miR-31 regulates interleukin 2 and kinase suppressor of ras 2 during T cell activation

Non-coding RNAs: Key players in T cell exhaustion

T cell exhaustion caused by continuous antigen stimulation in chronic viral infections and the tumor microenvironment is a major barrier to successful elimination of viruses and tumor cells. Although immune checkpoint inhibitors should reverse T cell exhaustion, shortcomings, such as off-target effects and single targets, limit their application. Therefore, it is important to identify molecular targets in effector T cells that simultaneously regulate the expression of multiple immune checkpoints. Over the past few years, non-coding RNAs, including microRNAs and long non-coding RNAs, have been shown to participate in the immune response against viral infections and tumors. In this review, we focus on the roles and underlying mechanisms of microRNAs and long non-coding RNAs in the regulation of T cell exhaustion during chronic viral infections and tumorigenesis. We hope that this review will stimulate research to provide more precise and effective immunotherapies against viral infections and tumors.

The Role of microRNAs in the Mammary Gland Development, Health, and Function of Cattle, Goats, and Sheep

Milk is an integral and therefore complex structural element of mammalian nutrition. Therefore, it is simple to conclude that lactation, the process of producing milk, is as complex as the mammary gland, the organ responsible for this biochemical activity. Nutrition, genetics, epigenetics, disease pathogens, climatic conditions, and other environmental variables all impact breast productivity. In the last decade, the number of studies devoted to epigenetics has increased dramatically. Reports are increasingly describing the direct participation of microRNAs (miRNAs), small noncoding RNAs that regulate gene expression post-transcriptionally, in the regulation of mammary gland development and function. This paper presents a summary of the current state of knowledge about the roles of miRNAs in mammary gland development, health, and functions, particularly during lactation. The significance of miRNAs in signaling pathways, cellular proliferation, and the lipid metabolism in agricultural ruminants, which are crucial in light of their role in the nutrition of humans as consumers of dairy products, is discussed.

Identification of candidate miRNA biomarkers for facioscapulohumeral muscular dystrophy using DUX4-based mouse models

Facioscapulohumeral muscular dystrophy (FSHD) is caused by misexpression of DUX4 in skeletal myocytes. As DUX4 is the key therapeutic target in FSHD, surrogate biomarkers of DUX4 expression in skeletal muscle are critically needed for clinical trials. Although no natural animal models of FSHD exist, transgenic mice with inducible DUX4 expression in skeletal muscles rapidly develop myopathic phenotypes consistent with FSHD. Here, we established a new, more-accurate FSHD-like mouse model based on chronic DUX4 expression in a small fraction of skeletal myonuclei that develops pathology mimicking key aspects of FSHD across its lifespan. Utilizing this new aged mouse model and DUX4-inducible mouse models, we characterized the DUX4-related microRNA signatures in skeletal muscles, which represent potential biomarkers for FSHD. We found increased expression of miR-31-5p and miR-206 in muscles expressing different levels of DUX4 and displaying varying degrees of pathology. Importantly, miR-206 expression is significantly increased in serum samples from FSHD patients compared with healthy controls. Our data support miR-31-5p and miR-206 as new potential regulators of muscle pathology and miR-206 as a potential circulating biomarker for FSHD.

This article has an associated First Person interview with the first author of the paper.

Summary: Candidate miRNA biomarkers for facioscapulohumeral muscular dystrophy (FSHD) were identified using FSHD-like mouse models that present cumulative pathology from chronic expression of DUX4 in skeletal muscles and confirmed in FSHD patient serum.

Mycoplasma hyopneumoniae J elicits an antioxidant response and decreases the expression of ciliary genes in infected swine epithelial cells

Mycoplasma hyopneumoniae is the most costly pathogen for swine production. Although several studies have focused on the host-bacterium association, little is known about the changes in gene expression of swine cells upon infection. To improve our understanding of this interaction, we infected swine epithelial NPTr cells with M. hyopneumoniae strain J to identify differentially expressed mRNAs and miRNAs. The levels of 1,268 genes and 170 miRNAs were significantly modified post-infection. Up-regulated mRNAs were enriched in genes related to redox homeostasis and antioxidant defense, known to be regulated by the transcription factor NRF2 in related species. Down-regulated mRNAs were enriched in genes associated with cytoskeleton and ciliary functions. Bioinformatic analyses suggested a correlation between changes in miRNA and mRNA levels, since we detected down-regulation of miRNAs predicted to target antioxidant genes and up-regulation of miRNAs targeting ciliary and cytoskeleton genes. Interestingly, most down-regulated miRNAs were detected in exosome-like vesicles suggesting that M. hyopneumoniae infection induced a modification of the composition of NPTr-released vesicles. Taken together, our data indicate that M. hyopneumoniae elicits an antioxidant response induced by NRF2 in infected cells. In addition, we propose that ciliostasis caused by this pathogen is partially explained by the down-regulation of ciliary genes.

miR-31 regulates energy metabolism and is suppressed in T cells from patients with Sjögren's syndrome

Systemic autoimmune diseases are characterized by the overexpression of type I IFN stimulated genes, and accumulating evidence indicate a role for type I IFNs in these diseases. However, the underlying mechanisms for this are still poorly understood. To explore the role of type I IFN regulated miRNAs in systemic autoimmune disease, we characterized cellular expression of miRNAs during both acute and chronic type I IFN responses. We identified a T cell-specific reduction of miR-31-5p levels, both after intramuscular injection of IFNβ and in patients with Sjögren's syndrome (SjS). To interrogate the role of miR-31-51p in T cells we transfected human CD4⁺ T cells with a miR-31-5p inhibitor and performed metabolic measurements. This identified an increase in basal levels of glucose metabolism after inhibition of miR-31-5p. Furthermore, treatment with IFN-α also increased the basal levels of human CD4⁺ T-cell metabolism. In all, our results suggest that reduced levels of miR-31-5p in T cells of SjS patients support autoimmune T-cell responses during chronic type I IFN exposure.

Control of Immunoregulatory Molecules by miRNAs in T Cell Activation

MiRNA targeting of key immunoregulatory molecules fine-tunes the immune response. This mechanism boosts or dampens immune functions to preserve homeostasis while supporting the full development of effector functions. MiRNA expression changes during T cell activation, highlighting that their function is constrained by a specific spatiotemporal frame related to the signals that induce T cell-based effector functions. Here, we update the state of the art regarding the miRNAs that are differentially expressed during T cell stimulation. We also revisit the existing data on miRNA function in T cell activation, with a special focus on the modulation of the most relevant immunoregulatory molecules.

Levels of miR-31 and its target genes in dermal mesenchymal cells of patients with psoriasis

BACKGROUND

Psoriasis is characterized by chronic inflammatory dermatosis, and the pathogenesis of psoriasis is associated with mesenchymal stem cells (MSCs) and deregulation of the expression of miR-31. This study aimed to clarify the function of miR-31 in dermal MSCs (DMSCs) in the pathogenesis of psoriasis.

METHODS

The expression of miR-31 was assayed by a microarray and that of target genes of miR-31 was tested by quantitative PCR.

RESULTS

The expression of miR-31 in the psoriasis group was 0.2677 folds that of the control group. The expression of EMP1 and EIG121L genes, whose products are located on the cell membrane, in the psoriasis group was 4.095579 and 5.367017 folds that in the control group, respectively. The expression of GRB10, PTPN14, QKI, RNF144B, and TACC2 genes, whose products are located in the cytoplasm, in the psoriasis group was 1.440428, 1.198335, 1.737285, 7.379546, and 1.531947 folds that of the control. The expression of PRELP, whose products are secreted in the extracellular space, in the psoriasis group was 1.351684 folds that of the control. The expression of RBMS1, KHDRBS3, and SATB2, whose products play a role in the nucleus, in the psoriasis group was 2.237199, 1.277159, and 1.005742 folds that of the control, respectively.

CONCLUSIONS

Our results suggest that the low expression of miR-31 in DMSCs in patients with psoriasis causes an increase in the expression of some of its target genes, which in turn facilitates T lymphocyte activation by inhibiting the proliferation of DMSCs and therefore participates in the pathogenesis of psoriasis.

Effect of tumor necrosis factor-α induced protein 8 like-2 on immune function of dendritic cells in mice following acute insults

Tumor necrosis factor-α induced protein 8 like-2 (TNFAIP8L2, TIPE2) is a lately discovered negative regulator of innate immunity and cellular immunity. The present study was designed to investigate whether naturally occurring dendritic cells (DCs) could express TIPE2 mRNA/protein and its potential significance. Expressions of co-stimulatory molecules on DC surface and cytokines were analyzed to assess the functional role of TIPE2 in controlling DC maturation as well as activation. The activated DCs were assessed for their capacity to stimulate the proliferation and differentiation of T cells. It was found that TIPE2 was a cytoplasmic protein expressed in DCs, and the percentage of DCs which expressed co-stimulatory molecules and cytokines were obviously up-regulated when TIPE2 gene silenced by siRNA in vitro and in vivo. DCs undergone TIPE2 knockdown were found to promote the maturation of DCs, T-cell proliferation as well as differentiation, and they were significantly elevated IL-2 level and intranuclear NF-AT activation. Conversely, in over-expressing TIPE2 DC cells, it could inhibit T-cell proliferation and differentiation, and markedly down-regulate IL-2 expression and intranuclear NF-AT activation after scald injury. The results suggested that TIPE2 appeared to be a critical immunoregulatory molecule which affected DC maturation and subsequent T-cell mediated immunity.

Identification of aminosulfonylarylisoxazole as microRNA-31 regulators

The discovery of small-molecule regulators of microRNAs remains challenging, but a few have been reported. Herein, we describe small-molecule inhibitors of miR-31, a tumor-associated microRNA (miRNA), identified by high-throughput screening using a cell-based reporter assay. Aminosulfonylarylisoxazole compounds exhibited higher specificity for miR-31 than for six other miRNAs, i.e., miR-15a, miR-16, miR-21, miR-92a-1, miR-146a, and miR-155, and increased the expression of miR-31 target genes. The down-regulation of mature miR-31 was observed, while its precursor form increased following treatment with the compounds. Thus, the compounds may target the processing of pre-miR-31 into mature miR-31 and thereby inhibit the production of mature miR-31.

The microRNA miR-31 inhibits CD8+ T cell function in chronic viral infection

During infection, antigen-specific T cells undergo tightly regulated developmental transitions controlled by transcriptional and post-transcriptional regulation of gene expression. We found that the microRNA miR-31 was strongly induced by activation of the T cell antigen receptor (TCR) in a pathway involving calcium and activation of the transcription factor NFAT. During chronic infection with lymphocytic choriomeningitis virus (LCMV) clone 13, miR-31-deficent mice recovered from clinical disease, while wild-type mice continued to show signs of disease. This disease phenotype was explained by the presence of larger numbers of cytokine-secreting LCMV-specific CD8⁺ T cells in miR-31-deficent mice than in wild-type mice. Mechanistically, miR-31 increased the sensitivity of T cells to type I interferons, which interfered with effector T cell function and increased the expression of several proteins related to T cell dysfunction during chronic infection. These studies identify miR-31 as an important regulator of T cell exhaustion in chronic infection.

Host Genetic Background Strongly Affects Pulmonary microRNA Expression before and during Influenza A Virus Infection

BACKGROUND

Expression of host microRNAs (miRNAs) changes markedly during influenza A virus (IAV) infection of natural and adaptive hosts, but their role in genetically determined host susceptibility to IAV infection has not been explored. We, therefore, compared pulmonary miRNA expression during IAV infection in two inbred mouse strains with differential susceptibility to IAV infection.

RESULTS

miRNA expression profiles were determined in lungs of the more susceptible strain DBA/2J and the less susceptible strain C57BL/6J within 120 h post infection (hpi) with IAV (H1N1) PR8. Even the miRNomes of uninfected lungs differed substantially between the two strains. After a period of relative quiescence, major miRNome reprogramming was detected in both strains by 48 hpi and increased through 120 hpi. Distinct groups of miRNAs regulated by IAV infection could be defined: (1) miRNAs (n = 39) whose expression correlated with hemagglutinin (HA) mRNA expression and represented the general response to IAV infection independent of host genetic background; (2) miRNAs (n = 20) whose expression correlated with HA mRNA expression but differed between the two strains; and (3) remarkably, miR-147-3p, miR-208b-3p, miR-3096a-5p, miR-3069b-3p, and the miR-467 family, whose abundance even in uninfected lungs differentiated nearly perfectly (area under the ROC curve > 0.99) between the two strains throughout the time course, suggesting a particularly strong association with the differential susceptibility of the two mouse strains. Expression of subsets of miRNAs correlated significantly with peripheral blood granulocyte and monocyte numbers, particularly in DBA/2J mice; miR-223-3p, miR-142-3p, and miR-20b-5p correlated most positively with these cell types in both mouse strains. Higher abundance of antiapoptotic (e.g., miR-467 family) and lower abundance of proapoptotic miRNAs (e.g., miR-34 family) and those regulating the PI3K-Akt pathway (e.g., miR-31-5p) were associated with the more susceptible DBA/2J strain.

CONCLUSION

Substantial differences in pulmonary miRNA expression between the two differentially susceptible mouse strains were evident even before infection, but evolved further throughout infection and could in part be attributed to differences in peripheral blood leukocyte populations. Thus, pulmonary miRNA expression both before and during IAV infection is in part determined genetically and contributes to susceptibility to IAV infection in this murine host, and likely in humans.

From cell biology to immunology: Controlling metastatic progression of cancer via microRNA regulatory networks

Recently, the study of microRNAs has expanded our knowledge of the fundamental processes of cancer biology and the underlying mechanisms behind tumor metastasis. Extensive research in the fields of microRNA and its novel mechanisms of actions against various cancers has more recently led to the trial of a first cancer-targeted microRNA drug, MRX34. Yet, these microRNAs are mostly being studied and clinically trialed solely based on the understanding of their cell biologic effects, thus, neglecting the important immunologic effects that are sometimes opposite of the cell biologic effects. Here, we summarize both the cell biologic and immunologic effects of various microRNAs and discuss the importance of considering both effects before using them in clinical settings. We stress the importance of understanding the miRNA's effect on cancer metastasis from a "systems" perspective before developing a miRNA-targeted therapeutic in treating cancer metastasis.

The role of microRNA-31 and microRNA-21 as regulatory biomarkers in the activation of T lymphocytes of Egyptian lupus patients

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by familial aggregation and genetic predisposition. MicroRNAs (MiRNAs) serve as critical biomarkers in lupus patients because of their aberrant expression in different SLE stages. The study aimed to investigate the correlation of miR-31 and miR-21 with IL-2 in SLE patients as regulatory biomarkers in the activation of T lymphocytes of Egyptian lupus patients. Quantitative RT-PCR is carried out to estimate the expressions of miR-31 and miR-21, and IL-2 levels were determined using ELISA in plasma of 40 patients with SLE, 20 of their first-degree relatives and 20 healthy controls. The study also determined the systemic lupus erythematosus disease activity index (SLEDAI) score and proteinuria in SLE patients. The results revealed that miR-31 was lower expressed, while miR-21 was high expressed in SLE patients compared to their first-degree relatives and controls. MiR-31 was negatively correlated with SLEDAI and proteinuria in lupus patients, while miR-21 showed positive correlation with them. Also we found that there is a significant positive correlation between miR-31 and IL-2 in SLE patients, while miR-21 was negatively correlated with IL-2 level in patients. In conclusion, the study disclosed a significant association between miR-31 and miR-21 expression with IL-2 level in SLE patients. The regulatory biomarkers of miR-31 and miR-21 might have an impact on regulating IL-2 pathway expression and in turn on the activation of T lymphocytes in SLE.

Function and regulation of microRNA-31 in development and disease

MicroRNAs (miRNAs) are small noncoding RNAs that orchestrate numerous cellular processes both under normal physiological conditions as well as in diseases. This review summarizes the functional roles and transcriptional regulation of the highly evolutionarily conserved miRNA, microRNA-31 (miR-31). miR-31 is an important regulator of embryonic implantation, development, bone and muscle homeostasis, and immune system function. Its own regulation is disrupted during the onset and progression of cancer and autoimmune disorders such as psoriasis and systemic lupus erythematosus. Limited studies suggest that miR-31 is transcriptionally regulated by epigenetics, such as methylation and acetylation, as well as by a number of transcription factors. Overall, miR-31 regulates diverse cellular and developmental processes by targeting genes involved in cell proliferation, apoptosis, cell differentiation, and cell motility. Mol. Reprod. Dev. 83: 654-674, 2016 © 2016 Wiley Periodicals, Inc.

ARG-walker: inference of individual specific strengths of meiotic recombination hotspots by population genomics analysis

BACKGROUND

Meiotic recombination hotspots play important roles in various aspects of genomics, but the underlying mechanisms for regulating the locations and strengths of recombination hotspots are not yet fully revealed. Most existing algorithms for estimating recombination rates from sequence polymorphism data can only output average recombination rates of a population, although there is evidence for the heterogeneity in recombination rates among individuals. For genome-wide association studies (GWAS) of recombination hotspots, an efficient algorithm that estimates the individualized strengths of recombination hotspots is highly desirable.

RESULTS

In this work, we propose a novel graph mining algorithm named ARG-walker, based on random walks on ancestral recombination graphs (ARG), to estimate individual-specific recombination hotspot strengths. Extensive simulations demonstrate that ARG-walker is able to distinguish the hot allele of a recombination hotspot from the cold allele. Integrated with output of ARG-walker, we performed GWAS on the phased haplotype data of the 22 autosome chromosomes of the HapMap Asian population samples of Chinese and Japanese (JPT+CHB). Significant cis-regulatory signals have been detected, which is corroborated by the enrichment of the well-known 13-mer motif CCNCCNTNNCCNC of PRDM9 protein. Moreover, two new DNA motifs have been identified in the flanking regions of the significantly associated SNPs (single nucleotide polymorphisms), which are likely to be new cis-regulatory elements of meiotic recombination hotspots of the human genome.

CONCLUSIONS

Our results on both simulated and real data suggest that ARG-walker is a promising new method for estimating the individual recombination variations. In the future, it could be used to uncover the mechanisms of recombination regulation and human diseases related with recombination hotspots.

Cross-regulation between cytokine and microRNA pathways in T cells

microRNA (miRNA) mediated regulation of protein expression has emerged as an important mechanism in T-cell physiology, from development and survival to activation, proliferation, and differentiation. One of the major classes of proteins involved in these processes are cytokines, which are both key input signals and major products of T-cell function. Here, we summarize the current data on the molecular cross-talk between cytokines and miRNAs: how cytokines regulate miRNA expression, and how specific miRNAs control cytokine production in T cells. We also describe the inflammatory consequences of deregulating the miRNA/cytokine axis in mice and humans. We believe this topical area will have key implications for immune modulation and treatment of autoimmune pathology.

miR-20a inhibits TCR-mediated signaling and cytokine production in human naïve CD4+ T cells

Upon TCR stimulation by peptide-MHC complexes, CD4+ T cells undergo activation and proliferation. This process will ultimately culminate in T-cell differentiation and the acquisition of effector functions. The production of specific cytokines by differentiated CD4+ T cells is crucial for the generation of the appropriate immune response. Altered CD4+ T-cell activation and cytokine production result in chronic inflammatory conditions and autoimmune disorders. miRNAs have been shown to be important regulators of T-cell biology. In this study, we have focused our investigation on miR-20a, a member of the miR-17-92 cluster, whose expression is decreased in patients suffering from multiple sclerosis. We have found that miR-20a is rapidly induced upon TCR-triggering in primary human naïve CD4+ T cells and that its transcription is regulated in a Erk-, NF-κB-, and Ca++-dependent manner. We have further shown that overexpression of miR-20a inhibits TCR-mediated signaling but not the proliferation of primary human naïve CD4+ T cells. However, miR-20a overexpression strongly suppresses IL-10 secretion and moderately decreases IL-2, IL-6 and IL8 production, which are crucial regulators of inflammatory responses. Our study suggests that miR-20a is a new player in the regulation of TCR signaling strength and cytokine production.

Immuno-miRs: critical regulators of T-cell development, function and ageing

MicroRNAs (miRNAs) are instrumental to many aspects of immunity, including various levels of T-cell immunity. Over the last decade, crucial immune functions were shown to be regulated by specific miRNAs. These 'immuno-miRs' regulate generic cell biological processes in T cells, such as proliferation and apoptosis, as well as a number of T-cell-specific features that are fundamental to the development, differentiation and function of T cells. In this review, we give an overview of the current literature with respect to the role of miRNAs at various stages of T-cell development, maturation, differentiation, activation and ageing. Little is known about the involvement of miRNAs in thymic T-cell development, although miR-181a and miR-150 have been implicated herein. In contrast, several broadly expressed miRNAs including miR-21, miR-155 and miR-17~92, have now been shown to regulate T-cell activation. Other miRNAs, including miR-146a, show a more T-cell-subset-specific expression pattern and are involved in the regulation of processes unique to that specific T-cell subset. Importantly, differences in the miRNA target gene repertoires of different T-cell subsets allow similar miRNAs to control different T-cell-subset-specific functions. Interestingly, several of the here described immuno-miRs have also been implicated in T-cell ageing and there are clear indications for causal involvement of miRNAs in immunosenescence. It is concluded that immuno-miRs have a dynamic regulatory role in many aspects of T-cell differentiation, activation, function and ageing. An important notion when studying miRNAs in relation to T-cell biology is that specific immuno-miRs may have quite unrelated functions in closely related T-cell subsets.

Characteristics of TCRζ, ZAP-70, and FcɛRIγ gene expression in patients with T- and NK/T-cell lymphoma

Abnormal expression of key signaling molecules and defective T-cell function play a crucial role in the pathogenesis of T-cell immunodeficiency in hematological malignancies. To understand the molecular basis of T-cell signaling abnormalities and TCRζ chain deficiencies in T- and NK/T-cell lymphoma, the expression level of the TCRζ, ZAP-70, and FcɛRIγ genes in peripheral blood mononuclear cells from 25 patients with T-cell lymphoma, 16 patients with NK/T-cell lymphoma (NK/T-CL), and 26 healthy individuals was determined. In addition, their relationship with disease stage and TCRζ 3' untranslated region (3'UTR) splice variants was analyzed in this study. The expression level of all three genes was significantly altered with disease progression, and a decreasing trend was found in patients compared with healthy controls. TCRζ and ZAP-70 were significantly positively related in all samples, and a negative relationship between TCRζ and FcɛRIγ was significantly lost in NK/T-CL patients. Moreover, distinct expression patterns were defined for patient groups with different TCRζ 3'UTR isoforms. In conclusion, a lower expression pattern for all three genes may indicate a weaker immune status based on reduced TCRζ and ZAP-70 expression without the complementary effects of FcɛRIγ, while aberrant TCRζ 3'UTR splicing may contribute to T-cell receptor (TCR) signaling regulation in T cells from patients with T- and NK/T-cell lymphoma.

MicroRNA Regulation in Systemic Lupus Erythematosus Pathogenesis

MicroRNAs (miRNAs) are endogenous small RNA molecules best known for their function in post-transcriptional gene regulation. Immunologically, miRNA regulates the differentiation and function of immune cells and its malfunction contributes to the development of various autoimmune diseases including systemic lupus erythematosus (SLE). Over the last decade, accumulating researches provide evidence for the connection between dysregulated miRNA network and autoimmunity. Interruption of miRNA biogenesis machinery contributes to the abnormal T and B cell development and particularly a reduced suppressive function of regulatory T cells, leading to systemic autoimmune diseases. Additionally, multiple factors under autoimmune conditions interfere with miRNA generation via key miRNA processing enzymes, thus further skewing the miRNA expression profile. Indeed, several independent miRNA profiling studies reported significant differences between SLE patients and healthy controls. Despite the lack of a consistent expression pattern on individual dysregulated miRNAs in SLE among these studies, the aberrant expression of distinct groups of miRNAs causes overlapping functional outcomes including perturbed type I interferon signalling cascade, DNA hypomethylation and hyperactivation of T and B cells. The impact of specific miRNA-mediated regulation on function of major immune cells in lupus is also discussed. Although research on the clinical application of miRNAs is still immature, through an integrated approach with advances in next generation sequencing, novel tools in bioinformatics database analysis and new in vitro and in vivo models for functional evaluation, the diagnostic and therapeutic potentials of miRNAs may bring to fruition in the future.

Characterization of microRNAs differentially expressed during bovine follicle development

Several different miRNAs have been proposed to regulate ovarian follicle function; however, very limited information exists on the spatiotemporal patterns of miRNA expression during follicle development. The objective of this study was to identify, using microarray, miRNA profiles associated with growth and regression of dominant-size follicles in the bovine monovular ovary and to characterize their spatiotemporal distribution during development. The follicles were collected from abattoir ovaries and classified as small (4-8  mm) or large (12-17  mm); the latter were further classified as healthy or atretic based on estradiol and CYP19A1 levels. Six pools of small follicles and individual large healthy (n=6) and large atretic (n=5) follicles were analyzed using Exiqon's miRCURY LNA microRNA Array 6th gen, followed by qPCR validation. A total of 17 and 57 sequences were differentially expressed (greater than or equal to twofold; P<0.05) between large healthy and each of small and large atretic follicles respectively. Bovine miRNAs confirmed to be upregulated in large healthy follicles relative to small follicles (bta-miR-144, bta-miR-202, bta-miR-451, bta-miR-652, and bta-miR-873) were further characterized. Three of these miRNAs (bta-miR-144, bta-miR-202, and bta-miR-873) were also downregulated in large atretic follicles relative to large healthy follicles. Within the follicle, these miRNAs were predominantly expressed in mural granulosa cells. Further, body-wide screening revealed that bta-miR-202, but not other miRNAs, was expressed exclusively in the gonads. Finally, a total of 1359 predicted targets of the five miRNAs enriched in large healthy follicles were identified, which mapped to signaling pathways involved in follicular cell proliferation, steroidogenesis, prevention of premature luteinization, and oocyte maturation.

microRNAs and the mammary gland: A new understanding of gene expression

MicroRNAs (miRNAs) have been identified in cells as well as in exosomes in biological fluids such as milk. In mammary gland, most of the miRNAs studied have functions related to immunity and show alterations in their pattern of expression during lactation. In mastitis, the inflammatory response caused by Streptococcus uberis alters the expression of miRNAs that may regulate the innate immune system. These small RNAs are stable at room temperature and are resistant to repeated freeze/thaw cycles, acidic conditions and degradation by RNAse, making them resistant to industrial procedures. These properties mean that miRNAs could have multiple applications in veterinary medicine and biotechnology. Indeed, lactoglobulin-free milk has been produced in transgenic cows expressing specific miRNAs. Although plant and animal miRNAs have undergone independent evolutionary adaptation recent studies have demonstrated a cross-kingdom passage in which rice miRNA was isolated from human serum. This finding raises questions about the possible effect that miRNAs present in foods consumed by humans could have on human gene regulation. Further studies are needed before applying miRNA biotechnology to the milk industry. New discoveries and a greater knowledge of gene expression will lead to a better understanding of the role of miRNAs in physiology, nutrition and evolution.