Dicer is required for haploid male germ cell differentiation in mice

Creating conditional dual fluorescence labeled transgenic animals for studying function of small noncoding RNAs

Because the function of most noncoding (nc) RNAs is unknown, Cre-lox transgenic mice are useful tools to determine their functions in a tissue or developmental stage-specific manner. However, the technology faces challenges because expression of ncRNA-transgene lacks protein product. No antibody or peptide-tag can be used to trace ncRNA expression in mouse tissues in real time. Furthermore, transgene integration at different locus or orientations in the genome may result in recombination of genomic fragments in the Cre-lox system. Establishing a reliable method that can be used to determine the precise copy number and orientation of the transgene is critical to the field. We developed a fast and straightforward method to determine ncRNA-transgene copy number, orientation, and insertion site in the genome. Furthermore, upon tissue-specific expression of ncRNA, a Cre-loxP-mediated dual-fluorescence expression system facilitates fluorescence signal switching from green to red, which enables real-time monitoring of ncRNA expression by fluorescence signals. As proof of concept, we demonstrate that after microRNA (miRNA)-Flox mice crossed with Col2a1-Cre mice, miRNA transgene expression could be detected successfully by red fluorescence signals in various cartilaginous tissues. This method of creating small ncRNA transgenic mice facilitates both tissue-specific ncRNA expression and real-time visualization of its expression. It is particularly suitable for in vivo studies of the functional roles and lineage tracing of small ncRNA.

Transcriptome profiling of the developing male germ line identifies the miR-29 family as a global regulator during meiosis

MicroRNAs are essential for spermatogenesis. However, the stage-specific requirements for particular miRNAs in the male mammalian germ line remain largely uncharacterized. The miR-34 family is, to date, the only miRNA proven to be necessary for the production of sperm in mammals, though its germline roles are poorly understood. Here, we generate and analyze paired small RNA and mRNA profiles across different stages of germline development in male mice, focusing on time points shortly before and during meiotic prophase I. We show that in addition to miR-34, miR-29 also mediates widespread repression of mRNA targets during meiotic prophase I in the male mouse germline. Furthermore, we demonstrate that predicted miR-29 target mRNAs in meiotic cells are largely distinct from those of miR-34, indicating that miR-29 performs a regulatory function independent of miR-34. Prior to this work, no germline role has been attributed to miR-29. To begin to understand roles for miR-29 in the germ line, we identify targets of miR-29 undergoing post transcriptional downregulation during meiotic prophase I, which likely correspond to the direct targets of miR-29. Interestingly, candidate direct targets of miR-29 are enriched in transcripts encoding extracellular matrix components. Our results implicate the miR-29 family as an important regulatory factor during male meiosis.

FYCO1 and autophagy control the integrity of the haploid male germ cell-specific RNP granules

Ribonucleoprotein (RNP) granules play a major role in compartmentalizing cytoplasmic RNA regulation. Haploid round spermatids that have exceptionally diverse transcriptomes are characterized by a unique germ cell-specific RNP granule, the chromatoid body (CB). The CB shares many characteristics with somatic RNP granules but also has germline-specific features. The CB appears to be a central structure in PIWI-interacting RNA (piRNA)-targeted RNA regulation. Here, we identified a novel CB component, FYCO1, which is involved in the intracellular transport of autophagic vesicles in somatic cells. We demonstrated that the CB is associated with autophagic activity. Induction of autophagy leads to the recruitment of lysosomal vesicles onto the CB in a FYCO1-dependent manner as demonstrated by the analysis of a germ cell-specific Fyco1 conditional knockout mouse model. Furthermore, in the absence of FYCO1, the integrity of the CB was affected and the CB was fragmented. Our results suggest that RNP granule homeostasis is regulated by FYCO1-mediated autophagy.

Role of Dicer1-Dependent Factors in the Paracrine Regulation of Epididymal Gene Expression

Dicer1 is an endoribonuclease involved in the biogenesis of functional molecules such as microRNAs (miRNAs) and endogenous small interfering RNAs (endo-siRNAs). These small non-coding RNAs are important regulators of post-transcriptional gene expression and participate in the control of male fertility. With the knowledge that 1) Dicer1-dependent factors are required for proper sperm maturation in the epididymis, and that 2) miRNAs are potent mediators of intercellular communication in most biological systems, we investigated the role of Dicer1-dependent factors produced by the proximal epididymis (initial segment/caput)- including miRNAs- on the regulation of epididymal gene expression in the distal epididymis regions (i.e. corpus and cauda). To this end, we performed comparative microarray and ANOVA analyses on control vs. Defb41iCre/wt;Dicer1fl/fl mice in which functional Dicer1 is absent from the principal cells of the proximal epididymis. We identified 35 and 33 transcripts that displayed significant expression level changes in the corpus and cauda regions (Fold change > 2 or < -2; p < 0.002), respectively. Among these transcripts, Zn-alpha 2-glycoprotein (Azgp1) encodes for a sperm equatorial protein whose expression in the epididymis of Dicer1 cKO mice is significantly increased compared to controls. In addition, 154 miRNAs, including miR-210, miR-672, miR-191 and miR-204, showed significantly impaired biogenesis in the absence of Dicer1 from the principal cells of the proximal epididymis (Fold change > 2 or < -2; p < 0.01). These miRNAs are secreted via extracellular vesicles (EVs) derived from the DC2 epididymal principal cell line, and their expression correlates with target transcripts involved in distinct biological pathways, as evidenced by in silico analysis. Albeit correlative and based on in silico approach, our study proposes that Dicer1-dependent factors trigger- directly or not-significant genes expression changes in distinct regions of this organ. The paracrine control of functions important to post-testicular sperm maturation by Dicer1-dependent factors may open new avenues for the identification of molecular targets important to male fertility control.

Epigenetic reprogramming of the zygote in mice and men: on your marks, get set, go!

Gametogenesis (spermatogenesis and oogenesis) is accompanied by the acquisition of gender-specific epigenetic marks, such as DNA methylation, histone modifications and regulation by small RNAs, to form highly differentiated, but transcriptionally silent cell-types in preparation for fertilisation. Upon fertilisation, extensive global epigenetic reprogramming takes place to remove the previously acquired epigenetic marks and produce totipotent zygotic states. It is the aim of this review to delineate the cellular and molecular events involved in maternal, paternal and zygotic epigenetic reprogramming from the time of gametogenesis, through fertilisation, to the initiation of zygotic genome activation for preimplantation embryonic development. Recent studies have begun to uncover the indispensable functions of epigenetic players during gametogenesis, fertilisation and preimplantation embryo development, and a more comprehensive understanding of these early events will be informative for increasing pregnancy success rates, adding particular value to assisted fertility programmes.

Extracellular microRNAs from the epididymis as potential mediators of cell-to-cell communication

Ribonucleic acid (RNA) was previously thought to remain inside cells as an intermediate between genes and proteins during translation. However, it is now estimated that 98% of the mammalian genomic output is transcribed as noncoding RNAs, which are involved in diverse gene expression regulatory mechanisms and can be transferred from one cell to another through extracellular communication. For instance, microRNAs are 22-nucleotide-long noncoding RNAs that are generated by endonuclease cleavage of precursors inside the cells and are secreted as extracellular microRNAs to regulate target cell posttranscriptional gene expression via RNA interference. We and others have shown that different populations of microRNAs are expressed in distinct regions of the human epididymis and regulate the expression of target genes that are involved in the control of male fertility as indicated by knock-out mouse models. Importantly, some microRNAs, including the microRNA-888 (miR-888) cluster that is exclusively expressed in the reproductive system of human and nonhuman primates, are released in the sperm-surrounding fluid in the epididymis via extracellular vesicles, the so-called epididymosomes. In addition to interacting with the membrane of maturing spermatozoa, these extracellular vesicles containing microRNAs communicate with epithelial cells located downstream from their release site, suggesting a role in the luminal exocrine control of epididymal functions. Apart from their potential roles as mediators of intercellular communication within the epididymis, these extracellular microRNAs are potent molecular targets for the noninvasive diagnosis of male infertility.

The role of Dicer1 in the male reproductive tract

Dicer1 is an RNase III enzyme necessary for microRNA (miRNA) biogenesis, as it cleaves pre-miRNAs into mature miRNAs. miRNAs are important regulators of gene expression. In recent years, several miRNA-independent roles of Dicer1 have been identified. They include the production of endogenous small interfering RNAs, detoxifying retrotransposon-derived transcripts, and binding to new targets; messenger RNAs and long noncoding RNAs. Further, in this review, the functional significance of Dicer1 in the male reproductive tract is discussed. Conditional Dicer1 knock-out mouse models have demonstrated a requisite role for Dicer in male fertility. Deletion of Dicer1 from somatic or germ cells in the testis cause spermatogenic problems rendering male mice infertile. The lack of Dicer1 in the proximal epididymis causes dedifferentiation of the epithelium, with unbalanced sex steroid receptor expression, defects in epithelial lipid homeostasis, and subsequent male infertility. In addition, Dicer1 ablation from the prostate leads to increased apoptosis of the differentiated luminal cells, followed by epithelial hypotrophy of the ventral prostate. However, further studies are needed to clarify which functions of Dicer1 are responsible for the observed phenotypes in the male reproductive tract.

The role of epigenetics in idiopathic male infertility

Infertility is a complex disorder with multiple genetic and environmental causes. Although some specific mutations have been identified, other factors responsible for sperm defects remain largely unknown. Despite considerable efforts to identify the pathophysiology of the disease, we cannot explain the underlying mechanisms of approximately half of infertility cases. This study reviews current data on epigenetic regulation and idiopathic male infertility. Recent data have shown an association between epigenetic modifications and idiopathic infertility. In this regard, epigenetics has emerged as one of the promising research areas in understanding male infertility. Many studies have indicated that epigenetic modifications, including DNA methylation in imprinted and developmental genes, histone tail modifications and short non-coding RNAs in spermatozoa may have a role in idiopathic male infertility.

A Role of MicroRNAs in Cell Differentiation During Gonad Development

MicroRNAs (miRNAs) are a group of small noncoding RNA molecules that play a major role in posttranscriptional regulation of gene expression and are expressed in an organ-specific manner. One miRNA can potentially regulate the expression of several genes, depending on cell type and differentiation stage. miRNAs are differentially expressed in the male and female gonads and have an organ-specific reproductive function. Exerting their affect through germ cells and gonadal somatic cells, miRNAs regulate key proteins necessary for gonad development. The role of miRNAs in the testes is only starting to emerge though they have been shown to be required for adequate spermatogenesis. Widely explored in the ovary, miRNAs were suggested to play a fundamental role in follicles' assembly, growth, differentiation, and ovulation. In this chapter, we focus on data obtained from mice in which distinct proteins that participate in the biosynthesis of miRNAs were conditionally knocked out from germ cells (spermatogonial cells or oocytes) or gonadal somatic cells (Sertoli or granulosa cells). We detail recent advances in identification of particular miRNAs and their significance in the development and function of male and female gonads. miRNAs can serve as biomarkers and therapeutic agents of pathological conditions; thus, elucidating the branched and complex network of reproduction-related miRNAs will aid understanding of gonads' physiology and managing reproduction disorders.

Non-coding RNA in Spermatogenesis and Epididymal Maturation

Testicular germ and somatic cells express many classes of small ncRNAs, including Dicer-independent PIWI-interacting RNAs, Dicer-dependent miRNAs, and endogenous small interfering RNA. Several studies have identified ncRNAs that are highly, exclusively, or preferentially expressed in the testis and epididymis in specific germ and somatic cell types. Temporal and spatial expression of proteins is a key requirement of successful spermatogenesis and large-scale gene transcription occurs in two key stages, just prior to transcriptional quiescence in meiosis and then during spermiogenesis just prior to nuclear silencing in elongating spermatids. More than 60 % of these transcripts are then stockpiled for subsequent translation. In this capacity ncRNAs may act to interpret and transduce cellular signals to either maintain the undifferentiated stem cell population and/or drive cell differentiation during spermatogenesis and epididymal maturation. The assignation of specific roles to the majority of ncRNA species implicated as having a role in spermatogenesis and epididymal function will underpin fundamental understanding of normal and disease states in humans such as infertility and the development of germ cell tumours.

Small non-coding RNAs and their associated proteins in spermatogenesis

The importance of the gene regulation roles of small non-coding RNAs and their protein partners is of increasing focus. In this paper, we reviewed three main small RNA species which appear to affect spermatogenesis. MicroRNAs (miRNAs) are single stand RNAs derived from transcripts containing stem-loops and hairpins which target corresponding mRNAs and affect their stability or translation. Many miRNA species have been found to be related to normal male germ cell development. The biogenesis of piRNAs is still largely unknown but several models have been proposed. Some piRNAs and PIWIs target transposable elements and it is these that may be active in regulating translation or stem cell maintenance. endo-siRNAs may also participate in sperm development. Some possible interactions between different kinds of small RNAs have even been suggested. We also show that male germ granules are seen to have a close relationship with a considerable number of mRNAs and small RNAs. Those special structures may also participate in sperm development.

The Role of Retinoic Acid (RA) in Spermatogonial Differentiation

Retinoic acid (RA) directs the sequential, but distinct, programs of spermatogonial differentiation and meiotic differentiation that are both essential for the generation of functional spermatozoa. These processes are functionally and temporally decoupled, as they occur in distinct cell types that arise over a week apart, both in the neonatal and adult testis. However, our understanding is limited in terms of what cellular and molecular changes occur downstream of RA exposure that prepare differentiating spermatogonia for meiotic initiation. In this review, we describe the process of spermatogonial differentiation and summarize the current state of knowledge regarding RA signaling in spermatogonia.

Downregulation of miR-320a/383-sponge-like long non-coding RNA NLC1-C (narcolepsy candidate-region 1 genes) is associated with male infertility and promotes testicular embryonal carcinoma cell proliferation

Long non-coding RNAs (lncRNAs), which are extensively transcribed from the genome, have been proposed to be key regulators of diverse biological processes. However, little is known about the role of lncRNAs in regulating spermatogenesis in human males. Here, using microarray technology, we show altered expression of lncRNAs in the testes of infertile men with maturation arrest (MA) or hypospermatogenesis (Hypo), with 757 and 2370 differentially down-regulated and 475 and 163 up-regulated lncRNAs in MA and Hypo, respectively. These findings were confirmed by quantitative real-time PCR (qRT-PCR) assays on select lncRNAs, including HOTTIP, imsrna320, imsrna292 and NLC1-C (narcolepsy candidate-region 1 genes). Interestingly, NLC1-C, also known as long intergenic non-protein-coding RNA162 (LINC00162), was down-regulated in the cytoplasm and accumulated in the nucleus of spermatogonia and primary spermatocytes in the testes of infertile men with mixed patterns of MA compared with normal control. The accumulation of NLC1-C in the nucleus repressed miR-320a and miR-383 transcript and promoted testicular embryonal carcinoma cell proliferation by binding to Nucleolin. Here, we define a novel mechanism by which lncRNAs modulate miRNA expression at the transcriptional level by binding to RNA-binding proteins to regulate human spermatogenesis.

DICER Regulates the Formation and Maintenance of Cell-Cell Junctions in the Mouse Seminiferous Epithelium

The endonuclease DICER that processes micro-RNAs and small interfering RNAs is essential for normal spermatogenesis and male fertility. We previously showed that the deletion of Dicer1 gene in postnatal spermatogonia in mice using Ngn3 promoter-driven Cre expression caused severe defects in the morphogenesis of haploid spermatid to mature spermatozoon, including problems in cell polarization and nuclear elongation. In this study, we further analyzed the same mouse model and revealed that absence of functional DICER in differentiating male germ cells induces disorganization of the cell-cell junctions in the seminiferous epithelium. We detected discontinuous and irregular apical ectoplasmic specializations between elongating spermatids and Sertoli cells. The defective anchoring of spermatids to Sertoli cells caused a premature release of spermatids into the lumen. Our findings may help also explain the abnormal elongation process of remaining spermatids because these junctions and the correct positioning of germ cells in the epithelium are critically important for the progression of spermiogenesis. Interestingly, cell adhesion-related genes were generally upregulated in Dicer1 knockout germ cells. Claudin 5 ( Cldn5 ) was among the most upregulated genes and we show that the polarized localization of CLAUDIN5 in the apical ectoplasmic specializations was lost in Dicer1 knockout spermatids. Our results suggest that DICER-dependent pathways control the formation and organization of cell-cell junctions in the seminiferous epithelium via the regulation of cell adhesion-related genes.

KIF1-binding protein interacts with KIF3A in haploid male germ cells

Male fertility relies on the production of functional spermatozoa. Spermatogenesis is a complex differentiation process that is characterized by meiosis and dramatic morphogenesis of haploid cells. Spermatogenesis involves active changes in the microtubular network to support meiotic divisions, cell polarization, the reshaping of the nucleus, and the formation of a flagellum. Previously, we have demonstrated that a microtubule-based anterograde transport motor protein KIF3A is required for the sperm tail formation and nuclear shaping during spermatogenesis. In this study, we show that KIF3A interacts with a KIF1-binding protein (KBP) in the mouse testis. We have characterized the expression and localization pattern of KBP during spermatogenesis and localized both KIF3A and KBP in the cytoplasm of round spermatids and manchette of elongating spermatids. Interestingly, KBP localized also in the late chromatoid body (CB) of elongating spermatids, whose function involves intracellular movement and association with the microtubular network. Altogether our results suggest a role for KBP in spermatid elongation and in the function of the late CB.

Expression of Flotilin-2 and Acrosome Biogenesis Are Regulated by MiR-124 during Spermatogenesis

MicroRNAs (miRNAs) are a class of short non-coding RNA molecules, which diversely regulate gene expression in organisms. Although the regulatory role of these small RNA molecules has been recently explored in animal spermatogenesis, the role of miR-124 in male germ cells is poorly defined. In our previous study, flotillin-2 was investigated as a novel Golgi-related protein involved in sperm acrosome biogenesis. The current study was designed to analyze the contribution of miR-124 in the regulation of flotillin-2 expression during mouse acrosome biogenesis. Luciferase assays revealed the target effects of miR-124 on flotillin-2 expression. Following intratesticular injection of miR-124 in 3-week-old male mice, quantitative real-time RT-PCR and western blot analysis were employed to confirm the function of miR-124 in regulating flotillin-2 after 48 hours. Sperm abnormalities were assessed 3 weeks later by ordinary optical microscopy, the acrosome abnormalities were also assessed by PNA staining and transmission electron microscopy. The results showed the proportion of sperm acrosome abnormalities was significantly higher than that of the control group. The expression of flotillin-2 and caveolin-1 was significantly downregulated during acrosome biogenesis. These results indicated that miR-124 could potentially play a role in caveolin-independent vesicle trafficking and modulation of flotillin-2 expression in mouse acrosome biogenesis.

Ablation of Dicer leads to widespread perturbation of signaling pathways

Dicer is an essential ribonuclease involved in the biogenesis of miRNAs. Previous studies have reported downregulation of Dicer in multiple cancers including hepatocellular carcinoma. To identify signaling pathways that are altered upon Dicer depletion, we carried out quantitative phosphotyrosine profiling of liver tissue from Dicer knockout mice. We employed antibody-based enrichment of phosphotyrosine containing peptides coupled with SILAC spike-in approach for quantitation. High resolution mass spectrometry-based analysis identified 349 phosphotyrosine peptides corresponding to 306 unique phosphosites of which 75 were hyperphosphorylated and 78 were hypophosphorylated. Several receptor tyrosine kinases including MET, PDGF receptor alpha, Insulin-like growth factor 1 and Insulin receptor as well as non-receptor tyrosine kinases such as Src family kinases were found to be hyperphosphorylated upon depletion of Dicer. In addition, signaling molecules such as IRS-2 and STAT3 were hyperphosphorylated. Activation of these signaling pathways has been implicated previously in various types of cancers. Interestingly, we observed hypophosphorylation of molecules including focal adhesion kinase and paxillin. Our study profiles the perturbed signaling pathways in response to dysregulated miRNAs resulting from depletion of Dicer. Our findings warrant further studies to investigate oncogenic effects of downregulation of Dicer in cancers.

Dgcr8 and Dicer are essential for sex chromosome integrity during meiosis in males

Small RNAs play crucial roles in regulating gene expression during mammalian meiosis. To investigate the function of microRNAs (miRNAs) and small interfering RNAs (siRNAs) during meiosis in males, we generated germ-cell-specific conditional deletions of Dgcr8 and Dicer in mice. Analysis of spermatocytes from both conditional knockout lines revealed that there were frequent chromosomal fusions during meiosis, always involving one or both sex chromosomes. RNA sequencing indicates upregulation of Atm in spermatocytes from miRNA-deficient mice, and immunofluorescence imaging demonstrates an increased abundance of activated ATM kinase and mislocalization of phosphorylated MDC1, an ATM phosphorylation substrate. The Atm 3′UTR contains many potential microRNA target sites, and, notably, target sites for several miRNAs depleted in both conditional knockout mice were highly effective at promoting repression. RNF8, a telomere-associated protein whose localization is controlled by the MDC1–ATM kinase cascade, normally associates with the sex chromosomes during pachytene, but in both conditional knockouts redistributed to the autosomes. Taken together, these results suggest that Atm dysregulation in microRNA-deficient germ lines contributes to the redistribution of proteins involved in chromosomal stability from the sex chromosomes to the autosomes, resulting in sex chromosome fusions during meiotic prophase I.

Highlighted Article: miRNA-deficient spermatocytes display frequent sex chromosome fusions and fail to progress through meiosis in a process that is probably mediated by dysregulation of Atm.

MicroRNAs and DNA methylation as epigenetic regulators of mitosis, meiosis and spermiogenesis

Spermatogenesis is composed of three distinctive phases, which include self-renewal of spermatogonia via mitosis, spermatocytes undergoing meiosis I/II and post-meiotic development of haploid spermatids via spermiogenesis. Spermatogenesis also involves condensation of chromatin in the spermatid head before transformation of spermatids to spermatozoa. Epigenetic regulation refers to changes of heritably cellular and physiological traits not caused by modifications in the DNA sequences of the chromatin such as mutations. Major advances have been made in the epigenetic regulation of spermatogenesis. In this review, we address the roles and mechanisms of epigenetic regulators, with a focus on the role of microRNAs and DNA methylation during mitosis, meiosis and spermiogenesis. We also highlight issues that deserve attention for further investigation on the epigenetic regulation of spermatogenesis. More importantly, a thorough understanding of the epigenetic regulation in spermatogenesis will provide insightful information into the etiology of some unexplained infertility, offering new approaches for the treatment of male infertility.

Breeding scheme and maternal small RNAs affect the efficiency of transgenerational inheritance of a paramutation in mice

Paramutations result from interactions between two alleles at a single locus, whereby one induces a heritable change in the other. Although common in plants, paramutations are rarely studied in animals. Here, we report a new paramutation mouse model, in which the paramutant allele was induced by an insertional mutation and displayed the "white-tail-tip" (WTT) phenotype. The paramutation phenotype could be transmitted across multiple generations, and the breeding scheme (intercrossing vs. outcrossing) drastically affected the transmission efficiency. Paternal (i.e., sperm-borne) RNAs isolated from paramutant mice could induce the paramutation phenotype, which, however, failed to be transmitted to subsequent generations. Maternal miRNAs and piRNAs appeared to have an inhibitory effect on the efficiency of germline transmission of the paramutation. This paramutation mouse model represents an important tool for dissecting the underlying mechanism, which should be applicable to the phenomenon of epigenetic transgenerational inheritance (ETI) in general. Mechanistic insights of ETI will help us understand how organisms establish new heritable epigenetic states during development, or in times of environmental or nutritional stress.

Role of microRNAs in mammalian spermatogenesis and testicular germ cell tumors

microRNAs (miRNAs) are a class of small endogenous RNAs, 19–25 nucleotides in size, which play a role in the regulation of gene expression at transcriptional and post-transcriptional levels. Spermatogenesis is a complex process through which spermatogonial stem cells (SSCs) proliferate and differentiate into mature spermatozoa. A large number of miRNAs are abundantly expressed in spermatogenic cells. Growing evidence supports the essential role of miRNA regulation in normal spermatogenesis and male fertility and cumulative research has shown that this form of regulation contributes to the etiology of testicular germ cell tumors (TGCTs). In this review, we addressed recent advancements of miRNA expression profiles in testis and focused on the regulatory functions of miRNA in the process of SSC renewal, spermatogonial mitosis, spermatocyte meiosis, spermiogenesis, and the occurrence of TGCTs.

Retromer vesicles interact with RNA granules in haploid male germ cells

Spermatozoa are produced during spermatogenesis as a result of mitotic proliferation, meiosis and cellular differentiation. Postmeiotic spermatids are exceptional cells given their haploid genome and remarkable sperm-specific structural transformations to compact and reshape the nucleus and to construct the flagellum and acrosome. These processes require delicate coordination and active communication between distinct cellular compartments. In this study, we elucidated the interplay between the haploid RNA regulation and the vesicular transport system. We identified a novel interaction between VPS26A/VPS35-containing retromer vesicles and the chromatoid body (CB), which is a large ribonucleoprotein (RNP) granule unique to haploid male germ cells. VPS26A/VPS35-positive vesicles were shown to be involved in the endosomal pathway, as well as in acrosomal formation that is dependent on the Golgi complex-derived vesicular trafficking. While the exact role of the retromer vesicles in the CB function remains unclear, our results suggest a direct functional link between vesicle transport and CB-mediated RNA regulation.

microRNA in Human Reproduction

microRNAs constitute a large family of approximately 21-nucleotide-long, noncoding RNAs. They emerged more than 20 years ago as key posttranscriptional regulators of gene expression. The regulatory role of these small RNA molecules has recently begun to be explored in the human reproductive system. microRNAs have been shown to play an important role in control of reproductive functions, especially in the processes of oocyte maturation, folliculogenesis, corpus luteum function, implantation, and early embryonic development. Knockout of Dicer, the cytoplasmic enzyme that cleaves the pre-miRNA to its mature form, results in postimplantation embryonic lethality in several animal models, attributing to these small RNA vital functions in reproduction and development. Another intriguing characteristic of microRNAs is their presence in body fluids in a remarkably stable form that is protected from endogenous RNase activity. In this chapter we will describe the current knowledge on microRNAs, specifically relating to human gonadal cells. We will focus on their role in the ovarian physiologic process and ovulation dysfunction, regulation of spermatogenesis and male fertility, and putative involvement in human normal and aberrant trophoblast differentiation and invasion through the process of placentation.

Small RNAs: Their Possible Roles in Reproductive Failure

Posttranscriptional gene regulation is a regulatory mechanism which occurs "above the genome" and confers different phenotypes and functions within a cell. Transcript and protein abundance above the level of transcription can be regulated via noncoding ribonucleic acid (ncRNA) molecules, which potentially play substantial roles in the regulation of reproductive function. MicroRNA (miRNA), endogenous small interfering RNA (endo-siRNA), and PIWI-interacting RNA (piRNA) are three primary classes of small ncRNA. Similarities and distinctions between their biogenesis and in the interacting protein machinery that facilitate their function distinguish these three classes. Characterization of the expression and importance of the critical components for the biogenesis of each class in different tissues contributes a clearer understanding of their contributions in specific reproductive tissues and their ability to influence fertility in both males and females. This chapter discusses the expression and potential roles of miRNA, endo-siRNA, and piRNA in the regulation of reproductive function. Additionally, this chapter elaborates on investigations aimed to address and characterize specific mechanisms through which miRNA may influence infertility and the use of miRNA as biomarkers associated with several reproductive calamities such as defective spermatogenesis in males, polycystic ovarian failure, endometriosis and obesity, and chemical-induced subfertility.

Differential expression of microRNAs in sexually immature and mature canine testes

Mammalian testis exhibits spatiotemporal gene expression patterns that are essential for successful and continuous spermatogenesis. Although microRNAs (miRNAs) modify gene expression through translational repression and degradation of target messenger RNAs, the precise molecular mechanisms of these regulatory processes are unclear. We used canine miScript miRNA polymerase chain reaction (PCR) Array technology to elucidate the repertoire of canine testis miRNAs and compared their expression patterns between sexually immature (prepubertal) and mature (adult) dog testes. Eighty-four well-characterized canine miRNAs were customized in this study. The data were analyzed by RT(2) Profiler PCR Array Data Analysis (version 3.5). Results identified upregulation of 32 and considerable downregulation of 12 miRNAs in adult dog testis. In conclusion, the two developmental stages had significantly different miRNAs expression patterns. The finding provides fundamental information of miRNAs which may help to elucidate their role in spermatogenesis and male infertility in this species. To the best of our knowledge, this study is the first to offer comparative profile of the miRNA transcriptome in prepubertal and adult canine testes using miRNA PCR array approach.

Germ cell-specific targeting of DICER or DGCR8 reveals a novel role for endo-siRNAs in the progression of mammalian spermatogenesis and male fertility

Small non-coding RNAs act as critical regulators of gene expression and are essential for male germ cell development and spermatogenesis. Previously, we showed that germ cell-specific inactivation of Dicer1, an endonuclease essential for the biogenesis of micro-RNAs (miRNAs) and endogenous small interfering RNAs (endo-siRNAs), led to complete male infertility due to alterations in meiotic progression, increased spermatocyte apoptosis and defects in the maturation of spermatozoa. To dissect the distinct physiological roles of miRNAs and endo-siRNAs in spermatogenesis, we compared the testicular phenotype of mice with Dicer1 or Dgcr8 depletion in male germ cells. Dgcr8 mutant mice, which have a defective miRNA pathway while retaining an intact endo-siRNA pathway, were also infertile and displayed similar defects, although less severe, to Dicer1 mutant mice. These included cumulative defects in meiotic and haploid phases of spermatogenesis, resulting in oligo-, terato-, and azoospermia. In addition, we found by RNA sequencing of purified spermatocytes that inactivation of Dicer1 and the resulting absence of miRNAs affected the fine tuning of protein-coding gene expression by increasing low level gene expression. Overall, these results emphasize the essential role of miRNAs in the progression of spermatogenesis, but also indicate a role for endo-siRNAs in this process.

Histone H3.3 regulates dynamic chromatin states during spermatogenesis

The histone variant H3.3 is involved in diverse biological processes, including development, transcriptional memory and transcriptional reprogramming, as well as diseases, including most notably malignant brain tumors. Recently, we developed a knockout mouse model for the H3f3b gene, one of two genes encoding H3.3. Here, we show that targeted disruption of H3f3b results in a number of phenotypic abnormalities, including a reduction in H3.3 histone levels, leading to male infertility, as well as abnormal sperm and testes morphology. Additionally, null germ cell populations at specific stages in spermatogenesis, in particular spermatocytes and spermatogonia, exhibited increased rates of apoptosis. Disruption of H3f3b also altered histone post-translational modifications and gene expression in the testes, with the most prominent changes occurring at genes involved in spermatogenesis. Finally, H3f3b null testes also exhibited abnormal germ cell chromatin reorganization and reduced protamine incorporation. Taken together, our studies indicate a major role for H3.3 in spermatogenesis through regulation of chromatin dynamics.

MicroRNAs and spermatogenesis

In mammals, male gametes are produced inside the testis by spermatogenesis, which has three phases: mitotic proliferation of spermatogonia, meiosis of spermatocytes, and haploid differentiation of spermatids. The genome of male germ cells is actively transcribed to produce phase-specific gene expression patterns. Male germ cells have a complex transcriptome. In addition to protein-coding messenger RNAs, many noncoding RNAs, including microRNAs (miRNAs), are produced. The miRNAs are important regulators of gene expression. They function mainly post-transcriptionally to control the stability or translation of their target messenger RNAs. The miRNAs are expressed in a cell-specific manner during spermatogenesis to participate in the control of each step of male germ cell differentiation. Genetically modified mouse models have demonstrated the importance of miRNA pathways for normal spermatogenesis, and functional studies have been designed to dissect the roles of specific miRNAs in distinct cell types. Clinical studies have exploited the well-defined expression profiles of miRNAs, and human spermatozoal or seminal plasma miRNAs have been explored as potential biomarkers for male factor infertility. This review article discusses the current findings that support the central role of miRNAs in the regulation of spermatogenesis and male fertility.

Murine follicular development requires oocyte DICER, but not DROSHA

Both DICER and DROSHA are RNase III enzymes involved in the biogenesis of small noncoding RNAs. DROSHA cleaves the stem-loop portion of the primary miRNAs and produces precursor miRNAs in the nucleus, whereas DICER processes double-stranded RNA precursors into mature miRNAs and endogenous small interference RNAs in the cytoplasm. Selective inactivation of Dicer in growing oocytes of primary follicles leads to female infertility due to oocyte spindle defects. However, it remains unknown if oocyte Dicer expression in the fetal ovary is required for proper follicular development in the postnatal ovary. Moreover, the role of Drosha in folliculogenesis has never been investigated. Here, we report that conditional knockout of Dicer in prophase I oocytes of the fetal ovary led to compromised folliculogenesis, premature ovarian failure, and female infertility in the adult ovary, whereas selective inactivation of Drosha in oocytes of either the fetal or the developing ovary had no effects on normal folliculogenesis and female fertility in adulthood. Our data indicate that oocyte DICER expression in the fetal ovary is required, and oocyte DROSHA is dispensable, for postnatal follicular development and female fertility in adulthood.

Regulation of microcystin-LR-induced toxicity in mouse spermatogonia by miR-96

Microcystin (MC)-LR is a cyclic heptapeptide that acts as a potent reproductive system toxin, especially by decreasing sperm quality through affecting spermatogonia. However, the molecular mechanisms of MC-induced spermatogonial cytotoxicity still remain unclear. The present study was designed to investigate changes in microRNA (miRNA) profiles and their potential functions in spermatogonia (GC-1 cell line) following treatment with MC-LR. With microarray analysis, 101 miRNAs were identified to be significantly altered in GC-1 cells treated with MC-LR. Among the 25 miRNAs associated with spermatogenesis, miR-96 was down-regulated most dramatically and thus selected for further functional analysis. Deleted-in azoospermia-associated protein 2 (DAZAP2) was predicted to have a binding sequence for miR-96 within its 3'-untranslated region. Fluorescent reporter assay confirmed that DAZAP2 was the target gene of miR-96. The expression of DAZAP2 decreased significantly when miR-96 was up-regulated. Consistently, down-regulation of miR-96 significantly increased the level of DAZAP2. Up-regulation of miR-96 promoted cell viability in GC-1 cells as a result of exposure to MC-LR. Our study suggested a crucial role for miR-96 in the regulation of cytotoxic effects of MC-LR in spermatogonia, which provides new perspectives in the diagnosis and treatment strategies for MC-induced male infertility.

Environmentally induced epigenetic transgenerational inheritance of male infertility

Decreasing male fertility has been observed for the past fifty years. Examples of affected reproductive parameters include decreases in sperm count and sperm quality and increases in testicular cancer, cryptorchidism and hypospadias. Exposures to environmental toxicants during fetal development and early postnatal life have been shown to promote infertility. Environmental exposures inducing epigenetic changes related to male infertility range from life style, occupational exposures, environmental toxicants and nutrition. Exposures during fetal gonadal sex determination have been shown to alter the epigenetic programming of the germline that then can transmit this altered epigenetic information to subsequent generations in the absence of any exposures. This environmentally induced epigenetic transgenerational inheritance of disease will be a component of the etiology of male infertility.

The small GTPase Rheb is required for spermatogenesis but not oogenesis

The process of germ cell development is under the tight control of various signaling pathways, among which the PI3K-Akt-mTOR pathway is of critical importance. Previous studies have demonstrated sex-specific roles for several components of this pathway. In the current study, we aimed to evaluate the role of Rheb, a member of the small GTPase superfamily and a critical component for mTORC1 activation, in male and female gametogenesis. The function of Rheb in development and the nervous system has been extensively studied, but little is known about its role in the germ line. We have exploited genetic approaches in the mouse to study the role of Rheb in the germ line and have identified an essential role in spermatogenesis. Conditional knockout (cKO) of Rheb in the male germ line resulted in severe oligoasthenoteratozoospermia and male sterility. More detailed phenotypic analyses uncovered an age-dependent meiotic progression defect combined with subsequent abnormalities in spermiogenesis as evidenced by abnormal sperm morphology. In the female, however, germ-cell specific inactivation of Rheb was not associated with any discernible abnormality; these cKO mice were fertile with morphologically unremarkable ovaries, normal primordial follicle formation, and subsequent follicle maturation. The absence of an abnormal ovarian phenotype is striking given previous studies demonstrating a critical role for the mTORC1 pathway in the maintenance of primordial follicle pool. In conclusion, our findings demonstrate an essential role of Rheb in diverse aspects of spermatogenesis but suggest the existence of functionally redundant factors that can compensate for Rheb deficiency within oocytes.

Expressions of miR-15a and its target gene HSPA1B in the spermatozoa of patients with varicocele

Hyperthermia and oxidative stresses are the two central elements contributing to varicocele-related sperm damage. Growing evidence indicates that microRNAs (miRNAs) are involved in the regulation of the heat and oxidative stress responses. In this study, we analyzed the expressions of several stress-related miRNAs in the sperm and found that the expression of miR-15a was significantly decreased in patients with varicocele compared with the control. Furthermore, miR-15a repressed the expression of HSPA1B, which is a typical stress-induced chaperone protein, through directly binding its 3'-UTR. The expressions of miR-15a and HSPA1B exhibited an inverse correlation in sperm. Our results provide a valuable insight into the varicocele-related sperm impairment and male infertility, and may help to develop potential therapeutic targets and novel biomarkers for male infertility.

Small RNAs in spermatogenesis

Spermatogenesis is characterized by meiotic divisions and major morphological changes to produce spermatozoa that are capable of independent movement and fertilization of an egg. Male germ cell differentiation is governed by orchestrated, phase-specific gene expression patterns that are tightly controlled at transcriptional and post-transcriptional level. Post-transcriptional regulation of protein-coding mRNAs becomes prominent during the late steps of spermatogenesis when the compacting sperm nucleus becomes transcriptionally inhibited. Small non-coding RNAs are important regulators of gene expression that mainly function post-transcriptionally to control the properties of their target mRNAs. Male germ cells express several classes of small RNAs, including Dicer-dependent microRNAs (miRNAs) and endogenous small interfering RNAs (endo-siRNAs), as well as Dicer-independent piwi-interacting RNAs (piRNAs). Increasing evidence supports the essential role of small RNA-mediated RNA regulation in normal spermatogenesis and male fertility.

Integrating microRNAs into the complexity of gonadotropin signaling networks

Follicle-stimulating hormone (FSH) is a master endocrine regulator of mammalian reproductive functions. Hence, it is used to stimulate folliculogenesis in assisted reproductive technologies (ART), both in women and in breeding animals. However, the side effects that hormone administration induces in some instances jeopardize the success of ART. Similarly, the luteinizing hormone (LH) is also of paramount importance in the reproductive function because it regulates steroidogenesis and the LH surge is a pre-requisite to ovulation. Gaining knowledge as extensive as possible on gonadotropin-induced biological responses could certainly lead to precise selection of their effects in vivo by the use of selective agonists at the hormone receptors. Hence, over the years, numerous groups have contributed to decipher the cellular events induced by FSH and LH in their gonadal target cells. Although little is known on the effect of gonadotropins on microRNA expression so far, recent data have highlighted that a microRNA regulatory network is likely to superimpose on the signaling protein network. No doubt that this will dramatically alter our current understanding of the gonadotropin-induced signaling networks. This is the topic of this review to present this additional level of complexity within the gonadotropin signaling network, in the context of recent findings on the microRNA machinery in the gonad.

"Breaking news" from spermatids

During the haploid phase of spermatogenesis, spermatids undergo a complex remodeling of the paternal genome involving the finely orchestrated replacement of histones by the highly-basic protamines. The associated striking change in DNA topology is characterized by a transient surge of both single- and double-stranded DNA breaks in the whole population of spermatids which are repaired before spermiation. These transient DNA breaks are now considered part of the normal differentiation program of these cells. Despite an increasing interest in the study of spermiogenesis in the last decade and the potential threat to the haploid genome, the origin of these DNA breaks still remains elusive. This review briefly outlines the current hypotheses regarding possible mechanisms that may lead to such transient DNA fragmentation including torsional stress, enzyme-induced breaks, apoptosis-like processes or oxidative stress. A better understanding of the origin of these DNA breaks will lead to further investigations on the genetic instability and mutagenic potential induced by the chromatin remodeling.

Dicer expression exhibits a tissue-specific diurnal pattern that is lost during aging and in diabetes

Dysregulation of circadian rhythmicity is identified as a key factor in disease pathogenesis. Circadian rhythmicity is controlled at both a transcriptional and post-transcriptional level suggesting the role of microRNA (miRNA) and double-stranded RNA (dsRNA) in this process. Endonuclease Dicer controls miRNA and dsRNA processing, however the role of Dicer in circadian regulation is not known. Here we demonstrate robust diurnal oscillations of Dicer expression in central and peripheral clock control systems including suprachiasmatic nucleolus (SCN), retina, liver, and bone marrow (BM). The Dicer oscillations were either reduced or phase shifted with aging and Type 2 diabetes. The decrease and phase shift of Dicer expression was associated with a similar decrease and phase shift of miRNAs 146a and 125a-5p and with an increase in toxic Alu RNA. Restoring Dicer levels and the diurnal patterns of Dicer-controlled miRNA and RNA expression may provide new therapeutic strategies for metabolic disease and aging-associated complications.

KIF3A is essential for sperm tail formation and manchette function

KIF3A motor protein is responsible for intraflagellar transport, which is required for protein delivery during axoneme formation in ciliated cells. The function of KIF3A during spermatogenesis is not known. In this study, we show that depletion of KIF3A causes severe impairments in sperm tail formation and interestingly, it also affects manchette organization and the shaping of sperm heads. Our results demonstrate the analogy between the mechanisms governing the formation of cilia in somatic cells and the formation of spermatozoa-specific flagella. Furthermore, this study reveals KIF3A as an important regulator of spermatogenesis and emphasizes the crucial role of KIF3A in maintaining male fertility. We also identified several novel interacting partners for KIF3A, including meiosis-specific nuclear structural protein 1 (MNS1) that colocalizes with KIF3A in the manchette and principal piece of the sperm tail. This study highlights the essential role of KIF3A-mediated microtubular transport in the development of spermatozoa and male fertility.

Epididymosomes convey different repertoires of microRNAs throughout the bovine epididymis

Epididymosomes are small membrane vesicles that are secreted by epididymal epithelial cells and are involved in posttesticular sperm maturation. Although their role in protein transfer to the sperm membrane is well documented, we report their capacity to transport microRNAs (miRNAs), which are potent regulators of posttranscriptional gene expression. Using a microperfusion technique combined with a global microarray approach, we demonstrated that epididymosomes from two discrete bovine epididymal regions (caput and cauda) possess distinct miRNA signatures. In addition, we also established that miRNA repertoires contained within epididymosomes differ from those of their parent epithelial cells, suggesting that miRNA populations released from the cells may be selectively sorted. Binding of DilC12-labeled epididymosomes to primary cultured epididymal cells was measured by flow cytometry, and the results indicated that epididymosomes from the median caput and their miRNA content may be incorporated into distal caput epithelial cells. Overall, these findings reveal that distinct miRNA repertoires are released into the intraluminal fluid in a region-specific manner and could be involved in a novel mechanism of intercellular communication throughout the epididymis via epididymosomes.

SOX9 regulates microRNA miR-202-5p/3p expression during mouse testis differentiation

MicroRNAs are important regulators of developmental gene expression, but their contribution to fetal gonad development is not well understood. We have identified the evolutionarily conserved gonadal microRNAs miR-202-5p and miR-202-3p as having a potential role in regulating mouse embryonic gonad differentiation. These microRNAs are expressed in a sexually dimorphic pattern as the primordial XY gonad differentiates into a testis, with strong expression in Sertoli cells. In vivo, ectopic expression of pri-miR-202 in XX gonads did not result in molecular changes to the ovarian determination pathway. Expression of the primary transcript of miR-202-5p/3p remained low in XY gonads in a conditional Sox9-null mouse model, suggesting that pri-miR-202 transcription is downstream of SOX9, a transcription factor that is both necessary and sufficient for male sex determination. We identified the pri-miR-202 promoter that is sufficient to drive expression in XY but not XX fetal gonads ex vivo. Mutation of SOX9 and SF1 binding sites reduced ex vivo transactivation of the pri-miR-202 promoter, demonstrating that pri-miR-202 may be a direct transcriptional target of SOX9/SF1 during testis differentiation. Our findings indicate that expression of the conserved gonad microRNA, miR-202-5p/3p, is downstream of the testis-determining factor SOX9, suggesting an early role in testis development.

Linking spermatid ribonucleic acid (RNA) binding protein and retrogene diversity to reproductive success

Spermiogenesis is a postmeiotic process that drives development of round spermatids into fully elongated spermatozoa. Spermatid elongation is largely controlled post-transcriptionally after global silencing of mRNA synthesis from the haploid genome. Here, rats that differentially express EGFP from a lentiviral transgene during early and late steps of spermiogenesis were used to flow sort fractions of round and elongating spermatids. Mass-spectral analysis of 2D gel protein spots enriched >3-fold in each fraction revealed a heterogeneous RNA binding proteome (hnRNPA2/b1, hnRNPA3, hnRPDL, hnRNPK, hnRNPL, hnRNPM, PABPC1, PABPC4, PCBP1, PCBP3, PTBP2, PSIP1, RGSL1, RUVBL2, SARNP2, TDRD6, TDRD7) abundantly expressed in round spermatids prior to their elongation. Notably, each protein within this ontology cluster regulates alternative splicing, sub-cellular transport, degradation and/or translational repression of mRNAs. In contrast, elongating spermatid fractions were enriched with glycolytic enzymes, redox enzymes and protein synthesis factors. Retrogene-encoded proteins were over-represented among the most abundant elongating spermatid factors identified. Consistent with these biochemical activities, plus corresponding histological profiles, the identified RNA processing factors are predicted to collectively drive post-transcriptional expression of an alternative exome that fuels finishing steps of sperm maturation and fitness.

The presence, role and clinical use of spermatozoal RNAs

BACKGROUND Spermatozoa are highly differentiated, transcriptionally inert cells characterized by a compact nucleus with minimal cytoplasm. Nevertheless they contain a suite of unique RNAs that are delivered to oocyte upon fertilization. They are likely integrated as part of many different processes including genome recognition, consolidation-confrontation, early embryonic development and epigenetic transgenerational inherence. Spermatozoal RNAs also provide a window into the developmental history of each sperm thereby providing biomarkers of fertility and pregnancy outcome which are being intensely studied. METHODS Literature searches were performed to review the majority of spermatozoal RNA studies that described potential functions and clinical applications with emphasis on Next-Generation Sequencing. Human, mouse, bovine and stallion were compared as their distribution and composition of spermatozoal RNAs, using these techniques, have been described. RESULTS Comparisons highlighted the complexity of the population of spermatozoal RNAs that comprises rRNA, mRNA and both large and small non-coding RNAs. RNA-seq analysis has revealed that only a fraction of the larger RNAs retain their structure. While rRNAs are the most abundant and are highly fragmented, ensuring a translationally quiescent state, other RNAs including some mRNAs retain their functional potential, thereby increasing the opportunity for regulatory interactions. Abundant small non-coding RNAs retained in spermatozoa include miRNAs and piRNAs. Some, like miR-34c are essential to the early embryo development required for the first cellular division. Others like the piRNAs are likely part of the genomic dance of confrontation and consolidation. Other non-coding spermatozoal RNAs include transposable elements, annotated lnc-RNAs, intronic retained elements, exonic elements, chromatin-associated RNAs, small-nuclear ILF3/NF30 associated RNAs, quiescent RNAs, mse-tRNAs and YRNAs. Some non-coding RNAs are known to act as epigenetic modifiers, inducing histone modifications and DNA methylation, perhaps playing a role in transgenerational epigenetic inherence. Transcript profiling holds considerable potential for the discovery of fertility biomarkers for both agriculture and human medicine. Comparing the differential RNA profiles of infertile and fertile individuals as well as assessing species similarities, should resolve the regulatory pathways contributing to male factor infertility. CONCLUSIONS Dad delivers a complex population of RNAs to the oocyte at fertilization that likely influences fertilization, embryo development, the phenotype of the offspring and possibly future generations. Development is continuing on the use of spermatozoal RNA profiles as phenotypic markers of male factor status for use as clinical diagnostics of the father's contribution to the birth of a healthy child.