Involvement of microRNA lethal-7a in the regulation of embryo implantation in mice

Effects of High-Butterfat Diet on Embryo Implantation in Female Rats Exposed to Bisphenol A

Bisphenol A (BPA) is an endocrine disruptor associated with poor pregnancy outcomes in human and rodents. The effects of butterfat diets on embryo implantation and whether it modifies BPA's actions are currently unknown. We aimed to determine the effects of butterfat diet on embryo implantation success in female rats exposed to an environmentally relevant dose of BPA. Female Sprague-Dawley rats were exposed to dietary butterfat (10% or 39% kcal/kg body weight [BW]) in the presence or absence of BPA (250 μg/kg BW) or ethinylestradiol (0.1 μg/kg BW) shortly before and during pregnancy to assess embryo implantation potentials by preimplantation development and transport, in vitro blastulation, outgrowth, and implantation. On gestational day (GD) 4.5, rats treated with BPA alone had higher serum total BPA level (2.3-3.7 ng/ml). They had more late-stage preimplantation embryos, whereas those receiving high butterfat (HBF) diet had the most advanced-stage embryos; dams cotreated with HBF and BPA had the most number of advanced embryos. BPA markedly delayed embryo transport to the uterus, but neither amount of butterfat had modifying effects. An in vitro implantation assay showed HBF doubled the outgrowth area, with BPA having no effect. In vivo, BPA reduced the number of implanted embryos on GD8, and cotreatment with HBF eliminated this adverse effect. HBF diet overall resulted in more and larger GD8 embryos. This study reveals the implantation disruptive effects of maternal exposure to an environmentally relevant dose of BPA and identifies HBF diet as a modifier of BPA in promoting early embryonic health.

SMiRK: an Automated Pipeline for miRNA Analysis

BACKGROUND

Micro RNAs (miRNAs), important regulators of cell function, can be interrogated by high-throughput sequencing in a rapid and cost-effective manner. However, the tremendous amount of data generated by such methods is not easily analyzed. In order to extract meaningful information and draw biological conclusions from miRNA data, many challenges in quality control, alignment, normalization, and analysis must be overcome. Typically, these would only be possible with the dedicated efforts of a specialized computational biologist for a sustained period of time.

RESULTS

Here, we present SMiRK, an automated pipeline that allows such tasks to be completed with minimal time and without dedicated bioinformatics personnel. SMiRK's flexibility also allows experienced users to exert more control, if they wish. We describe how SMiRK automatically normalizes the data, removes low-information miRNAs, and produces heatmaps of the processed data. We give details on SMiRK's implementation and use cases for novice and advanced users. As a demonstration of its capabilities, SMiRK was used to rapidly and automatically analyze a dataset taken from the literature.

CONCLUSION

SMiRK is a useful and efficient tool that can be used by investigators at multiple skill levels. Those who lack bioinformatics training can use it to easily and automatically analyze their data, while those with experience will find it beneficial to not need to write tools from scratch.

The Dog: Nonconformist, Not Only in Maternal Recognition Signaling

Although similar at the molecular and cellular levels, endocrine mechanisms governing reproductive function in the domestic dog (Canis familiaris) differ markedly at the regulatory level from those known in other domestic animal species. Some of the events, e.g., the lack of luteolysis in the absence of pregnancy, resulting in similar luteal function and, therefore, hormonal profiles in early pregnant and nonpregnant animals, are species-specific. Consequently, no early gestation marker has so far been identified for the dog. Following implantation, relaxin of fetal placental origin can be detected and used for pregnancy diagnosis. Characterized by the lack of an active luteolytic principle from intra- or extra-luteal sources, the canine reproductive cycle appears to represent a "basic" form of mammalian reproductive function with apparently reduced opportunities for facilitating fecundity and hastening reproduction. Nevertheless, in the dog some kind of mechanism for synchronization between blastocyst development and uterine preparation for pregnancy must have evolved in order to support gestation. Driven by this assumption, studies including our recent investigations have been initiated aimed at characterizing some of the embryo-mediated effects of the preimplantation embryo on the canine uterus. Moreover, the lack of a uterine luteolysin and consequently the absence of a need to develop an antiluteolytic strategy make the dog an interesting model for investigating early evolutionary mechanisms involved in the preparation for implantation and ensuring embryo survival. These mechanisms result in an inverse relationship between the duration of pregnancy and of the nonpregnant cycle in the dog, compared with all other domestic animal species.

MicroRNAome of porcine conceptuses and trophoblasts: expression profile of micrornas and their potential to regulate genes crucial for establishment of pregnancy

Tightly coordinated, reciprocal embryo-maternal interactions affect gene expression during early pregnancy. Recently, microRNAs (miRNAs) have emerged as new players in the fine tuning of embryo development and implantation in mammals via posttranscriptional gene regulation mechanisms. Here, we integrated transcriptomic and computational approaches to profile miRNAs and miRNA synthesis and transport-related genes at different developmental stages of porcine conceptuses and trophoblast during early pregnancy in the pig. Using semiquantitative RT-PCR, we examined mRNA levels of 10 genes encoding proteins involved in miRNA synthesis and transport: DROSHA, DGCR8, XPO5, DICER1, TARBP2, TNRC6A, AGO1, AGO2, AGO3, and AGO4. Custom, multispecies microarrays were used to profile miRNAs. Prediction algorithms of miRNA-mRNA interactions allowed identification of target transcripts for the analyzed miRNAs. These included VEGF, LIF, PTGS2, and IL-6R, known to be crucial components of embryo-maternal interactions in the pig. Two selected miRNAs, miR-26a and miR-125b, were tested for the presence in the extracellular vesicles isolated from uterine luminal flushings during pregnancy. Results of in vitro study demonstrated that miRNAs, such as miR-125b, can regulate expression of genes crucial for embryo development and implantation in porcine endometrial luminal epithelial cells. For the first time, expression profiles of miRNAs and related genes in porcine conceptuses and trophoblast during maternal recognition of pregnancy and embryo implantation in the pig were described. Altogether, our results indicate potential roles of these small, noncoding RNAs in the early development of embryos and embryo-maternal cross-talk during early pregnancy in the pig.

The bull sperm microRNAome and the effect of fescue toxicosis on sperm microRNA expression

Tall fescue [Schedonorus phoenix (Scop.) Holub] accounts for nearly 16 million hectares of pasture in the Southeastern and Mid-Atlantic U.S. due to its heat, drought, and pest resistance, conferred to the plant by its symbiotic relationship with the endophyte Neotyphodium coenophialum. The endophyte produces ergot alkaloids that have negative effects on the growth and reproduction of animals, resulting in the syndrome known as fescue toxicosis. The objectives of our study were to identify microRNA (miRNA) present in bovine sperm and to evaluate the effects of fescue toxicosis on sperm miRNA expression. Angus bulls were assigned to treatments of either toxic or non-toxic fescue seed diets. Semen was collected and subjected to RNA isolation. Three samples from each treatment group were chosen and pooled for deep sequencing. To compare miRNA expression between treatment groups, a microarray was designed and conducted. For each of the top ten expressed miRNA, target prediction analysis was conducted using TargetScan. Gene ontology enrichment was assessed using the Database for Annotation, Visualization and Integrated Discovery. Sequencing results elucidated the presence of 1,582 unique small RNA present in sperm. Of those sequences, 382 were known Bos taurus miRNA, 22 were known but novel to Bos taurus, and 816 were predicted candidate miRNA that did not map to any currently reported miRNA. Of the sequences chosen for microarray, twenty-two showed significant differential expression between treatment groups. Gene pathways of interest included: regulation of transcription, embryonic development (including blastocyst formation), Wnt and Hedgehog signaling, oocyte meiosis, and kinase and phosphatase activity. MicroRNA present in mature sperm appears to not only be left over from spermatogenic processes, but may actually serve important regulatory roles in fertilization and early developmental processes. Further, our results indicate the possibility that environmental changes may impact the expression of specific miRNA.

PreImplantation factor promotes neuroprotection by targeting microRNA let-7

Dysfunction and loss of neurons are the major characteristics of CNS disorders that include stroke, multiple sclerosis, and Alzheimer's disease. Activation of the Toll-like receptor 7 by extracellular microRNA let-7, a highly expressed microRNA in the CNS, induces neuronal cell death. Let-7 released from injured neurons and immune cells acts on neighboring cells, exacerbating CNS damage. Here we show that a synthetic peptide analogous to the mammalian PreImplantation factor (PIF) secreted by developing embryos and which is present in the maternal circulation during pregnancy inhibits the biogenesis of let-7 in both neuronal and immune cells of the mouse. The synthetic peptide, sPIF, destabilizes KH-type splicing regulatory protein (KSRP), a key microRNA-processing protein, in a Toll-like receptor 4 (TLR4)-dependent manner, leading to decreased production of let-7. Furthermore, s.c. administration of sPIF into neonatal rats following hypoxic-ischemic brain injury robustly rescued cortical volume and number of neurons and decreased the detrimental glial response, as is consistent with diminished levels of KSRP and let-7 in sPIF-treated brains. Our results reveal a previously unexpected mechanism of action of PIF and underscore the potential clinical utility of sPIF in treating hypoxic-ischemic brain damage. The newly identified PIF/TLR4/KSRP/let-7 regulatory axis also may operate during embryo implantation and development.

MicroRNA Let-7a and dicer are important in the activation and implantation of delayed implanting mouse embryos

STUDY QUESTION

Does Let-7a have a functional role in modulating dicer expression to activate dormant mouse blastocysts for implantation?

SUMMARY ANSWER

Let-7a post-transcriptionally regulates dicer expression altering microRNA expression to affect the implantation competency of the activated blastocysts.

WHAT IS KNOWN ALREADY

The Let-7a microRNA is up-regulated during blastocyst dormancy and its forced-expression suppresses embryo implantation in vitro and in vivo. Dicer is a Let-7 target, which processes pre-microRNA to mature microRNA.

STUDY DESIGN, SIZE, DURATION

The effects on the expression of Let-7a and dicer in dormant blastocysts during the first 12 h after estradiol-induced activation, and the relationship between Let-7a and dicer in preimplantation embryos were determined. The effects on the microRNA expression and embryo implantation in vivo in dicer-knockdown mouse 5-8 cell embryos and dormant blastocysts at 1 h post estradiol activation were also studied.

PARTICIPANTS/MATERIALS, SETTING, METHODS

ICR female mice at 6 weeks of age were ovariectomized on Day 4 of pregnancy to generate the delayed implantation model. Mouse 5-8 cell embryos and/or dormant blastocysts at 1 h after estradiol injection were electroporated with dicer siRNA and Let-7a precursor or Let-7a inhibitor. At 48 h post electroporation, the Let-7a expression, dicer transcripts and proteins in the embryos were determined using qPCR and immunostaining/western blotting, respectively. All experiments were repeated at least three times.

MAIN RESULTS AND THE ROLE OF CHANCE

Estradiol injection down-regulated Let-7a and up-regulated dicer in the dormant blastocysts during the first 12 h post-activation. Dicer knockdown at 1 h post-activation of blastocysts suppressed EGFR expression, attenuated EGF binding and compromised implantation of the transferred embryos. Let-7a transcriptionally regulated dicer by binding to the 3'-UTR of dicer in trophoblast cells. Dicer knockdown in blastocysts suppressed mature Let-7a expression and compromised implantation.

LIMITATIONS, REASONS FOR CAUTION

Gain- and loss-of-function approaches were used by analyzing transient expressions of transfected microRNA modulators or genes. The consequence of the Let-7a-dicer interaction on pregnancy remains to be determined. The study used the mouse as a model and the applicability of the observed phenomena in humans warrants further investigation.

WIDER IMPLICATIONS OF THE FINDINGS

Our results indicate that the Let-7a-dicer interaction leads to differential microRNA expression in dormant blastocysts after estradiol activation. Because the expression pattern of Let-7a in human blastocysts is similar to that in mouse blastocysts, our observation that the Let-7a-dicer interaction has a role in regulating the implantation potential of the mouse blastocysts could be applicable to humans.

STUDY FUNDING/COMPETING INTEREST(S)

This project is supported partly by a research grant from the Research Grant Council to W.S.B.Y. The authors have no competing interests to declare.

The expression of the let-7 miRNAs and Lin28 signalling pathway in human term gestational tissues

INTRODUCTION

Labour and delivery are processes associated with inflammation within intrauterine and cervical tissues. The mechanisms that induce labour-associated changes and, in particular, the role of microRNAs (miRNAs) remain to be elucidated. MiRNAs are small non-coding RNAs that repress gene expression via mRNA degradation and translational repression. Let-7 miRNAs are negatively regulated by RNA-binding protein, Lin28, and both function downstream of NF-κB signalling. In non-gestational tissues, let-7 and Lin28 reportedy function as negative and positive regulators of IL-6 expression. We hypothesised that labour-associated inflammation involves the downregulation of let-7 miRNAs and upregulation of Lin28 expression.

AIM

To determine the expression of Lin28 protein and let-7 miRNA in human gestational tissue obtained before and after labour.

METHOD

Gestational tissues were collected from women at term by Caesarean section with and without labour and following normal vaginal delivery (n = 6 per group). Protein and RNA was extracted and Lin28 and let-7 miRNA expression was measured by Western blotting and real-time PCR.

RESULTS

The data obtained established that let-7 miRNA and Lin28 display tissue-specific expression: Lin28 was strongly expressed in the placenta and choriodecidua, but not measurable in amnion; and let-7b and -7c expression were significantly lower in choriodecidua compare to placenta and amnion, whereas the amnion expressed less let-7d and -7f than other tissues.

CONCLUSION

While the expression of Lin28 protein and let-7 miRNA did not vary significantly with labour onset and delivery, changes in their bioactivity and impact on nuclear signalling pathways in human gestational tissues remain to be established.

Physiological and molecular determinants of embryo implantation

Embryo implantation involves the intimate interaction between an implantation-competent blastocyst and a receptive uterus, which occurs in a limited time period known as the window of implantation. Emerging evidence shows that defects originating during embryo implantation induce ripple effects with adverse consequences on later gestation events, highlighting the significance of this event for pregnancy success. Although a multitude of cellular events and molecular pathways involved in embryo-uterine crosstalk during implantation have been identified through gene expression studies and genetically engineered mouse models, a comprehensive understanding of the nature of embryo implantation is still missing. This review focuses on recent progress with particular attention to physiological and molecular determinants of blastocyst activation, uterine receptivity, blastocyst attachment and uterine decidualization. A better understanding of underlying mechanisms governing embryo implantation should generate new strategies to rectify implantation failure and improve pregnancy rates in women.