Nikolett Tokodyné Szabadi

Heat stress negatively affects bovine fertility and embryonic development, while cryopreservation imposes additional cellular stress that may impair embryo survival. The present study investigated whether controlled heat treatment applied during the early morula stage could influence subsequent blastocyst development, molecular stress responses, and post-thaw survival of bovine embryos. In vitro-produced bovine embryos were exposed to controlled thermal treatment involving gradual elevation in temperature from 38.8 °C to 40.0 °C followed by subsequent cooling. Blastocyst formation, post-thaw survival after slow freezing, and the expression of stress-associated genes and microRNAs were evaluated. Heat treatment did not significantly affect blastocyst formation rates or post-thaw embryo survival compared to the control groups. However, significant alterations in the expression of stress-associated markers were observed. The expression of HSP90AA1 and HSPB11 was significantly reduced following heat treatment, while cryopreservation induced increased expression of these markers compared to embryos exposed only to heat treatment. Significant alterations were also detected in the expression of several stress-associated microRNAs. These findings suggest that controlled heat exposure during the morula stage may induce molecular changes associated with the embryonic response to heat stress without compromising developmental competence or cryosurvival. The results contribute to a better understanding of the molecular mechanisms underlying embryonic responses to thermal and cryogenic stress and may support future optimization of embryo production and cryopreservation strategies.

MicroRNAs (miRNAs) are short, non-coding RNA molecules that play a crucial role in regulating various biological processes by influencing post-transcriptional gene expression and gene silencing. Background/Objectives: In this study, rabbit embryos were utilised as a model system to investigate potential biomarkers relevant to human embryo development. Seven microRNAs (miRNAs) identified in the embryo culture medium were evaluated as biomarkers by analysing the correlation between their expression levels and the developmental quality of rabbit embryos at days 4 and 6. Methods: We analysed the expression of seven development-specific miRNAs (miR-24-3p, miR-28-3p, miR-103a-3p, miR-181a-5p, miR-191-5p, miR-320a-3p, miR-378a-3p) in 4-day-old and 6-day-old rabbit embryos, along with their culture media. Results: Our findings revealed significant differences in the expression levels of these miRNAs between the 4-day-old and 6-day-old embryos. On the other hand, the expression patterns observed in the culture medium samples showed less variation between the two age groups. Nonetheless, analysis of miRNA expression profiles in the spent culture medium from individually cultured embryos enabled the identification of lower-quality embryos, characterised by smaller size and impaired or delayed development. Conclusions: The detection of these miRNAs in embryo culture medium may serve as a reliable indicator of successful progression to the blastocyst stage. Our experimental results identified specific miRNAs whose expression profiles differ according to embryonic stage and quality, thereby reflecting key developmental milestones. Notably, the detectability of these miRNAs in the medium—without prior RNA isolation—indicates their active secretion into the extracellular environment. By synthesising our findings with the existing literature, we refined a panel of miRNAs essential for the development of implantation-competent embryos in both rabbits and humans. Consequently, we developed a non-invasive assay for predicting implantation and pregnancy outcomes, which may have significant applications in human reproductive medicine.

MicroRNAs (miRNAs), small non-coding RNA molecules, regulate a wide range of critical biological processes, such as proliferation, cell cycle progression, differentiation, survival, and apoptosis, in many cell types. The regulatory functions of miRNAs in embryogenesis and stem cell properties have been extensively investigated since the early years of miRNA discovery. In this review, we will compare and discuss the impact of stem-cell-specific miRNA clusters on the maintenance and regulation of early embryonic development, pluripotency, and self-renewal of embryonic stem cells, particularly in vertebrates.

Recently, in vitro gene preservation has gained ground thanks to its lower cost and higher stability compared to in vivo techniques. One of the methods that can preserve female-specific W chromosome-linked genes is primordial germ cell (PGC) freezing. PGCs can be isolated from Hamburger–Hamilton stage 14–16 embryos via blood sampling. In our experiment, we used two newly established Black Transylvanian naked neck chicken cell lines and four cell lines from our gene bank. We compared two different freezing media (FAM1 and FAM2) in this study. The cell number and viability of the PGCs were measured before freezing (BF) and after thawing on Day 0, Day 1, and Day 7 of cultivation. We analyzed the germ cell-specific chicken vasa homologue (CVH) expression profile in PGCs using RT-qPCR. We found that on Day 0, immediately after thawing, the cell number in cell lines frozen with the FAM2 medium was significantly higher than in the FAM1-treated ones. On Day 1 and Day 7, the cell number and viability were also higher in most cell lines frozen with FAM2, but the difference was insignificant. The freezing also affected the chicken vasa homologue gene expression in male lines treated with both freezing media.

The primordial germ cells (PGCs) are the precursors for both the oocytes and spermatogonia. Recently, a novel culture system was established for chicken PGCs, isolated from embryonic blood. The possibility of PGC long-term cultivation issues a new advance in germ cell preservation, biotechnology, and cell biology. We investigated the consequence of gga-miR-302b-5P (5P), gga-miR-302b-3P (3P) and dual inhibition (5P/3P) in two male and two female chicken PGC lines. In treated and control cell cultures, the cell number was calculated every four hours for three days by the XLS Imaging system. Comparing the cell number of control and treated lines on the first day, we found that male lines had a higher proliferation rate independently from the treatments. Compared to the untreated ones, the proliferation rate and the number of apoptotic cells were considerably reduced at gga-miR-302b-5P inhibition in all PGC lines on the third day of the cultivation. The control PGC lines showed a significantly higher proliferation rate than 3P inhibited lines on Day 3 in all PGC lines. Dual inhibition of gga-miR-302b mature miRNAs caused a slight reduction in proliferation rate, but the number of apoptotic cells increased dramatically. The information gathered by examining the factors affecting cell proliferation of PGCs can lead to new data in stem cell biology.

Although numerous studies reported the effects of heat stress in chickens, it was not investigated in the Transylvanian Naked Neck breed. In our research, Transylvanian Naked Neck chickens, 24 h after hatching, were heat-treated at 38.5 °C for 12 h. We compared the control and heat-treated adult chickens’ productivity parameters following 12 weeks of heat-stress at 30 °C. We found that the heat-treated layers had significantly higher egg production in heat stress, but in cockerels, the sperm quality did not differ significantly between the two groups. To detect the effect of heat-treatment on a molecular level, the expression of two heat-shock proteins and four heat-shock factors were analysed in the gonads of control and heat-treated chickens. We found that the expression level of HSP90 and HSF4 increased significantly in heat-treated female chicken gonads. Still, in adult females, the expression of HSF2 and HSF3 were substantially lower compared to the control. In adult heat-treated males, the HSP70, HSF1 and HSF3 expression levels showed a significant increase in both gonads compared to the control. We think that the presented significant differences in egg production might be related to the increased expression level of HSP90 and HSF4 in heat-treated female gonads.