Extracellular vesicles: Novel regulators of conceptus-uterine interactions?

Extracellular vesicles: emerging paradigms in bovine embryo-maternal communication

The oviduct and uterus provide an optimal environment for early embryo development, where effective communication between the embryo and the maternal reproductive tract is crucial for establishing and maintaining pregnancy. Oviductal and uterine-derived EVs play pivotal roles in this maternal-embryonic communication and in facilitating early embryo development. However, despite the ability of in vitro culture methods to produce viable embryos, the lack of exchange between the embryo and the mother often results in lower-quality embryos than those derived in vivo. Therefore, there is a pressing need to increase our understanding of the physiological mechanisms underlying embryo interaction with the oviduct and endometrium through EVs and to develop models capable of mimicking the in vivo environment. This review aims to provide up-to-date insights into the communication between the mother and pre-implantation bovine embryo, exploring their applications and perspectives in the field.

Biosensor capability of the endometrium is mediated in part, by altered miRNA cargo from conceptus-derived extracellular vesicles

We tested the hypothesis that the biosensor capability of the endometrium is mediated in part, by the effect of different cargo contained in the extracellular vesicles secreted by the conceptus during the peri-implantation period of pregnancy. We transferred Bos taurus taurus embryos of different origin, in vivo (high developmental potential (IV)), in vitro (intermediate developmental potential (IVF)), or cloned (low developmental potential (NT)), into Bos taurus indicus recipients. Extracellular vesicles (EVs) recovered from Day 16 conceptus-conditioned medium were characterized and their microRNA (miRNA) cargo sequenced alongside RNA sequencing of their respective endometria. There were substantial differences in the endometrial response to in vivo versus in vitro and in vivo versus cloned conceptuses (1153 and 334DEGs respectively) with limited differences between in vitro Vs cloned conceptuses (36 DEGs). The miRNA cargo contained in conceptus-derived EVs was similar between all three groups (426 miRNA in common). Only 8 miRNAs were different between in vivo and cloned conceptuses, while only 6 miRNAs were different between in vivo and in vitro-derived conceptuses. Treatment of endometrial epithelial cells with mimic or inhibitors for miR-128 and miR-1298 changed the proteomic content of target cells (96 and 85, respectively) of which mRNAs are altered in the endometrium in vivo (PLXDC2, COPG1, HSPA12A, MCM5, TBL1XR1, and TTF). In conclusion, we have determined that the biosensor capability of the endometrium is mediated in part, by its response to different EVs miRNA cargo produced by the conceptus during the peri-implantation period of pregnancy.

Immersed in a reservoir of potential: amniotic fluid-derived extracellular vesicles

This review aims to encapsulate the current knowledge in extracellular vesicles extracted from amniotic fluid and amniotic fluid derived stem/stromal cells. Amniotic fluid (AF) bathes the developing fetus, providing nutrients and protection from biological and mechanical dangers. In addition to containing a myriad of proteins, immunoglobulins and growth factors, AF is a rich source of extracellular vesicles (EVs). These vesicles originate from cells in the fetoplacental unit. They are biological messengers carrying an active cargo enveloped within the lipid bilayer. EVs in reproduction are known to play key roles in all stages of pregnancy, starting from fertilisation through to parturition. The intriguing biology of AF-derived EVs (AF-EVs) in pregnancy and their untapped potential as biomarkers is currently gaining attention. EV studies in numerous animal and human disease models have raised expectations of their utility as therapeutics. Amniotic fluid stem cell and mesenchymal stromal cell-derived EVs (AFSC-EVs) provide an established supply of laboratory-made EVs. This cell-free mode of therapy is popular as an alternative to stem cell therapy, revealing similar, if not better therapeutic outcomes. Research has demonstrated the successful application of AF-EVs and AFSC-EVs in therapy, harnessing their anti-inflammatory, angiogenic and regenerative properties. This review provides an overview of such studies and discusses concerns in this emerging field of research.

Review: Endometrial function in pregnancy establishment in cattle

The endometrium is fundamentally required for successful pregnancy in ruminants and species where the posthatching conceptus undergoes a protracted elongation and peri-implantation phase of pregnancy. Moreover, there are substantial waves of pregnancy loss during this pre- and peri-implantation period of pregnancy the precise source of which has not been clearly defined i.e., the maternal uterine contribution to this loss. Understanding the molecular interactions required for successful pregnancy in cattle will allow us to intervene to support pregnancy success during this vulnerable window. The endometrium contributes to most key developmental milestones of pregnancy establishment, including (1) contributing to the regulation of the oestrus cycle, (2) nourishing the preimplantation conceptus, (3) responding to the conceptus to create a more receptive microenvironment, (4) providing essential biophysical support, and (5) signalling and producing factors which affect the mother systemically. This review will summarise what we currently know about conceptus-maternal interactions as well as identify the gaps in our knowledge that could be filled with newer in vitro model approaches. These include the use of microfluidics, organ-on-a-chip devices, and bioinformatic approaches. This will help maximise food production efficiency (both meat and dairy) and decrease the environmental burden, while enhancing our understanding of the fundamental processes required for successful implantation in cattle.

Androgen-induced exosomal miR-379-5p release determines granulosa cell fate: cellular mechanism involved in polycystic ovaries

Polycystic ovarian syndrome (PCOS) is a complex multi-factorial syndrome associated with androgen excess and anovulatory infertility. In the current study, we investigated the role of dihydrotestosterone-induced exosomal miR-379-5p release in determining the destiny of the developing follicles. Our hypothesis was that androgen regulates granulosa cell miR-379-5p content by facilitating its exosomal release in a follicular-stage dependent manner, a process which determines granulosa cell fate. Compared to human non-PCOS subjects, individuals with PCOS exhibit higher follicular fluid free testosterone levels, lower exosomal miR-379-5p content and granulosa cell proliferation. Androgenized rats exhibited lower granulosa cell miR-379-5p but higher phosphoinositide-dependent kinase-1 (PDK1; a miR-379-5p target) content and proliferation. Androgen reduced granulosa cell miR-379-5p content by increasing its exosomal release in preantral follicles, but not in antral follicles in vitro. Studies with an exosomal release inhibitor confirmed that androgen-induced exosomal miR-379-5p release decreased granulosa cell miR-379-5p content and proliferation. Ovarian overexpression of miR-379-5p suppressed granulosa cell proliferation, and basal and androgen-induced preantral follicle growth in vivo. These findings suggest that increased exosomal miR-379-5p release in granulosa cells is a proliferative response to androgenic stimulation specific for the preantral stage of follicle development and that dysregulation of this response at the antral stage is associated with follicular growth arrest, as observed in human PCOS.

Granulosa cell-derived miR-379-5p regulates macrophage polarization in polycystic ovarian syndrome

Polycystic ovarian syndrome (PCOS) is associated with hyperandrogenemia and ovarian antral follicle growth arrest. We have previously demonstrated that androgen-induced exosomal release of miR-379-5p (miR379) from preantral follicle granulosa cells increases the proliferation of target cells via phosphoinositide-dependent kinase 1 (PDK1) upregulation. Androgen also increases inflammatory M1 macrophage abundance, but reduces anti-inflammatory M2 polarization in rat antral and preovulatory follicles. However, the role of small extracellular vesicles (sEVs; also known as exosomes) secretion in determining the cellular content and function of miRNAs in exosome-receiving cells is largely unknown. Our objectives were to determine: 1) the regulatory role of granulosa cells (GC)-derived exosomal miR379 on macrophage polarization and ovarian inflammation; 2) whether miR379-induced M1 polarization regulates GC proliferation; and 3) if this regulated process is follicular stage-specific. Compared with non-PCOS subjects, PCOS subjects had a higher M1/M2 ratio, supporting the concept that PCOS is an inflammatory condition. Ovarian overexpression of miR379 increased the number of M1 macrophages and the M1/M2 ratio in preantral follicles specifically. Transfection of macrophages with a miR379 mimic reduced the cellular content of PDK1 and induced M0→M1 polarization; whereas its inhibitor polarized M0→M2. Conditioned media from macrophages transfected with miR379 mimic and follicular fluid from PCOS subjects had higher galectin-3 content, a pro-inflammatory cytokine which specifically suppresses human antral follicle GC proliferation. These results indicate that miR379 inhibits M2 macrophage polarization, a condition which suppresses GC proliferation in a follicle stage-dependent manner, as exhibited in PCOS.

miRNA profiling in intrauterine exosomes of pregnant cattle on day 7

Intrauterine exosomes have been identified to be involved in the embryo development and implantation. The aim of this study was to explore the role of miRNAs in intrauterine exosomes in bovine pregnancy. Intrauterine exosomes were collected from uterine flushing fluids of three donor and three recipient Xianan cows 7 days after fertilization. Intrauterine exosomes miRNAs were extracted and the exosomal miRNAs expression levels were analyzed. Sixty miRNAs differed significantly in their amounts between donors and recipients (p-value < 0.05, |log2(FoldChange)| > 1). Twenty-two miRNAs were upregulated and 38 downregulated in the group of donor cows. The bta-miR-184 was the most significant (P _{Benjamini-Hochberg} < 0.001). A total of 9,775 target genes were predicted using the 60 miRNAs. GO and KEGG analysis showed that the target genes were enriched in several biological processes or pathways associated with embryo implantation and endometrial development, such as cell adhesion, cell junction, focal adhesion, and Rap1 signaling pathway. Our findings suggest that, in cattle early pregnancy stage, these differently expressed miRNAs in intrauterine exosomes involved in embryo implantation and endometrial development, which may exert a significant effect and influence the uterine microenvironment for embryo implantation. These results could provide reference for screening and exploring the intrauterine exosomal miRNA affecting embryo implantation.

Porosomes in uterine epithelial cells: Ultrastructural identification and characterization during early pregnancy

Porosomes are plasma membrane structures in secretory cells that allow transient docking and/or partial fusion of vesicles during which they release their content then disengage. This is referred to as "kiss and run" exocytosis. During early pregnancy, at the time of receptivity, there is a high level of vesicle activity in uterine epithelial cells (UECs). One of the secretory pathways for these vesicles could be via porosomes, which have yet to be identified in UECs. This study identified porosomes in the apical plasma membrane of UECs for the first time. These structures were present on days 1, 5.5, and 6 of early pregnancy, where they likely facilitate partial secretion via "kiss and run" exocytosis. The porosomes were measured and quantified on days 1, 5.5, and 6, which showed there are significantly more porosomes on day 5.5 (receptive) compared to day 1 (nonreceptive) of pregnancy. This increase in porosome numbers may reflect major morphological and molecular changes in the apical plasma membrane at this time such as increased cholesterol and soluble NSF attachment protein receptor proteins, as these are structural and functional components of the porosome complex assembly. Porosomes were observed in both resting (inactive) and dilated (active) states on days 1, 5.5, and 6 of early pregnancy. Porosomes on day 5.5 are significantly more active than on day 1 as demonstrated by the dilation of their base diameter. Further two-way ANOVA analysis of base diameter in resting and dilated states found a significant increase in porosome activity in day 5.5 compared to day 1. This study therefore indicates an increase in the number and activity of porosomes at the time of uterine receptivity in the rat, revealing a mechanism by which the UECs modify the uterine luminal environment at this time.

Extracellular vesicles from oviductal and uterine fluids supplementation in sequential in vitro culture improves bovine embryo quality

Background

In vitro production of bovine embryos is a well-established technology, but the in vitro culture (IVC) system still warrants improvements, especially regarding embryo quality. This study aimed to evaluate the effect of extracellular vesicles (EVs) isolated from oviductal (OF) and uterine fluid (UF) in sequential IVC on the development and quality of bovine embryos. Zygotes were cultured in SOF supplemented with either BSA or EVs-depleted fetal calf serum (dFCS) in the presence (BSA-EV and dFCS-EV) or absence of EVs from OF (D1 to D4) and UF (D5 to D8), mimicking in vivo conditions. EVs from oviducts (early luteal phase) and uterine horns (mid-luteal phase) from slaughtered heifers were isolated by size exclusion chromatography. Blastocyst rate was recorded on days 7–8 and their quality was assessed based on lipid contents, mitochondrial activity and total cell numbers, as well as survival rate after vitrification. Relative mRNA abundance for lipid metabolism-related transcripts and levels of phosphorylated hormone-sensitive lipase (pHSL) proteins were also determined. Additionally, the expression levels of 383 miRNA in OF- and UF-EVs were assessed by qRT-PCR.

Results

Blastocyst yield was lower (P < 0.05) in BSA treatments compared with dFCS treatments. Survival rates after vitrification/warming were improved in dFCS-EVs (P < 0.05). EVs increased (P < 0.05) blastocysts total cell number in dFCS-EV and BSA-EV compared with respective controls (dFCS and BSA), while lipid content was decreased in dFCS-EV (P < 0.05) and mitochondrial activity did not change (P > 0.05). Lipid metabolism transcripts were affected by EVs and showed interaction with type of protein source in medium (PPARGC1B, LDLR, CD36, FASN and PNPLA2, P < 0.05). Levels of pHSL were lower in dFCS (P < 0.05). Twenty miRNA were differentially expressed between OF- and UF-EVs and only bta-miR-148b was increased in OF-EVs (P < 0.05).

Conclusions

Mimicking physiological conditions using EVs from OF and UF in sequential IVC does not affect embryo development but improves blastocyst quality regarding survival rate after vitrification/warming, total cell number, lipid content, and relative changes in expression of lipid metabolism transcripts and lipase activation. Finally, EVs miRNA contents may contribute to the observed effects.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-022-00763-7.

Uterine extracellular vesicles as multi-signal messengers during maternal recognition of pregnancy in the mare

In contrast to other domestic mammals, the embryo-derived signal(s) leading to maternal recognition of pregnancy (MRP) are still unknow in the mare. We hypothesize that these embryonic signals could be packed into uterine extracellular vesicles (uEVs), acting as multi-signal messengers between the conceptus and the maternal tract, and contributing to MRP. To unveil these signals, the RNA and protein cargos of uEVs isolated from uterine lavages collected from pregnant mares (P; day 10, 11, 12 and 13 after ovulation) and cyclic control mares (C; day 10 and 13 after ovulation) were analyzed. Our results showed a fine-tuned regulation of the uEV cargo (RNAs and proteins), by the day of pregnancy, the estrous cycle, and even the size of the embryo. A particular RNA pattern was identified with specific increase on P12 related to immune system and hormonal response. Besides, a set of proteins as well as RNAs was highly enriched in EVs on P12 and P13. Differential abundance of miRNAs was also identified in P13-derived uEVs. Their target genes were linked to down- or upregulated genes in the embryo and the endometrium, exposing their potential origin. Our study identified for first time specific molecules packed in uEVs, which were previously associated to MRP in the mare, and thus bringing added value to the current knowledge. Further integrative and functional analyses will help to confirm the role of these molecules in uEVs during MRP in the mare.

Epigenetics of pregnancy: looking beyond the DNA code

Epigenetics is the branch of genetics that studies the different mechanisms that influence gene expression without direct modification of the DNA sequence. An ever-increasing amount of evidence suggests that such regulatory processes may play a pivotal role both in the initiation of pregnancy and in the later processes of embryonic and fetal development, thus determining long-term effects even in adult life. In this narrative review, we summarize the current knowledge on the role of epigenetics in pregnancy, from its most studied and well-known mechanisms to the new frontiers of epigenetic regulation, such as the role of ncRNAs and the effects of the gestational environment on fetal brain development. Epigenetic mechanisms in pregnancy are a dynamic phenomenon that responds both to maternal-fetal and environmental factors, which can influence and modify the embryo-fetal development during the various gestational phases. Therefore, we also recapitulate the effects of the most notable environmental factors that can affect pregnancy and prenatal development, such as maternal nutrition, stress hormones, microbiome, and teratogens, focusing on their ability to cause epigenetic modifications in the gestational environment and ultimately in the fetus. Despite the promising advancements in the knowledge of epigenetics in pregnancy, more experience and data on this topic are still needed. A better understanding of epigenetic regulation in pregnancy could in fact prove valuable towards a better management of both physiological pregnancies and assisted reproduction treatments, other than allowing to better comprehend the origin of multifactorial pathological conditions such as neurodevelopmental disorders.

Extracellular vesicles and immune response during pregnancy: A balancing act

The mechanisms underlying maternal tolerance of the semi- or fully-allogeneic fetus are intensely investigated. Across gestation, feto-placental antigens interact with the maternal immune system locally within the trophoblast-decidual interface and distantly through shed cells and soluble molecules that interact with maternal secondary lymphoid tissues. The discovery of extracellular vesicles (EVs) as local or systemic carriers of antigens and immune-regulatory molecules has added a new dimension to our understanding of immune modulation prior to implantation, during trophoblast invasion, and throughout the course of pregnancy. New data on immune-regulatory molecules, located on EVs or within their cargo, suggest a role for EVs in negotiating immune tolerance during gestation. Lessons from the field of transplant immunology also shed light on possible interactions between feto-placentally derived EVs and maternal lymphoid tissues. These insights illuminate a potential role for EVs in major obstetrical disorders. This review provides updated information on intensely studied, pregnancy-related EVs, their cargo molecules, and patterns of fetal-placental-maternal trafficking, highlighting potential immune pathways that might underlie immune suppression or activation in gestational health and disease. Our summary also underscores the likely need to broaden the definition of the maternal-fetal interface to systemic maternal immune tissues that might interact with circulating EVs.

Biocompatible Nanomaterials as an Emerging Technology in Reproductive Health; a Focus on the Male

A growing body of research has confirmed that nanoparticle (NP) systems can enhance delivery of therapeutic and imaging agents as well as prevent potentially damaging systemic exposure to these agents by modifying the kinetics of their release. With a wide choice of NP materials possessing different properties and surface modification options with unique targeting agents, bespoke nanosystems have been developed for applications varying from cancer therapeutics and genetic modification to cell imaging. Although there remain many challenges for the clinical application of nanoparticles, including toxicity within the reproductive system, some of these may be overcome with the recent development of biodegradable nanoparticles that offer increased biocompatibility. In recognition of this potential, this review seeks to present recent NP research with a focus on the exciting possibilities posed by the application of biocompatible nanomaterials within the fields of male reproductive medicine, health, and research.

miREV: An Online Database and Tool to Uncover Potential Reference RNAs and Biomarkers in Small-RNA Sequencing Data Sets from Extracellular Vesicles Enriched Samples

Extracellular vesicles (EVs) are nano-sized, membrane-enclosed vesicles released by cells for intercellular communication. EVs are involved in pathological processes and miRNAs in EVs have gained interest as easily accessible biomolecules in liquid biopsies for diagnostic purposes. To validate potential miRNA biomarker, transcriptome analyses must be carried out to detect suitable reference miRNAs. miREV is a database with over 400 miRNA sequencing data sets and helps the researcher to find suitable reference miRNAs for their individual experimental setup. The researcher can put together a specific sample set in miREV, which is similar to his own experimental concept in order to find the most suitable references. This allows to run validation experiments without having to carry out a complex and costly transcriptome analysis priorly. Additional read count tables of each generated sample set are downloadable for further analysis. miREV is freely available at https://www.physio.wzw.tum.de/mirev/.

Insights into the lipidome and primary metabolome of the uterus from day 14 cyclic and pregnant sheep†

In ruminants, conceptus elongation requires the endometrium and its secretions. The amino acid, carbohydrate, and protein composition of the uterine lumen during early pregnancy has been defined in sheep; however, a comprehensive understanding of metabolomic changes in the uterine lumen is lacking, particularly with respect to lipids. Here, the lipidome and primary metabolome of the uterine lumen, endometrium, and/or conceptus was determined on day 14 of the estrous cycle and pregnancy. Lipid droplets and select triglycerides were depleted in the endometrium of pregnant ewes. In contrast, select ceramides, diglycerides, and non-esterified fatty acids as well as several phospholipid classes (phosphatidylcholine, phosphatidylinositol, phosphatidylglycerols, and diacylglycerols) were elevated in the uterine lumen of pregnant ewes. Lipidomic analysis of the conceptus revealed that triglycerides are particularly abundant within the conceptus. Primary metabolite analyses found elevated amino acids, carbohydrates, and energy substrates, among others, in the uterine lumen of pregnant ewes. Collectively, this study supports the hypothesis that lipids are important components of the uterine lumen that govern conceptus elongation and growth during early pregnancy.

Integrating LCM-Based Spatio-Temporal Transcriptomics Uncovers Conceptus and Endometrial Luminal Epithelium Communication that Coordinates the Conceptus Attachment in Pigs

Attachment of conceptus to the endometrial luminal epithelium (LE) is a critical event for early placentation in Eutheria. Since the attachment occurs at a particular site within the uterus, a coordinated communication between three spatially distinct compartments (conceptus and endometrial LE from two anatomical regions of the uterus to which conceptus attaches and does not attach) is essential but remains to be fully characterized. Using the laser capture microdissection (LCM) technique, we firstly developed an approach that can allow us to pair the pig conceptus sample with its nearby endometrial epithelium sample without losing the native spatial information. Then, a comprehensive spatio-temporal transcriptomic profile without losing the original conceptus-endometrium coordinates was constructed. The analysis shows that an apparent difference in transcriptional responses to the conceptus exists between the endometrial LE from the two anatomically distinct regions in the uterus. In addition, we identified the communication pathways that link the conceptus and endometrial LE and found that these pathways have important roles in conceptus attachment. Furthermore, a number of genes whose expression is spatially restricted in the two different anatomical regions within the uterus were characterized for the first time and two of them (SULT2A1 and MEP1B) may cooperatively contribute to establish conceptus attachment in pigs. The results from our study have implications in understanding of conceptus/embryo attachment in pigs and other large polytocous species.

Isolation and Characterization of Equine Uterine Extracellular Vesicles: A Comparative Methodological Study

Extracellular vesicles (EVs) have been identified in the uterine fluid in different species and have been pointed as key players in the embryo-maternal dialogue, maternal recognition of pregnancy and establishment of pregnancy. However, little is known about the uterine EVs in the mare. Therefore, the present study aimed at characterizing EVs from uterine lavage of cyclic mares by comparing five EVs isolation methods and the combination of them: (1) ultracentrifugation (UC); (2) concentration of lavage volume by Centricon ultrafiltration (CE); (3) the use of CE with different washing steps (phosphate-buffered saline with or without trehalose); (4) size-exclusion chromatography with iZON-qEV columns, and (5) a combination of the methods with best results based on EVs yield, purity, and protein cargo profiles. Transmission electron microscopy and Western blotting confirmed the isolation of EVs by all methods but with quantitative and qualitative differences. Mass spectrometry provided differences in protein profiles between methods, number of identified proteins, and protein classes. Our results indicate that the combination of CE/trehalose/iZON/UC is an optimal method to isolate equine uterine EVs with good yield and purity that can be applied in future studies to determine the role of equine uterine EVs in embryo-maternal interactions.

Endometrial receptivity and embryo implantation in carnivores-commonalities and differences with other mammalian species

Endometrial receptivity and embryo implantation processes are a major point of pregnancy failure in many mammalian species, including humans. Although reproductive biology in many carnivore species remains enigmatic, the few that have been studied so far are invaluable comparative models. The goals of this review are to (1) summarize current data on the mechanisms involved in uterine receptivity and embryo implantation in carnivores, including commonalities and differences with other mammalian species and (2) identify research priorities to better understand a key phenomenon in a critical group of mammals. Besides unique reproductive traits in some carnivores (induced vs. spontaneous ovulation in cats, ovulation at the germinal vesicle stage in dogs), preimplantation embryo development is comparable with other orders. However, the timing of implantation varies, especially in species having an embryonic diapause. Mechanisms involved in endometrial receptivity and decidualization still remain to be fully understood, but specific markers have already been identified. Importantly, the use of endogenous hormones to control the ovarian activity may impact endometrial receptivity and subsequent embryo implantation. Next, research efforts should take advantage of advanced technologies to further study embryo implantation in carnivores and to provide more relevant models to reproductive medicine or for the conservation of rare and endangered species.

Extracellular vesicles in spontaneous preterm birth

Feto-maternal communication helps to maintain pregnancy and contributes to parturition at term and preterm. Endocrine and immune factor are well-reported communication mediators. Recent advances in extracellular vesicle (EV) biology have introduced them as major communication channels between the mother and fetus. EVs are round structures with a lipid bilayer membrane. EVs are generally categorized based on their size and mode of biogenesis. The most commonly reported EVs are exosomes with a size range of 30-160 nm that are formed inside the intraluminal vesicles of multivesicular body. Microvesicles (MVs) are larger than > 200 nm and formed by outward budding of plasma membrane. Vesicles are released from all cells and carry various factors that reflect the physiologic state of cell at the time of their release. Analysis of vesicle provides a snapshot of origin cell. Recent studies in perinatal medicine have shown that exosomes are key communicators between feto-maternal units, and they can cross placenta. Fetal-derived exosomes released under term labor-associated conditions can cause parturition-associated changes in maternal uterine tissues. Exosomes carrying inflammatory cargo can cause preterm birth in animal models suggesting their functional role in parturition. A few reports have profiled differences between exosome cargos from term and preterm pregnancies and indicated their biomarker potential to predict high-risk pregnancy status. There are hardly any reports on MVs and their functional roles in reproduction. Herein, we review of EVs and MVs, their characteristics, function, and usefulness predicting adverse pregnancy complications such as preterm birth.

Scanning electron microscopy of the surface epithelium of the bovine endometrium

The surface epithelium of the bovine endometrium comprises at least 2 cell types (ciliated cells and secretory cells with microvilli), but their distribution and morphological changes over the estrous cycle are poorly understood. The objective was to quantify the number of ciliated cells and assess morphological changes in secretory cells on the uterine surface epithelium during the estrous cycle. Caruncular endometrium (CAR) and intercaruncular endometrium (ICAR) samples were collected from the uterine body, the horn ipsilateral to the corpus luteum or dominant follicle (H-CL/DF), and the horn contralateral to the corpus luteum or dominant follicle (H-NCL/NDF) from heifers following slaughter on d 0 (estrus; n = 5) or d 14 (mid-luteal phase; n = 5) of the estrous cycle. Samples were prepared for scanning electron microscopy at 1,000× magnification. Four to 10 fields (256 × 225 µm) for each sample were examined (n = 567 images). The number of ciliated cells was counted and the surface was scored for the morphology of the secretory cells (0 = absence of microvilli on surface; 3 = 100% of surface covered with microvilli). Ciliated cells were present in both the CAR and ICAR regions. The number of ciliated cells per field increased from d 0 to 14 in CAR and decreased from d 0 to14 in ICAR. The scanning electron microscopy revealed a general lack of uniformity in the lawn of microvilli on the surface of the endometrium. Based on the scores, approximately 25% of the fields had a surface that was <50% covered by microvilli. Depletion of microvilli may be explained by a normal process where apical protrusions are formed and either regress back into the cell surface or break to release their contents into the uterine lumen. These studies support the hypothesis that the surface of the luminal epithelium changes during the estrous cycle through a process that involves remodeling of the apical surface. The morphology of the apical surface may have a key role in governing pregnancy establishment.