Elucidating the origin of chromosomal aberrations in IVF embryos by preimplantation genetic analysis

Preimplantation genetic screening (PGS) has been proposed as a method for improving success rates in patients with repeated IVF failures. This approach is based on the hypothesis that such failures are the result of aneuploid embryos. It has been suggested that FISH analysis of blastomeres removed from preimplantation embryos represent the chromosomal constitution of the entire embryo. However, it is not yet clear whether it also represents the chromosomal constitution of the implanted embryo. PGS reanalysis on day 5 of embryos designated as "aneuploid" on day 3 may demonstrate a high rate of mosaicism for chromosomal aberration. Some of these mosaic embryos are capable of developing into normal embryos by "self-correction". Others, however, may accumulate additional chromosomal anomalies. It is therefore concluded that the chromosomal constitution of a preimplantation embryo may evolve during early cleavages. Meiotic and post zygotic mitotic errors may account for these chromosomal aberrations. This review will focus on elucidating the origin of chromosomal changes during preimplantation embryo development by studying their chromosomal constitution at different stages.

PGD-derived human embryonic stem cell lines as a powerful tool for the study of human genetic disorders

Human embryonic stem (ES) cells are derived from the inner cell mass (ICM) of blastocyst embryos. They are established from spare embryos that have been obtained by in vitro fertilization (IVF) and donated for research purposes. The ICM-derived cell lines have two unique properties, they can be propagated indefinitely in culture and have the potential to develop into practically any cell type in vitro and in vivo. Human embryonic stem (hES) cells carrying specific mutations can be used as a valuable tool for studying genetic disorders in human. One favorable approach to obtain such mutant ES cell lines is their derivation from affected preimplantation genetic diagnosed (PGD) embryos. This review focuses on the importance of deriving human ES cell lines from genetically abnormal embryos, especially in cases where no good cellular and/or animal models exist.

Preimplantation genetic diagnosis (PGD) for Duchenne muscular dystrophy (DMD) by triplex-nested PCR

OBJECTIVES

Duchenne muscular dystrophy (DMD) is a lethal X-linked recessive disorder with an incidence of approximately 1 in 3500 males, caused by mutation in the DMD gene. About 2/3 of DMD cases are caused by gross DMD gene deletion mutations. The purpose of this study was to develop a series of single-cell multiplex-nested PCR protocols for preimplantation genetic diagnosis (PGD) of the most prevalent DMD deletions.

METHODS

The protocols were developed on single blood leukocytes from normal males and females and patients with known DMD gene deletion. In the first reaction, 2 of 11 different primer sets (exons 4, 8, 12, 13, 17, 46, 47, 49, 50, 52 and intron 52) were used to allow the simultaneous amplification of different DMD loci and the SRY gender marker, in a single triplex-nested polymerase chain reaction (PCR). Aliquots of this reaction were then subjected to nested PCR in which each locus was amplified individually. Following the successful establishment of single-cell triplex-nested PCR in single leukocytes, the technique was employed in five clinical PGD cases.

RESULTS

For each DMD locus, more than 50 single leukocytes from healthy controls and more than 100 single leukocytes from affected individuals with known deletions were analyzed. Amplification efficiency for each tested locus was 98-100%. The false-negative rates for each analysis taken separately was <1%. Taken together, however, the results of the triplex-nested PCR analysis had a false-negative rate of 0%. No contamination was detected in all wash-drop blanks tested. We subsequently performed 18 PGD cycles in 5 DMD carriers. A total of 156 embryos were biopsied and successfully analyzed. Of these, 39 affected embryos were detected and 50 unaffected embryos were transferred (mean = 2.9 +/- 1.1 embryos per cycle). These resulted in three biochemical pregnancies and three clinical pregnancies, all of which have culminated in the birth of normal offspring.

CONCLUSION

Triplex-nested PCR using 2 of 11 DMD loci and the SRY gender marker allow PGD for >90% of DMD families with known deletions. These protocols are associated with a high amplification efficiency and accuracy.

Human embryonic stem cells as a powerful tool for studying human embryogenesis

Human embryonic stem cells (HESC) are pluripotent stem cell lines derived from the inner cell mass (ICM) of human blastocyst-stage embryos. They are characterized by their unlimited capacity to self-renew in culture. In addition, they have a broad developmental potential, as demonstrated by their ability to form practically any cell type in vivo and in vitro. These two features have made HESC extremely important in basic and applied research. In addition, they may serve as a powerful tool for studying human development. HESC can recapitulate embryogenesis by expressing developmentally regulated genes and by activating molecular pathways as they occur in vivo. Moreover, they can be used to analyze the effect of specific mutations on particular developmental events and may enable us to identify critical factors that play a role in the processes of cell commitment, differentiation, and adult cell reprogramming. Thus, modeling human embryogenesis by the use of HESC may allow new insights into developmental processes, which would otherwise be inaccessible for research.

Expression and possible involvement of calpain isoforms in mammalian egg activation

At fertilization in mammals, the spermatozoon triggers a unique signal transduction mechanism within the egg, leading to its activation. It is well accepted that the earliest event observed in all activated eggs is an abrupt rise in intracellular calcium concentrations. However, little is known regarding the downstream proteins that are activated by this rise in calcium. Calpains constitute a family of intracellular calcium-dependent cysteine proteases whose members are expressed widely in a variety of cells. We investigated the expression and possible role of the calpain isoforms mu and m throughout egg activation. Both calpains were expressed in the rat egg and localized at the egg cortex as well as in the meiotic spindle. m Calpain translocated to the membrane and to the spindle area during parthenogenetic egg activation and during in vivo fertilization, upon sperm binding to the egg. The cytoskeletal protein alpha-spectrin (fodrin) was proteolysed by calpain during the egg-activation process, as demonstrated by specific calpain-breakdown products. Following parthenogenetic activation by ionomycin or puromycin, the calpain-selective permeable inhibitor, calpeptin, inhibited the resumption of meiosis and cortical reaction in a dose-dependent manner. Calpeptin was also effective in inhibiting in vitro fertilization. These results may imply a correlation between calpain activation and mammalian egg activation at fertilization and a possible role for calpain in the cascade of cellular events leading to resumption of meiosis.

Severe hypospermatogenesis in cases of nonobstructive azoospermia: should we use fresh or frozen testicular spermatozoa?

The aim of this comparative clinical study was to examine whether the fertilizing potential of frozen-thawed testicular sperm in the most severe cases of hypospermatogenesis is reduced compared with fresh testicular sperm. The results could determine the necessity of using fresh testicular sperm cells, which mandates involving the spouse by performing simultaneous in vitro fertilization intracytoplasmic sperm injection (IVF-ICSI) treatment in this subgroup of nonobstructive azoospermia (NOA) patients. We studied 13 couples in which the husband was diagnosed as having NOA and few motile testicular sperm cells or only immotile testicular sperm cells were isolated by testicular sperm extraction (TESE). Each couple underwent both an ICSI cycle, in which fresh testicular sperm that were retrieved shortly beforehand were injected, and a consecutive cycle, which used frozen-thawed sperm that were retrieved in the original TESE procedure but were cryopreserved and stored until use. We found that motility was lost during the freezing and thawing process in some cases, which resulted in significantly more cycles with only immotile sperm cells for injection in the frozen-thawed sperm group (38.5%) than in the fresh sperm group (7.7%; P < .05). Availability of only immotile sperm cells significantly reduced fertilization rates in both fresh and frozen-thawed groups, but the respective overall fertilization rate (44.9% vs 41.1%) and quality of embryos and pregnancy rate (18.2% vs 15.4%) were not significantly different between groups. Implantation rates were more favorable in the fresh sperm group (10.5% vs 5.9%), but not significantly so. We conclude that, although cryopreservation does impair motility, which results in significantly more cycles with only immotile sperm cells for ICSI in the most severe forms of hypospermatogenesis, fertilization and pregnancy rates are not significantly compromised.

Expression and immunolocalization of the calpain-calpastatin system in the human oocyte

OBJECTIVE

To investigate the expression of the calpain-calpastatin system in the human oocyte.

DESIGN

The expression of the calpain-calpastatin system was determined by immunohistochemistry and immunoblot analysis.

SETTING

Academic research laboratory.

PATIENT(S)

Twenty Israeli women who underwent IVF for fertility problems.

INTERVENTION(S)

Oocytes that had no pronuclei 24 hours after insemination by either conventional IVF or intracytoplasmic sperm injection were retrieved for the study.

MAIN OUTCOME MEASURE(S)

Analysis of calpain isoforms (m, mu) and calpastatin distribution within the human oocyte.

RESULT(S)

Western blot analysis confirmed the expression of calpain and calpastatin. Immunohistochemistry of fixed, permeabilized oocytes exhibited localization of both calpains to the cortical region of the oocyte, as well as the cytosol. Calpastatin seemed to be distributed throughout the cytosol, with a marked accumulation in the cell membrane. We have demonstrated a negative correlation between the occurrence of cortical granule exocytosis and the stability of the metaphase plate.

CONCLUSION(S)

A complete calpain-calpastatin system is expressed in the human oocyte and might play a role in the various calcium-mediated processes occurring during activation of human oocytes.

Prospective randomized comparison of two embryo culture systems: P1 medium by Irvine Scientific and the Cook IVF Medium

PURPOSE

To compare the efficacy of two commercially available in vitro fertilization (IVF) and embryo culture media systems: the glucose-free P1 Medium supplemented with 20% synthetic serum substitute (SSS) (Irvine Scientific), and the Cook IVF Medium (Cook, Australia).

METHODS

A prospective randomized study. Medical center-based IVF Unit affiliated to the Faculty of Medicine of Tel Aviv University. IVF patients were randomly assigned to either P1 Medium supplemented with 20% SSS (182 patients, 196 cycles) or Cook Medium (167 patients, 179 cycles).

RESULTS

Fertilization rates were similar with both media (52.3 +/- 26.1 and 53.8 +/- 27.6, respectively). Likewise, no difference was found in morphological characteristics and grading of cultured embryos. However, a significantly higher proportion of the embryos incubated in the P1 Medium reached the four-cell stage on day 2 or the 6-cell stage on day 3 postfertilization, compared to those incubated in Cook Medium (54.3% vs. 41.9%, p < 0.0001). Clinical pregnancy and delivery rates were improved when oocytes and embryos were cultured in P1 Medium. Finally, Implantation rate was significantly higher in the P1 Medium Group (9.9% vs. 6%, respectively).

CONCLUSIONS

Our results suggest that the P1 Medium may be associated with a higher embryo cleavage rate and improved implantation rates compared to the Cook IVF Medium.

Divalent cation levels in serum and preovulatory follicular fluid of women undergoing in vitro fertilization embryo transfer

In this controlled clinical study, we determined the serum and follicular fluid concentrations of the biologically active fractions of magnesium (Mg) and calcium (Ca) in 39 women undergoing controlled ovarian stimulation (COH) for in vitro fertilization (IVF) embryo transfer (ET). Serum levels of ionized Ca (Ca2+) and ionized Mg (Mg2+) were measured during day 3 of the IVF cycle, on the day of ovum pickup and 12 days following ET. Follicular fluid levels were measured on the day of ovum pickup. Serum levels of Mg2+ decreased and Ca2+ levels increased during the IVF cycle. Mg levels were significantly higher in follicular fluid than in serum. Ca2+ and Mg2+ may play a role in the preovulatory follicle, a possibility that warrants further study.

Maternal serum HCG is higher in the presence of a female fetus as early as week 3 post-fertilization

BACKGROUND

Maternal serum HCG (MSHCG) is higher when the fetus is a female than when it is male. This has been demonstrated in the second and third trimesters of pregnancy, and recently at 10-14 weeks gestation. In this study we assessed whether this gender-related difference can be detected as early as week 3 post-fertilization.

METHODS

The IVF setting was chosen because it provides precise dating of gestational age and early sonography for the number of gestational sacs. The study included 347 IVF cycles from 335 patients. Only pregnancies with a single implanted embryo that resulted in a single live birth of known gender were included. MSHCG was measured on days 14-20 post-fertilization, and levels were expressed as gestational age-corrected multiples of the median (MoMs). The log10 MSHCG MoMs were compared according to fetal gender.

RESULTS

MSHCG levels were significantly higher (18.5%) in week 3 post-fertilization in the presence of a female fetus (P < 0.0002).

CONCLUSION

Because a fetal gender-related difference in MSHCG can be demonstrated as early as week 3 post-fertilization, the difference may be attributed to placental factors and not to the effects of the fetal hypothalamic-hypophyseal-gonadal axis.

The mitochondrial DNA mutation (deltamtDNA5286) in human oocytes: correlation with age and IVF outcome

PURPOSE

To evaluate the correlation between the presence of a newly described mitochondrial DNA (mtDNA) mutation (deltamtDNA5286), patients' age, and in vitro fertilization (IVF) outcomes.

METHODS

The presence of deltamtDNA5286 was analyzed by nested-primer PCR in 224 unfertilized oocytes of 81 women undergoing IVF for various reasons. Age, number of oocytes retrieved, fertilization and embryo cleavage, number of embryos transferred, and pregnancy rates were compared between patients with and without a mtDNA mutation in their oocytes.

RESULTS

The 23 patients in which deltamtDNA5286 was detected in at least one oocyte were significantly younger than the other 58 with no mutations (30.9 years vs. 33.8 years, respectively, P = 0.03), and had a significantly lower fertilization rate (28.9% vs. 42.1%, respectively, P = 0.01). No other outcome variable was significantly different between the two groups.

CONCLUSION(S)

The mtDNA mutation deltamtDNA5286 may serve as a marker of decreased oocyte quality in IVF.

Increasing synthetic serum substitute (SSS) concentrations in P1 glucose/phosphate-free medium improves implantation rate: a comparative study

PURPOSE

To assess the comparative efficacy of IVF medium (MediCult, with 5.2 mM glucose) and a glucose/phosphate-free medium, P1 (Irvine Scientific), and to investigate the influence of increasing the serum supplementation (synthetic serum substitute; SSS; Irvine Scientific) to P1 on embryo development and implantation.

METHODS

Patients were randomly assigned to IVF medium (Group 1, cycles n = 172) or P1 supplemented with 10% SSS (Group 2, cycles n = 229) according to the medium scheduled for use on the day of oocyte retrieval. Another 555 IVF consequent cycles (Group 3) were performed using increased SSS concentrations (20%) in P1 medium.

RESULTS AND CONCLUSION

In this large series of IVF cycles, we herein demonstrate that significantly higher pregnancy and implantation rates were found when embryos were cultured in glucose/phosphate-free medium P1 supplemented with 20% SSS compared to supplementation with the lower SSS concentration and with IVF medium.

Vascularity index distribution within the testis: a technique for guiding testicular sperm extraction

Azoospermia is defined as the absence of spermatozoa in the ejaculate, although some foci of spermatogenesis may exist in the testes of these men. Currently, there are no clinical, seminal or hormonal parameters for identifying spermatogenesis within the testis sufficient for achieving genetic offspring. As a result, multiple biopsies are performed at several arbitrary sites of both testes in search of spermatozoa. We developed a power Doppler (PD) ultrasound (US) image-based technique that predicts sites with the greatest potential for spermatogenesis. PDUS images of the testes of azoospermic men were acquired at seven cross-sections to reconstruct a 3-D matrix for constructing a spatial map of preferential regions where spermatozoa are most likely to exist. This technique may obviate the need for arbitrary multiple biopsies that inflict some degree of damage upon testicular tissue, and may increase the success rate of identifying viable spermatozoa in testicular biopsies.

Oocyte activation: lessons from human infertility

During fertilization, the spermatozoon penetrates through the cumulus cells and the zona pellucida that surrounds the oocyte, before it binds and fuses with the oocyte plasma membrane to induce activation. In vitro fertilization (IVF) studies performed in non-human mammals have contributed extensive knowledge regarding the mechanisms by which the spermatozoon activates the meiotic-arrested oocyte to resume meiosis, cleave and develop into an embryo. Although IVF has been used extensively for treating subfertile couples, not all of them were able to benefit from this procedure. In intracytoplasmic sperm injection (ICSI), one viable spermatozoon only is sufficient for successful fertilization of a single oocyte. Moreover, the injected fertilizing spermatozoon bypasses several physiological barriers, compared with IVF, which together could explain the high success rate for this procedure. ICSI has also allowed the identification of sperm components that are required for successful fertilization.

Testicular sperm retrieval and cryopreservation prior to initiating ovarian stimulation as the first line approach in patients with non-obstructive azoospermia

The potency for fertilization and successful implantation was compared between fresh and cryopreserved testicular spermatozoa obtained from the same patient with non-obstructive azoospermia. Spermatozoa cryopreserved at the outset were also evaluated. Non-obstructive azoospermic men (n = 55) underwent testicular sperm extraction (TESE); mature spermatozoa were found in 33 (60%) of them. Of 57 intracytoplasmic sperm injection (ICSI) cycles in 25 patients, 15 used fresh spermatozoa (14 patients, group 1), 24 used the excess spermatozoa cryopreserved after 'fresh' ICSI (11 couples who did not conceive in the 'fresh' cycle, group 2) and 18 cycles used cryopreserved spermatozoa at the outset (11 other patients, group 3). Fertilization, cleavage, embryo quality, implantation and take home baby rates were not significantly different in groups 1 and 2, and 6/14 couples ultimately had healthy babies (42.8% cumulative take home baby rate per TESE). In group 3, neither the fertilization rate, embryo development, pregnancy nor implantation rates per embryo transfer were significantly different from groups 1 and 2. The cumulative delivery and ongoing pregnancy rate in this group was 36. 4%. Cryopreservation did not impair the availability of motile spermatozoa for ICSI. When immotile spermatozoa were injected, however, fertilization rate decreased dramatically. Since criteria for predicting the presence of spermatozoa in the testicular tissue of patients with non-obstructive azoospermia are inadequate, it is suggested that TESE be performed prior to initiating ovarian stimulation.

Early ionic events in activation of the mammalian egg

At fertilization of the mammalian egg, the spermatozoon initially binds to and then fuses with the egg plasma membrane. This critical event activates specific biochemical pathways within the egg. Activation of the egg induces resumption of meiosis and the start of rapid embryonic mitotic divisions on the one hand, and cortical granule exocytosis leading to modification of the zona pellucida and a block to polyspermy on the other. It has been shown in different systems that changes in intracellular ion concentrations can serve as second messengers of signal transduction mechanisms. The use of specific fluorescence probes, combined with the image analysis technique, facilitates the measurement of their dynamics in real time in the living cell and, thereby, assessment of their role in activation of the mammalian egg. This review focuses on the dynamics of intracellular Ca2+ and pH and their role in transducing the sperm signal to downstream cell cycle regulators.

High levels of anticardiolipin antibodies in patients with abnormal embryo morphology who attended an in vitro fertilization program

PROBLEM

Recently, it has been suggested that anticardiolipin antibodies (ACAs) may serve as possible markers for reproductive failure. The association between ACAs and embryo morphology in patients undergoing in vitro fertilization (IVF) was investigated.

METHOD OF STUDY

This prospective study comprised 117 patients with either tubal factor or unexplained infertility. Embryo morphology was blindly scored from I to IV according to blastomere regularity and the presence of fragments. Anticardiolipin antibodies (immunoglobulin [Ig] G and IgM) were detected.

RESULTS

Anticardiolipin antibodies were found in 26 (50%) of the 52 patients with abnormal morphology, compared with 13 (20%) of the 65 patients with normal embryo morphology (P = 0.001). No statistically significant differences were found between the prevalence of ACAs among patients with tubal factor and those with unexplained infertility (29.6% and 36.5%, respectively).

CONCLUSIONS

Our study shows an association between embryo morphology and the presence of ACAs. This association may explain the low implantation rate and early pregnancy loss in patients with ACAs.

Tyrosyl-phosphorylated proteins are involved in regulation of meiosis in the rat egg

Fertilization in invertebrates results in tyrosine (Tyr) phosphorylation of several egg proteins. However, the involvement of Tyr phosphorylation in mediating mammalian egg activation has not yet been investigated. Using an antibody specific for phosphotyrosine (P-Tyr), immunoblotting, and densitometric analysis, we found that maturation of the oocyte is accompanied by a generalized increase in the P-Tyr content of almost all egg proteins detected. After sperm penetration, 5 of the 17 protein bands detected demonstrated a small increase in their P-Tyr content, while at the pronuclear (PN) stage the signal was markedly reduced. Ionomycin emulated the changes observed at fertilization in most protein bands detected, demonstrating a small increase in their P-Tyr content within 15 min of exposure. Analysis of the involvement of the tyrosyl-phosphorylated, mitogen-activated protein (MAP) kinase during meiosis revealed comigration of the phosphotyrosyl bands with the protein and a good correlation with its enzyme activity. Maturation was accompanied by an increase in MAP kinase activity. The activity dropped partially after sperm penetration and furthermore later at the PN stage. A larger quantity accompanied by a more significant change in the P-Tyr content implies for extracellular regulated kinase (ERK) 2 being the dominant isoform present in the rat egg. Our results indicate that fertilization in mammals involves changes in activity of protein tyrosine kinases (PTKs) or in the balance between PTKs and protein tyrosine phosphatases. The single, ionomycin-induced Ca2+ rise is sufficient to imitate fertilization-induced changes in MAP kinase activity, as well as in tyrosine phosphorylation of other proteins within the egg.

Segregation of the pathways leading to cortical reaction and cell cycle activation in the rat egg

At fertilization of the mammalian egg, resumption of the cell cycle and the cortical reaction are two events of egg activation, correlated with an increase in intracellular Ca2+ concentration and activation of protein kinase C. To evaluate the pathways leading to both events, rat eggs were parthenogenetically activated by the calcium ionophore ionomycin, or by the protein kinase C activators 12-O-tetradecanoyl phorbol-13-acetate (TPA) or 1-oleoyl-2-acetylglycerol (OAG). Cortical granule exudate was visualized by the lectin Lens culinaris and Texas Red streptavidin, using a confocal microscope. Resumption of meiosis was detected by Hoechst dye, and intracellular Ca2+ concentration by fura-2. Ionomycin triggered both a cortical reaction and resumption of meiosis, while chelation of intracellular Ca2+ rise by BAPTA-AM (1,2-bis-(O-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester) revealed a segregation between these two events. A low Ca2+ transient (approximately 150 nM) induced a partial cortical reaction in half of the eggs, but the meiotic status was not affected. TPA triggered a cortical reaction with neither resumption of meiosis nor intracellular Ca2+ rise, while OAG induced both aspects of activation, as well as a significant intracellular Ca2+ rise. We conclude that in the cascade of events leading to egg activation, the initial Ca2+ rise is followed by a segregation in the pathway. A relatively low Ca2+ rise is sufficient to induce a partial cortical reaction. However, a higher level of Ca2+ is required to complete the cortical reaction and resumption of meiosis. The activation of the cell cycle is Ca2+-dependent, but protein kinase C-independent.

Changes in calpain during meiosis in the rat egg

Resumption of meiosis at fertilization is mediated by increased levels of calcium which activate several calcium-dependent enzymes. Calpain, a neutral calcium-activated thiol protease, is present in the cytoplasm of many cells. Its activation is associated with limited autolysis and relocalization in the cell. Calpain is thought to participate in the regulation of mitosis and resumption of meiosis in Xenopus oocytes. In this study we followed the activation and localization of calpain during maturation and fertilization in rat eggs using a polyclonal antibody raised against chicken muscle calpain. A band of 80 kDa was detected in GV oocytes and its level increased in unfertilized MII eggs. At the early stages of fertilization, we observed a transient decrease in the level of calpain which was regained at the pronuclear stage. Adding Ca2+ to lysate of MII eggs resulted in an additional band, representing the degraded fragment of the activated protein. In eggs activated by ionomycin, calpain level decreased, followed by an increase in a dynamic similar to that observed in fertilized eggs. Egg activation also led to changes in calpain localization. A homogenous distribution was observed in GV and in MII eggs, while in activated eggs it was localized predominantly overlying the metaphase plate. In the current study we demonstrate the presence of calpain in the rat egg. During maturation, calpain level increases; however, during egg activation, in response to [Ca2+]i changes, calpain undergoes autolysis, translocaton, and fluctuation in its level. We therefore suggest a correlation between calpain activation and fertilization.

Interleukin-10 in preovulatory follicular fluid of patients undergoing in-vitro fertilization and embryo transfer

PROBLEM

The present study aimed at investigating the presence of Interleukin-10 (IL-10) in preovulatory follicular fluid (FF) and its possible correlation with 17-beta-estradiol (E2) and progesterone (P) levels, and treatment outcome in patients undergoing in-vitro fertilization-embryo transfer (IVF-ET).

METHODS

Twenty consecutive patients with tubal factor infertility who underwent oocyte retrieval for IVF-ET were assayed for pooled, preovulatory FF levels of IL-10, E2, and P.

RESULTS

The mean FF levels of IL-10, E2, and P were 78.7 +/- 104.7 pg/ml, 2,787.0 +/- 726.1 pg/ml, and 1.5 +/- 0.8 ng/ml, respectively. No correlation was found between preovulatory FF concentration of IL-10, E2, oocyte number, oocyte fertilization rate, embryo quality, and pregnancy rate. The levels of IL-10 were found to be negatively correlated with P concentration, although not significantly (P = 0.057).

CONCLUSION

Interleukin-10 exists in the preovulatory FF. Further investigations are needed to determine the role of IL-10 in the folliculogenesis.

Intracellular pH of rat eggs is not affected by fertilization and the resulting calcium oscillations

Penetration of the oocyte by a spermatozoon is the first in the series of events resulting in the transition of the egg from a quiescent to a proliferative state. A critical regulatory role for intracellular calcium ([Ca2+]i) ion activity has been demonstrated in all species studied so far. On the other hand, it has been demonstrated that the intracellular pH (pHi) changes, but only in a small number of species. This change also has been proposed as one of the most important events in egg activation. The present study was undertaken to monitor pHi in rat eggs during fertilization, using the membrane-permeable indicator BCECF-AM and fluorescence ratio imaging. Furthermore, we proposed to evaluate the relationship between pHi and [Ca2+]i changes during egg activation. We found that the ovulated rat egg has a cytoplasmic pH significantly different from that of the follicular oocyte. Insemination with capacitated sperm resulted in a microscopically visible sperm attachment, yet no change in pHi was observed. Eggs double-loaded with fura-2-AM and BCECF-AM before insemination were used to measure [Ca2+]i and pHi simultaneously. Eggs with a normal pattern of [Ca2+]i transients (i.e., fertilized eggs) did not show any change in pHi at least for 30 min following sperm binding. Data for eggs fertilized in vivo were recorded at later times after sperm binding; these served to exclude the possibility of a transient change that occurs between sperm-egg interaction and the pronuclear stage. We conclude that the pHi of rat eggs does not change during fertilization and therefore that fertilization-induced [Ca2+]i changes do not affect pHi in these eggs.

Restraint stress-induced changes in lymphocyte subsets and the expression of adhesion molecules

The effect of restraint stress on the distribution of lymphocyte subsets were studied in young BALB/c male mice. Loss of whole body weight, a reduction in the weights of spleen and lymph nodes, and higher levels of serum corticosterone were evident after a single continuous restraint period of 16-18 h. Tissue sections of spleens from restrained animals revealed erythrocyte depletion in the contracted red pulp. Furthermore, there was a significantly higher proportion of CD4+, but not of CD8+, lymphocytes in the spleen. The proportion of the CD4+ subset was markedly diminished in peripheral blood, whereas no changes were detected in lymph nodes. Restraint resulted in enhanced allogeneic mixed lymphocyte reactivity and in altered expression of some CD4+, but not CD8+, splenocyte adhesion molecules (CD44, LFA-1 and VLA-4). Removal of circulating corticosteroids by surgical adrenalectomy abolished the restraint-induced changes in lymphocyte adhesion molecule expression. The findings suggest that the observed differences in lymphocytes subset distribution of lymphoid organs may be due to changes in the pattern of adhesion molecule expression.

Low temperature and fertilization-induced Ca2+ changes in rat eggs

In mammalian eggs, activation by sperm that leads to resumption of meiosis is characterized by an explosive transient increase in intracellular calcium ion concentration ([Ca2+]i), followed by [Ca2+]i oscillations. In addition to the spermatozoon, various treatments can induce parthenogenetic activation, accompanied by an elevation of [Ca2+]i. It has been reported that cooling can induce egg activation, yet the mechanism of this phenomenon has not been elucidated. In the present study we followed changes in egg [Ca2+]i (measured by Fura-2 fluorescence ratio imaging) during activation by cooling, using conditions that ensure a low rate of spontaneous activation. Our present findings demonstrate that cooling induces egg activation as manifested by [Ca2+]i transient(s) and second polar body extrusion. Seventy-eight of 104 eggs responded to cooling with increased [Ca2+]i. Thirty-five percent of the responding eggs displayed a single [Ca2+]i transient, while 65% exhibited at least two [Ca2+]i transients within the time window of the experiment (30-40 min). Twenty-two percent of these eggs displayed high-frequency oscillations (intervals of 3.5-5.9 min). In these eggs, the overall pattern of calcium dynamics was similar to that observed in eggs activated by sperm, as judged by the transient's intervals, duration, and a gradual increase in the amplitude of successive transients. The amplitudes of [Ca2+]i transients, however, were 2-3 times lower. We propose that cooling affects [Ca2+]i homeostasis to produce fertilization-like changes in [Ca2+]i, possibly associated with parthenogenetic activation. Moreover, great care should be exercised to prevent temperature changes during egg handling.

Prolonged, repetitive calcium transients in rat oocytes fertilized in vitro and in vivo

Zona-free rat oocytes inseminated with capacitated sperm, under conditions that allow polyspermic fertilization, exhibited a rapid, transient elevation of cellular calcium (from 147 +/- 10 to 607 +/- 55 nM, n = 19, measured by Fura 2 fluorescence ratio imaging) immediately after sperm attachment. This peak was followed by a series of dramatic calcium transients of high amplitude (maximal 847 +/- 32 nM) and frequency (range 2.1 +/- 0.07 - 3.9 +/- 0.07 min), which continued for several hours. A similar pattern was seen also in zona-free oocytes fertilized with low sperm density (i.e. producing mainly monospermic attachment) and in zona-enclosed oocytes fertilized in vitro. Moreover, single or repetitive calcium transients were observed in rat oocytes fertilized in vivo. These findings indicate that in normal fertilization in vivo, sperm-oocyte interaction initiates a prolonged train of cyclical calcium changes in the oocyte. This activity may be necessary for the early events in the fertilization process.

Fertilization and early development of rat oocytes induced to mature by forskolin

Forskolin has been shown to successfully induce maturation of rat oocytes as assessed by morphological markers. The present study was designed in an attempt to elucidate whether oocytes, induced to mature by forskolin (10(-4) M, group A) in a follicle-enclosed oocyte culture, are fertilizable and can further develop into two-cell embryos. Oocytes exposed in vitro to either luteinizing hormone (LH, 5 micrograms/ml, group B) or a GnRH agonist analogue (10(-7) M, group C) as well as oocytes that underwent maturation in vivo (group D), served as positive controls. We found that similar rates of fertilization were obtained in the experimental and all of the above mentioned control groups (A = 78.9 +/- 4.2%, B = 77.9 +/- 3.1%, C = 77.5 +/- 5.5% and D = 84.7 +/- 2.7%). Cleavage rate of fertilized eggs from group A was significantly higher than that of eggs from groups B & C, and similar to that of eggs from group D (A = 63.1 +/- 6.7%, B = 37.8 +/- 4.9%, C = 50.0 +/- 4.1%, D = 67.8 +/- 4.1%). Using functional parameters we hereby demonstrate that forskolin and LH are at least equally potent in producing fertilizable eggs that have a high potential of development into two cell embryos. These results further support the idea that cAMP is a mediator of LH action in inducing oocyte maturation.

Rat oocytes induced to mature by epidermal growth factor are successfully fertilized

Epidermal growth factor (EGF), which is a known mitogen, can also induce resumption of meiosis in the rat oocyte. The present study was designed in an attempt to elucidate whether oocytes, induced to mature by EGF in a follicle-enclosed oocyte culture, are fertilizable and can further develop into two-cell embryos. For further clarification of the effect of EGF on steroidogenesis in the ovarian follicle, progesterone concentrations were determined by radioimmunoassay. We found that oocytes matured by EGF (100 ng/ml) were successfully fertilized. Even though their rate of fertilization was relatively lower as compared to that of oocytes stimulated by luteinizing hormone (LH) both in vitro and in vivo (61%, 79%, and 83% respectively), once fertilized they exhibit an equal potential for further development (EGF: 48%, LH: 45%). On the other hand, EGF-induced progesterone production was very poor. These findings strongly support the idea that both mitogenesis and meiogenesis can be mediated by common signals. The results further suggest that progesterone production and oocyte maturation, in the rat, are independent events.