Let-7 Research Articles

The role of let-7b in the inhibition of hepatic stellate cell activation by rSjP40.

BackgroundHepatic stellate cells (HSCs) are one of the main cell types involved in liver fibrosis induced by many factors, including schistosomes. Previous studies in our lab have shown that recombinant P40 protein from Schistosoma japonicum (rSjP40) can inhibit HSC activation in vitro. Let-7b is a member of the let-7 microRNA family and plays an inhibitory role in a variety of diseases and inflammatory conditions. In this study, we investigated the role of let-7b in the inhibition of HSC activation by rSjP40.MethodsExpression of let-7b was detected by quantitative real-time PCR. A dual luciferase assay was used to confirm direct interaction between let-7b and collagen I. We also used western blot to assess protein levels of TGFβRI and collagen type I α1 (COL1A1).ResultsWe found that rSjP40 up-regulates expression of let-7b in HSCs. Let-7b inhibits collagen I expression by directly targeting the 3’UTR region of the collagen I gene. Furthermore, we discovered that let-7b inhibitor partially restores the loss of collagen I expression caused by rSjP40.ConclusionOur research clarifies the role of let-7b in the inhibition of HSC activation by rSjP40 and will provide new insights and ideas for the inhibition of HSC activation and treatment of liver fibrosis.

Genetic and epigenetic bases of prostate tumor cell radioresistance.

Radiation therapy plays aleading role in the treatment of prostate cancer, but the emergence of radioresistant forms of this disease dictates the need for apersonalized ap-proach based on the data from genetic and epigenetic markers. Such markers include the copy number variation as well as gene and microRNA expression. The aim of the study was to validate the list of potential predictors of radioresistance of prostate tumor cells in amodel experiment based on the determination of gene copy number variation, gene transcriptional activity and microRNA expression. The study used aPC-3prostate cancer cell culture. The determination of the relative copy number variation and expression of 32genes (BRCA1, BRCA2, PTEN, CASP3, CASP8, BAX, BCL2, CASP9, P53, MDM2, AKT1, ATM, BRIP1, CDK1, CDKN1B, CCND1, CCND3, FGFR2, KU70, RAD50, RAP80, Rif1, RNF168, TopBP1, HIST, H2AX, EXO1, XRCC4, RBBP8, EP300, LIG4, C-FLIP), as well as 15microRNAs (let-7, miR15a/ 16, miR-17, miR-18a, miR-21, miR-24, miR-26b, miR-99a, miR-100, miR-101, miR-106a, miR-663a, miR-143, miR-145) was performed using the real-time quantitative polymerase chain reaction method. It was found that daily irradiation of PC-3cells on aNovalis TX linear accelerator at doses of 6and 7Gy for 5days leads to asignificant decrease in the total number of cells and the number of viable cells. Nevertheless, after 5days of irradiation, about 15% of the initial number of prostate tumor cells retained their viability, which is due to their special genetic and epigenetic characteristics: increased copy number and expression of genes BRCA2, CDK1, CDKN1B, H2AX, RAD50, XRCC4, RBBP8and EP300and reduced copy number and expression of CCND3, TP53, and BCL2genes, as well as differential expression of sixmicroRNAs (hsa-miR-18a-5p, hsa-miR-24-5p, hsa-miR-99a-5p, hsa-miR-100-5p, hsa-miR-145-5p, hsa-let-7a-3p). This study enabled to identify genetic and epigenetic markers of prostate tumor cells resistance to radiation therapy.

Lin28A promotes the proliferation and stemness of lung cancer cells via the activation of mitogen-activated protein kinase pathway dependent on microRNA let-7c.

BackgroundAmong patients with lung cancer, metastatic and relapsed cases account for the largest proportion of disease-associated deaths. Tumor metastasis and relapse are believed to originate from cancer stem cells (CSCs), which have the capacity to be highly proliferative and invasive. In our previous studies, we established a conditional basement membrane extract-based (BME-based) 3-dimensional (3D) culture system to mimic the tumor growth environment in vivo and further amplified lung cancer stem cells (LCSCs) in our system. However, the molecular mechanisms of LCSC amplification and development in our 3D culture system have not been fully uncovered.MethodWe established the conditional 3D culture system to amplify LCSCs in other lung cancer cell lines, followed by examining the expression of Lin28A and let-7 microRNAs in them. We also explored the expression of Lin28A and let-7 microRNAs in LCSCs from clinical lung cancer tissue samples and even analyzed the correlation of Lin28A/let-7c and patients’ survival outcomes. We further constructed A549 cells either knockdown of Lin28A or overexpression of let-7c, followed by investigating stemness marker gene expression, and stemness phenotypes including mammosphere culture, cell migration and invasion in vitro, as well as tumorigenicity in vivo.ResultsHere, we observed that Lin28A/let-7c was dysregulated in LCSCs in both the 3D culture system and lung cancer tissues. Further, the abnormal expression of Lin28A/let-7c was correlated with poor survival outcomes. Via the construction of A549 cells with let-7c over-expression, we found that let-7c inhibited the maintenance of LCSC properties, while the results of Lin28A knockdown showed that Lin28A played a critical role in the enrichment and proliferation of LCSCs via mitogen-activated protein kinase (MAPK) signaling pathway. Importantly, we found that LCSCs with knockdown of Lin28A or over-expression of let-7c exhibited inhibited carcinogenesis and disrupted expansion in vivo.ConclusionsOur study uncovered the functions and mechanisms of the Lin28A/let-7c/MAPK signaling pathway in promoting the proliferation and cancer stemness of LCSCs, which might be a potential therapeutic target for reducing and even eliminating LCSCs in the future.

Let-7 microRNAs: Their Role in Cerebral and Cardiovascular Diseases, Inflammation, Cancer, and Their Regulation.

The let-7 family is among the first microRNAs found. Recent investigations have indicated that it is highly expressed in many systems, including cerebral and cardiovascular systems. Numerous studies have implicated the aberrant expression of let-7 members in cardiovascular diseases, such as stroke, myocardial infarction (MI), cardiac fibrosis, and atherosclerosis as well as in the inflammation related to these diseases. Furthermore, the let-7 microRNAs are involved in development and differentiation of embryonic stem cells in the cardiovascular system. Numerous genes have been identified as target genes of let-7, as well as a number of the let-7’ regulators. Further studies are necessary to identify the gene targets and signaling pathways of let-7 in cardiovascular diseases and inflammatory processes. The bulk of the let-7’ regulatory proteins are well studied in development, proliferation, differentiation, and cancer, but their roles in inflammation, cardiovascular diseases, and/or stroke are not well understood. Further knowledge on the regulation of let-7 is crucial for therapeutic advances. This review focuses on research progress regarding the roles of let-7 and their regulation in cerebral and cardiovascular diseases and associated inflammation.

Insects defend against fungal infection by employing microRNAs to silence virulence-related genes

Chemical insecticides remain the main strategy to combat mosquito-borne diseases, but the growing threat of insecticide resistance prompts the urgent need to develop alternative, ecofriendly, and sustainable vector control tools. Entomopathogenic fungi can overcome insecticide resistance and represent promising biocontrol tools for the control of mosquitoes. However, insects have evolved robust defense mechanisms against infection. Better understanding of mosquito defenses against fungal infection is critical for improvement of fungal efficacy. Here, we show that as the pathogenic fungus Beauveria bassiana penetrates into the host hemocoel, mosquitoes increase expression of the let-7 and miR-100 microRNAs (miRNAs). Both miRNAs translocate into fungal hyphae to specifically silence the virulence-related genes sec2p and C6TF, encoding a Rab guanine nucleotide exchange factor and a Zn(II)2Cys6 transcription factor, respectively. Inversely, expression of a let-7 sponge (anti-let-7) or a miR-100 sponge (anti-miR-100) in the fungus efficiently sequesters the corresponding translocated host miRNA. Notably, B. bassiana strains expressing anti-let-7 and anti-miR-100 are markedly more virulent to mosquitoes. Our findings reveal an insect defense strategy that employs miRNAs to induce cross-kingdom silencing of pathogen virulence-related genes, conferring resistance to infection.

MicroRNA Let-7 targets AMPK and impairs hepatic lipid metabolism in offspring of maternal obese pregnancies

Nutritional status during gestation may lead to a phenomenon known as metabolic programming, which can be triggered by epigenetic mechanisms. The Let-7 family of microRNAs were one of the first to be discovered, and are closely related to metabolic processes. Bioinformatic analysis revealed that Prkaa2, the gene that encodes AMPK α2, is a predicted target of Let-7. Here we aimed to investigate whether Let-7 has a role in AMPKα2 levels in the NAFLD development in the offspring programmed by maternal obesity. Let-7 levels were upregulated in the liver of newborn mice from obese dams, while the levels of Prkaa2 were downregulated. Let-7 levels strongly correlated with serum glucose, insulin and NEFA, and in vitro treatment of AML12 with glucose and NEFA lead to higher Let-7 expression. Transfection of Let-7a mimic lead to downregulation of AMPKα2 levels, while the transfection with Let-7a inhibitor impaired both NEFA-mediated reduction of Prkaa2 levels and the fat accumulation driven by NEFA. The transfection of Let-7a inhibitor in ex-vivo liver slices from the offspring of obese dams restored phospho-AMPKα2 levels. In summary, Let-7a appears to regulate hepatic AMPKα2 protein levels and lead to the early hepatic metabolic disturbances in the offspring of obese dams.

Lin28, a major translation reprogramming factor, gains access to YB-1-packaged mRNA through its cold-shock domain

The RNA-binding protein Lin28 (Lin28a) is an important pluripotency factor that reprograms translation and promotes cancer progression. Although Lin28 blocks let-7 microRNA maturation, Lin28 also binds to a large set of cytoplasmic mRNAs directly. However, how Lin28 regulates the processing of many mRNAs to reprogram global translation remains unknown. We show here, using a structural and cellular approach, a mixing of Lin28 with YB-1 (YBX1) in the presence of mRNA owing to their cold-shock domain, a conserved β-barrel structure that binds to ssRNA cooperatively. In contrast, the other RNA binding-proteins without cold-shock domains tested, HuR, G3BP-1, FUS and LARP-6, did not mix with YB-1. Given that YB-1 is the core component of dormant mRNPs, a model in which Lin28 gains access to mRNPs through its co-association with YB-1 to mRNA may provide a means for Lin28 to reprogram translation. We anticipate that the translational plasticity provided by mRNPs may contribute to Lin28 functions in development and adaptation of cancer cells to an adverse environment.

BCDIN3D RNA methyltransferase stimulates Aldolase C expression and glycolysis through let-7 microRNA in breast cancer cells.

Type II diabetes (T2D) and specific cancers share many risk factors, however the molecular mechanisms underlying these connections are often not well-understood. BCDIN3D is an RNA modifying enzyme that methylates specific precursor microRNAs and tRNAHis. In addition to breast cancer, BCDIN3D may also be linked to metabolism, as its gene locus is associated with obesity and T2D. In order to uncover metabolic pathways regulated by BCDIN3D in cancer, we performed an unbiased analysis of the metabolome, transcriptome, and proteome of breast cancer cells depleted for BCDIN3D. Intersection of these analyses showed that BCDIN3D-depleted cells have increased levels of Fructose 1,6 Bisphosphate (F1,6-BP), the last six-carbon glycolytic intermediate accompanied by reduced glycolytic capacity. We further show that elevated F1,6-BP is due to downregulation of Aldolase C (ALDOC), an enzyme that cleaves F1,6-BP mainly in the brain, but whose high expression/amplification is associated with poor prognosis in breast cancer. BCDIN3D regulates ALDOC through a non-canonical mechanism involving the crucial let-7 microRNA family and its target site on the 3’UTR of ALDOC. Overall, our results reveal an important connection between BCDIN3D, let-7 and glycolysis that may be relevant to breast cancer, obesity and T2D.

Trisubstituted Pyrrolinones as Small-Molecule Inhibitors Disrupting the Protein-RNA Interaction of LIN28 and Let-7.

Modulation of protein–RNA interaction (PRI) using small molecules is a promising strategy to develop therapeutics. LIN28 is an RNA-binding protein that blocks the maturation of the tumor suppressor let-7 microRNAs. Herein, we performed a fluorescence polarization-based screening and identified trisubstituted pyrrolinones as small-molecule inhibitors disrupting the LIN28–let-7 interaction. The most potent compound C902 showed dose-dependent inhibition in an EMSA validation assay, enhanced thermal stability of the cold shock domain of LIN28, and increased mature let-7 levels in JAR cells. The structure–activity relationship study revealed key structural features contributing to either PRI inhibition or stabilization of protein–protein interaction (PPI). The pyrrolinones identified in this study not only represent a new class of LIN28-binding molecules that diversify the limited available LIN28 inhibitors but also represent the first examples of small molecules that showed substituent-dependent PRI inhibitory and PPI activating activities.

Lin28 Inhibits the Differentiation from Mouse Embryonic Stem Cells to Glial Lineage Cells through Upregulation of Yap1.

The RNA-binding protein Lin28 regulates neurogliogenesis in mammals, independently of the let-7 microRNA. However, the detailed regulatory mechanism remains obscured. Here, we established Lin28a or Lin28b overexpression mouse embryonic stem cells (ESCs) and found that these cells expressed similar levels of the core pluripotent factors, such as Oct4 and Sox2, and increased Yap1 but decreased lineage-specific markers compared to the control ESCs. Further differentiation of these ESCs to neuronal and glial lineage cells revealed that Lin28a/b overexpression did not affect the expression of neuronal marker βIII-tubulin, but dramatically inhibited the glial lineage markers, such as Gfap and Mbp. Interestingly, overexpression of Yap1 in mouse ESCs phenocopied Lin28a/b overexpression ESCs by showing defect in glial cell differentiation. Inhibition of Yap1/Tead-mediated transcription with verteporfin partially rescued the differentiation defect of Lin28a/b overexpression ESCs. Mechanistically, we demonstrated that Lin28 can directly bind to Yap1 mRNA, and the induction of Yap1 by Lin28a in mESCs is independent of Let7. Taken together, our results unravel a novel Lin28-Yap1 regulatory axis during mESC to glial lineage cell differentiation, which may shed light on glial cell generation in vitro.

Repressing Ago2 mRNA translation by Trim71 maintains pluripotency through inhibiting let-7 microRNAs.

The regulation of stem cell fate is poorly understood. Genetic studies in Caenorhabditis elegans lead to the hypothesis that a conserved cytoplasmic double-negative feedback loop consisting of the RNA-binding protein Trim71 and the let-7 microRNA controls the pluripotency and differentiation of stem cells. Although let-7-microRNA-mediated inhibition of Trim71 promotes differentiation, whether and how Trim71 regulates pluripotency and inhibits the let-7 microRNA are still unknown. Here, we show that Trim71 represses Ago2 mRNA translation in mouse embryonic stem cells. Blocking this repression leads to a specific post-transcriptional increase of mature let-7 microRNAs, resulting in let-7-dependent stemness defects and accelerated differentiation in the stem cells. These results not only support the Trim71-let-7-microRNA bi-stable switch model in controlling stem cell fate, but also reveal that repressing the conserved pro-differentiation let-7 microRNAs at the mature microRNA level by Ago2 availability is critical to maintaining pluripotency.

RanBP2/Nup358 enhances miRNA activity by sumoylating Argonautes.

Mutations in RanBP2 (also known as Nup358), one of the main components of the cytoplasmic filaments of the nuclear pore complex, contribute to the overproduction of acute necrotizing encephalopathy (ANE1)-associated cytokines. Here we report that RanBP2 represses the translation of the interleukin 6 (IL6) mRNA, which encodes a cytokine that is aberrantly up-regulated in ANE1. Our data indicates that soon after its production, the IL6 messenger ribonucleoprotein (mRNP) recruits Argonautes bound to let-7 microRNA. After this mRNP is exported to the cytosol, RanBP2 sumoylates mRNP-associated Argonautes, thereby stabilizing them and enforcing mRNA silencing. Collectively, these results support a model whereby RanBP2 promotes an mRNP remodelling event that is critical for the miRNA-mediated suppression of clinically relevant mRNAs, such as IL6.

A cohort of Caenorhabditis species lacking the highly conserved let-7 microRNA.

The let-7 gene encodes a highly conserved microRNA with critical functions integral to cell fate specification and developmental progression in diverse animals. In Caenorhabditis elegans, let-7 is a component of the heterochronic (developmental timing) gene regulatory network, and loss-of-function mutations of let-7 result in lethality during the larval to adult transition due to misregulation of the conserved let-7 target, lin-41. To date, no bilaterian animal lacking let-7 has been characterized. In this study, we identify a cohort of nematode species within the genus Caenorhabditis, closely related to C. elegans, that lack the let-7 microRNA, owing to absence of the let-7 gene. Using Caenorhabditis sulstoni as a representative let-7-lacking species to characterize normal larval development in the absence of let-7, we demonstrate that, except for the lack of let-7, the heterochronic gene network is otherwise functionally conserved. We also report that species lacking let-7 contain a group of divergent let-7 paralogs—also known as the let-7-family of microRNAs—that have apparently assumed the role of targeting the LIN-41 mRNA.

Accurate Detection of Target MicroRNA in Mixed Species of High Sequence Homology Using Target-Protection Rolling Circle Amplification.

The close relationships of miRNAs with human diseases highlight the urgent needs for miRNA detection. However, the accurate detection of a target miRNA in mixed miRNAs of high sequence homology presents a great challenge. Herein, a novel method called target-protection rolling circle amplification (TP-RCA) is proposed for this purpose. The protective probe is designed so that it can form a fully complementary duplex with the target miRNA and can also mismatch duplexes with other nontarget miRNAs. These duplexes are treated with a single strand-specific nuclease. Consequently, only the target miRNA in a perfect-match duplex can resist the cleavage of nuclease, whereas the nontarget miRNAs in mismatched duplexes will be digested completely. The protected target miRNA can be detected using RCA reactions. MicroRNA let-7 family members (let-7a–let-7f) and nuclease CEL I were used as proof-of-concept models to evaluate the feasibility of the TP-RCA method under different experimental conditions. The experimental results show that the TP-RCA method can unambiguously detect the target let-7 species in mixtures of let-7 family members even though they may differ by only a single nucleotide. This TP-RCA method significantly improves the detection specificity of miRNAs.

The Potential Diagnostic Accuracy of Let-7 Family for Cancer: A Meta-Analysis.

Background:Cancer is a global public health problem affecting human health. Early stage of cancer diagnosis, when it is not too large and has not spread is important for successful treatment. Many researchers have proposed that the let-7 microRNA family can be used as a biomarker for cancer diagnosis. The aim of this meta-analysis is to evaluate whether let-7 family can be used as a diagnostic tool for cancer patients.Methods:We conducted a comprehensive literature search on PubMed, EMBASE, Web of Science, Cochrane Library, Google Scholar, China National Knowledge Infrastructure (CNKI) and Wanfang database, updated to October 23, 2020. A random effects model was used to pool the sensitivity and specificity. Besides, we measured the diagnostic value using positive likelihood ratio (PLR), negative likelihood ratio (NLR), diagnostic odds ratio (DOR) and area under the curve (AUC) were pooled. In addition, meta-regression and subgroup analysis were performed to explore the possible sources of heterogeneity, and Deeks’ funnel chart was used to assess whether there was publication bias.Results:31 studies from 15 articles were included in the current meta-analysis. The overall sensitivity, specificity, PLR, NLR, DOR and AUC were 0.80 (95% CI: 0.75-0.85), 0.81 (95% CI: 0.74-0.86), 4.2 (95% CI: 2.9-5.9), 0.24 (95% CI: 0.19-0.32), 17 (95% CI: 10-29) and 0.87 (95% CI: 0.84-0.90), respectively. Subgroup analysis shows that the let-7 family cluster of serum type showed a better diagnostic accuracy of cancer, especially the breast cancer. Although there is no publication bias, it still has some limitations.Conclusions:let-7 family can be considered as a promising non-invasive diagnostic biomarker for cancer.

β-Catenin/Lin28/let-7 regulatory network determines type II alveolar epithelial stem cell differentiation phenotypes following thoracic irradiation.

The contribution of type II alveolar epithelial stem cells (AEC II) to radiation-induced lung fibrosis (RILF) is largely unknown. Cell differentiation phenotypes are determined by the balance between Lin28 and lethal-7 microRNA (let-7 miRNA). Lin28 is activated by β-catenin. The aim of this study was to track AEC II phenotypes at different phases of injury following thoracic irradiation and examine the expression of β-catenin, Lin28 and let-7 to identify their role in AEC II differentiation. Results showed that coexpression of prosurfactant protein C (proSP-C, an AEC II biomarker) and HOPX (homeobox only protein X, an AEC I biomarker) or vimentin (a differentiation marker) was detected in AEC II post-irradiation. The protein expression levels of HOPX and proSP-C were significantly downregulated, but vimentin was significantly upregulated following irradiation. The expression of E-cadherin, which prevents β-catenin from translocating to the nucleus, was downregulated, and the expression of β-catenin and Lin28 was upregulated after irradiation (P < 0.05 to P < 0.001). Four let-7 miRNA members (a, b, c and d) were upregulated in irradiated lungs (P < 0.05 to P < 0.001), but let-7d was significantly downregulated at 5 and 6 months (P < 0.001). The ratios of Lin28 to four let-7 members were low during the early phase of injury and were slightly higher after 2 months. Intriguingly, the Lin28/let-7d ratio was strikingly increased after 4 months. We concluded that β-catenin contributed to RILF by promoting Lin28 expression, which increased the number of AEC II and the transcription of profibrotic molecules. In this study, the downregulation of let-7d miRNA by Lin28 resulted in the inability of AEC II to differentiate into type I alveolar epithelial cells (AEC I).

GCT-73. EXPRESSION PROFILING OF INTRACRANIAL GERM CELL TUMORS REVEALS UPREGULATION OF RAS THROUGH mRNA-microRNA SIGNALING PATHWAY

Intracranial germ cell tumors (IGCTs) account for 3% of CNS tumors in children in the U.S. and 11% in Japan and East Asian countries. IGCTs are separated into two distinct subtypes based on histology: germinomas and non-germinomatous germ cell tumors (NGGCTs). The deep central location of IGCTs makes surgical resection and therefore molecular subtype classification difficult, and previous gene expression studies are limited. We performed mRNA expression profiling (Human Genome U133 Plus 2.0) and microRNA expression profiling (ABI TaqMan) with 36 and 49 IGCTs, respectively. Sample stratification using non-negative matrix factorization clustering of gene expression revealed two distinct subgroups that delineated germinomas from NGGCTs. Employing stepwise model building in each data set separately, we were able to separate these groups using only mRNA probes for the LIN28B and L1TD1 genes, and two microRNA, microRNA-26a and microRNA-373. MicroRNA26a suppresses the LIN28B gene and is down-regulated in germinoma. LIN28B directly binds and suppresses the let-7 microRNA family, which suppress the KRAS oncogene, previously found to be mutated in ~19% of IGCTs. L1TD1 is required for human stem cell renewal and directly interacts with LIN28B for its RNA binding function. LIN28B and L1TD1 are both known to be upregulated in other systemic germ cell tumors, but this has not yet been documented in IGCTs. In conclusion, these results show that intracranial germinomas have similar gene expression compared to systemic seminoma, and suggest a mechanism by which activation of LIN28B and L1TD1 downregulates the let-7 microRNA and subsequently upregulates KRAS.

PSIV-22 Validation of 26a and let7 microRNA as early pregnancy markers in single cow blood samples, at day 28 after embryo transfer

Abstract In this work we validated the previous scientific reports done in pooled samples by two different groups, over the miRNA expression in single blood from pregnant cows. Particularly we indagate the expression at day 28 after embryo transfer of let 7a, and 26a as well as 16 microRNAs (miRNA) family. By qPCR technique, we demonstrated that let 7a, and 26a increase maximum 2.1 and 2.6 fold change respectively in pregnant vs non-pregnant nulliparous heifers. This represents an exciting opportunity to use the differential expression of these miRNAs as early pregnancy markers and better understand the relationship with the cellular and molecular interaction between mother and embryo.

Functional Characterization of the Lin28/let-7 Circuit During Forelimb Regeneration in Ambystoma mexicanum and Its Influence on Metabolic Reprogramming.

The axolotl (Ambystoma mexicanum) is a caudate amphibian, which has an extraordinary ability to restore a wide variety of damaged structures by a process denominated epimorphosis. While the origin and potentiality of progenitor cells that take part during epimorphic regeneration are known to some extent, the metabolic changes experienced and their associated implications, remain unexplored. However, a circuit with a potential role as a modulator of cellular metabolism along regeneration is that formed by Lin28/let-7. In this study, we report two Lin28 paralogs and eight mature let-7 microRNAs encoded in the axolotl genome. Particularly, in the proliferative blastema stage amxLin28B is more abundant in the nuclei of blastemal cells, while the microRNAs amx-let-7c and amx-let-7a are most downregulated. Functional inhibition of Lin28 factors increase the levels of most mature let-7 microRNAs, consistent with an increment of intermediary metabolites of the Krebs cycle, and phenotypic alterations in the outgrowth of the blastema. In summary, we describe the primary components of the Lin28/let-7 circuit and their function during axolotl regeneration, acting upstream of metabolic reprogramming events.

Downregulation of the Polycomb-Associated Methyltransferase Ezh2 during Maturation of Hippocampal Neurons Is Mediated by MicroRNAs Let-7 and miR-124.

Ezh2 is a catalytic subunit of the polycomb repressive complex 2 (PRC2) which mediates epigenetic gene silencing through depositing the mark histone H3 lysine 27 trimethylation (H3K27me3) at target genomic sequences. Previous studies have demonstrated that Enhancer of Zeste Homolog 2 (Ezh2) was differentially expressed during maturation of hippocampal neurons; in immature neurons, Ezh2 was abundantly expressed, whereas in mature neurons the expression Ezh2 was significantly reduced. Here, we report that Ezh2 is downregulated by microRNAs (miRs) that are expressed during the hippocampal maturation process. We show that, in mature hippocampal neurons, lethal-7 (let-7) and microRNA-124 (miR-124) are robustly expressed and can target cognate motifs at the 3′-UTR of the Ezh2 gene sequence to downregulate Ezh2 expression. Together, these data demonstrate that the PRC2 repressive activity during hippocampal maturation is controlled through a post-transcriptional mechanism that mediates Ezh2 downregulation in mature neurons.