Epidermal growth factor enhances meiotic resumption of canine oocytes in the presence of BSA

Interaction between epidermal growth factor receptor and C-C motif chemokine receptor 2 in the ovulatory cascade

The epidermal growth factor receptor (EGFR) signaling pathway is one of the main pathways responsible for propagating the luteinizing hormone (LH) signal throughout the cumulus cells and the oocyte. Recently, we have proposed the C-C motif chemokine receptor 2 (CCR2) and its main ligand (monocyte chemoattractant protein-1, MCP1) as novel mediators of the ovulatory cascade. Our previous results demonstrate that the gonadotropins (GNT), amphiregulin (AREG), and prostaglandin E2 (PGE2) stimulation of periovulatory gene mRNA levels occurs, at least in part, through the CCR2/MCP1 pathway, proposing the CCR2 receptor as a novel mediator of the ovulatory cascade in a feline model. For that purpose, feline cumulus-oocyte complexes (COCs) were cultured in the presence or absence of an EGFR inhibitor, recombinant chemokine MCP1, and gonadotropins [as an inducer of cumulus-oocyte expansion (C-OE), and oocyte maturation] to further assess the mRNA expression of periovulatory key genes, C-OE, oocyte nuclear maturation, and steroid hormone production. We observed that MCP1 was able to revert the inhibition of AREG mRNA expression by an EGFR inhibitor within the feline COC. In accordance, the confocal analysis showed that the GNT-stimulated hyaluronic acid (HA) synthesis, blocked by the EGFR inhibitor, was recovered by the addition of recombinant MCP1 in the C-OE culture media. Also, MCP1 was able to revert the inhibition of progesterone (P4) production by EGFR inhibitor in the C-OE culture media. Regarding oocyte nuclear maturation, recombinant MCP1 could also revert the inhibition triggered by the EGFR inhibitor, leading to a recovery in the percentage of metaphase II (MII)-stage oocytes. In conclusion, our results confirm the chemokine receptor CCR2 as a novel intermediate in the ovulatory cascade and demonstrate that the EGFR/AREG and the CCR2/MCP1 signaling pathways play critical roles in regulating feline C-OE and oocyte nuclear maturation, with CCR2/MCP1 signaling pathway being downstream EGFR/AREG pathway within the ovulatory cascade.

Oocyte maturation-related gene expression in the canine oviduct, cumulus cells, and oocytes and effect of co-culture with oviduct cells on in vitro maturation of oocytes

PURPOSE

In contrast to most other mammals, canine oocytes are ovulated in an immature state and undergo oocyte maturation within the oviduct during the estrus stage. The aim of the study was to investigate whether oviduct cells from the estrus stage affect the maturation of oocytes and show gene expression patterns related to oocyte maturation.

METHODS

We analyzed MAPK1/3, SMAD2/3, and BMP6/15 expression in oviduct cells, cumulus cells, and oocytes from anestrus, estrus, and diestrus stages. Next, we investigated the effect of co-culture with oviduct cells derived from the estrus stage upon in vitro maturation (IVM) of canine oocytes.

RESULTS

There was significantly higher MAPK1/3 (1.42 ± 0.02 and 2.23 ± 0.06), SMAD2/3 (0.77 ± 0.03 and 2.39 ± 0.07), and BMP15 (2.21 ± 0.16) expression in oviduct cells at the estrus stage (P < 0.05). In cumulus cells, MAPK1 (1.26 ± 0.07), SMAD2/3 (0.82 ± 0.01, 1.04 ± 0.01), and BMP6 (13.09 ± 0.11) expression was significantly higher in the estrus stage (P < 0.05). In oocytes, significant upregulation of MAPK1/3 (14,960 ± 3121 and 1668 ± 253.4), SMAD3 (774.6 ± 79.62), and BMP6 (8500 ± 895.4) expression was found in the estrus stage (P < 0.05). After 72 h of IVM culture, a significantly higher maturation rate was observed in oocytes co-cultured with oviduct cells (10.0 ± 1.5%) than in the control group (3.2 ± 1.4%).

CONCLUSIONS

We demonstrate that oviduct cells at the estrus stage highly expressed MAPK1/3, SMAD2/3, and BMP15. Furthermore, canine oviduct cells from the estrus stage enhance the culture environment for canine oocyte maturation.

Effects of 5α-dihydrotestosterone and 17β-estradiol on the mouse ovarian follicle development and oocyte maturation

We have previously reported that androstenedione induces abnormalities of follicle development and oocyte maturation in the mouse ovary. In granulosa cells of the ovarian follicle, androstenedione is aromatized to 17β-estradiol (E₂). To determine whether the androgen or estrogen acts directly on the follicle to induce the above-mentioned abnormalities, we compared the effects of a non-aromatizable androgen, 5α-dihydrotestosterone (DHT), with those of E₂ on murine follicular development and oocyte maturation in a single follicle culture system. The high dose (10⁻⁶ M) of DHT prompted normal follicular development, and there was no effect on oocyte meiotic maturation after stimulation with human chorionic gonadotropin (hCG) and epidermal growth factor (EGF). In contrast, culture with the high dose (10⁻⁶ M) of E₂ delayed follicular growth and also suppressed proliferation of granulosa cells and antrum formation. Furthermore, culture with E₂ delayed or inhibited oocyte meiotic maturation, such as chromosome alignment on the metaphase plate and extrusion of the first polar body, after addition of hCG and EGF. In conclusion, these findings demonstrate that E₂, but not DHT, induces abnormalities of follicular development, which leads to delay or inhibition of oocyte meiotic maturation.

The in vitro culture supplements and selected aspects of canine oocytes maturation

The maturation of oocytes is one of the most important steps determining their developmental competence. Due to the low percentage of oocytes of bitches that reach the MII stage, searching for reagents that may stimulate the growth and maturation of oocytes is still present in this species of mammals. The most important media supplements include gonadotropins (LH, FSH, hCG), growth factors (IGF, TGF, EGF, FGF), progesterone and follicular fluid. It is suggested that the supplement of EGF, and/or follicular cells may have an important influence on the percentage of cells that reach the MII stage. Despite plenty of research based on the improvement of bitch oocytes in vitro culture, the results obtained are still unsatisfactory. Moreover, in the long stages of canine oocytes maturation many molecular and morphological modifications (including changes in mitochondria structure and configuration in the cytoplasm) are involved. In this article, the influence of selected media supplements on the efficiency of bitch oocytes in vitro maturation was described. The molecular and morphological modifications during canine oocytes maturation were also considered in the text.

Reliability of Hoechst 33342 staining under wide-field microscopy for evaluation of the nuclear status of living dog oocytes

Due to the marked cytoplasmic opacity of canine oocytes, the diagnosis of their nuclear status is difficult. The objective of the present study was to evaluate the accuracy of Hoechst staining observed under epifluorescence wide-field microscopy [living oocyte observation (LivOO)] by comparison to a reference technique [DNA staining with ethidium homodimer-2 under confocal microscopy; fixed oocyte observation (FixOO)]. Four Hoechst 33342 concentrations (200 ng, 500 ng, 1 μg, 2 μg/mL) were tested and 1 μg/mL was the lowest one with the lowest proportion of oocytes in which DNA was missed. At this concentration, LivOO procedure did not affect the degeneration rate. On 379 oocytes observed individually with the two techniques successively, diagnosis of meiosis resumption by LivOO was exact in 87.3% of the cases, but the meiosis resumption rate was underestimated (23.5% versus 34.3% with FixOO; p < 0.001). Diagnosis for metaphase II was exact in 80% of the cases, but LivOO detected only 72.7% of the metaphase II oocytes present. Metaphase rates did not differ between LivOO and FixOO. This study contributes to a better interpretation of in vitro maturation results. The developmental potential of metaphase II canine oocytes sorted after Hoechst staining is to be evaluated.

The influence of 9-cis-retinoic acid on nuclear and cytoplasmic maturation and gene expression in canine oocytes during in vitro maturation

Retinoids have important roles in regulation of oocyte nuclear and cytoplasmic maturation. The present study investigated the effects of a retinoid metabolite on nuclear maturation, cytoplasmic maturation, and gene expression in canine oocytes during in vitro maturation (IVM). Cumulus-oocyte complexes (COCs) were harvested from ovaries by slicing. Only oocytes that were >120 μm in diameter, with a homogeneous dark cytoplasm and three or more layers of compact cumulus cells were used. Varying concentrations of 9-cis retinoic acid (9-cis-RA; 0, 5, 50, and 500 nm) were included in the maturation medium, and the following were measured: (i) oocyte nuclear maturation after culture for 48 h; (ii) cytoplasmic granular migration by labeling of oocytes with fluorescein isothiocyanate labeled lectins; and (iii) relative expression of genes related to apoptosis (BAX and BclII) in cumulus cells detached from oocytes, by semiquantitative reverse transcriptase-polymerase chain reaction. After 48 h culture with IVM, the highest percentage of oocytes that had developed to the metaphase II (MII) stage were in the 5 nm 9-cis-RA treatment group (18.3 ± 2.5%; P < 0.05). Complete granular migration was observed in oocytes matured with 5 nm 9-cis-RA, consistent with a commensurate gain in developmental competence. Treatment with 5 nm 9-cis-RA had no effect on BclII gene expression, but downregulated BAX expression. In conclusion, since 5 nm 9-cis-RA was beneficial to nuclear and cytoplasmic maturation of canine oocytes, we inferred an important role for 9-cis-RA during IVM.

The canine oocyte: uncommon features of in vivo and in vitro maturation

The biology of the canine oocyte is unusual compared with that of other mammalian females. The present paper reviews both in vivo and in vitro specificities of canine oocytes. Final follicular growth in the bitch is characterised by an early appearance of LH binding sites in the granulosa, a high proportion of polyovular follicles and a preovulatory luteinisation, starting at the time of the LH surge. Through follicular fluid, preovulatory oocytes are thus exposed to high levels of progesterone, as high as 1000-fold plasma concentrations. The composition of the follicular fluid is affected by the size of the female. The more specific aspect of oocyte biology in the bitch is ovulation: oocytes are expelled immature, at the Prophase I stage. Ovulatory follicles are 6–8 mm in diameter, releasing oocytes from 110 µm, with dark cytoplasm. Resumption of meiosis occurs from 48 h postovulation, MII stages appearing 48–54 h after ovulation. The mechanisms controlling such a late meiotic resumption are still unknown. Granulosa cells seem to play a central role as in other mammalian species, but not with cAMP as the principal mediator. The importance of a transient reactivation of oocyte transcription a few hours before meiotic resumption is to be explored. These specific features may contribute to the low efficiency of IVM. Only 10–20% oocytes reach the metaphase stage and suffer from a poor cytoplasmic maturation. Moreover, in vitro culture of canine oocytes is associated with a high proportion of degeneration. To date, IVM of the oocytes is the main limiting factor for the development of assisted reproductive techniques in the canine. A better knowledge of the basic physiology of folliculogenesis and the molecular mechanisms controlling oocyte meiosis resumption in this species may allow us to overcome this obstacle.

Influence of epidermal growth factor supplementation during in vitro maturation on nuclear status and gene expression of canine oocytes

This study evaluated the effect of epidermal growth factor (EGF) supplementation during in vitro maturation on the meiotic status and the expression of EGF receptor (EGFr), luteinizing hormone receptor (LHr) and gap junction protein α 5 (GJA5) in canine cumulus-oocyte-complexes (COCs). COCs of ≥110 μm diameter, exhibiting dark pigmentation and completely surrounded by three or more layers of cumulus cells collected from anestrus stage ovaries in natural cycle were matured in TCM-199 supplemented with 10% fetal bovine serum, 0.57 mM cysteine, 10 μg/ml LH and FSH, and different concentrations of EGF (0, 10 and 30 ng/ml). Oocytes cultured for 72 h were fixed to assess the nuclear maturation. Expression of EGFr, LHr and GAJ5 was assessed by immunocytochemistry and real-time PCR. Proportion of metaphase II status of oocytes cultured in in vitro maturation (IVM) medium supplemented with 10 ng/ml EGF for 72 h was significantly (P<0.05) higher than 0 and 30 ng/ml EGF supplemented IVM medium (9.8% vs. 6.5% and 5.2%). In both cumulus cells and oocytes, EGFr protein was undetectable, LHr protein level of expression was low and a strong expression of GJA5 protein was observed. The relative abundance (RA) of EGFr transcript revealed low levels and the LHr expression decreased steadily with addition of EGF. However it did not vary among different concentrations of EGF supplementation. The RA of GJA5 transcript exhibited lower level at 10 ng/ml EGF supplementation. In conclusion, the supplementation of 10 ng/ml EGF in IVM media exerted a positive influence on the progression of maturation to MII phase and the expression level of GJA5 at 72 h, but did not demonstrate any stimulatory role on the expression of EGFr and LHr during the maturation of the canine IVM oocytes.

Effects of estrous cycle stage and transport temperature of ovaries on in vitro maturation of canine oocytes

Unlike other domestic animals, in vitro maturation (IVM) of canine oocytes still has limited success. The present study investigated the effects of estrous cycle stage and transport temperature of ovaries on in vitro maturation of canine oocytes. The donor bitches were categorized into three groups based on stage of estrus cycle: follicular (proestrus or estrous), luteal (diestrus) and anestrus. One ovary of each pair collected from 39 mature bitches was transported in Phosphate Buffer Saline (PBS) at 4 degrees C while the other was transported at 37 degrees C. A total of 1138 Grade I COCs obtained from all ovaries were grouped and matured in modified synthetic oviduct fluid (mSOF) supplemented with follicle stimulating hormone (FSH), luteinizing hormone (LH), essential and non-essential amino acids at 38.5 degrees C in a humidified 5% CO(2), 5% O(2), and 90% N(2) atmosphere for 72 h. The nuclear maturation rates were evaluated by aceto-orcein staining. Oocytes harvested from follicular and luteal ovaries have a significantly higher maturation rates (MI+MII) than the oocytes from anestrual ovaries in the 37 degrees C group (p<0.05). However, oocytes harvested from anestrual ovaries transported at 4 degrees C had the highest maturation (MI+MII) rate, and the difference between anestrual and luteal ovary groups was significant (p<0.05). The oocytes from anestrual ovaries transported at 4 degrees C have significantly higher maturation rates than those transported at 37 degrees C (p<0.0001). However, the transport temperature (37 or 4 degrees C) did not significantly affect the maturation (MI+MII) rates of oocytes harvested from the luteal (p=0.61) and follicular (p=0.48) stage ovaries. It can be concluded from this study that (1) both transport temperature and transport temperaturexestrus cycle stage interaction effected the maturation rates, while estrus cycle stage alone did not, and (2) transporting canine ovaries at 4 degrees C can improve in vitro maturation rates in oocytes harvested from anestrous ovaries.

The effects of hCG and growth factors on in vitro nuclear maturation of dog oocytes obtained during anoestrus

The effects of human chorionic gonadotrophin (hCG) and a combination of growth factors on the developmental competence of canine oocytes during in vitro maturation was examined. Oocytes recovered from domestic dog ovaries at routine ovariectomy were cultured in a basic tissue culture medium with 0.3% BSA, 7 μg mL–1 progesterone and antibiotics. After the appropriate culture periods (up to 96 h), they were fixed and labelled by double-antibody immunofluorescence for tubulin and with propidium iodide for chromatin. Human chorionic gonadotrophin increased the proportion of oocytes resuming meiosis and reduced the degeneration rate. Supplementing with hCG in declining concentrations was of no superior benefit but the presence of a combination of growth factors (growth hormone, insulin-like growth factor-1, transforming growth factor-α and fibroblast growth factor) improved both the resumption of meiosis and the degeneration rate. No particular synergisms between pairs of growth factors could be demonstrated. Human chorionic gonadotrophin and growth factors together gave poorer results, implying that hCG inhibited the beneficial effects of the growth factors. A growth factor combination is the present most successful treatment, with 49% of total oocytes (inclusive of degenerated) recovered from anoestrous bitches at MI or MII by 96 h of culture. This is the highest result so far demonstrated for cultured dog oocytes.

Nuclear maturation and development of IVM/IVF canine embryos in synthetic oviductal fluid or in co-culture with buffalo rat liver cells

In vitro embryo production in the domestic bitch can provide valuable insights for conservation of endangered canids. In the present study, canine oocytes underwent in vitro maturation (IVM) in simple or complex media, with production of in vitro matured and fertilized (IVM/IVF) canine embryos. Cumulus-oocyte complexes (COCs) were harvested from ovaries by slicing and subjected to IVM in four media (SOF, TCM 199, Ham-F10, and DMEM/F12). After culture for 48h, oocytes were stained and examined for nuclear maturation. There were no significant differences in the mean (+/-S.D.) percentage of nuclear maturation (metaphase II) of oocytes cultured in SOF (18.6+/-7.6%), TCM 199 (18.3+/-4.5%), Ham-F10 (13.9+/-8.2%), or DMEM/F12 (11.9+/-4.2%). For assessment of embryo development, oocytes were matured for 48h in synthetic oviductal fluid (SOF), fertilized with frozen-thawed sperm, and presumptive zygotes were cultured for 7 d, either in SOF or as co-cultures with BRL cells in TCM 199. Percentages of IVM/IVF oocytes that developed to the 2-cell, 3-4-cell, and 5-7-cell stages were higher (P<0.05) following culture in SOF versus BRL cell co-cultures (33.6+/-1.2% vs 13.7+/-1.2%, 24.7+/-0.5% vs 8.7+/-1.1%, and 15.1+/-2.2% vs 4.3+/-1.3%, respectively). However, none of the embryos developed beyond the 8-16-cell stage. In conclusion, simple or complex media successfully induced resumption of meiosis and nuclear maturation of canine oocytes. Furthermore, SOF supported in vitro development of IVM/IVF canine embryos to the 8-16-cell stage.

Effect of follicle stimulation hormone and luteinizing hormone on cumulus cell expansion and in vitro nuclear maturation of canine oocytes

In general, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) play important roles in the regulation of cumulus cell expansion and oocyte maturation. We investigated the effects of supplementation of FSH or LH in in vitro maturation (IVM) medium on the incidence of cumulus cell expansion and nuclear maturation in canine oocytes. Cumulus-oocyte complexes (COCs) were cultured in TCM-199 supplemented with 10% foetal bovine serum (FBS), 1 mg/ml cysteine, 0.2 mm pyruvic acid and different concentrations of FSH or LH (control, 0.5, 5 or 50 microg/ml) at 38.5 degrees C, 5% CO(2) in air for 72 h. The cumulus cell expansion was measured by microscopic visualization, and nuclear maturation of denuded oocytes was determined by staining with 10 microg/ml Hoechst33342 for 30 min. The cumulus cell expansion in the 5 microg/ml FSH group (397.2 +/- 64.3 microm) was significantly higher than those in the control, 0.5, and 50 microg/ml FSH groups (168.3 +/- 19.1, 286.0 +/- 69.7 and 300.0 +/- 84.3 microm, respectively; p < 0.05). However, there was no difference in cumulus cell expansion among the control, 0.5, 5 and 50 microg/ml LH groups (165.6 +/- 20.2, 160 +/- 26.5, 172 +/- 20.5 and 168 +/- 23.1 microm, respectively; p > 0.05). After 72 h of IVM, the proportion of nuclear development to the MI-MII stage in the 0.5 microg/ml FSH group (15.1%) was higher than those in the control, 0.5 and 50 microg/ml FSH groups (0.9%, 6.5% and 8.0%, respectively; p < 0.05). However, there was no significant difference in nuclear maturation to the MI-MII stage among control, 0.5, 5 and 50 microg/ml LH groups (4.6%, 2.3%, 5.4% and 8.6%, respectively; p > 0.05). This study indicated that a FSH supplement in IVM medium can increase cumulus cell expansion and nuclear maturation, while the nuclear maturation rate remained low. Further studies are required to improve the nuclear development to the MI-MII stages in canine oocytes.

In vitro maturation, in vitro fertilization and embryonic development of canine oocytes

In this study we have investigated the efficiency of in vitro maturation (IVM) as a basic way to study the development of canine oocytes after in vitro fertilization (IVF). We decided, therefore, to perform two-part experiments. Firstly, experiment I compared the effects of TCM199 without fetal bovine serum (FBS) with TCM199 supplemented with 5% FBS on the in vitro nuclear maturation rate of canine oocytes. For the efficiency of meiotic development to the metaphase II (MII) stage, we found that 4.7% (4/64) of all oocytes grown in TCM199 without FBS developed to the MII stage compared with only 1.7% (1/59) of those grown in TCM199 with 5% FBS for 48 h. Therefore, FBS did not increase in vitro nuclear maturation. In experiment II, the cleavage rate of canine oocytes used for IVF was investigated following heparin treatment. Canine oocytes were fertilized in four groups: Fert-TALP medium without heparin (Fert I) or Fert-TALP medium supplemented with 10, 20 or 30 microg/ml heparin (Fert II, Fert III, Fert IV, respectively). Oocytes that were grown for 24 h in Fert I following fertilization showed the highest rate of all of the groups, 6.5% (5/77) and developed to the early morula stage. Markedly, the oocytes cultured in Fert I for 24 h following insemination had a higher rate of embryonic development than other groups. We can assert that, unlike findings in other mammals, heparin treatment in canine IVF does not increase the efficiency of the fertilization rate and is therefore not an important factor.

Synchronisation of canine germinal vesicle stage oocytes prior to in vitro maturation alters the kinetics of nuclear progression during subsequent resumption of meiosis

Inhibition of meiosis before in vitro maturation (IVM) can improve meiotic competence in immature mammalian oocytes. Therefore, meiosis-inhibiting agents were evaluated singularly for the ability to arrest and synchronise germinal vesicle (GV) stage canine oocytes, and the most effective treatments were combined to improve meiotic resumption rates. Oocytes cultured in 2 ng mL–1 oestradiol (E2), 10 IU mL–1 eCG, or both (EG) for 72 h resulted in significantly fewer oocytes resuming meiosis in EG than the control, E2, or with eCG. Oocytes cultured in 50 or 100 μmol L–1 of butyrolactone 1 or roscovitine (ROS) for up to 48 h did not resume meiosis nor increase subsequent meiotic resumption rates following IVM. A combination of 50 μmol L–1 ROS and EG treatment for 48 h significantly increased the proportion of canine oocytes in meiotic arrest. More importantly, following 48 h of IVM, ROS+EG-treated oocytes demonstrated a dramatic increase in the ability to resume meiosis compared with the non-treated controls (51.3 ± 8.2% and 10.8 ± 4.5%, respectively; P < 0.05). These data indicate that chemical and biological meiotic inhibitors are effective at inducing GV arrest in canine oocytes. Furthermore, these inhibitors are reversible and beneficial to subsequent meiotic resumption in vitro.