Oocyte developmental capacity is influenced by intrinsic ovarian factors in a bovine model for individual embryo production

Corpus luteum presence in the bovine ovary increase intrafollicular progesterone concentration: consequences in follicular cells gene expression and follicular fluid small extracellular vesicles miRNA contents

BACKGROUND

It is well described that circulating progesterone (P4) plays a key role in several reproductive events such as oocyte maturation. However, during diestrus, when circulating P4 is at the highest concentrations, little is known about its local impact on the follicular cells such as intrafollicular P4 concentration due to corpus luteum (CL) presence within the same ovary. Based on that, our hypothesis is that the CL presence in the ovary during diestrus alters intrafollicular P4 concentrations, oocyte competence acquisition, follicular cells gene expression, and small extracellular vesicles (sEVs) miRNAs contents.

RESULTS

P4 hormonal analysis revealed that ipsilateral to the CL follicular fluid (iFF) presented higher P4 concentration compared to contralateral follicular fluid (cFF). Furthermore, oocyte maturation and miRNA biogenesis pathways transcripts (ADAMTS-1 and AGO2, respectively) were increased in cumulus and granulosa cells of iFF, respectively. Nevertheless, a RT-PCR screening of 382 miRNAs showed that three miRNAs were upregulated and two exclusively expressed in sEVs from iFF and are predicted to regulate cell communication pathways. Similarly, seven miRNAs were higher and two exclusively expressed from cFF sEVs and are predicted to modulate proliferation signaling pathways.

CONCLUSION

In conclusion, intrafollicular P4 concentration is influenced by the presence of the CL and modulates biological processes related to follicular cell development and oocyte competence, which may influence the oocyte quality. Altogether, these results are crucial to improve our knowledge about the follicular microenvironment involved in oocyte competence acquisition.

Manual versus deep learning measurements to evaluate cumulus expansion of bovine oocytes and its relationship with embryo development in vitro

Cumulus expansion is an important indicator of oocyte maturation and has been suggested to be indicative of greater oocyte developmental capacity. Although multiple methods have been described to assess cumulus expansion, none of them is considered a gold standard. Additionally, these methods are subjective and time-consuming. In this manuscript, the reliability of three cumulus expansion measurement methods was assessed, and a deep learning model was created to automatically perform the measurement. Cumulus expansion of 232 cumulus-oocyte complexes was evaluated by three independent observers using three methods: (1) measurement of the cumulus area, (2) measurement of three distances between the zona pellucida and outer cumulus, and (3) scoring cumulus expansion on a 5-point Likert scale. The reliability of the methods was calculated in terms of intraclass-correlation coefficients (ICC) for both inter- and intra-observer agreements. The area method resulted in the best overall inter-observer agreement with an ICC of 0.89 versus 0.54 and 0.30 for the 3-distance and scoring methods, respectively. Therefore, the area method served as the base to create a deep learning model, AI-xpansion, which reaches a human-level performance in terms of average rank, bias and variance. To evaluate the accuracy of the methods, the results of cumulus expansion calculations were linked to embryonic development. Cumulus expansion had increased significantly in oocytes that achieved successful embryo development when measured by AI-xpansion, the area- or 3-distance method, while this was not the case for the scoring method. Measuring the area is the most reliable method to manually evaluate cumulus expansion, whilst deep learning automatically performs the calculation with human-level precision and high accuracy and could therefore be a valuable prospective tool for embryologists.

Disorder of Biological Quality and Autophagy Process in Bovine Oocytes Exposed to Heat Stress and the Effectiveness of In Vitro Fertilization

The main problem in dairy herds is reproductive disorders, which are influenced by many factors, including temperature. Heat stress reduces the quality of oocytes and their maturation through the influence of, e.g., mitochondrial function. Mitochondria are crucial during oocyte maturation as well as the process of fertilization and embryonic development. Disturbances related to high temperature will be increasingly observed due to global warming. In present studies, we have proven that exposure to high temperatures during the cleaving of embryos statistically significantly (at the level of p < 0.01) reduces the percentage of oocytes that cleaved and developed into blastocysts eight days after insemination. The study showed the highest percentage of embryos that underwent division in the control group (38.3 °C). The value was 88.10 ± 6.20%, while the lowest was obtained in the study group at 41.0 °C (52.32 ± 8.40%). It was also shown that high temperature has a statistically significant (p < 0.01) effect on the percentage of embryos that developed from the one-cell stage to blastocysts. The study showed that exposure to a temperature of 41.0 °C significantly reduced the percentage of embryos that split relative to the control group (38.3 °C; 88.10 ± 6.20%). Moreover, it was noted that the highest tested temperature limits the development of oocytes to the blastocyst stage by 5.00 ± 9.12% compared to controls (33.33 ± 7.10%) and cleaved embryos to blastocysts by 3.52 ± 6.80%; the control was 39.47 ± 5.40%. There was also a highly significant (p < 0.0001) effect of temperature on cytoplasmic ROS levels after 6 and 12 h IVM. The highest level of mitochondrial ROS was found in the group of oocytes after 6 h IVM at 41.0 °C and the lowest was found in the control group. In turn, at 41.0 °C after 12 h of IVM, the mitochondrial ROS level had a 2.00 fluorescent ratio, and the lowest in the group was 38.3 °C (1.08). Moreover, with increasing temperature, a decrease in the expression level of both LC3 and SIRT1 protein markers was observed. It was proved that the autophagy process was impaired as a result of high temperature. Understanding of the cellular and molecular responses of oocytes to elevated temperatures will be helpful in the development of heat resistance strategies in dairy cattle.

Postmortem Collection of Gametes for the Conservation of Endangered Mammals: A Review of the Current State-of-the-Art

The collection of gametes from recently deceased domestic and wildlife mammals has been well documented in the literature. Through the utilization of gametes recovered postmortem, scientists have successfully produced embryos in 10 different wildlife species, while in 2 of those, offspring have also been born. Thus, the collection of gametes from recently deceased animals represents a valuable opportunity to increase genetic resource banks, obviating the requirement for invasive procedures. Despite the development of several protocols for gamete collection, the refinement of these techniques and the establishment of species-specific protocols are still required, taking into account both the limitations and the opportunities. In the case of wildlife, the optimization of such protocols is impeded by the scarcity of available animals, many of which have a high genetic value that must be protected rather than utilized for research purposes. Therefore, optimizing protocols for wildlife species by using domestic species as a model is crucial. In this review, we focused on the current advancements in the collection, preservation, and utilization of gametes, postmortem, in selected species belonging to Equidae, Bovidae, and Felidae, both domestic and wildlife.