Effects of hormonal supplementation on nuclear maturation and cortical granules distribution of canine oocytes during various reproductive stages

Fighting Like Cats and Dogs: Challenges in Domestic Carnivore Oocyte Development and Promises of Innovative Culture Systems

In vitro embryo production in cats and dogs still presents some challenges, and it needs to be optimized to transfer efficient protocols to related wild, endangered species. While the chemical composition of culture media has been the focus of several studies, the importance of culture substrates for oocyte and embryo culture has often been neglected. Traditional in vitro systems, i.e., two-dimensional cultures, do not resemble the physiological environments where cells develop, and they may cause morphological and functional alterations to oocytes and embryos. More modern three-dimensional and microfluidic culture system better mimic the structure and the stimuli found in in vivo conditions, and they could better support the development of oocytes and embryos in vitro, as well as the maintenance of more physiological behaviors. This review describes the different culture systems tested for domestic carnivore reproductive cells along the years, and it summarizes their effects on cultured cells with the purpose of analyzing innovative options to improve in vitro embryo production outcomes.

"Immunolocalization and effect of low concentrations of Insulin like growth factor-1 (IGF-1) in the canine ovary"

Insulin like growth factor‐1 (IGF‐1) plays an important role in the regulation of ovarian function. Despite its extensive study in several species, there is a paucity of information about IGF‐1`s function and localization in the canine ovary. The aim of the present study was to assess the effect of IGF‐1 on oocyte nuclear maturation and to immunolocalize the IGF‐1 and its receptor (IGF‐1R) in the ovary. Cumulus‐oocyte complexes (COCs) were obtained from 34 bitches. The COCs from each bitch were incubated in TCM 199‐HEPES in the absence (n = 199) or presence (n = 204) of 100 ng/ml IGF‐1 for 96 hr at 38ºC in 5% CO₂, stained and evaluated for nuclear maturation by fluorescence microscopy. The results showed that the addition of IGF‐1 did not have an effect (p ˃ 0.05) on the nuclear maturation under these conditions. The immunohistochemical study revealed nuclear and cytoplasmic staining for IGF‐1 and IGF‐1R, respectively. Both were localized in all ovarian structures including the corpus luteum, but not in the granulosa cells from primordial follicles. In addition, IGF‐1 was not localized in the oocytes in tertiary follicles. The results obtained show the presence of IGF‐1 through the stages of follicular growth and in the corpus luteum of the canine ovary. However, its role on oocyte nuclear maturation could not be demonstrated.

Effects of serum and follicular fluid on the in vitro maturation of canine oocytes

The effects of gonadotropin, serum and follicular fluid on the in vitro maturation of canine oocytes were examined. Additionally, spindle size and spindle migration in MI-stage oocytes derived by in vivo or in vitro maturation were evaluated for the first time. Mature oocytes collected from beagle dog ovaries were divided into two experiments. In experiment I, oocytes were cultured in basic TCM 199 medium supplemented with different levels of P4, E2 and FSH. In experiment II, oocytes in the estrus or anestrus stage were cultured in basic medium supplemented with 30% or 40% canine serum plus 20% or 10% follicular fluid. Our results showed that in experiment I, more oocytes reached MI-MII (18.57%) after supplementation with 1 IU/ml FSH+ 5 IU/ml P4 + 5 IU/ml E2 than after supplementation with other levels of reagents. However, there were no significant differences among the groups (three different concentration groups and a control group) with respect to the proportions of oocytes that resumed meiosis, completed meiosis or degenerated. In experiment II, the number of oocytes from the estrus stage that reached MI-MII in TCM 199 medium supplemented with 40% canine serum and 10% follicular fluid (46.72%) was significantly higher (p < 0.01) than the number of oocytes from the anestrus stage that reached MI-MII in medium supplemented with 30% canine serum and 20% follicular fluid (21.84%). In addition, the degeneration rate was significantly lower (p < 0.05) in the 40% canine serum/10% follicular fluid group from follicular stage than in the other three groups. The average spindle length of the MI-stage oocytes that matured in vivo was significantly (p < 0.01) longer than that of the MI-stage oocytes that matured in vitro (21.75 vs. 14.39 μm). These results suggest that supplementation of the culture medium with 40% estrus serum and 10% follicular fluid had a positive influence on the in vitro maturation of canine oocytes and greatly affected spindle size in MI-stage oocytes.

Nuclear competence and genetic expression of growth differentiation factor-9 (GDF-9) of canine oocytes in 3D culture

To evaluate the ability of a 3D culture system in improving the nuclear and molecular competence of canine oocytes, barium alginate microcapsules were used for in vitro maturation (IVM) and the expression profile of one selected oocyte-secreted factor, the growth differentiation factor-9 (GDF-9) was analysed. In Experiment I, canine grade I cumulus-oocyte complexes (COCs) were in vitro matured in 3D microcapsules in a controlled atmosphere for 72 hr, and meiosis resumption rates were compared to those of oocytes cultured in traditional 2D microdrops of medium. In Experiment II, a primer pair specific for canine GDF-9 was designed, and preliminary tested in conventional PCR on genomic DNA. Total RNA content was isolated from oocytes at different time intervals (T0-T24-T48-T72) during in vitro 3D culture, and a reverse transcription to cDNA was performed. The expression of target gene was assessed by quantitative Reverse Transcription Real-Time PCR (qRT-PCR), and the obtained amplicons were sequenced to check the specificity of the analysis. Canine COCs resumed meiosis at higher rates in 3D microcapsules than in 2D microdrops (p < 0.05), even though no significant differences in the proportions of oocytes achieving full maturational stages were obtained. A significant dynamic decrease in GDF-9 expression was recorded during culture: after 72 hr of IVM, the GDF-9 transcription significantly dropped (p = 0.018) compared to 24 and 48 hr. In conclusion, in vitro 3D culture represents an efficient system for IVM of canine oocytes, and the expression profile of GDF-9 well reflects temporal dynamics for the acquisition of developmental competence in this species.

Differential gene-expression profiles from canine cumulus cells of ovulated versus in vitro-matured oocytes

We compared the nuclear maturation status and gene-expression profiles of canine cumulus cells (CCs) derived from cumulus-oocyte complexes (COCs) that were spontaneously ovulated versus those that were matured in vitro. Cumulus-oocyte complexes were retrieved from uteri by surgical flushing (after spontaneous ovulation) or by ovariectomy follicle aspiration and in vitro maturation. The objective of Experiment 1 was to investigate the nuclear maturation status of in vivo- versus in vitro-matured oocytes. The objective of Experiment 2 was to compare gene-expression profiles of CCs derived from in vivo- versus in vitro-matured COCs. Genes analysed are related to cell maturation, development and apoptosis, including GDF9, MAPK1, PTX3, CX43, Bcl2 and BAX; mRNA expression for all of these genes, except for GDF9, differed (P<0.05) between in vivo- and in vitro-matured CCs. In conclusion, we found that gene-expression profiles are related to the quality of CCs and therefore posit that monitoring gene expression could be a useful strategy to guide attempts to improve in vitro culture systems.

Impact of gonadotropins on oocyte maturation, fertilisation and developmental competence in vitro

The aim of the present study was to evaluate the dose-dependent effects of gonadotropins, either singly (Bravelle (B), Luveris (L), Menupur (M), Repronex (R), Gonal-F (G), Follism (F) and Norvarel (N)) or in combination (Menupur+Bravelle; Repronext+Bravelle; and Bravelle+Norvarel), on rates of oocyte maturation, fertilisation and early embryo development in vitro in an animal model. Bovine cumulus-oocyte complexes (COCs) were purchased commercially and cultured in TCM-199 with 10% fetal bovine serum supplemented with varying concentrations of gonadotropin (0, 5, 10, 20, 40IU or United States Pharmacopoeia (USP) mL-1) for 24 and 48h according to current IVF clinical stimulation protocols. All gonadotropins enhanced oocyte maturation in vitro in a dose-dependent manner. Individually, Gonal-F (Merck KGaA, Darmstadt, Germany), Follism (Merck Co, Whitehouse Station, NJ, USA) and Repronext (Ferring, Parsippany, NJ, USA) promoted oocyte maturation; in combination, they effectively enhanced COC expansion and increased the maturation competence of MII oocytes. However, high concentrations of gonadotropins may result in maturation arrest. Specific combinations of gonadotropins may change the rate of early embryonic development (8-16-cells) and morula-blastocyst formation. These data provide support for the responsiveness of bovine oocytes to gonadotropins in vitro and the need to consider variations in the relative concentrations and ratio of combinations (FSH/LH or human chorionic gonadotropin) for optimisation of oocyte developmental competence. The results of the present study could be applied to therapeutic clinical stimulation protocols and help improve IVF success rates.