Dicer1 Deletion Research Articles

Differential requirement for DICER1 activity during the development of mitral and tricuspid valves.

Mitral and tricuspid valves are essential for unidirectional blood flow in the heart. They are derived from similar cell sources, and yet congenital dysplasia affecting both valves is clinically rare, suggesting the presence of differential regulatory mechanisms underlying their development. Here, we specifically inactivated Dicer1 in the endocardium during cardiogenesis and found that Dicer1 deletion caused congenital mitral valve stenosis and regurgitation, whereas it had no impact on other valves. We showed that hyperplastic mitral valves were caused by abnormal condensation and extracellular matrix (ECM) remodeling. Our single-cell RNA sequencing analysis revealed impaired maturation of mesenchymal cells and abnormal expression of ECM genes in mutant mitral valves. Furthermore, expression of a set of miRNAs that target ECM genes was significantly lower in tricuspid valves compared to mitral valves, consistent with the idea that the miRNAs are differentially required for mitral and tricuspid valve development. We thus reveal miRNA-mediated gene regulation as a novel molecular mechanism that differentially regulates mitral and tricuspid valve development, thereby enhancing our understanding of the non-association of inborn mitral and tricuspid dysplasia observed clinically.

Brain Dicer1 Is Down-Regulated in a Mouse Model of Alzheimer's Disease Via Aβ42-Induced Repression of Nuclear Factor Erythroid 2-Related Factor 2.

Dicer1 is a microRNA-processing enzyme which plays critical roles in neuronal survival and neuritogenesis. Dicer1 deletion induces neurodegeneration or degeneration in retinal pigment epithelium, which is associated with oxidative stress. Oxidative stress is thought to be central in the pathogenesis of Alzheimer's disease (AD). Therefore, we hypothesize that Dicer1 may play roles in AD. Using immunoblotting and quantitative real-time PCR, Dicer1 protein and mRNA were reduced in the hippocampi of the AD mouse model APPswe/PSEN1dE9 compared with littermate controls. SiRNA-mediated Dicer1 knockdown induced oxidative stress and apoptosis and reduced mitochondrial membrane potential in cultured neurons. Chronic Aβ42 exposure decreased Dicer1 and nuclear factor erythroid 2-related factor 2 (Nrf2) which were reversed by N-acetyl-cystein. Nrf2 overexpression increased Dicer1 mRNA and protein and reverted the Aβ42-induced Dicer1 reduction. We further cloned Dicer1 promoter variants harboring the Nrf2-binding site, the antioxidant response elements (ARE), into a luciferase reporter and found that simultaneous transfection of Nrf2-expressing plasmid increased luciferase expression from these promoter constructs. ChIP assays indicated that Nrf2 directly interacted with the ARE motifs in the Dicer1 promoter. Furthermore, Dicer1 overexpression in cultured neurons reverted Aβ42-induced neurite deficits. Notably, injection of Dicer1-expressing adenovirus into the hippocampus of the mice significantly improved spatial learning. Altogether, we found novel roles of Dicer1 in AD and a novel regulatory pathway for Dicer1. These results suggest that Dicer1 is a target in AD therapy, especially at the early stage of this disorder. In this study, we found that Dicer1 was reduced in the brain of AD mice which is the first report to examine Dicer1 in AD. We further found (i) that Aβ42 exposure decreased Dicer1 via attenuating Nrf2-ARE signaling and (ii) injection of Dicer1-expressing adenovirus into the hippocampus of the AD mice significantly improved spatial learning. Altogether, we found novel roles of Dicer1 in AD and a novel regulatory pathway for Dicer1. This study may open new avenues for investigating potential pathognomonics and pathogenesis in AD.

Dicer1 facilitates liver regeneration in a manner dependent on the inhibitory effect of miR-21 on Pten and Rhob expression

AimsTamoxifen-induced liver-specific Dicer1 deletion (iDicer1−/−) in mature mice may provide clues demonstrating the genuine effects of acute loss of Dicer1 and miRNAs in the liver regeneration process. Main methodsIn this study, mice with tamoxifen-induced Dicer1 deletion through the Cre/LoxP system were constructed and then underwent classic 70% partial hepatectomy or CCl4-induced liver injury. To rescue the inhibitory effect of Dicer1 ablation on liver regeneration, miR-21 agomir was injected into the tail vein of iDicer1−/− mice. Key findingsUnlike constitutive embryonic deletion of Dicer1, tamoxifen-induced Dicer1 deletion did not result in severe liver injury or lesions, providing an ideal model for investigating acute loss of Dicer1 and miRNAs in liver regeneration. Dicer1 deletion led to impaired liver regeneration through the inhibitory effect of miR-21 on PTEN and Rhob expression. SignificanceIn our previous study, we found that embryonic loss of Dicer1 impairs hepatocyte survival and leads to chronic inflammation and progenitor cell activation, while the role of Dicer1 in liver regeneration remains largely unknown. We clearly identified the promotion effect of Dicer1 on liver regeneration by increasing miR-21 expression, which inhibits the expression of two negative cell proliferation regulators, Pten and Rhob.

Abstract 4631: Modeling the vascular sarcoma spectrum with genetically engineered mice

Abstract Angiosarcomas are highly aggressive vascular sarcomas with an extremely poor prognosis. Angiosarcomas can develop spontaneously or are associated with prior radiation, chronic lymphedema, or exposure to toxic chemicals such as vinyl chloride. Sequencing efforts have identified a number of genetic alterations in angiosarcoma, however the genetic drivers and actionable targets remain unclear. Despite the poor outcome for patients, there are limited resources for studying angiosarcoma, highlighting the need for genetic, in vivo models to better elucidate the underlying biology of the disease. In studying the role of DICER1 and microRNAs in mouse models of tumorigenesis, we found that Dicer1 deletion with aP2-Cre leads to aggressive and metastatic angiosarcoma development with 100% penetrance. ERK and S6 hyperphosphorylation in the aP2-Cre;Dicer1cKO (AD) tumors suggest Dicer1 loss results in activation of the RAS-MEK-ERK and mTOR pathways. To determine if direct activation of the these pathways could similarly transform aP2-Cre expressing cells we first interrogated the combination of oncogenic KrasG12D with Cdkn2a inactivation. We found that aP2-Cre;LSL-KrasG12D;Cdkn2acKO (AKC) mice rapidly develop angiosarcomas providing an accelerated model for assessing cooperating alleles and therapies. To activate the mTOR pathway we tested conditional Tsc1 deletion with aP2-Cre and found that all aP2-Cre;Tsc1cKO (AT) animals develop vascular tumors in the paws. In contrast to the AD and AKC tumors, AT tumors express markers of lymphatic endothelial cells such as PROX1. In addition, the tumors display a distinct nodular spindle cell-like morphology that is consistent with a low grade angiosarcoma resembling human kaposiform hemangioendotheliomas, a vascular tumor occurring predominantly in the extremities of infants. The distinct onset, growth kinetics, anatomic locations, and histologic presentation of the tumors from AD, AT, and AKC mice provide a mechanism to interrogate the drivers of angiosarcoma in less aggressive AT paw tumors and more aggressive AD and AKC tumors. Furthermore, the aP2-Cre driven mouse models provide a platform to study angiosarcoma initiation, progression, and metastasis for the identification of novel therapeutics to improve outcomes for this understudied and devastating disease. Citation Format: Jason A. Hanna, Casey G. Langdon, Matthew R. Garcia, David Finkelstein, Jerold E. Rehg, Mark E. Hatley. Modeling the vascular sarcoma spectrum with genetically engineered mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4631.

DICER1 regulates antibacterial function of epididymis by modulating transcription of β-defensins.

DICER1 is a key enzyme responsible for the maturation of microRNAs. Recent evidences suggested that DICER1 and microRNAs expressed in epididymis were involved in the control of male fertility. However, the exact mechanism remains to be elucidated. Here, we created a mouse line by targeted disruption of Dicer1 gene in the principal cells of distal caput epididymis. Our data indicated that a set of β-defensin genes were downregulated by DICER1 rather than by microRNAs. Moreover, DICER1 was significantly enriched in the promoter of β-defensin gene and controlled transcription. Besides, the antibacterial ability of the adult epididymis significantly declined upon Dicer1 deletion both in vitro and in vivo. And a higher incidence of reproductive defect was observed in middle-aged Dicer1−/− males. These results suggest that DICER1 plays an important role in transcription of β-defensin genes, which are associated with the natural antibacterial properties in a microRNA-independent manner, and further impacts the male fertility.

DICER1 Is Essential for Self-Renewal of Human Embryonic Stem Cells.

SummaryMicroRNAs (miRNAs) are the effectors of a conserved gene-silencing system with broad roles in post-transcriptional regulation. Due to functional overlaps, assigning specific functions to individual miRNAs has been challenging. DICER1 cleaves pre-miRNA hairpins into mature miRNAs, and previously Dicer1 knockout mouse embryonic stem cells have been generated to study miRNA function in early mouse development. Here we report an essential requirement of DICER1 for the self-renewal of human embryonic stem cells (hESCs). Utilizing a conditional knockout approach, we found that DICER1 deletion led to increased death receptor-mediated apoptosis and failure of hESC self-renewal. We further devised a targeted miRNA screening strategy and uncovered essential pro-survival roles of members of the mir-302-367 and mir-371-373 clusters that bear the seed sequence AAGUGC. This platform is uniquely suitable for dissecting the roles of individual miRNAs in hESC self-renewal and differentiation, which may help us better understand the early development of human embryos.

Abstract A31: Biallelic Dicer1 loss in endothelial cells drives angiosarcoma development

Abstract Angiosarcoma is an aggressive and highly metastatic vascular sarcoma with an extremely poor prognosis. Because of the rarity of the disease, the molecular drivers and optimal treatment strategies for patients remain unclear, highlighting the need for novel genetic and in vivo animal models. MicroRNAs are small RNAs that regulate gene expression and DICER1 is the RNase III endoribonuclease that processes pre-microRNAs into mature microRNAs. DICER1 and microRNAs are central to numerous cellular processes and are often dysregulated in many cancers, including sarcomas. Here we show that biallelic Dicer1 deletion with endothelial expression of aP2-Cre drives aggressive and metastatic angiosarcoma independent of other genetically engineered oncogenes or tumor suppressor loss. Angiosarcomas in aP2-Cre;Dicer1Flox/- mice histologically and genetically resemble human angiosarcoma, and we found microRNA-23 target genes enriched in mouse and human angiosarcoma. Because Ras mutations and Cdkn2a loss are common in angiosarcoma, we interrogated them as angiosarcoma modifiers. Interestingly, we found that both oncogenic LSL-KrasG12D and loss of conditional Cdkn2aFlox decreased tumor latency. In addition, aP2-Cre;LSL-KrasG12D;Cdkn2aFlox/Flox mice developed angiosarcomas, providing a model with Dicer1 expression intact to further study the function of microRNAs in angiosarcoma. Thus, these findings illustrate that Dicer1 can function as a traditional loss-of-function tumor-suppressor gene and provide simple and fully penetrant animal models for the study of angiosarcoma development and metastasis. Citation Format: Jason A. Hanna, Catherine J. Drummond, Matthew R. Garcia, Jonathan C. Go, David Finkelstein, Jerold E. Rehg, Mark E. Hatley. Biallelic Dicer1 loss in endothelial cells drives angiosarcoma development [abstract]. In: Proceedings of the AACR Special Conference: Advances in Modeling Cancer in Mice: Technology, Biology, and Beyond; 2017 Sep 24-27; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(10 Suppl):Abstract nr A31.

Issues with the Specificity of Immunological Reagents for NLRP3: Implications for Age-related Macular Degeneration

Contradictory data have been presented regarding the implication of the NACHT, LRR and PYD domains-containing protein 3 (NLRP3) inflammasome in age-related macular degeneration (AMD), the leading cause of vision loss in the Western world. Recognizing that antibody specificity may explain this discrepancy and in line with recent National Institutes of Health (NIH) guidelines requiring authentication of key biological resources, the specificity of anti-NLRP3 antibodies was assessed to elucidate whether non-immune RPE cells express NLRP3. Using validated resources, NLRP3 was not detected in human primary or human established RPE cell lines under multiple inflammasome-priming conditions, including purported NLRP3 stimuli in RPE such as DICER1 deletion and Alu RNA transfection. Furthermore, NLRP3 was below detection limits in ex vivo macular RPE from AMD patients, as well as in human induced pluripotent stem cell (hiPSC)-derived RPE from patients with overactive NLRP3 syndrome (Chronic infantile neurologic cutaneous and articulate, CINCA syndrome). Evidence presented in this study provides new data regarding the interpretation of published results reporting NLRP3 expression and upregulation in RPE and addresses the role that this inflammasome plays in AMD pathogenesis.

M\xfcller glial microRNAs are required for the maintenance of glial homeostasis and retinal architecture

To better understand the roles of microRNAs in glial function, we used a conditional deletion of Dicer1 (Dicer-CKOMG) in retinal Müller glia (MG). Dicer1 deletion from the MG leads to an abnormal migration of the cells as early as 1 month after the deletion. By 6 months after Dicer1 deletion, the MG form large aggregations and severely disrupt normal retinal architecture and function. The most highly upregulated gene in the Dicer-CKOMG MG is the proteoglycan Brevican (Bcan) and overexpression of Bcan results in similar aggregations of the MG in wild-type retina. One potential microRNA that regulates Bcan is miR-9, and overexpression of miR-9 can partly rescue the effects of Dicer1 deletion on the MG phenotype. We also find that MG from retinitis pigmentosa patients display an increase in Brevican immunoreactivity at sites of MG aggregation, linking the retinal remodeling that occurs in chronic disease with microRNAs.

Biallelic Dicer1 Loss Mediated by aP2-Cre Drives Angiosarcoma.

Angiosarcoma is an aggressive vascular sarcoma with an extremely poor prognosis. Because of the relative rarity of this disease, its molecular drivers and optimal treatment strategies are obscure. DICER1 is an RNase III endoribonuclease central to miRNA biogenesis, and germline DICER1 mutations result in a cancer predisposition syndrome, associated with an increased risk of many tumor types. Here, we show that biallelic Dicer1 deletion with aP2-Cre drives aggressive and metastatic angiosarcoma independent of other genetically engineered oncogenes or tumor suppressor loss. Angiosarcomas in aP2-Cre;Dicer1Flox/- mice histologically and genetically resemble human angiosarcoma. miR-23 target genes, including the oncogenes Ccnd1 as well as Adam19, Plau, and Wsb1 that promote invasiveness and metastasis, were enriched in mouse and human angiosarcoma. These studies illustrate that Dicer1 can function as a traditional loss-of-function tumor suppressor gene, and they provide a fully penetrant animal model for the study of angiosarcoma development and metastasis. Cancer Res; 77(22); 6109-18. ©2017 AACR.

NKp46-mediated Dicer1 inactivation results in defective NK-cell differentiation and effector functions in mice.

MicroRNAs control developmental pathways and effector functions in immune cells. Previous studies have studied the role of microRNAs in natural killer (NK) cells. However, the mouse models of microRNA depletion used were nonNK-specific and only partially depleting, hampering the interpretation of the data obtained. To clarify the role of microRNAs in murine NK cells, we deleted the RNase III enzyme Dicer1 in NKp46-expressing cells. We observed a drastic decrease in several microRNAs specifically in NK cells. Furthermore, the overall size of the "NK-cell" pool was severely decreased, a phenotype associated with compromised survival. Moreover, performing a broad flow cytometry profiling, we show that Dicer1-deficient NK cells failed to complete their differentiation program. In particular, several integrins were inappropriately expressed in mature NK cells. These defects coincided with decreased response to IL-15, a cytokine responsible for "NK-cell" maturation and survival. In addition, Dicer1 deletion impaired key "NK-cell" functions: target cell killing and production of IFN-γ, leading to defective control of metastasis. Dicer1 deletion thus affects "NK-cell" biology in a cell intrinsic manner at several distinct stages.

Abstract PR05: Dicer1 deletion: Sufficient for angiosarcoma development and a haploinsufficient tumor suppressor in rhabdomyosarcoma

Abstract In this study, the role of Dicer and microRNAs (miRNAs) is investigated in pediatric and adult soft tissue sarcomas with the hypothesis that understanding miRNAs and their biogenesis may provide biological insights into the pathogenesis of these diseases and identify novel therapeutic targets. In several mouse models of cancer, Dicer1 is thought to function as a haploinsufficient tumor suppressor where loss of a single allele promotes tumorigenesis yet loss of both alleles is detrimental to tumor formation. Heterozygous germline mutations in DICER1 in humans is associated with rare malignant and benign neoplasias including embryonal rhabdomyosarcoma (ERMS). With DICER1 syndrome mutations found in ERMS, a pediatric soft tissue sarcoma resembling skeletal muscle precursors that fail to differentiate, we sought to further understand the role of Dicer and miRNAs utilizing a transgenic mouse model of ERMS combined with conditional Dicer1Flox/Flox null mice. The ERMS mouse model results from activation of a constitutively active SmoM2 allele with Cre recombinase expressed from the adipose protein 2 (aP2) promoter resulting in unrestrained hedgehog signaling in the aP2 lineage. Heterozygous Dicer1 loss led to increased penetrance of and a decrease in latency to onset of tumors. In agreement with the haploinsufficient tumor suppressor model, homozygous Dicer1Flox/Flox mice rarely developed tumors in stark contrast to wild type and heterozygous littermates. Furthermore, tumors that did develop in Dicer1Flox/Flox mice escaped Cre recombination and retained a flox allele indicating functional Dicer1 activity. Serendipitously, aP2-Cre; SmoM2; Dicer1Flox/Flox mice that did not develop ERMS all developed multifocal angiosarcomas. This finding prompted the analysis of Dicer loss alone in the aP2 lineage and remarkably Dicer1Flox/Flox mice similarly developed angiosarcoma whereas Dicer1Flox/+ do not, providing evidence for Dicer loss independent of a cooperating oncogene driving tumorigenesis in a mouse model. This study provides evidence for the role of Dicer and miRNAs in rhabdomyosarcoma and angiosarcomas. Further understanding the molecular mechanisms and genetic drivers of soft tissue sarcomas is critical for the development of novel targeted therapeutics. This is true especially for soft tissue sarcomas where treatment strategies and survival outcomes have not changed in decades despite numerous clinical trials. This abstract is also presented as Poster B06. Citation Format: Jason A. Hanna, Matthew R. Garcia, Jerold Rehg, Mark E. Hatley. Dicer1 deletion: Sufficient for angiosarcoma development and a haploinsufficient tumor suppressor in rhabdomyosarcoma. [abstract]. In: Proceedings of the AACR Special Conference on Noncoding RNAs and Cancer: Mechanisms to Medicines ; 2015 Dec 4-7; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2016;76(6 Suppl):Abstract nr PR05.

Dicer Ablations in Bone Marrow Niche Impair Hematopoietic Progenitor/Stem Cells and Induce Myelodysplasia in Young Mice but Are Dispensable for Adult Hematopoiesis

MicroRNAs (miRNAs) regulate hematopoietic cell fate and their global down-regulation by Dicer1 deletion promotes tumorigenesis in a cancer-cell-autonomous manner (Kumar M.S. et al, 2007). Raajimakers MH et al. (2010) using neonatal Osterix specific dicer deletion showed altered hematopoiesis and developed myelodysplasia. However, there is no study illustrating the role of the ablation of bone marrow (BM) niche specific miRNA processing machinery in the adult mice. Since expression and functions of different mesenchymal and osteoprogenitors vary from embryonic development to adulthood, studying the dicer ablation in adult mice may provide more insight about the role of miRNA processing in adult mice niche.Here we investigate whether adult Osterix expressing cells play a similar role in the HSC niche compared to fetal Osterix expressing cells. We crossed Osx-GFP-tTA-Cre recombinase mice with mice with floxed Dicer1 allele. Crossing generated Osx- GFP-tTA-Cre+Dicerfl/+ (OCDfl/+control) and Osx-GFP- tTA-Cre+ Dicerfl/fl (OCDfl/fl mutant) mice. Osx-GFP-tTA-Cre expression was either activated during embryonic development (young dicer KO) or suppressed using tetracycline until mice were 6 weeks of age (adult dicer KO). We found young dicer KO mice had reduced weight (p=0.0031), leukopenia, anemia, reduced mature CD19+B220- B lymphocytes (p=0.0034) and increased CD11b+Gr- monocytes and CD11b+Gr+ neutrophils (p=0.02 and p=0.04 respectively) in peripheral blood compared to OCDfl/+ control aged littler mates. The leucocytes and platelets showed dysplastic changes suggestive of myelodysplasia and had extra-medullary hematopoiesis. Adult dice KO, on the other hand, show no leukemia development 6 months after Cre activation. The number of BM hematopoietic progenitors (Lin-Sca1+ c-Kit+ cells, LSK) and long term hematopoietic stem cells (LT-HSCs, LSK CD150+CD48+ cells) in young dicer KO mice were significantly reduced compared to age matched control (OCDfl/+ control) mice. We observed increased Annexin V positive LSK, LT-HSCs and megakaryocytes erythroid progenitors (MEP) in the young dicer KO mice indicating increased apoptosis. Adult dicer KO mice didn't have significant changes in apoptosis in different hematopoietic progenitors. In young dicer KO mice, BM derived LSK and LT-HSCs showed increased cycling (SG2M phase, p=0.0133) and less quiescenece (Go phase, p=0.013). However LT-HSC from adult dicer KO didn't show any difference in cell cycling (p=0.18 and 0.09 respectively). Together these results indicate that while Osterix expressing cells in fetal and young mice give rise to a variety of HSC niche supporting cells the adult expression is limited to more mature osteoblast that are not absolutely essential for HSC maintenance. Our study provides the rationale for further exploration of the complexity in hierarchy of activity within niche constituting mesenchymal stroma progenitors and their role in different developmental stages to maintain hematopoiesis. DisclosuresNo relevant conflicts of interest to declare.

MicroRNA-mediated non-cell-autonomous regulation of cortical radial glial transformation revealed by a Dicer1 knockout mouse model.

Radial glia (RG), as neurogenic progenitors and neuronal migration scaffolds, play critical roles during cortical neurogenesis. RG transformation into astrocytes, marking the transition from developmental to physiological function of these cells, is an important step during cortical development. In this study, we aim to determine the roles of microRNAs (miRNAs) during this biological process. In a conditional Dicer1-null mouse where Dicer1 is deleted in both RG and their neuronal progeny, we observe delayed RG transformation as revealed by the persistence of their radial processes, and reduced number and complexity of translocated RG cell bodies in the postnatal cerebral cortex. Downregulation of Notch1 signaling is crucial to RG transformation, and consistently we find that Notch1 signaling is enhanced in the Dicer1-null cerebral cortex. In addition, we show that, among the Notch1 ligands, Jagged2 (Jag2) is preferentially upregulated in the postnatal Dicer1-null cerebral cortex as well as primary embryonic cortical cultures with instant Dicer1 deletion. Functionally, Dicer1-deleted postnatal cerebellar cells with elevated Jag2 expression stimulate a stronger Notch1 signaling in a RG clone L2.3 when co-cultured than control cells. Therefore, we unravel a novel non-cell-autonomous mechanism that regulates RG transformation by modulating Notch1 signaling via miRNA-mediated suppression of the Nocth1 ligand Jag2. Furthermore, we validate Jag2 as a miR-124 target gene and demonstrate in vitro that Jag2 expression is highly sensitive to Dicer1 deletion. Finally, we propose a new concept of MiRNA-Sensitive target genes, identification of which may unravel a unique mode of miRNA-mediated gene expression regulation.

Thyrocyte-Specific Dicer1 Deficiency Alters Thyroid Follicular Organization and Prevents Goiter Development

MicroRNAs (miRNAs) are important regulators of posttranscriptional gene expression and involved in embryonic development, regulation of cell differentiation, and growth. Dicer1 is a key enzyme in the maturation process of functional miRNAs. However, miRNA-mediated regulation of normal thyroid function and growth is largely unknown. To understand the role of miRNAs in the thyroid, we generated constitutive and tamoxifen-inducible, thyrocyte-specific Dicer1 knockout mice. The mice with perinatal Dicer1 deletion (cTgDcrKO) showed impaired follicular organization, increased fibrosis, and accumulation of adipocytes in the thyroid. Similar histological changes were observed in tamoxifen-induced adult Dicer1-deficient mice (iTgDcrKO). The thyroid phenotype in both knockout (KO) lines was associated with significantly down-regulated mRNA expression of thyroid transcription factor 1 (Ttf-1/Nkx2-1), thyroid peroxidase, and thyroglobulin (Tg) and up-regulated expression of genes involved in Tgf-β signaling. Furthermore, in cTgDcrKO mice, which developed mild hypothyroidism, the protein expression of Nkx2-1, thyroglobulin, Paired box 8, and TSH receptor were clearly down-regulated compared with controls. Despite similar down-regulation of Dicer1 in cTgDcrKO and iTgDcrKO compared with controls, Dicer1 deletion in adult mice thyrocytes did not lead to acute hypothyroidism. No significant differences in thyroid weights between cTgDcrKO, iTgDcrKO, and controls were observed. However, a goitrogenic diet induced a 4-fold increase in thyroid weight in control animals, whereas it had no effect on iTgDcrKO thyroids. In summary, Dicer1 deficiency in thyrocytes is associated with intrathyroid fibrosis, adipogenesis, and enhanced expression of Tgf-β signaling genes. Furthermore, our data indicate that Dicer1 is required for thyroid follicular organization, thyrocyte differentiation, and goiter development.

Abstract 3538: Obligate haploinsufficiency of the microRNA-processing molecule dicer1 in a murine colitis-associated tumorigenesis model

Abstract Background: A widespread downregulated expression of microRNAs (miRNAs) is commonly observed in human cancers. Similarly, deregulated expression of miRNA-processing pathway components, which results in the reduction of global miRNA expression, may also be associated with tumorigenesis. Thus, we hypothesized that the deregulation of microRNA-processing molecule Dicer1 in intestinal epithelial cells may accelerate intestinal inflammation-associated tumorigenesis. Methods & Results: We constructed Dicer1 gene-disrupted mice with monoallelic and biallelic loss of its locus. Inflammation-associated colon tumors were induced by azoxymethane (AOM) injection with the treatment by three cycles of Dextran Sulfate Sodium (DSS). 1) Dicer1 protein expression and subsequent mature miRNA levels in the isolated intestinal epithelial cells were inversely correlated with the number of intact Dicer1 alleles. 2) Although the severity of inflammation after the induction in this model was comparable in control and Dicer1-mutant mice, the number of colon tumors was significantly higher in heterozygous mice but not in homozygous mice. 3) Because the expression levels of Dicer1 were retained in tumors and its surrounding tissues even after induction of colitis-associated tumors, the effects of Dicer1 deletion on tumorigenesis were considered as cell-autonomous. 4) While the expression levels of representative oncogenes and tumor suppressor genes were in most cases inversely correlated with the expression levels of Dicer1, some genes were not affected by Dicer1 deletion. Conclusion: Specific ablation of Dicer1 in intestinal epithelial cells accelerates intestinal inflammation-associated tumorigenesis. However, this effect was apparent only when a single copy of Dicer1 was deleted, but not with complete Dicer1 gene ablation. Generally, complete loss of the function of most tumor suppressor genes is advantageous for tumor development. However, our results suggest that, in case of Dicer1 gene, complete loss is deleterious for cancer development, while its partial inactivation promotes tumor formation. This unique “obligate haploinsufficient role” colitis-associated colon tumor of Dicer and miRNAs needs further attention to elucidate the pathogenesis of tumorigenesis related with deregulated miRNAs. Citation Format: Takeshi Yoshikawa, Motoyuki Otsuka, Kazuhiko Koike. Obligate haploinsufficiency of the microRNA-processing molecule dicer1 in a murine colitis-associated tumorigenesis model. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3538. doi:10.1158/1538-7445.AM2014-3538

Loss of functional Dicer in mouse radial glia cell-autonomously prolongs cortical neurogenesis

Radial glia of the mouse cerebral cortex emerge from neuroepithelial stem cells around embryonic day 11 and produce excitatory cortical neurons until a few days before birth. The molecular mechanisms that regulate the end of cortical neurogenesis remain largely unknown. Here we investigated if the Dicer-dependent microRNA (miRNA) pathway is involved. By electroporating a cre-recombinase expression vector into the cortex of E13.5 embryos carrying a conditional allele of Dicer1, we induced mosaic recombination causing Dicer1 deletion and reporter activation in a subset of radial glia. We analysed the long-term fates of their progeny. We found that mutant radial glia produced abnormally large numbers of Cux1-positive neurons, many of which populated the superficial cortical layers. Injections of the S-phase marker bromodeoxyuridine between postnatal days 3 and 14 showed that much of this population was generated postnatally. Our findings suggest a role for Dicer-dependent processes in limiting the timespan of cortical neurogenesis.

Unique Haploinsufficient Role of the MicroRNA-Processing Molecule Dicer1 in a Murine Colitis-Associated Tumorigenesis Model

A widespread downregulated expression of microRNAs (miRNAs) is commonly observed in human cancers. Similarly, deregulated expression of miRNA-processing pathway components, which results in the reduction of global miRNA expression, may also be associated with tumorigenesis. Here, we show that specific ablation of Dicer1 in intestinal epithelial cells accelerates intestinal inflammation-associated tumorigenesis. This effect was apparent only when a single copy of Dicer1 was deleted, but not with complete Dicer1 ablation. DICER expression and subsequent mature miRNA levels were inversely correlated with the number of intact Dicer1 alleles. Because the expression levels of DICER were retained in tumors and its surrounding tissues even after induction of colitis-associated tumors, the effects of Dicer1 deletion were cell-autonomous. Although the expression levels of representative oncogenes and tumor suppressor genes were in most cases inversely correlated with the expression levels of DICER, some genes were not affected by Dicer1 deletion. Thus, deregulating the delicate balance between the expression levels of tumor-promoting and -suppressive genes may be crucial for tumorigenesis in this unique haploinsufficient case.

A miR-19 regulon that controls NF-κB signaling

Fine-tuning of inflammatory responses by microRNAs (miRNAs) is complex, as they can both enhance and repress expression of pro-inflammatory mediators. In this study, we investigate inflammatory responses following global miRNA depletion, to better define the overall contribution of miRNAs to inflammation. We demonstrate that miRNAs positively regulate Toll-like receptor signaling using inducible Dicer1 deletion and global miRNA depletion. We establish an important contribution of miR-19b in this effect, which potentiates nuclear factor-κB (NF-κB) activity in human and mouse cells. Positive regulation of NF-κB signaling by miR-19b involves the coordinated suppression of a regulon of negative regulators of NF-κB signaling (including A20/Tnfaip3, Rnf11, Fbxl11/Kdm2a and Zbtb16). Transfection of miR-19b mimics exacerbated the inflammatory activation of rheumatoid arthritis primary fibroblast-like synoviocytes, demonstrating its physiological importance in the pathology of this disease. This study constitutes, to our knowledge, the first description of a miR-19 regulon that controls NF-κB signaling, and suggests that targeting this miRNA and linked family members could regulate the activity of NF-κB signaling in inflammation.

Dicer1 deletion in myeloid-committed progenitors causes neutrophil dysplasia and blocks macrophage/dendritic cell development in mice

AbstractMicroRNAs (miRNAs) have the potential to regulate cellular differentiation programs; however, miRNA deficiency in primary hematopoietic stem cells (HSCs) results in HSC depletion in mice, leaving the question of whether miRNAs play a role in early-lineage decisions un-answered. To address this issue, we deleted Dicer1, which encodes an essential RNase III enzyme for miRNA biogenesis, in murine CCAAT/enhancer-binding protein α (C/EBPA)–positive myeloid-committed progenitors in vivo. In contrast to the results in HSCs, we found that miRNA depletion affected neither the number of myeloid progenitors nor the percentage of C/EBPA–positive progenitor cells. Analysis of gene-expression profiles from wild-type and Dicer1-deficient granulocyte-macrophage progenitors (GMPs) revealed that 20 miRNA families were active in GMPs. Of the derepressed miRNA targets in Dicer1-null GMPs, 27% are normally exclusively expressed in HSCs or are specific for multipotent progenitors and erythropoiesis, indicating an altered gene-expression landscape. Dicer1-deficient GMPs were defective in myeloid development in vitro and exhibited an increased replating capacity, indicating the regained self-renewal potential of these cells. In mice, Dicer1 deletion blocked monocytic differentiation, depleted macrophages, and caused myeloid dysplasia with morphologic features of Pelger-Huët anomaly. These results provide evidence for a miRNA-controlled switch for a cellular program of self-renewal and expansion toward myeloid differentiation in GMPs.