The evolution of porcine embryo in vitro production

The in vitro production of porcine embryos has presented numerous challenges to researchers over the past four decades. Some of the problems encountered were specific to porcine gametes and embryos and needed the concerted efforts of many to overcome. Gradually, porcine embryo in vitro production systems became more reliable and acceptable rates of blastocyst formation were achieved. Despite the significant improvements, the problem of polyspermic fertilization has still not been adequately resolved and the embryo in vitro culture conditions are still considered to be suboptimal. Whereas early studies focused on increasing our understanding of the reproductive processes involved, the technology evolved to the point where in vitro-matured oocytes and in vitro-produced embryos could be used as research material for developing associated reproductive technologies, such as SCNT and embryo cryopreservation. Today, the in vitro procedures used to mature oocytes and culture embryos are integral to the production of transgenic pigs by SCNT. This review discusses the major achievements, advances, and knowledge gained from porcine embryo in vitro production studies and highlights the future research perspectives of this important technology.     

Production of female bovine embryos with sex-sorted sperm using intracytoplasmic sperm injection: Efficiency and in vitro developmental competence

The production of embryos with a preselected sex sperm is important in the livestock industry. In this study, we examined the efficiency of producing female embryos by intracytoplasmic sperm injection (ICSI) with flow cytometry sorted (ssICSI) and unsorted (usICSI) bovine sperm, and their developmental competence in vitro. For comparison, bovine embryos were also produced by in vitro fertilization (IVF) with sorted (ssIVF) and unsorted (usIVF) bovine sperm. The semen used in this study was from a bull selected for its high fertility and blastocyst developmental competence among four bulls. We first examined and compared pronuclear (PN) formation and cleavage rates of the produced embryos among the treatment groups. Our results demonstrated that PN formation rates (judged by two pronucleus [2PN]) and cleavage rates in ssIVF group (23.1% and 43.6%) were lower than those in the usIVF (71.1% and 71.6%), usICSI (73.1% and 92.8%) and ssICSI (75% and 79.1%) groups, respectively (P < 0.05). Moreover, the blastocyst formation rate in the ssIVF group was less than those in the usIVF, usICSI, and ssICSI groups (2.7% vs. 30.2%, 28.7% and 24.7%, respectively; P < 0.05). Importantly, we reported that the blastocyst formation rate in the ssICSI group was similar to that in the usICSI group, which indicated that ICSI can rescue the damage introduced to sperm by flow cytometry–mediated sex-sorting. Of note, we achieved a blastocyst formation rate in the ssICSI group to be comparable with the usIVF group. We then examined embryo quality by counting the number of normal and apoptotic cells in blastocysts. It was found that, despite the fact that blastocyst formation rate in the ssIVF group was significantly lower than those in the usIVF, usICSI and ssICSI groups, there was no difference in total and apoptotic cell numbers among these groups (P > 0.05). Finally, karyotyping analysis demonstrated that the proportion of female embryos in the ssICSI and ssIVF groups was 100%, whereas it was 58.8% and 57.8% in the usIVF and usICSI groups, respectively. In conclusion, ICSI with flow cytometry sorted bovine sperm provides an alternative approach to produce embryos with predetermined sex.     

Novel and traditional traits of frozen-thawed porcine sperm related to in vitro fertilization success

Cryopreserved semen allows the use of single ejaculates for repeated analyses, potentially improving IVF consistency by eliminating interejaculate variability observed with fresh semen. However, the freezing and thawing processes result in compromised sperm function and IVF success. Semen samples are often screened for motility before use for IVF. Samples that are below a designated motility threshold may be discarded. Our objectives were to determine if post-thaw sperm motility, other traits that may be indicative of sperm function, or a novel assay of oviduct binding were related to IVF success. Semen from 16 boars was cooled to 15 °C for overnight shipment before cryopreservation. Semen was thawed and motility was recorded microscopically and confirmed using computer-automated sperm assessment. Each sample was tested by IVF in two to three independent replicates. Regression and correlation analyses were employed to determine the interrelationships between sperm traits and the relationships between post-thaw motility, sperm-oviduct binding and IVF outcomes. Among the sperm traits examined, sperm acrosome integrity was negatively correlated with post-thaw motility (r² = 0.64) but not with IVF results. The number of sperm bound to oviduct aggregates was correlated with IVF polyspermy rates (r² = 0.62, P < 0.05) but less with overall IVF rates (r² = 0.31, P > 0.10). There was some relationship of post-thaw motility with IVF monospermic fertilization (P = 0.06, r² = 0.08) but not to other IVF outcomes. Our results indicate that post-thaw motility of frozen-thawed boar sperm is strongly related to acrosome integrity but has limited use for predicting IVF success. The number of sperm bound to oviduct cells was related to IVF polyspermy rates and may be more indicative of in vitro sperm function than traditional sperm motility and acrosome status evaluation.     

Glutathione-S-transferase: Role in buffalo (Bubalus bubalis) sperm capacitation and cryopreservation

In this study, glutathione-S-transferase Mu3 (GST) has been reported to play an important role in sperm capacitation, acrosome reaction, and fertilization. The freshly ejaculated buffalo spermatozoa were in vitro capacitated using heparin (10 μg/mL) or cryopreserved in egg yolk citrate extender. Glutathione-S-transferase was identified and characterized in terms of their isozymic forms, tyrosine phosphorylation, and immunolocalization patterns in cryopreserved buffalo spermatozoa in comparison with freshly ejaculated and in vitro capacitated spermatozoa. Two-dimensional gel electrophoresis, immunoblot, immunocytochemistry, and enzyme activity analyses were done to characterize GST in this study. Five and eight isozymic forms of GST were detected in cryopreserved and capacitated spermatozoa, respectively. Differential tyrosine phosphorylation of these enzymes was observed in cryopreserved and capacitated spermatozoa. The tyrosine phosphorylation of this enzyme involved cAMP protein kinase-A dependent and extracellular signal-regulated kinase independent pathways during in vitro capacitation of the spermatozoa. Differential immunolocalization patterns of GST were observed in freshly ejaculated, capacitated, and cryopreserved spermatozoa. Glutathione-S-transferase Mu3 enzyme activity was found to be significantly (P < 0.05) different in freshly ejaculated, capacitated, and cryopreserved spermatozoa. Activity of GST was significantly (P < 0.05) increased with the progression of capacitation. The cryopreserved spermatozoa showed significantly (P < 0.05) greater enzyme activity compared with fresh spermatozoa and was equal to 2-hour capacitated spermatozoa. The cryopreserved spermatozoa showed significant (P < 0.05) loss of GST enzyme protein. Tyrosine phosphorylated GST showed significantly (P < 0.05) greater activity compared with their dephosphorylated forms. The information generated in this study can be used to understand the molecular mechanism of the effects of GST on capacitation. Regulation of GST during sperm cryopreservation could be a good target to improve fertility of cryopreserved spermatozoa for their use in assisted reproductive technologies.     

Pregnancy rate and birth rate of calves from a large-scale IVF program using reverse-sorted semen in Bos indicus, Bos indicus-taurus, and Bos taurus cattle

Obtaining sexed sperm from previously frozen doses (reverse-sorted semen [RSS]) provides an important advantage because of the possibility of using the semen of bulls with desired genetic attributes that have died or have become infertile but from whom frozen semen is available. We report the efficiency of RSS on the pregnancy rate and birth rate of calves in a large-scale program using ovum pick-up and in vitro embryo production (IVEP) from Bos indicus, Bos indicus-taurus, and Bos taurus cattle. From 645 ovum pick-up procedures (Holstein, Gir, and Nelore), 9438 viable oocytes were recovered. A dose of frozen semen (Holstein, Nelore, Brahman, Gir, and Braford) was thawed, and the sperm were sex-sorted and cooled for use in IVF. Additionally, IVF with sperm from three Holstein bulls with freeze-thawed, sex-sorted (RSS) or sex-sorted, freeze-thawed (control) was tested. A total of 2729 embryos were produced, exhibiting a mean blastocyst rate of 29%. Heifers and cows selected for adequate body condition, estrus, and health received 2404 embryos, and 60 days later, a 41% average pregnancy rate was observed. A total of 966 calves were born, and 910 were of a predetermined sex, with an average of 94% accuracy in determining the sex. Despite the lower blastocyst rate with freeze-thawed, sex-sorted semen compared with sex-sorted semen, (P < 0.05), the pregnancy rate (bull I, 45% vs. 40%; II, 35% vs. 50%; and III, 47% vs. 48% for RSS and control, respectively; P > 0.05) and sex-sorted efficiency (bull I, 93% vs. 98%; II, 96% vs. 94%; and III, 96% vs. 97% for RSS and control, respectively; P > 0.05) were similar for each of the three bulls regardless of the sperm type used in the IVF. The sexing of previously frozen semen, associated with IVEP, produces viable embryos with a pregnancy rate of up to 40%, and calves of the desired sex are born even if the paternal bull has acquired some infertility, died, or is located a long distance from the sexing laboratory. Furthermore, these data show the feasibility of the process even when used in a large-scale IVEP program.     

Risk of Coxiella burnetii transmission via embryo transfer using in vitro early bovine embryos

Coxiella burnetii, an obligate intracellular bacterium of worldwide distribution, is responsible for Q fever. Domestic ruminants are the main source of infection for humans. The objectives of this study were to determine (1) whether C. burnetii would adhere to the intact zona pellucida (ZP-intact) of early in vitro–produced bovine embryos; (2) whether the bacteria would adhere to or infect the embryos (ZP-free) after in vitro infection; and (3) the efficacy of the International Embryo Transfer Society (IETS) washing protocol. One hundred and sixty, eight- to 16-cell bovine embryos produced in vitro, were randomly divided into 16 batches of 10 embryos. Twelve batches (eight ZP-intact and four ZP-free) were incubated in a medium containing C. burnetii CbB1 (Infectiologie Animale et Santé Publique, Institut National de Recherche Agronomique Tours, France). After 18 hours of incubation at 37 °C and 5% CO₂ in air, the embryos were washed in 10 successive baths of a PBS and 5% fetal calf serum solution in accordance with the IETS guidelines. In parallel, four batches (two ZP-intact and two ZP-free) were subjected to similar procedures but without exposure to C. burnetii to act as controls. Ten washing fluids from each batch were collected and centrifuged for 1 hour at 13,000× g. The embryos and wash pellets were tested using conventional polymerase chain reaction. C. burnetii DNA was found in all ZP-intact and ZP-Free embryos after 10 successive washes. It was also detected in the first four washing fluids for ZP-intact embryos and in the 10th wash fluid for two of the four batches of ZP-free embryos. In contrast, none of the embryos or their washing fluids in the control batches were DNA positive. These results demonstrate that C. burnetii adheres to and/or penetrates the early embryonic cells and the ZP of in vitro bovine embryos after in vitro infection, and that the standard washing protocol recommended by the IETS for bovine embryos, failed to remove it. The persistence of these bacteria after washing makes the embryo a potential means of transmission of the bacterium during embryo transfer from infected donor cows to healthy recipients and/or their offspring. Further studies are required to investigate whether enzymatic and/or antibiotic treatment of bovine embryos infected by C. burnetii would eliminate the bacteria from the ZP and to verify if similarly results are obtained with in vivo–derived embryos.     

Potency testing of veterinary vaccines: The way from in vivo to in vitro

Current quality control of inactivated animal vaccines still focuses on the potency of final products in a batch-wise manner. Animal welfare concerns as well as scientific considerations have led to the ‘3Rs-concept’ that comprises the refinement of animal procedures, the reduction of animal numbers, and the replacement of animal models. Although the 3Rs-concept has been widely accepted as a fundamental principle, the number of approved alternatives for in vivo tests is still limited. To promote further progress, the international scientific workshop ‘Potency Testing of Veterinary Vaccines: The Way from in vivo to in vitro’ was held at the Paul-Ehrlich-Institut in Langen, Germany, on 01-03 December 2010. More than 130 participants from industry, academia and regulatory authorities discussed the current state of the 3Rs-concept, examples of its successful implementation as well as still existing hurdles. Special emphasis was laid on the ‘consistency approach’ that aims to ensure relevant quality attributes of vaccine batches by in vitro analyses during production rather than by in vivo potency tests on the final product. This report provides an overview of the insights gained, including the recommendations produced at the end of the workshop.     

In vitro production of small ruminant embryos: Late improvements and further research

Beyond the potential use of in vitro production of embryos (IVP) in breeding schemes, embryos are also required for the establishment of new biotechnologies such as cloning and transgenesis. Additionally, the knowledge of oocyte and embryo physiology acquired through IVP techniques may stimulate the further development of other techniques such as marker assisted and genomic selection of preimplantation embryos, and also benefit assisted procreation in human beings. Efficient in vitro embryo production is currently a major objective for livestock industries, including small ruminants. The heterogeneity of oocytes collected from growing follicles by laparoscopic ovum pick up or in ovaries of slaughtered females, remains an enormous challenge for IVM success, and still limits the rate of embryo development. In addition, the lower quality of the IVP embryos, compared with their in vivo–derived counterparts, translates into poor cryosurvival, which restricts the wider use of this promising technology. Therefore, many studies have been reported in an attempt to determine the most suitable conditions for IVM, IVF, and in vitro development to maximize embryo production rate and quality. This review aims to present the current panorama of IVP production in small ruminants, describing important steps for its success, reporting the recent advances and also the main obstacles identified for its improvement and dissemination.     

Validation of a heterologous fertilization assay and comparison of fertilization rates of equine oocytes using in vitro fertilization,perivitelline, and intracytoplasmic sperm injections

IVF in horses is rarely successful. One reason for this could be the failure of sperm to fully capacitate or exhibit hyperactive motility. We hypothesized that the zona pellucida (ZP) of equine oocytes prevents fertilization in vitro, and bypassing the ZP would increase fertilization rates. Limited availability of equine oocytes for research has necessitated the use of heterologous oocyte binding assays using bovine oocytes. We sought to validate an assay using bovine oocytes and equine sperm and then to demonstrate that bypassing the ZP using perivitelline sperm injections (PVIs) with equine sperm capacitated with dilauroyl phosphatidylcholine would result in higher fertilization rates than standard IVF in bovine and equine oocytes. In experiment 1, bovine oocytes were used for (1) IVF with bovine sperm, (2) IVF with equine sperm, and (3) intracytoplasmic sperm injections (ICSIs) with equine sperm. Presumptive zygotes were either stained with 4′,6-diamidino-2-phenylindole from 18 to 26 hours at 2-hour intervals or evaluated for cleavage at 56 hours after addition of sperm. Equine sperm fertilized bovine oocytes; however, pronuclei formation was delayed compared with bovine sperm after IVF. The delayed pronuclear formation was not seen after ICSI. In experiment 2, bovine oocytes were assigned to the following five groups: (1) cumulus oocyte complexes (COCs) coincubated with bovine sperm; (2) COC exposed to sucrose then coincubated with bovine sperm; (3) COC coincubated with equine sperm; (4) COC exposed to sucrose, and coincubated with equine sperm; and (5) oocytes exposed to sucrose, and 10 to 15 equine sperm injected into the perivitelline (PV) space. Equine sperm tended (P = 0.08) to fertilize more bovine oocytes when injected into the PV space than after IVF. In experiment 3, oocytes were assigned to the following four groups: (1) IVF, equine, and bovine COC coincubated with equine sperm; (2) PVI of equine and bovine oocytes; (3) PVI with equine oocytes pretreated with sucrose; and (4) ICSI of equine oocytes. Oocytes were examined at 24 hours for cleavage. No equine oocytes cleaved after IVF or PVI. However, ICSI conducted with equine sperm treated with dilauroyl phosphatidylcholine resulted in 85% of the oocytes cleaving. Sperm injected into the PV space of equine oocytes did not appear to enter the ooplasm. This study validated the use of bovine oocytes for equine sperm studies and indicates that failure of equine IVF is more than an inability of equine sperm to penetrate the ZP.     

The new system of shorter porcine oocyte in vitro maturation (18 hours) using ≥8 mm follicles derived from cumulus-oocyte complexes

Despite recent efforts to improve in vitro maturation (IVM) systems for porcine oocytes, developmental competence of in vitro-matured oocytes is still suboptimal compared with those matured in vivo. In this study, we compared oocytes obtained from large (≥8 mm; LF) and medium (3–7 mm; MF) sized follicles in terms of nuclear maturation, intracellular glutathione and reactive oxygen species levels, gene expression, and embryo developmental competence after IVM. In the control group, cumulus-oocyte complexes (COCs) were aspirated from MF and matured for 22 hours with hormones and subsequently matured for 18 to 20 hours without hormones at 39 °C, 5% CO₂in vitro. In the LF group, COCs were obtained from follicles larger than 8 mm and were subjected to IVM for only 18 hours. The ovaries have LF were averagely obtained with 1.7% per day during 2012 and it was significantly higher in the winter season. The results of the nuclear stage assessment of the COCs from the LFs are as follows: before IVM (0 hours); germinal vesicle stage (15.2%), metaphase I (MI) stage (55.4%), anaphase and telophase I stages (15.8%), and metaphase II (MII) stage (13.6%). After 6 hours IVM; germinal vesicle (4.2%), MI (43.6%), anaphase and telophase I (9.4%), and MII (42.8%). After 18-hour IVM; MI (9.7%) and MII (90.3%). Oocytes from LF showed a significant (P < 0.001) increase in intracellular glutathione (1.41 vs. 1.00) and decrease in reactive oxygen species (0.8 vs. 1.0) levels compared with the control. The cumulus cells derived from LFs showed lower (P < 0.1) mRNA expression of COX-2 and TNFAIP6, and higher (P < 0.1) mRNA expression of PCNA and Nrf2 compared with the control group-derived cumulus cells. After parthenogenetic activation, in vitro fertilization and somatic cell nuclear transfer (SCNT) using matured oocytes from LFs, the embryo development was significantly improved (greater blastocyst formation rates and total cell numbers in blastocysts) compared with the control group. In conclusion, oocytes from LFs require only 18 hours to complete oocyte maturation in vitro and their developmental competence is significantly greater than those obtained from MFs. Although their numbers are limited, oocytes from LFs might offer an alternative source for the efficient production of transgenic pigs using SCNT.     

In vitro production of embryos in South American camelids

Studies in reproductive biotechnology techniques have been minimal in South American camelids (SAC). Complex reproductive characteristics of these species contribute to slow progress. Nevertheless, some techniques, such as in vitro fertilization, intracytoplasmic sperm injection and nuclear transfer have been applied and have produced advances in knowledge on embryo environment and in vitro conditions necessary for development. Embryo production may have a high impact in both domestic and wild camelids population. Studies addressed to improve in vitro embryo production and oocyte collection could be a potential key to develop IVF and embryo production as a routine procedure in camelids.     

Removal of GPI-anchored membrane proteins causes clustering of lipid microdomains in the apical head area of porcine sperm

The release of extracellular proteins is a part of the sperm capacitation process; this allows the sperm surface reorganization that enables the sperm to fertilize an oocyte. Some of the components released are ‘decapacitation factors’, an uncoordinated or early release of which may cause inappropriate surface destabilization and premature capacitation. We studied the involvement of glycosylphosphatidylinositol-anchored proteins (GPI-APs) in sperm capacitation, and reported that CD52 and CD55 exhibit bicarbonate-dependent release during in vitro sperm capacitation. Treating sperm with phosphatidylinositol-specific phospholipase C (PIPLC) resulted in the enzymatic cleavage of CD55, in both capacitating and noncapacitating conditions. Moreover, PIPLC treatment in noncapacitating conditions caused surface reorganization events that included exposure of the ganglioside GM1, aggregation of flotillin-1, and the swelling of the apical acrosome region; all of which have been reported to be associated with sperm capacitation. The acrosomal swelling was monitored using wet mount atomic force microscopy, a new imaging technique that allows nanometer-level sperm surface measurements in samples hydrated with physiological buffer rather than dried. Despite these surface changes, PIPLC treatment in identical incubation conditions did not stimulate hyperactive sperm motility or protein tyrosine phosphorylation (other hallmarks of sperm capacitation in vitro). In full capacitating conditions (i.e., the presence of bicarbonate and albumin), PIPLC treatment caused sperm deterioration. The possible role of GPI-APs removal from the sperm surface during sperm capacitation is discussed.     

Impact of in vitro fertilization by refrigerated versus frozen buffalo semen on developmental competence of buffalo embryos

The objective of this study was to evaluate the fertility of buffalo semen for in vitro embryo production (IVEP) by comparing the effectiveness of refrigerated versus frozen semen. Three OPU sessions were held at 30-day intervals. For oocyte fertilization three buffalo bulls were used, one per session. At each OPU-IVEP session, one ejaculate was collected and divided into two equal aliquots. Each aliquot was either refrigerated at 5ºC/24 hours or frozen. A TRIS extender containing 10% low density lipoproteins, 0.5% lecithin and 10 mM acetylcysteine was used adding 7% glycerol for freezing. Sperm motility/kinetic was evaluated by CASA and sperm membrane integrity by the hypoosmotic swelling test. The evaluations were performed at 0 h (post final dilution at 37ºC), at 4 and 24 hs post-incubation at 5ºC and post-thaw. At 24 hs incubation and immediately post thaw sperm cells were used for in vitro fertilization of buffalo oocytes equally distributed between both groups. Cleavage rates and embryo development were followed. The embryo/matured and embryo/cultured rates were 25.4 x 14.0% and 29.4 x 18.5% (P<0.05), for chilled and frozen semen, respectively. It is concluded that cooled semen can be used for in vitro embryo production in buffalo and that a better efficiency may be expected for cooled compared to frozen semen.     

Integration of future biotechnologies into the equine industry

There has and will continue to be reproductive techniques available that have a positive impact upon the equine breeding industry. This review focuses on semen technologies that have been developed or are in the process of being developed. The use of fluorescent dyes and flow cytometry has provided the researcher and clinician with powerful tools to evaluate several sperm attributes. These procedures have been utilized to evaluate sperm viability, acrosome status, mitochondrial status, DNA integrity and stages of capacitation. Flow cytometry allows several sperm attributes to be evaluated on thousands of spermatozoa in a matter of seconds. Development of procedures for insemination of mares with relatively small numbers of spermatozoa has the potential to change how stallions and their semen are managed. This review discusses the use of insemination of fresh, frozen and sex-sorted spermatozoa in relatively small numbers compared with conventional insemination technologies. The recent acceptance of frozen-thawed semen by many of the major breed registries has stimulated an increase in research on frozen semen. Many of the studies have focused on identifying damage during the freezing and thawing process. Numerous studies also have been conducted to modify freezing extenders so that the sperm are protected during the freezing and thawing process. The production of in vitro-produced embryos is extremely limited in the horse due to the failure of in vitro fertilization. However, intracytoplasmic sperm injection (ICSI) has been used for the production of foals from stallions that have less than typical sperm numbers or from stallions that have died and a limited quantity of frozen semen is available. This technique has been used by several laboratories to produce embryos in vitro. The breeder and veterinarian now have access to techniques that allow assessment of semen quality, improvement of procedures for freezing and thawing and insemination of mares with fewer numbers of spermatozoa. It is likely that the next decade will also produce tremendous advances in semen technologies that can be utilized in the horse industry.     

The development of the metacercariae of Microphallus similis in vitro and in the mouse

The development of the progenetic metacercariae of Microphallus similis in the mouse and under a range of in vitro cultivation systems was studied and compared. The flukes began egg production after 24 h in the mouse and by Day 4 post infection large numbers of eggs were present. These eggs began to embryonate in utero and contained a ball of cells; however, subsequent incubation in sea water failed to produce recognisable miracidia. In the majority of culture systems, gametogenesis and vitellogenesis occurred. Large numbers of abnormal eggs of three basic types were produced in vitro; these defects were probably related to the premature tanning of the eggshell precursors within the vitellaria and ducts. Apparently normal eggs were also produced, but they were probably unfertilized since sperm were rarely observed in vitro and they failed to embryonate.     

Alterations of sperm DNA integrity during cryopreservation procedure and in vitro incubation of bull semen

An association between sperm DNA integrity and fertility was recently shown for frozen–thawed Norwegian Red (NRF) bull semen diluted in skimmed milk egg yolk (SMEY). In general the fertility of NRF cattle is high, however, in comparison with NRF semen in SMEY, NRF semen diluted in Tris EY based extenders has shown reduced fertility. The aim of the present study was to do a split-sample comparison of sperm DNA integrity of NRF bull semen (n = 20) in SMEY and Triladyl^® (Tris EY based) during routine cryopreservation procedure and during in vitro incubation of frozen–thawed semen in modified synthetic oviduct fluid (mSOF). In contrast to the high fertility of NRF cattle, Holstein cattle are experiencing a marked decline in fertility. Therefore, the present study also aimed to compare sperm DNA integrity of NRF (n = 20) and Holstein (n = 20) semen diluted in Triladyl^® during in vitro incubation. The sperm DNA integrity was measured by susceptibility to in situ acid induced denaturation by the Sperm chromatin structure assay (SCSA). Compared to initial values of frozen neat semen, an increase in DNA damage was observed after dilution and cooling (5 °C) and after freezing–thawing of NRF semen in SMEY, but only after freezing–thawing for NRF semen diluted in Triladyl^®. Sperm DNA damage of NRF semen increased during in vitro incubation in mSOF; the increase in percentage of spermatozoa with DNA damage was more prominent in SMEY than in Triladyl^®, while the degree of damage was higher in Triladyl^®, throughout the incubation period. However, while the correlation between DNA damage and sperm survival was negative in SMEY throughout the incubation period, a positive correlation was observed in Triladyl^® after 9 h of incubation, indicating a higher presence of DNA damage in the live sperm population. In comparison with Holstein spermatozoa, the sperm DNA integrity of NRF semen reflected a better ability to withstand alterations induced during in vitro incubation in mSOF. In conclusion, sperm DNA integrity of NRF bull semen was altered during the cryopreservation procedure and in vitro incubation in mSOF. Dilution in Triladyl^® maintained bull sperm DNA integrity better than dilution in SMEY. Furthermore, alterations in Holstein sperm DNA integrity was more pronounced during in vitro incubation in mSOF compared to NRF bull spermatozoa.     

“Effect of the addition of different catalase concentrations to a TRIS-egg yolk extender on quality and in vitro fertilization rate of frozen-thawed bull sperm’’

The aim of this study was to investigate the effects of different concentrations of catalase in a TRIS-egg yolk extender on sperm quality and embryonic development after in vitro fertilization of frozen-thawed bull sperm. For this purpose, from each of 7 bulls 2 ejaculates were collected and diluted with a TRIS-egg yolk extender containing 0, 5, 10, 15 or 20 IU catalase/mL. Sperm quality was evaluated 0, 3, 6, 12 and 24 h after thawing by using computer assisted analysis of motility and by flow cytometric assays. Embryonic development was determined after in vitro fertilization of bovine oocytes. Semen diluted with TRIS-egg yolk extender containing different concentrations of catalase showed more motile sperm, more sperm with intact plasma membranes, acrosomes and DNA, a high mitochondrial membrane potential, a high esterase activity, a low calcium level, a lower amount of synthesis of reactive oxygen species and lower degree of lipid peroxidation of sperm compared to semen frozen without catalase (P < 0.05), but not before 3 h after thawing. There was a dose-response relationship with the most prominent effect of 20 IU catalase/mL. However, the improvement of sperm quality had no effect (P ≥ 0.05) on embryonic development after in vitro fertilization with 20 IU catalase/mL. In conclusion, the addition of catalase to the sperm extender improved sperm quality with no obvious effect on in vitro fertility.     

Inhibiting Sperm Pyruvate Dehydrogenase Complex and Its E3 Subunit,Dihydrolipoamide Dehydrogenase Affects Fertilization in Syrian Hamsters

Background/Aims

The importance of sperm capacitation for mammalian fertilization has been confirmed in the present study via sperm metabolism. Involvement of the metabolic enzymes pyruvate dehydrogenase complex (PDHc) and its E3 subunit, dihydrolipoamide dehydrogenase (DLD) in hamster in vitro fertilization (IVF) via in vitro sperm capacitation is being proposed through regulation of sperm intracellular lactate, pH and calcium.

Methodology and Principal Findings

Capacitated hamster spermatozoa were allowed to fertilize hamster oocytes in vitro which were then assessed for fertilization, microscopically. PDHc/DLD was inhibited by the use of the specific DLD-inhibitor, MICA (5-methoxyindole-2-carboxylic acid). Oocytes fertilized with MICA-treated (MT) [and thus PDHc/DLD-inhibited] spermatozoa showed defective fertilization where 2^nd polar body release and pronuclei formation were not observed. Defective fertilization was attributable to capacitation failure owing to high lactate and low intracellular pH and calcium in MT-spermatozoa during capacitation. Moreover, this defect could be overcome by alkalinizing spermatozoa, before fertilization. Increasing intracellular calcium in spermatozoa pre-IVF and in defectively-fertilized oocytes, post-fertilization rescued the arrest seen, suggesting the role of intracellular calcium from either of the gametes in fertilization. Parallel experiments carried out with control spermatozoa capacitated in medium with low extracellular pH or high lactate substantiated the necessity of optimal sperm intracellular lactate levels, intracellular pH and calcium during sperm capacitation, for proper fertilization.

Conclusions

This study confirms the importance of pyruvate/lactate metabolism in capacitating spermatozoa for successful fertilization, besides revealing for the first time the importance of sperm PDHc/ DLD in fertilization, via the modulation of sperm intracellular lactate, pH and calcium during capacitation. In addition, the observations made in the IVF studies in hamsters suggest that capacitation failures could be a plausible cause of unsuccessful fertilization encountered during human assisted reproductive technologies, like IVF and ICSI. Our studies indicate a role of sperm capacitation in the post-penetration events during fertilization.     

DsRed-mediated oligomerization stabilizes HMGB1 on chromatin in vivo and on DNA in vitro

High-mobility group box-1 (HMGB1) is remarkably mobile in living cells, which reflects its ability to interact only transiently with both DNA and protein. This property is likely essential for HMGB1 nuclear activities. Nonetheless the weak interaction of HMGB1 with DNA and/or protein partners has also been a major limitation for investigating HMGB1 subnuclear localisation and for the identification of HMGB1 containing complexes by conventional biochemical approaches. In the present study, FRAP experiments demonstrated that DsRed-mediated oligomerization strongly reduces HMGB1 mobility due to an increased affinity for cellular chromatin. Moreover, oligomerized DsRed–HMGB1 exhibited a higher affinity for supercoiled DNA in vitro compared to its monomeric counterpart. These results indicate that DsRed-meditated oligomerization is prone to stabilize labile interactions involving HMGB1 both in vivo and in vitro.