C]AA to incorporate the fatty acid into cell phospholipids, and then treated in different ways to evaluate AA release. hCG (25 mIU) increased the release of AA to 180+/-12% when compared with AA released from control cells, arbitrarily set as 100%. Mepacrine and parabromophenacyl bromide (pBpB), two PLA(2) inhibitors, decreased the hormone-stimulated AA release to 85+/-9 and 70+/-24% respectively. Conversely, melittin, a PLA(2) stimulator, increased the release of AA up to 200% over control. The inhibitory effect of mepacrine on the release of AA was evident in hCG-treated Leydig cells, but not in the melittin-treated cells. To determine if the release of AA was also mediated through a G protein, cells were first permeabilized and subsequently treated with pertussis toxin or GTPgammaS, a non-hydrolyzable analog of GTP. Results demonstrate that GTPgammaS was able to induce a similar level of the release of AA as hCG. In addition, pertussis toxin completely abolished the stimulatory effect of hCG on the release of AA, indicating that a member of the G(i) family was involved in the hCG-dependent release of AA. Cells treated with PLA(2) inhibitors did not modify cAMP production, but exogenously added AA significantly reduced cAMP production from hCG-treated Leydig cells, in a manner dependent on the concentration of AA and hCG. Results presented here suggest an involvement of PLA(2) and G proteins in the release of AA from hCG-stimulated Leydig cells, and under particular conditions, regulation of cAMP production by this fatty acid in these cells.

Effect of human chorionic gonadotropin derivatives on leydig cell function

BACKGROUND

Several human chorionic gonadotropin (hCG) derivatives have been detected in healthy human subjects, indicating that they may play a role in cell function. These hCG derivatives include deglycosylated hCG, proteolytic digestion products of hCG and free alpha and beta subunits of the hormone. It is well documented that testicular Leydig cells are responsive to luteinising hormone (LH) or its analogue hCG. These hormones have high affinity for LH/hCG receptors on the plasma membrane.

METHODS

We designed functional and binding studies to compare the effects of native hCG and several hCG derivatives on a rat Leydig cell system. The molecular weight of the hCG derivatives was determined by SDS-PAGE and the binding affinity to LH/hCG receptors was measured by a radioligand assay. In addition, their ability to produce testosterone, cyclic AMP and arachidonic acid release was also studied.

RESULTS

These hCG derivatives, with the exception of the free beta subunit, were able to bind to LH/hCG plasma membrane receptors with different affinities than that of native hCG. In addition, hCG derivatives did not increase intracellular cAMP levels or arachidonic acid release. However, they did increase testosterone production.

CONCLUSION

Taken together, the results of this study lead us to suggest that these hCG derivatives may regulate the action of the native hormone in Leydig cells and are, thus, molecules of physiological relevance.

Detection of progesterone receptors in human spermatozoa and their correlation with morphological and functional properties

In previous reports, it has been demonstrated that progesterone (P) stimulates capacitation, hyperactivation of human sperm motility and initiates the acrosome reaction (AR). This last effect has been related to the presence of non-genomic receptors for the steroid, localized on the sperm head plasma membrane. These receptors can be detected after treating spermatozoa with the non-permeable conjugate Progesterone - 3-(O-carboxymethyl) oxime: bovine serum albumin-fluorescein isothiocyanate (P-BSA-FITC). In the present study, the presence of progesterone receptors was determined in a selected sperm population with normal morphology and high progressive motility. In addition, other parameters such as the AR, hypo-osmotic swelling test, stability of chromatin and capacitating effect of P were evaluated. The percentage of P-BSA-FITC positive-spermatozoa present in the selected sperm population was higher than in total seminal spermatozoa. Furthermore, spermatozoa incubated with P showed a higher percentage motility and AR than did control spermatozoa. The HOS test indicated that membrane integrity of P-treated spermatozoa was not different to that found in the control sperm suspensions. Unexpectedly, the total sperm population treated with P showed a marked susceptibility to nuclear decondensation with reducing agents. According to these results, the selected sperm population of this study, able to respond to P, may be similar to that with good motility and normal morphology selected in the female reproductive tract, before fertilization.

Hamster sperm glycine receptor: evidence for its presence and involvement in the acrosome reaction

Recent reports have provided evidence for the presence of amino acid neurotransmitter receptor/chloride channels in human and porcine spermatozoa and their involvement in the acrosome reaction (AR). In this work we investigated whether a glycine receptor (GlyR) was present in golden hamster sperm, and whether it had a role in the hamster AR. The neuronal GlyR agonist glycine, stimulated in a dose-dependent manner, the AR of hamster spermatozoa previously capacitated for at least 3 hr. This stimulation was completely inhibited by 50 microM (+)-bicuculline and by concentrations of strychnine as low as 10-50 nM; both agents are antagonists of neuronal GlyR when used at the concentrations reported in this study. beta-Alanine, another agonist of the neuronal GlyR, also stimulated the AR. The AR-stimulatory effect of this compound was completely abolished by 50 nM strychnine. The inhibitory effect of strychnine on the glycine-induced hamster sperm AR was completely overcome by subsequent treatment with the calcium ionophore ionomycin, demonstrating that the strychnine effect was specific for GlyR. Additional binding studies with (3)[H]-strychnine, the typical radioligand used to detect GlyR in several cells, demonstrated for the first time the presence of specific binding sites for strychnine in the hamster spermatozoa. Interestingly, binding increased during in vitro capacitation, particularly in those sperm suspensions showing high percentages of AR. Taken together these results strongly suggest the presence of a GlyR in the hamster spermatozoa, with a role in the AR when activated.

Thapsigargin stimulates acrosomal exocytosis in hamster spermatozoa

Thapsigargin (TG), a plant-derived sesquiterpene lactone, inhibits several isoforms of both the sarcoplasmic and endoplasmic reticulum Ca2+-ATPases. Thus, intracellular Ca2+ stores found in the endoplasmic reticulum can be released by this compound. The mammalian sperm acrosome reaction (AR) depends on influx of extracellular Ca2+. However, few reports have presented evidence for the involvement of putative Ca2+ stores and intracellular Ca2+ mobilization in the AR. Thus, we designed experiments to evaluate the effect of TG on the hamster sperm AR. Thapsigargin stimulated-in a dose-dependent manner-the AR of spermatozoa previously capacitated for at least 3 hr, not affecting sperm motility. A maximal stimulatory effect was apparent 3 min after addition of TG to spermatozoa previously capacitated for 4 hr and was dependent on external Ca2+ since ethyleneglycol-bis-(b-amino-ethyl ether) N,N'-tetra-acetic acid added 1 min before TG completely inhibited AR stimulation. The Ca2+ channel blockers diltiazem and nifedipine also abolished the TG-stimulatory effect when added to capacitated spermatozoa 10 min before the inhibitor. In addition, the trypsin inhibitors p-nitrophenyl-p'-guanidine-benzoate hydrochloride and benzamidine added to the sperm suspensions 10 min before TG inhibited by 70-80% the TG-induced AR. These results indicate that putative Ca2+ stores release may be involved in stimulation of extracellular Ca2+ influx required for the occurrence of the AR. In addition, a sperm trypsin-like protease may be part of the mechanism by which TG induces the hamster sperm AR.

Arachidonic acid release from rat Leydig cells depends on the presence of luteinizing hormone/human chorionic gonadotrophin receptors

In this work, the involvement of arachidonic acid (AA) in the luteinizing hormone and human chorionic gonadotrophin (LH/hCG) action on Leydig cells was studied. Experiments were first designed to evaluate [14C]AA incorporation into membrane phospholipids. Subsequently, time-course, pulse-chase and dose-response studies of the effect of hCG on [14C]AA release were performed. Results indicated that 4 h was optimal for maximal incorporation of [14C]AA into membrane phospholipids of viable Leydig cells. Pulse-chase experiments and studies performed to evaluate the effect of different doses of hCG on [14C]AA release demonstrated that this hormone stimulates [14C]AA release in a dose-response and time-dependent manner. Furthermore, using a desensitised animal model, a link between the presence of LH/hCG receptors and LH/hCG-stimulated [14C]AA release in Leydig cells could be established. In fact, the amount of [14C]AA released was significantly dependent on, and directly proportional to, the concentration of LH/hCG binding sites. Thus [14C]AA released from intact rat Leydig cells decreased when animals had been previously injected with a high single dose of hCG (desensitised animals), which is known to cause a dramatic decrease in the number of LH/hCG binding sites. These results demonstrate that the mechanism of AA release in Leydig cells depends on LH/hCG-receptor interaction and also suggest that AA could act as an additional intracellular messenger associated with the hormonal action of LH/hCG.

Studies related to progesterone-induced hamster sperm acrosome reaction

Experiments were designed to characterize the effect of progesterone on the hamster sperm acrosome reaction (AR). Progesterone stimulated exocytosis of previously capacitated spermatozoa in a dose-dependent manner. Progesterone-3-(O-carboxymethyl)oxime:BSA conjugate also induced AR when added to capacitated sperm suspensions. EGTA and La3+, added 10 min before progesterone, completely abolished the steroid-stimulatory effect. Benzamidine, a trypsin inhibitor, also inhibited AR when added to sperm cells 10 min before progesterone. This effect was avoided when spermatozoa were treated with the Ca2+ ionophore ionomycin. Conversely, the H+ ionophore FCCP, or the Na+/K+ ionophore nigericin, did not prevent the effect of the inhibitor. Results suggest that progesterone acts on the hamster sperm plasma membrane to stimulate exocytosis, which requires external Ca2+ and presumably Ca2+ influx. In addition, a sperm trypsin-like protease may be part of the mechanism by which progesterone stimulates AR. Since the ionomycin-induced AR does not require this proteolytic activity, the possible involvement of such an enzyme in the progesterone-stimulated Ca2+ influx necessary for the occurrence of AR is discussed.

Sperm phospholipid methyltransferase activity during preparation for exocytosis

The present report describes experiments to evaluate phospholipid methyltransferase activity in golden hamster spermatozoa incubated under different conditions. Washed cauda epididymal sperm were incubated with taurine, in the presence or absence of epinephrine. At various times, the sperm were separated, and phospholipid methyltransferase activity measured. Also, at each time, aliquots of the sperm suspension were assayed for motility, and acrosome reactions. Some sperm incubated in the presence of taurine and epinephrine were capacitated by 3.5 h, because about 40 per cent of them can undergo the acrosome reaction 10 min after addition of the fusogen lysophosphatidylcholine. In epinephrine-free incubations the fusogen failed to stimulate acrosome reactions. On the other hand, epinephrine stimulated by twofold phospholipid methyltransferase activity from '0 time' incubated sperm, in comparison to that observed in taurine-treated cells. Enzyme activities from both taurine or epinephrine plus taurine-treated cells decreased as the incubation time of the sperm suspension increased. Kinetic properties of the sperm phospholipid methyltransferase activity were modified by the presence of taurine and epinephrine when S-adenosylmethionine was used as the substrate. These results suggest that refined molecular events occur in the sperm cell during the acquisition of fertilizing ability.

Evidence in support of a role for Ca(2+)-activated K+ channels in the hamster sperm acrosome reaction

The sperm acrosome reaction (AR) is a crucial step for mammalian fertilization. This work describes experiments to test the effect of the cesium ion (Cs+) and charybdotoxin (ChTX) on the Ca2+ or Na+/K+ ionophores stimulated hamster sperm AR in vitro. Cs+ and ChTX, a polypeptide toxin from the venom of the scorpion Leirus quinquestriatus, are considered blockers of Ca(2+)-activated K+ channels in several somatic cells. Both agents inhibited the AR by 55-66%. The inhibition was completely reversed by the Na+/K+ ionophore nigericin, but not by the Ca2+ ionophore A-23187. Results give evidence in support of a role for Ca(2+)-activated K+ channels in K+ influx required for the occurrence of the hamster sperm acrosome reaction.

Evidences for the presence of chymotrypsin-like activity in human spermatozoa with a role in the acrosome reaction

The effect of chymotrypsin inhibitors and substrates on the human sperm acrosome reaction stimulated by the human zonae pellucidae or follicular fluid were evaluated. Motile spermatozoa, selected by a Percoll gradient, were incubated at 1 x 10(7) cells/ml, 37 degrees C, and 5% CO2. After 4.5 hr, the chymotrypsin inhibitor TPCK (N-Tosyl-L-Phenylalanine-Chloromethyl Ketone) or the substrate ATEE (N-Acetyl-L-Tyrosine Ethyl Ester) were added for 30 min. Then, four oocytes were added and the percentage of acrosome-reacted spermatozoa on the zona was determined. TPCK and ATEE inhibited the zona pellucida-induced acrosome reaction. The chymotrypsin inhibitors TPCK and chymostatin and the chymotrypsin substrates ATEE, BTEE (N-Benzoyl-L-Tyrosine Ethyl Ester), Succinyl-Ala-Ala-Phe-7-Amido-4-Methyl-Coumarin (Suc-Ala-Ala-Phe-AMC), and Succinyl-Leu-Leu-Val-Tyr-7-Amido-4-Methyl-Coumarin (Suc-Leu-Leu-Val-Tyr-AMC) inhibited the human follicular fluid-induced acrosome reaction. Sperm extracts exhibited hydrolytic activity toward Suc-Ala-Ala-Phe-AMC and Suc-Leu-Leu-Val-Tyr-AMC. This enzyme activity was abolished by TPCK and chymostatin, was independent of Ca2+, and was not modified by 1,10 phenanthroline. In addition, the activity was present in the supernatant after the acrosome reaction was induced with calcium ionophore and in epididymal spermatozoa recovered from the cauda region. Electron microscopic observations indicated that the inhibitors prevented the membrane events of the acrosome reaction. These data suggest an association between human spermatozoa and chymotrypsin-like activity with a possible role in the acrosome reaction.

Studies of lysophospholipids related to the hamster sperm acrosome reaction in vitro

Phospholipase A2 and lysophospholipids have been implicated in the mammalian sperm acrosome reaction. In this study we further investigated the role of this enzyme and lysophospholipids on the acrosome reaction of hamster spermatozoa. Hamster epididymal spermatozoa were incubated under capacitation and acrosome reaction-inducing conditions. After 3.0 and 3.5 h, the spermatozoa were treated with different doses of lysophosphatidylcholine for 12 min. Then the percentage of motility, hyperactivation, and acrosome reaction was evaluated by light microscopy. Lysophosphatidylcholine, 10 micrograms/ml, was the highest acrosome reaction-inducing dose without an effect on sperm motility. Lysophosphatidylcholine induced the acrosome reaction only when added to spermatozoa capacitated for a minimum of 2 h. This effect was apparent after 1 min of its addition and reached a plateau after 5 min. Lysophosphatidylethanolamine and lysophosphatidylinositol were also effective in inducing the acrosome reaction. Lysophosphatidylserine did not have any effect on the reaction, but caused an increase in sperm hyperactivation. Sperm treated with the phospholipase A2 inhibitors quinacrine dihydrochloride and p-bromophenacyl-bromide showed an inhibition of the spontaneous occurrence of the acrosome reaction. These inhibitors, however, did not block the acrosome reaction induced by lysophosphatidylcholine. The time course of the lysophosphatidylcholine-induced acrosome reaction was the same whether control or inhibitor treated spermatozoa were used. These results suggest that the membrane events of the acrosome reaction initiate with the activation of the phospholipase A2, thus producing the fusogen agents necessary for this exocytotic event.

Human chorionic gonadotropin and free beta subunits stimulate phospholipid methylation in intact rat Leydig cells

The effect of human chorionic gonadotropin (hCG) on intact Leydig cell phospholipid methylation was studied. Hormonal stimulation of rat Leydig cells increased the incorporation of [methyl-3H]methionine into phospholipids threefold. This effect was observed after 10 minutes of incubation time and was time and dose dependent with a maximal stimulation at 67 ng/ml of hCG. In the presence of hCG, 3H-labeled methyl groups were preferentially incorporated into phosphatidyl-N-monomethylethanolamine. This effect of hCG was not reproduced by dibutyryl cyclic adenosine monophosphate (cAMP), cholera toxin, or forskolin. Purified hCG beta subunit but not hCG alpha subunit had stimulatory activity on Leydig cell phospholipid methylation. We conclude that luteinizing hormone (LH)/hCG stimulates specifically Leydig cell phospholipid methylation, because LH-releasing hormone or [Arg8]-vasopressin did not modify these reactions. We postulate that these reactions are occurring at a cellular level that involves hormone-receptor interaction. It is also suggested that this biological response involves hCG beta subunit receptor interaction and does not require cAMP synthesis.

[Acrosome reaction in mammalian spermatozoa. Biochemical aspects]

Mammalian sperm capacitation and the acrosome reaction (AR) are essential prerequisites for fertilization. This report examines part of the molecular events developed during capacitation and the AR of mammalian spermatozoa; especially those events related to sperm head membrane bound enzymes and phospholipids. For this purpose, it has been analysed results obtained from an in vitro capacitation/acrosome reaction inducing system for golden hamster spermatozoa. First of all, the analysis is focused in the phospholipid transmethylation reactions possibly occurring at plasma membrane level during capacitation and the AR; it is suggested too, that this pathway could provide the substrate for a sperm head membrane bound phospholipase A2 which is able to produce a lysophospholipid (a fusogen) and fatty acids; both of them, very likely involved in the late steps of the AR. These assumptions are confirmed by experiments demonstrating that exogenous lysophospholipids and/or cis-unsaturated fatty acids are able to accelerate AR in previously capacitated spermatozoa. It is also suggested future research in this field, which could involve a sperm phospholipase C specific for phosphatydil-inositol, 4.5 bisphosphate; its products, Inositol trisphosphate and diacylglycerol could act as second messengers with a probable physiological function during capacitation. Finally, an integrative mechanism for the AR-involving phospholipid methylation, acrosin activation, phospholipase A2 activation and endogenous lysophospholipids and fatty acids production is proposed as a model for discussion.

The transmethylations inhibitor 3-deazaadenosine, inhibits in vitro testosterone production by rat testis interstitial cells stimulated with HCG

3-Deazaadenosine (3-DZA), an inhibitor of somatic cell transmethylations, inhibited in vitro HCG-stimulated testosterone synthesis by rat testis interstitial cells. A maximal inhibition of 50% was observed with 100 microM 3-DZA; in addition homocysteine-thiolactone (Hcy) enhanced the inhibitory effect of 3-DZA. On the other hand, when cells were stimulated with dibutyryl cyclic AMP (Bt)2-cAMP, 3-DZA did not exert any effect on the stimulation. The presence of 3-DZA in the incubation medium neither modified HCG Kd values nor the number of its binding sites to Leydig cells. These results demonstrate that inhibitors of transmethylation reactions interfere with hormone-stimulated testosterone synthesis, suggesting that those reactions (presumably phospholipid methylation) at the plasma membrane level are involved in hormone-stimulated testosterone synthesis by rat Leydig cells.

Evidence for the involvement of a sperm trypsinlike enzyme in the membrane events of the hamster sperm acrosome reaction

Previous studies from this laboratory have suggested a role for sperm trypsinlike activity in the membrane events of the hamster sperm acrosome reaction, but these conclusions have been disputed by studies done with guinea pig, mouse, and ram sperm. This study was designed to further investigate the role of such activity in the hamster sperm acrosome reaction. Washed hamster epididymal sperm were examined by electron microscopy after incubation in a defined medium. Fewer sperm incubated in the presence of the trypsin inhibitor benzamidine underwent the membrane events of the acrosome reaction compared to controls. Benzamidine did not interfere with the loss of the acrosomal contents in the sperm which did undergo acrosome reactions. The trypsin inhibitor NPGB (previously shown to inhibit the hamster acrosome reaction under other conditions) did not inhibit the membrane events or the loss of acrosomal contents when the acrosome reaction was induced by the fusogen lysophosphatidyl choline (a method of induction which may have bypassed the need for a trypsinlike enzyme). In a bioassay designed to measure acrosome reactions, fewer sperm preincubated with benzamidine subsequently penetrated zona-pellucida-free hamster eggs. The present results together with those of an earlier study by this laboratory strongly suggest that a sperm trypsinlike enzyme has a direct or indirect role in the membrane events of hamster sperm acrosome reaction. The relationship of these results to studies with other species is discussed.

Phospholipid methylation increases during capacitation of golden hamster sperm in vitro

The present report describes in vitro experiments with golden hamster sperm designed to determine whether there is any relationship between sperm phospholipid methylation and capacitation and/or the acrosome reaction. Washed cauda epididymal hamster sperm were incubated in a capacitation medium containing [methyl-3H] methionine. After 0.5, 1.5, 2.5 and 3.5 h of incubation, sperm were extracted with a chloroform:methanol:2 N HCl mixture to extract total phospholipids. Liquid scintillation counting revealed that the methyl-3H-group was incorporated into phospholipids with maximum incorporation at 3.5 h and an increase of 50% between 2.5 and 3.5 h. Uptake of labeled methionine by sperm reached its plateau by 1.5 h of incubation. Some sperm were capacitated by 3.5 h because that is the time at which the rate of acrosome reactions began to increase and because at least 50% of them were able to undergo the acrosome reaction 10 min after the addition of the fusogen lysophophatidylcholine (LPC) at 3.5 h but not at 2.5 h. Homocysteine thiolactone and 3-deazadenosine, inhibitors of transmethylation, inhibited incorporation of methyl-3H into phospholipids at 3.5 h by approximately 90% and also inhibited LPC-induced acrosome reactions by 60%. Separation of methylated sperm phospholipid by thin-layer chromatography demonstrated the presence of 3H-labeled phosphatidyl-N-monomethylethanolamine, phosphatidyl-N,N-dimethylethanolamine, and to a lesser extent phosphatidylcholine. In addition, an unidentified lipid was also highly labeled. These results strongly suggest a positive correlation between phospholipid methylation and capacitation and/or the acrosome reaction of hamster sperm in vitro. Possible mechanisms for phospholipid methylation involvement in these events are discussed.