Preovulatory follicular fluid during in vitro maturation decreases polyspermic fertilization of cumulus-intact porcine oocytes

Pre-fertilization approach using α-l-fucosidase modulates zona pellucida hardening during bovine in vitro embryo production

The polyspermy occurrence is considerably lower under in vivo compared to in vitro embryo culture conditions, suggesting that the presence of some factors in the maternal environment is responsible for this. The α-L-fucosidase (FUCA) is a natural glycosidase present in the oviductal fluid, therefore, this study aimed at investigating the effect of adding FUCA to the hardening of the zona pellucida (ZP), polyspermy control, and embryonic yield and quality of bovine blastocysts produced in vitro. In the first experiment, the effect of FUCA (0.125 U/mL) was evaluated during the entire in vitro fertilization (IVF). However, it was demonstrated to be embryotoxic by completely inhibiting the blastocyst formation. In the second experiment, the FUCA (0.125 U/mL) was tested as short-term incubation before IVF (pre-fertilization step) for 30 min or 2 h, which demonstrated that FUCA treatment for 30 min resulted in ZP hardening. In the third experiment, a pre-fertilization FUCA treatment (1 h) at different concentrations (0, 0.0625, and 0.125 U/mL) showed that FUCA (0.0625 U/mL) improved pre-fertilization ZP hardening and tended to increase monospermic fertilization rates but did not improve embryo yield and quality. Together, it has been demonstrated that FUCA can induce oocyte pre-fertilization ZP hardening and might improve monospermic fertilization performance, and this effect is dependent on both variables (protein concentration and incubation time).

Prediction of major microRNAs in follicular fluid regulating porcine oocyte development

PURPOSE

The aim of the present study was to identify key microRNAs (miRNAs) in porcine follicular fluid (FF) that regulate oocyte growth.

METHODS

miRNAs contained in FF were determined by small RNA-seq of exosome RNA. Upstream regulator miRNA was determined by ingenuity pathway analysis using differentially expressed genes in granulosa cells (GCs) between small follicles (1-2 mm in diameter) and large follicles (3-5 mm), and between follicles containing oocytes of high developmental ability and follicles containing oocytes of low developmental ability. The candidate miRNAs overlapping among the three miRNAs group were determined. Lastly, the effect of supplementation with FF, exosome-depleted FFs, or each miRNA on in vitro oocyte growth was examined.

RESULTS

The miRNAs determined were miR-17, -27, -92a, and -145. These miRNAs were found in the spent culture medium of oocytes and granulosa cells complexes and serum by small RNA sequencing. Culturing of oocytes and granulosa cells complexes collected from porcine early antral follicles (0.5-0.7 mm in diameter) with FF for 14 days improved oocyte growth; depletion of exosomes from the FFs neutralized the beneficial effect observed. miR-92a mimic increased the antrum formation and diameter, together with acetylated levels of H4K12 in oocytes. In addition, supplementation of miRNA mimics miR-17b, -92a, and -145b improved the rate of chromatin configuration, and miR-17b and -92a mimics improved the developmental ability of oocytes to the blastocyst stage.

CONCLUSION

miR-17, -92a, and -145 are major miRNA candidates in follicular fluids regulating oocyte growth.

Follicular factors determining granulosa cell number and developmental competence of porcine oocytes

PURPOSE

Granulosa cell (GC) number in follicles is a simple characteristic of follicles. The present study examined the hypothesis that follicular fluid (FF) determines GC number and oocyte developmental ability and revealed the molecular background determining the number of follicular GCs.

METHODS

FF was collected from antral follicles (3-5 mm in diameter), after which the number of GCs per follicle was determined for each donor gilt using real time PCR targeting single copy gene. GCs were analyzed by next-generation RNA sequencing and IPA pathway analysis.

RESULTS

When oocyte cumulus cell-oocyte-complexes (COCs) were cultured in maturation medium containing 10% of each individual FF, the rate of development to the blastocyst stage was significantly correlated with the number of GCs in the donor gilt. In addition, when GCs were cultured in medium containing FF, the proliferative activity of the GCs was also significantly correlated to the number of GCs in the donor gilt. Moreover, when the FFs were categorized based on the number of GCs in the follicle, it was found that supplementation of culture media with GC-rich FF improved the developmental ability of oocytes compared to those supplemented with GC-poor FF. RNA sequencing and a pathway analysis of GCs from GC-rich and -poor follicles revealed the key regulatory pathway determining GC number in follicles.

CONCLUSION

GC number may be a useful marker for "good" follicles and oocytes, and the characteristics of the FFs determine granulosa cell number and oocyte developmental ability.

Non-esterified fatty acid-associated ability of follicular fluid to support porcine oocyte maturation and development

Purpose

The effect of supplementing maturation medium with follicular fluid (FF) was examined according to its non‐esterified fatty acid (NEFA) content or with a fatty acid mixture (FA‐Mix) on the developmental competence of oocytes, as well as the mitochondrial quality and quantity in the oocytes and cumulus cells.

Method

Porcine oocytes from a slaughterhouse were used.

Results

The FF or FA‐Mix in maturation medium increased the lipid content in both the oocytes and the cumulus cells, but the adenosine triphosphate content was differentially affected. The FF supplementation increased the mitochondrial DNA copy number, survival of cumulus cells, and rate of oocyte development to the blastocyst stage, whereas the FA‐Mix supplementation did not show these effects. The expression levels of GPC4,PFKP,PRDX3, and TFAM in the cumulus cells increased after FF supplementation, but the expression of GJA1 decreased, compared with the cells that were cultured without FF.

Conclusion

Adding FF and FA‐Mix to the maturation medium increased the lipid content in the oocytes and cumulus cells. The effects of FF on the cumulus cells and oocytes were not observed after FA‐Mix supplementation, indicating that the concentration of the NEFAs in the FF are closely associated with an ability to support oocyte maturation and the metabolism of cumulus cells and oocytes.

The dynamic pattern of PLIN3 in pig oocytes and cumulus cells during in vitro maturation

Lipid droplets (LDs) are the main energy resource for porcine preimplantation embryonic development. PLIN3 has been implicated in LD formation and regulation. Therefore, this study aimed to detect the dynamic pattern of PLIN3 in pig oocytes and cumulus cells (CC) during in vitro maturation (IVM), and to determine the relationship between PLIN3 and LD content. IVM with cumulus-enclosed oocytes (CEO), cumulus-denuded oocytes (DO) and the CCs denuded from the corresponding oocytes (DCC) was performed in porcine follicular fluid (PFF) or PFF-free optimized medium. DO and the DCC were cultured together under the same conditions as described above, while the DO was named DTO and the DCC was named DTCC in this group. Firstly, our results revealed LDs distributed widely in oocytes and CC, while the PLIN3 protein coated these LDs and spread out ubiquitously in the cytoplasm. Secondly, not only the mRNA level but also at protein level of PLIN3 in immature naked oocytes (IO) was higher than that in matured CEO, DO and DTO. Although PLIN3 was expressed at lower levels in CC from immature oocytes (ICC), the protein level of PLIN3 was comparably higher in the ECC and DCC groups. The triglyceride (TG) content in CEO and DO was significantly less abundant compared with that in IO. Therefore, our results indicated that co-culturing of oocytes and CC might affect PLIN3 expression levels in CC but not in oocytes. Lipid accumulation in pig oocytes during maturation might be affected by PLIN3 cross-talk between oocytes and CC.

Meiotic arrest with roscovitine and follicular fluid improves cytoplasmic maturation of porcine oocytes by promoting chromatin de-condensation and gene transcription

The developmental capacity of in vitro matured oocytes is inferior to that of the in vivo matured ones due to insufficient cytoplasmic maturation. Although great efforts were made to accomplish better cytoplasmic maturation by meiotic arrest maintenance (MAM) before in vitro maturation (IVM), limited progress has been achieved in various species. This study showed that MAM of porcine oocytes was better achieved with roscovitine than with dibutyryl cyclic adenosine monophosphate (db-cAMP) or 3-isobutyl-1-methylxanthine. Oocyte developmental competence after IVM was significantly improved following MAM in 199 + FF medium (TCM-199 containing 10% porcine follicular fluid and 25 µM roscovitine) to a level even higher than that in control oocytes matured without pre-MAM. Observations on other markers further confirmed the positive effects of MAM in 199 + FF on oocyte cytoplasmic maturation. During MAM culture in 199 + FF, re-decondensation (RDC) of condensed chromatin occurred, and transcription of genes beneficial to cytoplasmic maturation was evident in some of the oocytes with surrounded nucleoli (SN). However, MAM with db-cAMP neither induced RDC nor improved oocyte developmental potential. Together, the results suggest that MAM in the presence of FF and roscovitine improved the developmental competence of porcine oocytes by promoting a pre-GVBD chromatin de-condensation and expression of beneficial genes.

Glycosidases in porcine follicular fluid and their effect on zona pellucida-AWN 1 spermadhesin interaction

Oligosaccharide moieties on the surface of the oocyte belong to the key molecules that direct the course of fertilization and are subjected to changes during oocyte maturation in the follicle. In our study, we focused on the activities of five glycosidases in the fluids from porcine secondary and preovulatory follicles (α-l-fucosidase, α-d-galactosidase, β-d-galactosidase, β-D-N-acetylhexosaminidase, and α-d-mannosidase). All of them were detected active at neutral and acidic pH. However, changes in their activities associated with follicle development were observed only in the case of α-d-mannosidase, which was increased (P < 0.001), and β-d-galactosidase, which was decreased (P < 0.001) at neutral pH, and of α-d-galactosidase and β-N-acetylhexosaminidase, which were decreased (P < 0.0001) at the acidic pH. The comparison of glycosidases from follicular fluid and from blood plasma using red native electrophoresis revealed that most of the glycosidases are present in more than one isoenzyme form; some of them were detected mainly in the follicular fluid. Finally, we tested the effect of glycosidases on the interaction between zona pellucida and AWN 1 spermadhesin (putative sperm receptor of zona pellucida) and demonstrated that the effect of both β-d-galactosidase and to a lesser degree α-d-mannosidase led to a decrease in this interaction. We can hypothesize that these two glycosidases modulate the amount of zona pellucida oligosaccharide moieties and/or their structures for an optimal sperm binding in pigs.

Hampered cumulus expansion of porcine cumulus-oocyte complexes by excessive presence of alpha2 -macroglobulin is likely mediated via inhibition of zinc-dependent metalloproteases

In vitro maturation (IVM) in serum causes hampered expansion of porcine cumulus-oocyte complexes (COCs) due to excessive alpha₂ -macroglobulin (A2M). This study investigated two hypotheses that could explain the effect of A2M: (i) binding of epidermal growth factor (EGF) to A2M, followed by its decreased availability; and (ii) inhibition of zinc-dependent metalloproteases. Cumulus expansion was evaluated based on the diameter of the COCs, the proportion of COCs participating in a floating cloud and the proportion of COCs with loss of cumulus cells. The first hypothesis of decreased EGF availability was tested by increasing the EGF concentration (20 and 50 ng/mL vs. 10 ng/mL), but was not confirmed because cumulus expansion did not improve. To verify the second hypothesis of inhibited zinc-dependent metalloproteases, the effect of tissue inhibitor of metalloproteases-3 (TIMP-3) on cumulus expansion during IVM with and without A2M was investigated. To immuno-neutralize A2M, serum was pre-incubated with A2M antibodies. Impaired cumulus expansion because of TIMP-3 could only be observed during IVM in 10% of serum with A2M antibodies. No effect of TIMP-3 was observed in medium without A2M antibodies. These results indicate that A2M and TIMP-3 share a common target, a zinc-dependent metalloprotease. Future research is directed toward the identification of the protease involved.

Porcine oocyte maturation in vitro: role of cAMP and oocyte-secreted factors - A practical approach

Polyspermy or the penetration of more than one sperm cell remains a problem during porcine in vitro fertilization (IVF). After in vitro culture of porcine zygotes, only a low percentage of blastocysts develop and their quality is inferior to that of in vivo derived blastocysts. It is unknown whether the cytoplasmic maturation of the oocyte is sufficiently sustained in current in vitro maturation (IVM) procedures. The complex interplay between oocyte and cumulus cells during IVM is a key factor in this process. By focusing on this bidirectional communication, it is possible to control the coordination of cumulus expansion, and nuclear and cytoplasmic maturation during IVM to some extent. Therefore, this review focuses on the regulatory mechanisms between oocytes and cumulus cells to further the development of new in vitro embryo production (IVP) procedures, resulting in less polyspermy and improved oocyte developmental potential. Specifically, we focused on the involvement of cAMP in maturation regulation and function of oocyte-secreted factors (OSFs) in the bidirectional regulatory loop between oocyte and cumulus cells. Our studies suggest that maintaining high cAMP levels in the oocyte during the first half of IVM sustained improved oocyte maturation, resulting in an enhanced response after IVF and cumulus matrix disassembly. Recent research indicated that the addition of OSFs during IVM enhanced the developmental competence of small follicle-derived oocytes, which was stimulated by epidermal growth factor (EGF) via developing EGF-receptor signaling.

Interaction between differential gene expression profile and phenotype in bovine blastocysts originating from oocytes exposed to elevated non-esterified fatty acid concentrations

Maternal metabolic disorders linked to lipolysis are major risk factors for reproductive failure. A notable feature of such disorders is increased non-esterified fatty acid (NEFA) concentrations in the blood, which are reflected in the ovarian follicular fluid. Elevated NEFA concentrations impact on the maturing oocyte and even alter subsequent embryo physiology. The aetiological mechanisms have not been fully elucidated. Therefore, in the present study, bovine in vitro maturing cumulus-oocyte complexes were exposed (24 h) to three different maturation treatments containing: (1) physiological (72 µM) NEFA concentrations (=control); (2) elevated (75 µM) stearic acid (SA) concentrations (=HIGH SA); and (3) elevated (425 µM) NEFA concentrations (=HIGH COMBI). Zygotes were fertilised and cultured following standard procedures. Transcriptomic analyses in resulting Day 7.5 blastocysts revealed that the major pathways affected are related to lipid and carbohydrate metabolism in HIGH COMBI embryos and to lipid metabolism and cell death in HIGH SA embryos. Furthermore, lower glutathione content and a reduced number of lipid droplets per cell were observed in HIGH SA-exposed oocytes and resulting morulae, respectively, compared with their HIGH COMBI-exposed counterparts. Vitrified embryos originating from HIGH SA-exposed oocytes tended to exhibit lower survival rates compared with controls. These data suggest possible mechanisms explaining why females across species suffering lipolytic disorders experience difficulties in conceiving.

Influence of co-culture with denuded oocytes during in vitro maturation on fertilization and developmental competence of cumulus-enclosed porcine oocytes in a defined system

Co-culture of cumulus-oocyte complexes (COCs) with denuded oocytes (DOs) during in vitro maturation (IVM) was reported to improve the developmental competence of oocytes via oocyte-secreted factors in cattle. The aim of the present study was to investigate if addition of DOs during IVM can improve in vitro fertilization (IVF) and in vitro culture (IVC) results for oocytes in a defined in vitro production system in pigs. The maturation medium was porcine oocyte medium supplemented with gonadotropins, dbcAMP and β-mercaptoethanol. Cumulus-oocyte complexes were matured without DOs or with DOs in different ratios (9 COC, 9 COC+16 DO and 9 COC+36 DO). Consequently; oocytes were subjected to IVF as intact COCs or after denudation to examine if DO addition during IVM would affect cumulus or oocyte properties. After fertilization, penetration and normal fertilization rates of zygotes were not different between all tested groups irrespective of denudation before IVF. When zygotes were cultured for 6 days, no difference could be observed between all treatment groups in cleavage rate, blastocyst rate and cell number per blastocyst. In conclusion, irrespective of the ratio, co-culture with DOs during IVM did not improve fertilization parameters and embryo development of cumulus-enclosed porcine oocytes in a defined system.

A critical assessment of the effect of serine protease inhibitors on porcine fertilization and quality parameters of porcine spermatozoa in vitro

Proteases play an important role during mammalian fertilization. Their function is frequently investigated using specific inhibitors. We analyzed four serine protease inhibitors [4-(2-aminoethyl) benzene sulfonyl fluoride hydrochloride (AEBSF), soybean trypsin inhibitor from glycine max (STI), Nα-tosyl-L-lysine-chloromethyl ketone hydrochloride (TLCK) and N(p)-tosyl-L-phenylalanine-chloromethyl ketone (TPCK)] for their in vitro effect on fertilization and sperm quality in pigs. Inhibitor concentrations were chosen based on the reduction of fertilization rate during preliminary dose-response experiments with cryopreserved epididymal spermatozoa. The inhibitor effects on in vitro fertilization (IVF) and sperm parameters (membrane and acrosomal integrity, motility and mitochondrial membrane potential - MMP) were evaluated using diluted fresh semen. AEBSF (100 μM), TLCK (100 μM) and TPCK (100 μM) decreased total fertilization and polyspermy rates by at least 50%. STI (5 μM) lowered total fertilization rates but not the level of polyspermy. AEBSF and TPCK reduced fertilization parameters to a similar degree using cryopreserved epididymal spermatozoa (dose-response experiment) or diluted fresh semen. Inhibition by STI was more pronounced using cryopreserved epididymal spermatozoa, whereas TLCK inhibited IVF only with diluted fresh semen. AEBSF and STI had no effect on sperm parameters, and TLCK significantly reduced motility. TPCK diminished MMP and motility and affected membrane and acrosomal integrity in a negative way. In summary, serine protease inhibitors differed in the way they reduce the fertilization rate. These results emphasize the necessity of inhibitor testing before they can be applied in fertilization studies. AEBSF and STI can be used in the future IVF studies without compromising sperm quality.

Increasing the cAMP concentration during in vitro maturation of pig oocytes improves cumulus maturation and subsequent fertilization in vitro

Porcine IVF faces various problems such as incomplete cytoplasmic maturation of the oocyte and polyspermy. Previous studies proved the importance of cAMP in regulating nuclear and cytoplasmic maturation of oocytes. This study investigated the effect of the cAMP-modulating agents 3-isobutyl-1-methylxanthine (IBMX) and dibutyryl cAMP sodium salt (dbcAMP) on several parameters during in vitro production of porcine embryos. First, we wanted to see if oocyte collection in IBMX could meiotically arrest oocytes and, as such, improve synchronization of nuclear and cytoplasmic maturation. To this end, cumulus-oocyte complexes (COCs) were collected from gilts in HEPES-buffered Tyrode balanced salt solution medium with 0.5-mM IBMX or without IBMX. At the end of oocyte collection, the effect of IBMX on chromatin configuration was evaluated. However, no differences could be observed in nuclear configuration between IBMX- and IBMX+ oocytes (P > 0.05). Second, we added dbcAMP during IVM to improve cytoplasmic maturation and evaluated cumulus expansion (lack of adhesion), a disintegrin and metalloproteinase with thrombospondin-like repeats (ADAMTS-1) levels in cumulus cells, fertilization, and blastocyst rates. Cumulus-oocyte complexes were matured in modified North Carolina State University medium 37 with or without 1-mM dbcAMP. Frozen-thawed, epididymal, boar spermatozoa were used for IVF. After IVF, presumed zygotes were cultured for 7 days in North Carolina State University medium 23. Penetration rate decreased in dbcAMP+ (57.3%) compared with dbcAMP- (67.8%), but the polyspermy rate also decreased (43.3% vs. 53.4%, respectively) leading to an increased normal fertilization rate (56.7% vs. 46.6%, respectively; P < 0.05). Only 7.2% of the COCs showed adhesion in dbcAMP+ which was lower than 15.7% in dbcAMP- (P < 0.05) probably because of an upregulation of the ADAMTS-1 protein by dbcAMP. When the adherent oocytes were removed during maturation, no difference could be detected between the blastocyst rate of dbcAMP- and dbcAMP+ (17.1% and 21.0% on Day 7, respectively; P > 0.05). In conclusion, the use of IBMX during collection did not cause a meiotic arrest. Using dbcAMP during IVM caused a greater normal fertilization rate, a lower rate of adherent COCs during IVM, higher levels of ADAMTS-1 in cumulus cells, and an equal blastocyst rate after screening out adherent COCs. These findings contribute to a better understanding of cAMP involvement in porcine oocyte maturation and provide a basis to develop an improved system with less polyspermy and higher blastocyst rates.

Effects of WT1 down-regulation on oocyte maturation and preimplantation embryo development in pigs

The Wilms' tumour 1 (WT1) gene originally identified as a tumour suppressor associated with WTs encodes a zinc finger-containing transcription factor that is expressed in multiple tissues and is an important regulator of cellular and organ growth, proliferation, development, migration and survival. However, there is a deficiency of data regarding the expression and function ofWT1during oocyte maturation and preimplantation embryonic development. Herein, we sought to define the expression characteristics and functions ofWT1during oocyte maturation and preimplantation embryonic development in pigs. We show thatWT1is expressed in porcine oocytes and at all preimplantation stages in embryos generated by ICSI. We then evaluated the effects of down-regulatingWT1expression at germinal vesicle and early ICSI stages using a recombinant plasmid (pGLV3-WT1-shRNA). Down-regulation ofWT1did not affect oocyte maturation but significantly decreased preimplantation embryonic development and increased apoptosis in blastocysts. These results indicate thatWT1plays important roles in the development of porcine preimplantation embryos.

Role of insulin-like growth factor-I and follicular fluid from ovarian follicles with different diameters on porcine oocyte maturation and fertilization in vitro

The objective of this study was to determine the effects of insulin-like growth factor-I (IGF-I) (0, 60, 120, 180, and 240 ng/mL) and follicular fluid (FF) derived from 2 to 5 and 6 to 10 mm diameter follicles (SpFFs and LpFFs, respectively) added during in vitro maturation (IVM) of porcine oocytes on nuclear maturation and IVF. Cumulus-oocyte complexes (COCs) were matured in NCSU-37 medium supplemented with SpFFs or LpFFs and various IGF-I concentrations. The COCs were cultured for 44 hours, and then fertilized in vitro. Maturation and IVF results were recorded 18 hours after insemination. The IVM (%) was higher (P < 0.05) in the COCs matured in LpFFs than with SpFFs when 0 (90.0 ± 6.9 vs. 76.3 ± 10.7) or 60 ng/mL IGF-I (92.0 ± 8.1 vs. 81.8 ± 10.2) was added. In SpFFs media, there was a quadratic relationship (P < 0.01) between IGF-I concentration and IVM (peak results at IGF-I = 129 ng/mL). However, when the COCs were matured with LpFFs, there was a decreasing linear effect between IGF-I concentration and IVM. At all concentrations of IGF-I, the percentage of degenerated oocytes was higher in COCs matured in SpFFs than in LpFFs. Penetration (%) did not differ (P > 0.05) between COCs matured with SpFFs or LpFFs when 60 (66.8 ± 9.4 vs. 72.7 ± 11.3) or 180 ng/mL of IGF-I (75.7 ± 10.4 vs. 73.8 ± 13.2) were used. Monospermy (%) was similar between SpFFs and LpFFs only with addition of 120 ng/mL IGF-I. The IVF performance (%) did not differ between COCs matured with SpFFs or LpFFs when IGF-I concentrations of 120 (28.5 ± 8.8 vs. 38.5 ± 8.3) and 180 ng/mL (24.3 ± 10.2 vs. 30.12 ± 8.2) were used. There was no effect of IGF-I concentration or of FF type on the number of penetrated sperm per oocyte and on male pronuclear formation. For COCs matured with SpFFs, there was a quadratic relationship between IGF-I concentration and penetration, monospermy, and IVF performance (peak results at IGF-I = 179, 122, and 135 ng/mL, respectively). Thus, on the basis of the observed quadratic relationships, we inferred that when using SpFFs, the addition of IGF-I (122-179 ng/mL) to the IVM medium produced results similar to those obtained with LpFFs without adding IGF-I. In conclusion, the addition of IGF-I to the IVM medium supplemented with SpFFs increased maturation and improved IVF results. Alternatively, IGF-I had no effect on IVM or IVF when used with LpFFs.

Liver condition affects bovine oocyte qualities by changing the characteristics of follicular fluid and plasma

The liver is an important organ that contributes to milk production in dairy cows. The aim of this study was to examine whether liver conditions affect the characteristics of blood plasma and follicular fluid (FF) and whether supplementing in vitro maturation medium with FF from either cows with damaged livers (DL) or those with healthy livers (HL) affects oocyte developmental competence. Biochemical characteristics of FF were significantly correlated with those in plasma. As such, the characteristics of both plasma and FF were similarly affected by liver conditions in that the concentrations of total protein and inorganic phosphorus were higher for the DL cow group than for the HL cow group, whereas the concentrations of albumin, lactate dehydrogenase and calcium were lower for DL cows than for HL cows. In addition, supplementing the medium with DL-FF retarded the progression of the nuclear maturation of oocytes collected from the HL cows. On culturing oocytes in maturation medium containing HL-FF, DL-FF or foetal calf serum, the highest developmental rate to the blastocyst stage was observed in the HL-FF group, while the lowest developmental ratio was observed in the DL-FF group. The growth factor array of the FFs revealed that 10 growth factors were significantly downregulated in the DL-FF compared with those in HL-FF. In conclusion, the characteristics of plasma and FF are affected by liver conditions in a similar way. Concentrations of several growth factors were low in DL-FF, as was the ability of DL-FF to support oocyte maturation compared with that of HL-FF.

Dynamic regulation of sperm interactions with the zona pellucida prior to and after fertilisation

Recent findings have refined our thinking on sperm interactions with the cumulus–oocyte complex (COC) and our understanding of how, at the molecular level, the sperm cell fertilises the oocyte. Proteomic analyses has identified a capacitation-dependent sperm surface reordering that leads to the formation of functional multiprotein complexes involved in zona–cumulus interactions in several mammalian species. During this process, multiple docking of the acrosomal membrane to the plasma membrane takes place. In contrast with the dogma that the acrosome reaction is initiated when spermatozoa bind to the zona pellucida (ZP), it has been established recently that, in mice, the fertilising spermatozoon initiates its acrosome reaction during its voyage through the cumulus before it reaches the ZP. In fact, even acrosome-reacted mouse spermatozoa collected from the perivitelline space can fertilise another ZP-intact oocyte. The oviduct appears to influence the extracellular matrix properties of the spermatozoa as well as the COC. This may influence sperm binding and penetration of the cumulus and ZP, and, in doing so, increase monospermic while decreasing polyspermic fertilisation rates. Structural analysis of the ZP has shed new light on how spermatozoa bind and penetrate this structure and how the cortical reaction blocks sperm–ZP interactions. The current understanding of sperm interactions with the cumulus and ZP layers surrounding the oocyte is reviewed with a special emphasis on the lack of comparative knowledge on this topic in humans, as well as in most farm mammals.

Bovine dominant follicular fluid promotes the in vitro development of goat preantral follicles

The aim of this study was to evaluate the effect of follicular fluid collected from bovine dominant follicles (bFF) on the in vitro development of goat preantral follicles and determine the best time to add this supplement to the culture medium. The preantral follicles were isolated and randomly distributed into four treatments in absence (control) or presence of 10% of bFF added on Days 0 (FF0-18), 6 (FF6-18) or 12 (FF12-18) of culture onwards. After 18 days, follicular development was assessed based on follicular survival, antral cavity formation, increased follicular diameter as well as fully grown oocyte (>110 μm) viability and meiosis resumption. The oocytes from the cultured follicles were in vitro-matured and processed for fluorescence or ultrastructural analysis. The results showed that on Day 18 the treatment FF0-18 had a significantly higher (P<0.05) survival than control and FF12-18, but not FF6-18. The addition of bFF at the beginning of culture (FF0-18 and FF6-18) promoted a high percentage of follicular growth, meiosis resumption and early antrum formation. Moreover, this study described for the first time the ultrastructural analysis of caprine oocytes grown in vitro. This evaluation revealed that in the presence of bFF on (FF0-18) the in vitro-grown oocytes presented normal organelle distribution and well-defined, intact plasma and nuclear membranes. In conclusion, bFF originating from dominant follicles maintain the survival and promote the in vitro growth of goat preantral follicles when added at the beginning of culture.

Advances on in vitro production and cryopreservation of porcine embryos

There have been intensive attempts to establish reliable in vitro production (IVP) and cryopreservation methods of embryos in pigs. Although a great deal of progress has been made, current IVP systems and cryopreservation still suffer from insufficient cytoplasmic abilities of in vitro matured oocytes, polyspermic fertilization, poor quality of in vitro produced embryos and low efficiency of embryo cryopreservation. Compared to other mammalian species, pig oocytes and embryos are characterized by large amounts of lipid content stored mainly in the form of lipid droplets in the cytoplasm. This fact has a negative influence on biotechnological applications on porcine oocytes and embryos. In this review, we will discuss recent studies about methods and techniques for modifying porcine embryo IVP system and embryo cryopreservation that produces high quality of pig blastocysts using in vitro maturation, in vitro fertilization, in vitro culture, microsurgical manipulation, addition of protein, the use of cytoskeleton stabilizing agents and various physical methods. The presented methods and techniques make it possible to modify the characteristics of oocytes and embryos and thus may become major tools in mammalian gamete and embryo agricultural or biotechnological applications in the future.

Regulation of oocyte mitochondrial DNA copy number by follicular fluid, EGF, and neuregulin 1 during in vitro maturation affects embryo development in pigs

Little is known about mitochondrial DNA (mtDNA) replication during oocyte maturation and its regulation by extracellular factors. The present study determined the effects of supplementation of maturation medium with porcine follicular fluid (pFF; 0, 10%, 20%, and 30%) on mtDNA copy number and oocyte maturation in experiment 1; the effects on epidermal growth factor (EGF; 10 ng/mL), neuregulin 1 (NRG1; 20 ng/mL), and NRG1 + insulin-like growth factor 1 (IGF1; 100 ng/mL + NRG1 20 ng/mL), on mtDNA copy number, oocyte maturation, and embryo development after parthenogenic activation in experiment 2; and effects on embryo development after in vitro fertilization in experiment 3. Overall, mtDNA copy number increased from germinal vesicle (GV) to metaphase II (MII) stage oocytes after in vitro maturation (GV: 167 634.6 ± 20 740.4 vs. MII: 275 131.9 ± 9 758.4 in experiment 1; P < 0.05; GV: 185 004.7 ± 20 089.3 vs. MII: 239 392.8 ± 10 345.3 in experiment 2; P < 0.05; Least Squares Means ± SEM). Supplementation of IVM medium with pFF inhibited mtDNA replication (266 789.9 ± 11 790.4 vs. 318 510.1 ± 20 377.4; P < 0.05) and oocyte meiotic maturation (67.3 ± 0.7% vs. 73.2 ± 1.2%, for the pFF supplemented and zero pFF control, respectively; P < 0.01). Compared with the control, addition of growth factors enhanced oocyte maturation. Furthermore, supplementation of NRG1 stimulated mitochondrial replication, increased mtDNA copies in MII oocytes than in GV oocytes, and increased percentage of blastocysts in both parthenogenetic and in vitro fertilized embryos. In this study, mitochondrial biogenesis in oocytes was stimulated during in vitro maturation. Oocyte mtDNA copy number was associated with developmental competence. Supplementation of maturation medium with NRG1 increased mtDNA copy number, and thus provides a means to improve oocyte quality and developmental competence in pigs.

Differential apoptotic staining of mammalian blastocysts based on double immunofluorescent CDX2 and active caspase-3 staining

Several approaches have been described for differential staining of blastocysts, but these methods are often time-consuming and unreliable. Here we describe a method for simultaneous differential staining and detection of apoptosis. The differential staining is based on the transcription factor CDX2 which is localized in the nucleus of trophectoderm (TE) cells but absent in the inner cell mass (ICM). Apoptosis is detected by staining of active caspase-3, a key player in several apoptotic pathways. This new approach represents a robust method for quantifying simultaneously ICM/TE ratio and apoptotic cell ratio in bovine, murine, porcine, and human blastocysts.

Relationship between cumulus cell apoptosis, progesterone production and porcine oocyte developmental competence: temporal effects of follicular fluid during IVM

The objective of the present study was to determine the temporal effects of sow follicular fluid (FF) in vitro on cumulus cell viability and function, as well as oocyte nuclear and cytoplasmic maturation. Cumulus–oocyte complexes (COCs) recovered from the ovaries of prepubertal pigs were matured in medium with (+FF) or without (–FF) follicular fluid for the first 22 h of IVM. At 22 h of IVM, each group of COCs was then transferred to medium with or without FF and matured for another 22 h, forming four treatment groups (–FF/–FF, –FF/+FF, +FF/–FF and +FF/+FF). The concentration of progesterone in spent IVM medium and the incidence of cumulus cell apoptosis in individual COCs were determined at 22 and 44 h of IVM. Cumulus expansion was also recorded at 44 h of IVM. Finally, the ability of oocytes to complete meiosis to the MII stage and form blastocysts after IVF and embryo culture was assessed. Maturation with FF for part or the whole of IVM increased cumulus expansion and progesterone production and decreased the incidence of cumulus cell apoptosis compared with the –FF/–FF group (P < 0.05). The changes were greatest for the +FF/+FF group and intermediate for the –FF/+FF and +FF/–FF groups. Regression analysis revealed a negative association between cumulus cell progesterone production and the incidence of cumulus cell apoptosis (P < 0.001). Meiotic maturation was enhanced when FF was present during the first half of IVM. Oocytes matured in the presence of FF during the first and/or second half of IVM displayed an increased ability to form blastocysts compared with the –FF/–FF group (P < 0.05). The extent of the increase was similar for all FF-supplemented groups. The results show that FF exerts several beneficial effects at different times during IVM and suggest that a major role of FF is to provide protection from oxidative stress. We propose that the incidence of cumulus cell apoptosis in COCs must be kept below a certain threshold to ensure adequate functionality, including steroidogenic activity, is maintained for the acquisition of oocyte developmental competence.

Comparative proteome analysis of porcine follicular fluid and serum reveals that excessive alpha(2)-macroglobulin in serum hampers successful expansion of cumulus-oocyte complexes

Porcine follicular fluid (pFF) constitutes the micro-environment of the maturing oocyte. Although pFF is a transudate of serum, in pigs, it is superior to serum in promoting in vitro expansion of the cumulus cells, a specialized cell population surrounding the oocyte. A comparative proteome analysis of autologous serum and pFF was performed to investigate proteins involved in successful cumulus expansion of porcine oocytes. iTRAQ labeling followed by 2-D LC ESI-Q-TOF MS/MS revealed 63 proteins common to both fluids of which the abundance of 13 proteins was significantly different (p<0.05). Seven proteins were more concentrated in serum whereas six proteins were more abundant in pFF. To investigate the importance of these proteins, the cumulus matrices of COCs were collected after in vitro maturation in media supplemented with either of both biologically fluids and then subjected to 2-D PAGE analysis. alpha(2)-Macroglobulin and CH4 and secrete domains of swine IgM, which were both less abundant in pFF, were absent from cumulus matrix extracts after in vitro maturation in pFF. Although both proteins were incorporated in the matrices of cumulus-oocyte complexes matured in serum, depletion of alpha(2)-macroglobulin from serum could significantly compensate for the impaired cumulus expansion of oocytes matured in serum.

Two new splice variants in porcine PPARGC1A

Background

Peroxisome proliferator-activated receptor γ coactivator 1α (PPARGC1A) is a coactivator with a vital and central role in fat and energy metabolism. It is considered to be a candidate gene for meat quality in pigs and is involved in the development of obesity and diabetes in humans. How its many functions are regulated, is however still largely unclear. Therefore a transcription profile of PPARGC1A in 32 tissues and 4 embryonic developmental stages in the pig was constructed by screening its cDNA for possible splice variants with exon-spanning primers.

Findings

This led to the discovery of 2 new splice variants in the pig, which were subsequently also detected in human tissues. In these variants, exon 8 was either completely or partly (the last 66 bp were conserved) spliced out, potentially coding for a much shorter protein of respectively 337 and 359 amino acids (aa), of which the first 291 aa would be the same compared to the complete protein (796 aa).

Conclusion

Considering the functional domains of the PPARGC1A protein, it is very likely these splice variants considerably affect the function of the protein and alternative splicing could be one of the mechanisms by which the diverse functions of PPARGC1A are regulated.