Trophectoderm-Specific Knockdown of LIN28 Decreases Expression of Genes Necessary for Cell Proliferation and Reduces Elongation of Sheep Conceptus

The transposable element-derived transcript of LIN28B has a placental origin and is not specific to tumours

Transposable elements (TEs) are genetic elements that have evolved as crucial regulators of human development and cancer, functioning as both genes and regulatory elements. When TEs become dysregulated in cancer cells, they can serve as alternate promoters to activate oncogenes, a process known as onco-exaptation. This study aimed to explore the expression and epigenetic regulation of onco-exaptation events in early human developmental tissues. We discovered co-expression of some TEs and oncogenes in human embryonic stem cells and first trimester and term placental tissues. Previous studies identified onco-exaptation events in various cancer types, including an AluJb SINE element-LIN28B interaction in lung cancer cells, and showed that the TE-derived LIN28B transcript is associated with poor patient prognosis in hepatocellular carcinoma. This study further characterized the AluJb-LIN28B transcript and confirmed that its expression is restricted to the placenta. Targeted DNA methylation analysis revealed differential methylation of the two LIN28B promoters between placenta and healthy somatic tissues, indicating that some TE-oncogene interactions are not cancer-specific but arise from the epigenetic reactivation of developmental TE-derived regulatory events. In conclusion, our findings provide evidence that some TE-oncogene interactions are not limited to cancer and may originate from the epigenetic reactivation of TE-derived regulatory events that are involved in early development. These insights broaden our understanding of the role of TEs in gene regulation and suggest the potential importance of targeting TEs in cancer therapy beyond their conventional use as cancer-specific markers.

MEL regulates miR-21 and let-7b through the STAT3 cascade in the follicular granulosa cells of Tibetan sheep

Under physiological and pathological conditions, melatonin (MEL) can regulate microRNA (miRNA) expression. However, the mechanisms underlying the regulatory effects of MEL on miRNAs in ovaries are not understood. Firstly, by using fluorescence in situ hybridisation, we found that in ovaries and follicular granulosa cells (FGCs), MT1 co-located with miR-21 and let-7b. Additionally, immunofluorescence revealed that MT1, STAT3, c-MYC and LIN28 proteins co-located. The mRNA and protein levels of STAT3, c-MYC and LIN28 increased under treatment with 10^-7 M MEL. MEL induced an increase in miR-21 and a decrease in let-7b. The LIN28/let-7b and STAT3/miR-21 axes are related to cell differentiation, apoptosis and proliferation. We explored whether the STAT3/c-MYC/LIN28 pathway was involved in miRNA regulation by MEL to explore the putative mechanism of the above relationship. AG490, an inhibitor of the STAT3 pathway, was added before MEL treatment. AG490 inhibited the MEL-induced increases in STAT3, c-MYC, LIN28 and MT1 and changes in miRNA. Through live-cell detection, we discovered that MEL enhanced the proliferation of FGCs. However, the ki67 protein levels decreased when AG490 was added in advance. Furthermore, the dual-luciferase reporter assay verified that STAT3, LIN28 and MT1 were target genes of let-7b. Furthermore, STAT3 and SMAD7 were target genes of miR-21. In addition, the protein levels of the STAT3, c-MYC, LIN28 and MEL receptors decreased when let-7b was overexpressed in FGCs. Overall, MEL might regulate miRNA expression through the STAT3 pathway. In addition, a negative feedback loop between the STAT3 and miR-21 formed; MEL and let-7b antagonized each other in FGCs. These findings may provide a theoretical basis for improving the reproductive performance of Tibetan sheep through MEL and miRNAs.

Characterization of trophoblast mitochondrial function and responses to testosterone treatment in ACH-3P cells

INTRODUCTION

Trophoblast mitochondria play important roles in placental energy metabolism, physiology and pathophysiology. Hyperandrogenism has been associated with mitochondrial abnormalities in pregnancy disorders such as pre-eclampsia, gestational diabetes, and intrauterine growth restriction, but the direct impacts of androgen exposure on placental mitochondrial function are unknown. Given the inherent limitations of studying the human placenta during pregnancy, trophoblast cell lines are routinely used to model placental biology in vitro. The aim of this study was to characterize mitochondrial respiratory function in four commonly used trophoblast cell lines to provide a basis for selecting one well-suited to investigating the impact of androgens on trophoblast mitochondrial function.

METHODS

Androgen receptor expression, mitochondrial respiration (JO₂) and reactive oxygen species (ROS) release rates were evaluated in three human trophoblast cell lines (ACH-3P, BeWo and Swan-71) and one immortalized ovine trophoblast line (iOTR) under basal and substrate-stimulated conditions using high-resolution fluorespirometry.

RESULTS

ACH-3P cells exhibited the greatest mitochondrial respiratory capacity and coupling efficiency of the four trophoblast lines tested, along with robust expression of androgen receptor protein that was found to co-localize with mitochondria by immunoblot and immunofluorescence. Acute testosterone administration (10 nM) tended to decrease ACH-3P mitochondrial JO₂ and increase ROS release, while chronic (7 days) testosterone exposure increased expression of mitochondrial proteins, JO₂, and ROS release.

DISCUSSION

These studies establish ACH-3P as a suitable cell line for investigating trophoblast mitochondrial function, and provide foundational evidence supporting links between hyperandrogenism and placental mitochondrial ROS production with potential relevance to several common pregnancy disorders.

PPARγ/mTOR Regulates the Synthesis and Release of Prostaglandins in Ovine Trophoblast Cells in Early Pregnancy

Trophoblast cells synthesize and secrete prostaglandins (PGs), which are essential for ruminants in early gestation to recognize pregnancy. Hormones in the intrauterine environment play an important role in regulating PGs synthesis during implantation, but the underlying mechanism remains unclear. In this study, co-treatment of sheep trophoblast cells (STCs) with progesterone (P4), estradiol (E2), and interferon-tau (IFN-τ) increased the ratio of prostaglandin E2 (PGE2) to prostaglandin F2α (PGF2α) and upregulated peroxisome proliferator-activated receptor γ (PPARγ) expression, while inhibiting the mechanistic target of rapamycin (mTOR) pathway and activating cellular autophagy. Under hormone treatment, inhibition of PPARγ activity decreased the ratio of PGE2/PGF2α and cellular activity, while activating expression of the mTOR downstream marker-the phosphorylation of p70S6K (p-p70S6K). We also found that the PPARγ/mTOR pathway played an important role in regulating trophoblast cell function. Inhibition of the mTOR pathway by rapamycin increased the ratio of PGE2/PGF2α and decreased the expression of apoptosis-related proteins after inhibiting PPARγ activity. In conclusion, our findings provide new insights into the molecular mechanism of prostaglandin regulation of trophoblast cells in sheep during early pregnancy, indicating that the PPARγ/mTOR pathway plays an important role in PGs secretion and cell viability.

Impact of Placental SLC2A3 Deficiency during the First-Half of Gestation

In the ruminant placenta, glucose uptake and transfer are mediated by facilitative glucose transporters SLC2A1 (GLUT1) and SLC2A3 (GLUT3). SLC2A1 is located on the basolateral trophoblast membrane, whereas SLC2A3 is located solely on the maternal-facing, apical trophoblast membrane. While SLC2A3 is less abundant than SLC2A1, SLC2A3 has a five-fold greater affinity and transport capacity. Based on its location, SLC2A3 likely plays a significant role in the uptake of glucose into the trophoblast. Fetal hypoglycemia is a hallmark of fetal growth restriction (FGR), and as such, any deficiency in SLC2A3 could impact trophoblast glucose uptake and transfer to the fetus, thus potentially setting the stage for FGR. By utilizing in vivo placenta-specific lentiviral-mediated RNA interference (RNAi) in sheep, we were able to significantly diminish (p ≤ 0.05) placental SLC2A3 concentration, and determine the impact at mid-gestation (75 dGA). In response to SLC2A3 RNAi (n = 6), the fetuses were hypoglycemic (p ≤ 0.05), exhibited reduced fetal growth, including reduced fetal pancreas weight (p ≤ 0.05), which was associated with reduced umbilical artery insulin and glucagon concentrations, when compared to the non-targeting sequence (NTS) RNAi controls (n = 6). By contrast, fetal liver weights were not impacted, nor were umbilical artery concentrations of IGF1, possibly resulting from a 70% increase (p ≤ 0.05) in umbilical vein chorionic somatomammotropin (CSH) concentrations. Thus, during the first half of gestation, a deficiency in SLC2A3 results in fetal hypoglycemia, reduced fetal development, and altered metabolic hormone concentrations. These results suggest that SLC2A3 may be the rate-limiting placental glucose transporter during the first-half of gestation in sheep.

Regulatory roles of non-coding RNAs and m6A modification in trophoblast functions and the occurrence of its related adverse pregnancy outcomes

Adverse pregnancy outcomes, such as preeclampsia, gestational diabetes mellitus, fetal growth restriction, and recurrent miscarriage, occur frequently in pregnant women and might further induce morbidity and mortality for both mother and fetus. Increasing studies have shown that dysfunctions of human trophoblast are related to these adverse pregnancy outcomes. Recent studies also showed that environmental toxicants could induce trophoblast dysfunctions. Moreover, non-coding RNAs (ncRNAs) have been reported to play important regulatory roles in various cellular processes. However, the roles of ncRNAs in the regulation of trophoblast dysfunctions and the occurrence of adverse pregnancy outcomes still need to be further investigated, especially with exposure to environmental toxicants. In this review, we analyzed the regulatory mechanisms of ncRNAs and m6A methylation modification in the dysfunctions of trophoblast cells and the occurrence of adverse pregnancy outcomes and also summarized the harmful effects of environmental toxicants. In addition to DNA replication, mRNA transcription, and protein translation, ncRNAs and m6A modification might be considered as the fourth and fifth elements that regulate the genetic central dogma, respectively. Environmental toxicants might also affect these processes. In this review, we expect to provide a deeper scientific understanding of the occurrence of adverse pregnancy outcomes and to discover potential biomarkers for the diagnosis and treatment of these outcomes.

Inhibition of SHMT2 mRNA translation increases embryonic mortality in sheep

The one-carbon metabolism (OCM) pathway provides purines and thymidine for synthesis of nucleic acids required for cell division, and S-adenosyl methionine for polyamine and creatine syntheses and the epigenetic regulation of gene expression. This study aimed to determine if serine hydroxymethyltransferase 2 (SHMT2), a key enzyme in the OCM pathway, is critical for ovine trophectoderm (oTr) cell function and conceptus development by inhibiting translation of SHMT2 mRNA using a morpholino antisense oligonucleotide (MAO). In vitro treatment of oTr cells with MAO-SHMT2 decreased expression of SHMT2 protein, which was accompanied by reduced proliferation (P = 0.053) and migration (P < 0.05) of those cells. Intrauterine injection of MAO-SHMT2 in ewes on Day 11 post-breeding tended to decrease the overall pregnancy rate (on Days 16 and 18) compared to MAO-control (3/10 vs 7/10, P = 0.07). The three viable conceptuses (n = 2 on Day 16 and n = 1 on Day 18) recovered from MAO-SHMT2 ewes had only partial inhibition of SHMT2 mRNA translation. Conceptuses from the three pregnant MAO-SHMT2 ewes had similar levels of expression of mRNAs and proteins involved in OCM as compared to conceptuses from MAO-control ewes. These results indicate that knockdown of SHMT2 protein reduces proliferation and migration of oTr cells (in vitro) to decrease elongation of blastocysts from spherical to elongated forms. These in vitro effects suggest that increased embryonic deaths in ewes treated with MAO-SHMT2 are the result of decreased SHMT2-mediated trophectoderm cell proliferation and migration supporting a role for the OCM pathway in survival and development of ovine conceptuses.

LIN28 Family in Testis: Control of Cell Renewal, Maturation, Fertility and Aging

Male reproductive development starts early in the embryogenesis with somatic and germ cell differentiation in the testis. The LIN28 family of RNA-binding proteins promoting pluripotency has two members—LIN28A and LIN28B. Their function in the testis has been investigated but many questions about their exact role based on the expression patterns remain unclear. LIN28 expression is detected in the gonocytes and the migrating, mitotically active germ cells of the fetal testis. Postnatal expression of LIN28 A and B showed differential expression, with LIN28A expressed in the undifferentiated spermatogonia and LIN28B in the elongating spermatids and Leydig cells. LIN28 interferes with many signaling pathways, leading to cell proliferation, and it is involved in important testicular physiological processes, such as cell renewal, maturation, fertility, and aging. In addition, aberrant LIN28 expression is associated with testicular cancer and testicular disorders, such as hypogonadotropic hypogonadism and Klinefelter’s syndrome. This comprehensive review encompasses current knowledge of the function of LIN28 paralogs in testis and other tissues and cells because many studies suggest LIN28AB as a promising target for developing novel therapeutic agents.

In vivo investigation of ruminant placenta function and physiology-a review

The placenta facilitates the transport of nutrients to the fetus, removal of waste products from the fetus, immune protection of the fetus and functions as an endocrine organ, thereby determining the environment for fetal growth and development. Additionally, the placenta is a highly metabolic organ in itself, utilizing a majority of the oxygen and glucose derived from maternal circulation. Consequently, optimal placental function is required for the offspring to reach its genetic potential in utero. Among ruminants, pregnant sheep have been used extensively for investigating pregnancy physiology, in part due to the ability to place indwelling catheters within both maternal and fetal vessels, allowing for steady-state investigation of blood flow, nutrient uptakes and utilization, and hormone secretion, under non-stressed and non-anesthetized conditions. This methodology has been applied to both normal and compromised pregnancies. As such, our understanding of the in vivo physiology of pregnancy in sheep is unrivalled by any other species. However, until recently, a significant deficit existed in determining the specific function or significance of individual genes expressed by the placenta in ruminants. To that end, we developed and have been using in vivo RNA interference (RNAi) within the sheep placenta to examine the function and relative importance of genes involved in conceptus development (PRR15 and LIN28), placental nutrient transport (SLC2A1 and SLC2A3), and placenta-derived hormones (CSH). A lentiviral vector is used to generate virus that is stably integrated into the infected cell's genome, thereby expressing a short-hairpin RNA (shRNA), that when processed within the cell, combines with the RNA Induced Silencing Complex (RISC) resulting in specific mRNA degradation or translational blockage. To accomplish in vivo RNAi, day 9 hatched and fully expanded blastocysts are infected with the lentivirus for 4 to 5 h, and then surgically transferred to synchronized recipient uteri. Only the trophectoderm cells are infected by the replication deficient virus, leaving the inner cell mass unaltered, and we often obtain ~70% pregnancy rates following transfer of a single blastocyst. In vivo RNAi coupled with steady-state study of blood flow and nutrient uptake, transfer and utilization can now provide new insight into the physiological consequences of modifying the translation of specific genes expressed within the ruminant placenta.

Trophectoderm Transcriptome Analysis in LIN28 Knockdown Ovine Conceptuses Suggests Diverse Roles of the LIN28-let-7 Axis in Placental and Fetal Development

The proper conceptus elongation in ruminants is critical for the successful placentation and establishment of pregnancy. We have previously shown that the trophectoderm-specific knockdown of LIN28A/B in day 9 ovine blastocysts resulted in increased let-7 miRNAs and reduced conceptus elongation at day 16 of gestation. In this current study, by transcriptome analysis of LIN28A knockdown (AKD) or LIN28B knockdown (BKD) trophectoderm (TE), we explored the downstream target genes of the LIN28-let-7 axis and their roles in the placental and fetal development. We identified 449 differentially expressed genes (DEGs) in AKD TE and 1214 DEGs in BKD TE compared to non-targeting control (NTC). Our analysis further revealed that 210 downregulated genes in AKD TE and 562 downregulated genes in BKD TE were the potential targets of let-7 miRNAs. Moreover, 16 downregulated genes in AKD TE and 57 downregulated and 7 upregulated genes in BKD TE were transcription factors. The DEGs in AKD and BKD TE showed enrichment in the biological processes and pathways critical for placental development and function, and fetal development and growth. The results of this study suggest the potential roles of the LIN28-let-7 axis in placental and fetal development beyond its involvement in trophoblast proliferation and conceptus elongation.

Overexpression of Lin28A in neural progenitor cells in vivo does not lead to brain tumor formation but results in reduced spine density

LIN28A overexpression has been identified in malignant brain tumors called embryonal tumors with multilayered rosettes (ETMR) but its specific role during brain development remains largely unknown. Radial glia cells of the ventricular zone (VZ) are proposed as a cell of origin for ETMR. We asked whether an overexpression of LIN28A in such cells might affect brain development or result in the formation of brain tumors.Constitutive overexpression of LIN28A in hGFAP-cre::lsl-Lin28A (GL) mice led to a transient increase of proliferation in the cortical VZ at embryonic stages but no postnatal brain tumor formation. Postnatally, GL mice displayed a pyramidal cell layer dispersion of the hippocampus and altered spine and dendrite morphology, including reduced dendritic spine densities in the hippocampus and cortex. GL mice displayed hyperkinetic activity and differential quantitative MS-based proteomics revealed altered time dependent molecular functions regarding mRNA processing and spine morphogenesis. Phosphoproteomic analyses indicated a downregulation of mTOR pathway modulated proteins such as Map1b being involved in microtubule dynamics.In conclusion, we show that Lin28A overexpression transiently increases proliferation of neural precursor cells but it is not sufficient to drive brain tumors in vivo. In contrast, Lin28A impacts on protein abundancy patterns related to spine morphogenesis and phosphorylation levels of proteins involved in microtubule dynamics, resulting in decreased spine densities of neurons in the hippocampus and cortex as well as in altered behavior. Our work provides new insights into the role of LIN28A for neuronal morphogenesis and development and may reveal future targets for treatment of ETMR patients.

In Utero Fetal Weight in Pigs Is Regulated by microRNAs and Their Target Genes

Impaired skeletal muscle growth in utero can result in reduced birth weight and poor carcass quality in pigs. Recently, we showed the role of microRNAs (miRNAs) and their target genes in prenatal skeletal muscle development and pathogenesis of intrauterine growth restriction (IUGR). In this study, we performed an integrative miRNA-mRNA transcriptomic analysis in longissimus dorsi muscle (LDM) of pig fetuses at 63 days post conception (dpc) to identify miRNAs and genes correlated to fetal weight. We found 13 miRNAs in LDM significantly correlated to fetal weight, including miR-140, miR-186, miR-101, miR-15, miR-24, miR-29, miR-449, miR-27, miR-142, miR-99, miR-181, miR-199, and miR-210. The expression of these miRNAs decreased with an increase in fetal weight. We also identified 1315 genes significantly correlated to fetal weight at 63 dpc, of which 135 genes were negatively correlated as well as identified as potential targets of the above-listed 13 miRNAs. These miRNAs and their target genes enriched pathways and biological processes important for fetal growth, development, and metabolism. These results indicate that the transcriptomic profile of skeletal muscle can be used to predict fetal weight, and miRNAs correlated to fetal weight can serve as potential biomarkers of prenatal fetal health and growth.

Dietary phosphorus and calcium in feed affects miRNA profiles and their mRNA targets in jejunum of two strains of laying hens

Phosphorus (P) and calcium (Ca) are critical for egg production in laying hens. Most of P in plant-based poultry diet is bound as phytic acid and needs to be hydrolysed before absorption. To increase P bioavailability, exogenous phytases or bioavailable rock phosphate is added in feed. There is growing evidence of the importance of miRNAs as the epicentre of intestinal homeostasis and functional properties. Therefore, we demonstrated the expression of miRNA profiles and the corresponding target genes due to the different levels of P (recommended vs. 20% reduction) and/or Ca (recommended vs. 15% reduction) in feed. Jejunal miRNA profiles of Lohmann Selected Leghorn (LSL) and Lohmann Brown (LB) laying hens strains were used (n = 80). A total of 34 and 76 miRNAs were differentially expressed (DE) in the different diet groups within LSL and LB strains respectively. In LSL, the DE miRNAs and their targets were involved in calcium signaling pathway, inositol phosphate metabolism, and mitochondrial dysfunction. Similarly, in LB miRNAs targets were enriched in metabolic pathways such as glutathione metabolism, phosphonate metabolism and vitamin B6 metabolism. Our results suggest that both strains employ different intrinsic strategies to cope with modulated P and Ca supply and maintain mineral homeostasis.

HMGA1 Is a Potential Driver of Preeclampsia Pathogenesis by Interference with Extravillous Trophoblasts Invasion

Preeclampsia (PE) is a serious disease that can be fatal for the mother and fetus. The two-stage theory has been proposed as its cause, with the first stage comprising poor placentation associated with the failure of fertilized egg implantation. Successful implantation and placentation require maternal immunotolerance of the fertilized egg as a semi-allograft and appropriate extravillous trophoblast (EVT) invasion of the decidua and myometrium. The disturbance of EVT invasion during implantation in PE results in impaired spiral artery remodeling. PE is thought to be caused by hypoxia during remodeling failure-derived poor placentation, which results in chronic inflammation. High-mobility group protein A (HMGA) is involved in the growth and invasion of cancer cells and likely in the growth and invasion of trophoblasts. Its mechanism of action is associated with immunotolerance. Thus, HMGA is thought to play a pivotal role in successful pregnancy, and its dysfunction may be related to the pathogenesis of PE. The evaluation of HMGA function and its changes in PE might confirm that it is a reliable biomarker of PE and provide prospects for PE treatment through the induction of EVT proliferation and invasion during the implantation.

Prenatal Skeletal Muscle Transcriptome Analysis Reveals Novel MicroRNA-mRNA Networks Associated with Intrauterine Growth Restriction in Pigs

Intrauterine growth restriction (IUGR) occurs in 15–20% of pig neonates and poses huge economic losses to the pig industry. IUGR piglets have reduced skeletal muscle growth, which may persist after birth. Prenatal muscle growth is regulated by complex molecular pathways that are not well understood. MicroRNAs (miRNAs) have emerged as the main regulators of vital pathways and biological processes in the body. This study was designed to identify miRNA–mRNA networks regulating prenatal skeletal muscle development in pigs. We performed an integrative miRNA–mRNA transcriptomic analysis in longissimus dorsi muscle from IUGR fetuses and appropriate for gestational age (AGA) fetuses at 63 days post conception. Our data showed that 47 miRNAs and 3257 mRNAs were significantly upregulated, and six miRNAs and 477 mRNAs were significantly downregulated in IUGR compared to AGA fetuses. Moreover, 47 upregulated miRNAs were negatively correlated and can potentially target 326 downregulated genes, whereas six downregulated miRNAs were negatively correlated and can potentially target 1291 upregulated genes. These miRNA–mRNA networks showed enrichment in biological processes and pathways critical for fetal growth, development, and metabolism. The miRNA–mRNA networks identified in this study can potentially serve as indicators of prenatal fetal growth and development as well as postnatal carcass quality.

Impact of chorionic somatomammotropin RNA interference on uterine blood flow and placental glucose uptake in the absence of intrauterine growth restriction

Chorionic somatomammotropin (CSH) is one of the most abundantly produced placental hormones, yet its exact function remains elusive. Near-term [135 days of gestational age (dGA)], CSH RNA interference (RNAi) results in two distinct phenotypes: 1) pregnancies with intrauterine growth restriction (IUGR), and 2) pregnancies with normal fetal and placental weights. Here, we report the physiological changes in CSH RNAi pregnancies without IUGR. The trophectoderm of hatched blastocysts (9 dGA) were infected with lentiviral-constructs expressing either a scrambled control (Control RNAi) or CSH-specific shRNA (CSH RNAi), prior to transfer into synchronized recipient ewes. At 126 dGA, Control RNAi (n = 6) and CSH RNAi (n = 6) pregnancies were fitted with maternal and fetal catheters. Uterine and umbilical blood flows were measured at 132 dGA and nutrient uptakes were calculated by the Fick's principle. Control RNAi and CSH RNAi pregnancies were compared by analysis of variance, and significance was set at P ≤ 0.05. Absolute (mL/min) and relative (mL/min/kg fetus) uterine blood flows were reduced (P ≤ 0.05) in CSH RNAi pregnancies, but umbilical flows were not impacted. The uterine artery-to-vein glucose gradient (mmol/L) was significantly (P ≤ 0.05) increased. The uteroplacental glucose uptake (μmoL/min/kg placenta) was increased (P ≤ 0.05), whereas umbilical glucose uptake (μmoL/min/kg fetus) was reduced. Our results demonstrate that CSH RNAi has significant physiological ramifications, even in the absence of IUGR, and comparing CSH RNAi pregnancies exhibiting both IUGR and non-IUGR phenotypes may help determine the direct effects of CSH and its potential impact on fetal development.

MicroRNA-Mediated Gene Regulatory Mechanisms in Mammalian Female Reproductive Health

Mammalian reproductive health affects the entire reproductive cycle starting with the ovarian function through implantation and fetal growth. Various environmental and physiological factors contribute to disturbed reproductive health status leading to infertility problems in mammalian species. In the last couple of decades a significant number of studies have been conducted to investigate the transcriptome of reproductive tissues and organs in relation to the various reproductive health issues including endometritis, polycystic ovarian syndrome (PCOS), intrauterine growth restriction (IUGR), preeclampsia, and various age-associated reproductive disorders. Among others, the post-transcriptional regulation of genes by small noncoding miRNAs contributes to the observed transcriptome dysregulation associated with reproductive pathophysiological conditions. MicroRNAs as a class of non-coding RNAs are also known to be involved in various pathophysiological conditions either in cellular cytoplasm or they can be released to the extracellular fluid via membrane-bounded extracellular vesicles and proteins. The present review summarizes the cellular and extracellular miRNAs and their association with the etiology of major reproductive pathologies including PCOS, endometritis, IUGR and age-associated disorders in various mammalian species.

The Role of LIN28-let-7-ARID3B Pathway in Placental Development

Placental disorders are a major cause of pregnancy loss in humans, and 40–60% of embryos are lost between fertilization and birth. Successful embryo implantation and placental development requires rapid proliferation, invasion, and migration of trophoblast cells. In recent years, microRNAs (miRNAs) have emerged as key regulators of molecular pathways involved in trophoblast function. A miRNA binds its target mRNA in the 3ʹ-untranslated region (3ʹ-UTR), causing its degradation or translational repression. Lethal-7 (let-7) miRNAs induce cell differentiation and reduce cell proliferation by targeting proliferation-associated genes. The oncoprotein LIN28 represses the biogenesis of mature let-7 miRNAs. Proliferating cells have high LIN28 and low let-7 miRNAs, whereas differentiating cells have low LIN28 and high let-7 miRNAs. In placenta, low LIN28 and high let-7 miRNAs can lead to reduced proliferation of trophoblast cells, resulting in abnormal placental development. In trophoblast cells, let-7 miRNAs reduce the expression of proliferation factors either directly by binding their mRNA in 3ʹ-UTR or indirectly by targeting the AT-rich interaction domain (ARID)3B complex, a transcription-activating complex comprised of ARID3A, ARID3B, and histone demethylase 4C (KDM4C). In this review, we discuss regulation of trophoblast function by miRNAs, focusing on the role of LIN28-let-7-ARID3B pathway in placental development.