Bta-miR-10b Secreted by Bovine Embryos Negatively Impacts Preimplantation Embryo Quality

Selection and application of small non-coding RNAs for normalizing RT-qPCR data of bovine preimplantation embryo conditioned medium

Small non-coding RNAs (sncRNAs) present in the conditioned medium (CM) of bovine preimplantation embryos are potential noninvasive biomarkers for assessing embryo quality. Accurate quantification of sncRNA levels in the spent CM is of utmost importance in this regard. RT-qPCR is considered as the gold standard for quantifying RNA. In order to standardize RT-qPCR data in the sample type under investigation, the use of suitable stable sncRNAs is essential. Here, we selected 10 sncRNAs from small RNA sequencing of CM samples derived from both bovine blastocysts and degenerate embryos, and evaluated their expression stability together with that of cel-miR-39 as a spike and the often-used U6 small nuclear RNA at different embryo developmental stages. In CM of 2-cell embryos, rsRNA-1044 showed the most stable expression, while tDR-1:32-Gly-CCC-1 was the most stable expressed sncRNA in CM of the stages beyond the 2-cell stage. Next, tDR-1:32-Gly-CCC-1 was used for normalizing the RT-qPCR data from the CM of blastocysts and degenerate embryos. Bta-miR-155 and tDR-39:75-Arg-CCG-2 were found to be significantly up-regulated in the CM of blastocysts compared to that of the degenerated embryos (P = 0.028 and P = 0.017, respectively), suggesting their expression levels are related to embryo development stage. In conclusion, tDR-1:32-Gly-CCC-1 can serve as a suitable reference sncRNA for normalization of RT-qPCR data of the CM from bovine blastocysts.

MicroRNA-148b secreted by bovine oviductal extracellular vesicles enhance embryo quality through BPM/TGF-beta pathway

BACKGROUND

Extracellular vesicles (EVs) and their cargoes, including MicroRNAs (miRNAs) play a crucial role in cell-to-cell communication. We previously demonstrated the upregulation of bta-mir-148b in EVs from oviductal fluid of cyclic cows. This miRNA is linked to the TGF-β pathway in the cell proliferation. Our aim was to verify whether miR-148b is taken up by embryos through gymnosis, validate its target genes, and investigate the effect of miR-148b supplementation on early embryo development and quality.

METHODS

Zygotes were cultured in SOF + 0.3% BSA (Control) or supplemented with: 1 µM miR-148b mimics during: D1-D7 (miR148b) or D1-D4 (miR148b-OV: representing miRNA effect in the oviduct) or D4-D7 (miR148b-UT: representing miRNA effect in the uterus) or 1 µM control mimics was used during: D1-D7 (CMimic). Embryos at ≥ 16-cells and D7 blastocysts (BD7) were collected to examine the mRNA abundance of transcripts linked to the TGF-β pathway (TGFBR2, SMAD1, SMAD2, SMAD3, SMAD5, BMPR2, RPS6KB1, POU5F1, NANOG), total cell number (TC), trophectoderm (TE), and inner cell mass (ICM) were also evaluated. One-way ANOVA was used for all analyses.

RESULTS

We demonstrated that miR-148b can be taken up in both 16-cell embryos and BD7 by gymnosis, and we observed a decrease in SMAD5 mRNA, suggesting it's a potential target of miR-148b. Cleavage and blastocysts rates were not affected in any groups; however, supplementation of miR-148b mimics had a positive effect on TC, TE and ICM, with values of 136.4 ± 1.6, 92.5 ± 0.9, 43.9 ± 1.3 for miR148b and 135.3 ± 1.5, 92.6 ± 1.2, 42.7 ± 0.8, for miR148b-OV group. Furthermore, mRNA transcripts of SMAD1 and SMAD5 were decreased (P ≤ 0.001) in 16-cell embryos and BD7 from miR148b and miR148b-OV groups, while POU5F1 and NANOG were upregulated (P ≤ 0.001) in BD7 and TGFBR2 was only downregulated in 16-cell embryos. pSMAD1/5 levels were higher in the miR148b and miR148b-OV groups.

CONCLUSIONS

Our findings suggest that supplementation of bta-miR-148b mimics during the entire culture period (D1 - D7) or from D1 - D4 improves embryo quality and influences the TGF-β signaling pathway by altering the transcription of genes associated with cellular differentiation and proliferation. This highlights the importance of miR-148b on embryo quality and development.

tRNAGlu-derived fragments from embryonic extracellular vesicles modulate bovine embryo hatching

Transfer RNA-derived small RNAs (tsRNAs) have been shown to be involved in early embryo development and repression of endogenous retroelements in embryos and stem cells. However, it is unknown whether tsRNAs also regulate embryo hatching. In this study, we mined the sequencing data of a previous experiment in which we demonstrated that the microRNA (miRNA) cargo of preimplantation embryonic extracellular vesicles (EVs) influences embryo development. We thus profiled the tsRNA cargo of EVs secreted by blastocysts and non-blastocysts. The majority of tsRNAs was identified as tRNA halves originating from the 5´ ends of tRNAs. Among the 148 differentially expressed tsRNAs, the 19 nt tRNA fragment (tRF) tDR-14:32-Glu-CTC-1 was found to be significantly up-regulated in EVs derived from non-blastocysts. RT-qPCR assays confirmed its significant up-regulation in non-blastocyst embryos and their conditioned medium compared to the blastocyst group (P < 0.05). Inhibition of tDR-14:32-Glu-CTC-1 by supplementing antagomirs to the conditioned medium improved embryo hatching (P < 0.05). Transcriptomic analysis of embryos treated with tDR-14:32-Glu-CTC-1 antagomirs further showed differential expression of genes that are associated with embryo hatching and implantation. In summary, tDR-14:32-Glu-CTC-1 is up-regulated in non-blastocyst embryos and their secretions, and inhibition of tDR-14:32-Glu-CTC-1 promotes embryo hatching, while influencing embryo implantation-related genes and pathways. These results indicate that embryonic EVs containing specific tRFs may regulate preimplantation embryo development.

Hatching is modulated by microRNA-378a-3p derived from extracellular vesicles secreted by blastocysts

Hatching from the zona pellucida is a prerequisite for embryo implantation and is less likely to occur in vitro for reasons unknown. Extracellular vesicles (EVs) are secreted by the embryo into the culture medium. Yet the role that embryonic EVs and their cargo microRNAs (miRNAs) play in blastocyst hatching has not been elucidated, partially due to the difficulties of isolating them from low amounts of culture medium. Here, we optimized EV-miRNA isolation from medium conditioned by individually cultured bovine embryos and subsequently showed that miR-378a-3p, which was up-regulated in EVs secreted by blastocysts, plays a crucial role in promoting blastocyst hatching. This demonstrates the regulatory effect of miR-378-3p on hatching, which is an established embryo quality parameter linked with implantation.

Extracellular vesicles (EVs) and their cargo microRNAs (miRNAs) are important regulators of embryo development to the blastocyst stage and beyond. Before implantation can take place, hatching of blastocysts from their zona pellucida is required. However, underlying mechanisms by which blastocyst formation and hatching are initiated remain largely unknown. Here, we provide evidence that embryonic EVs containing bta-miR-378a-3p play a crucial role in blastocyst hatching, using a bovine model. A customized procedure was used to isolate EV-miRNAs from culture droplets conditioned by individual bovine embryos that either developed to the blastocyst stage or did not (nonblastocyst). RNA sequencing identified 69 differentially expressed miRNAs between EVs derived from blastocyst conditioned medium (CM) and nonblastocyst CM. Among the miRNAs up-regulated in blastocyst CM, we selected bta-miR-378a-3p for further validation by functionality testing on developing in vitro embryos by means of mimics and inhibitors. Supplementing the embryo culture medium with miR-378a-3p mimic significantly improved blastocyst quality, with higher cell numbers and reduced apoptosis, and improved hatching, while the opposite was found after supplementation with miR-378a-3p inhibitor (P < 0.01). Transcriptomic analysis of embryos treated with miR-378 mimic/inhibitor showed differential expression (P < 0.01) of genes associated with embryo development and implantation, including RAP1GAP, ARFGEF2, SLC7A6, CENPA, SP1, LDLR, PYCR1, MYD88, TPP1, and NCOA3. In conclusion, miR-378a-3p is up-regulated in EVs secreted by embryos that develop to the blastocyst stage, and this EV-derived miR-378a-3p increases blastocyst quality and regulates embryo hatching, which is essential for embryo implantation.

Role of reproductive fluids and extracellular vesicles in embryo&#x2013;maternal interaction during early pregnancy in cattle

The coordinated interaction between the developing embryo and the maternal reproductive tract is essential for the establishment and maintenance of pregnancy in mammals. An early cross-talk is established between the oviduct/uterus and the gametes and embryo. This dialogue will shape the microenvironment in which gamete transport, fertilisation, and early embryonic development occur. Due to the small size of the gametes and the early embryo relative to the volume of the oviductal and uterine lumina, collection of tissue and fluid adjacent to these cells is challenging in cattle. Thus, the combination of in vivo and in vitro models seems to be the most appropriate approach to better understand this fine dialogue. In this respect, the aim of this review is to summarise the recent findings in relation to gamete/embryo-maternal interaction during the pre-elongation period.

Murine Blastocysts Release Mature MicroRNAs Into Culture Media That Reflect Developmental Status

Extracellular microRNA (miRNA) sequences derived from the pre-implantation embryo have attracted interest for their possible contributions to the ongoing embryonic-uterine milieu, as well as their potential for use as accessible biomarkers indicative of embryonic health. Spent culture media microdroplets used to culture late-stage E4.0 murine blastocysts were screened for 641 mature miRNA sequences using a reverse transcription-quantitative polymerase chain reaction-based array. We report here 39 miRNAs exclusively detected in the conditioned media, including the implantation-relevant miR-126a-3p, miR-101a, miR-143, and miR-320, in addition to members of the highly expressed embryonic miR-125 and miR-290 families. Based on these results, an miRNA panel was assembled comprising five members of the miR-290 family (miR-291-295) and five conserved sequences with significance to the embryonic secretome (miR-20a, miR-30c, miR-142-3p, miR-191, and miR-320). Panel profiling of developing embryo cohort lysates and accompanying conditioned media microdroplets revealed extensive similarities in relative quantities of miRNAs and, as a biomarker proof of concept, enabled distinction between media conditioned with differently staged embryos (zygote, 4-cell, and blastocyst). When used to assess media conditioned with embryos of varying degrees of degeneration, the panel revealed increases in all extracellular panel sequences, suggesting cell death is an influential and identifiable factor detectable by this assessment. In situ hybridization of three panel sequences (miR-30c, miR-294, and miR-295) in late-stage blastocysts revealed primarily inner cell mass expression with a significant presence of miR-294 throughout the blastocyst cavity. Furthermore, extracellular miR-290 sequences responded significantly to high centrifugal force, suggesting a substantial fraction of these sequences may exist within a vesicle such as an exosome, microvesicle, or apoptotic bleb. Together, these results support the use of extracellular miRNA to assess embryonic health and enable development of a non-invasive viability diagnostic tool for clinical use.

Emerging genetic complexity and rare genetic variants in neurodegenerative brain diseases

Knowledge of the molecular etiology of neurodegenerative brain diseases (NBD) has substantially increased over the past three decades. Early genetic studies of NBD families identified rare and highly penetrant deleterious mutations in causal genes that segregate with disease. Large genome-wide association studies uncovered common genetic variants that influenced disease risk. Major developments in next-generation sequencing (NGS) technologies accelerated gene discoveries at an unprecedented rate and revealed novel pathways underlying NBD pathogenesis. NGS technology exposed large numbers of rare genetic variants of uncertain significance (VUS) in coding regions, highlighting the genetic complexity of NBD. Since experimental studies of these coding rare VUS are largely lacking, the potential contributions of VUS to NBD etiology remain unknown. In this review, we summarize novel findings in NBD genetic etiology driven by NGS and the impact of rare VUS on NBD etiology. We consider different mechanisms by which rare VUS can act and influence NBD pathophysiology and discuss why a better understanding of rare VUS is instrumental for deriving novel insights into the molecular complexity and heterogeneity of NBD. New knowledge might open avenues for effective personalized therapies.

Extracellular vesicles, microRNA and the preimplantation embryo: non-invasive clues of embryo well-being

Elective single embryo transfer is rapidly becoming the standard of care in assisted reproductive technology for patients under the age of 35 years with a good prognosis. Clinical pregnancy rates have become increasingly dependent on the selection of a single viable embryo for transfer, and diagnostic techniques facilitating this selection continue to develop. Current progress in elucidating the extracellular vesicle and microRNA components of the embryonic secretome is reviewed, and the potential for these findings to improve clinical embryo selection discussed. Key results have shown that extracellular vesicles and microRNAs are rapidly detectable constituents of the embryonic secretome. Evidence suggests that the vesicular population is largely exosomal in nature, secreted at all stages of preimplantation development and capable of traversing the zona pellucida. Both extracellular vesicle and microRNA concentrations within the secretome are elevated for blastocysts with diminished developmental competence, as indicated either by degeneracy or implantation failure, whereas studies have yet to firmly correlate individual microRNA sequences with pregnancy outcome. These emerging correlations support the viability of extracellular vesicles and microRNAs as the basis for a new diagnostic test to supplement or replace morphokinetic assessment.

MicroRNAs from Extracellular Vesicles Secreted by Bovine Embryos as Early Biomarkers of Developmental Competence

During early development, embryos secrete extracellular vesicles (EVs) that participate in embryo–maternal communication. Among other molecules, EVs carry microRNAs (miRNAs) that interfere with gene expression in target cells; miRNAs participate in embryo–maternal communication. Embryo selection based on secreted miRNAs may have an impact on bovine breeding programs. This research aimed to evaluate the size, concentration, and miRNA content of EVs secreted by bovine embryos with different developmental potential, during the compaction period (days 3.5–5). Individual culture media from in vitro–produced embryos were collected at day 5, while embryos were further cultured and classified at day 7, as G1 (conditioned-culture media by embryos arrested in the 8–16-cells stage) and G2 (conditioned-culture media by embryos that reached blastocyst stages at day 7). Collected nanoparticles from embryo conditioned culture media were cataloged as EVs by their morphology and the presence of classical molecular markers. Size and concentration of EVs from G1 were higher than EVs secreted by G2. We identified 95 miRNAs; bta-miR-103, bta-miR-502a, bta-miR-100, and bta-miR-1 were upregulated in G1, whereas bta-miR-92a, bta-miR-140, bta-miR-2285a, and bta-miR-222 were downregulated. The most significant upregulated pathways were fatty acid biosynthesis and metabolism, lysine degradation, gap junction, and signaling pathways regulating pluripotency of stem cells. The characteristics of EVs secreted by bovine embryos during the compaction period vary according to embryo competence. Embryos that reach the blastocyst stage secrete fewer and smaller vesicles. Furthermore, the loading of specific miRNAs into the EVs depends on embryo developmental competence.