The histone methyltransferase ESET is required for the survival of spermatogonial stem/progenitor cells in mice

Testis-specific knockout of Kdm2a reveals nonessential roles in male fertility but partially compromises spermatogenesis

Lysine-specific histone demethylase 2 (Kdm2a) is a regulatory factor of histone modifications that participates in gametogenesis and embryonic development. The mis-regulation of Kdm2a can lead to aberrant gene expression, thereby contributing to abnormal cell proliferation, differentiation, apoptosis, and tumorigenesis. However, due to the potential confounding effects that are secondary to the loss of Kdm2a function from the soma in existing whole-animal mutants, the in vivo function of Kdm2a in spermatogenesis for male fertility remains unknown. Herein, we focus on exploring the spatiotemporal expression profile and biological functions of Kdm2a in the spermatogenesis and fertility of male mice. A testis-specific knockout Kdm2a model (Kdm2a cKO) was established by using the Stra8-Cre/loxP recombinase system to explore the roles of Kdm2a in male fertility. Our results showed that Kdm2a was ubiquitously expressed and dynamically distributed in multiple tissues and cell types in the testis of mice. Surprisingly, Kdm2a-deficient adult males were completely fertile and comparable with their control (Kdm2aflox/flox) counterparts. Despite the significantly reduced total number of sperm and density of seminiferous tubules in Kdm2a cKO testis accompanied by the degeneration of spermatogenesis, the fertilization ability and embryonic developmental competence of the Kdm2a cKO were comparable with those of their control littermates, suggesting that Kdm2a disruption did not markedly affect male fertility, at least during younger ages. Furthermore, Kdm2a homozygous mutants exhibited a lower total number and motility of sperm than the control group and showed notably affected serum 17β-estradiol concentration. Interestingly, the transcriptome sequencing revealed that the loss of Kdm2a remarkably upregulated the expression level of Kdm2b. This effect, in turn, may induce compensative effects in the case of Kdm2a deficiency to maintain normal male reproduction. Together, our results reveal that Kdm2a shows spatiotemporal expression during testicular development and that its loss is insufficient to compromise the production of spermatozoa completely. The homologous Kdm2b gene might compensate for the loss of Kdm2a. Our work provides a novel Kdm2a cKO mouse allowing for the efficient deletion of Kdm2a in a testis-specific manner, and further investigated the biological function of Kdm2a and the compensatory effects of Kdm2b. Our study will advance our understanding of underlying mechanisms in spermatogenesis and male fertility.

The cytoplasmic fraction of the histone lysine methyltransferase Setdb1 is essential for embryonic stem cells

The major lysine methyltransferase (KMT) Setdb1 is essential for self-renewal and viability of mouse embryonic stem cells (mESCs). Setdb1 was primarily known to methylate the lysine 9 of histone 3 (H3K9) in the nucleus, where it regulates chromatin functions. However, Setdb1 is also massively localized in the cytoplasm, including in mESCs, where its role remains elusive. Here, we show that the cytoplasmic Setdb1 (cSetdb1) is essential for the survival of mESCs. Yeast two-hybrid analysis revealed that cSetdb1 interacts with several regulators of mRNA stability and protein translation machinery, such as the ESCs-specific E3 ubiquitin ligase and mRNA silencer Trim71/Lin41. We found that cSetdb1 is required for the integrity of Trim71 complex(es) involved in mRNA metabolism and translation. cSetdb1 modulates the abundance of mRNAs and the rate of newly synthesized proteins. Altogether, our data uncovered the cytoplasmic post-transcriptional regulation of gene expression mediated by a key epigenetic regulator.

Transcriptome-wide Dynamics of m6A mRNA Methylation During Porcine Spermatogenesis

Spermatogenesis is a continual process that occurs in the testes, in which diploid spermatogonial stem cells (SSCs) differentiate and generate haploid spermatozoa. This highly efficient and intricate process is orchestrated at multiple levels. N6-methyladenosine (m6A), an epigenetic modification prevalent in mRNAs, is implicated in the transcriptional regulation during spermatogenesis. However, the dynamics of m6A modification in non-rodent mammalian species remains unclear. Here, we systematically investigated the profile and role of m6A during spermatogenesis in pigs. By analyzing the transcriptomic distribution of m6A in spermatogonia, spermatocytes, and round spermatids, we identified a globally conserved m6A pattern between porcine and murine genes with spermatogenic function. We found that m6A was enriched in a group of genes that specifically encode the metabolic enzymes and regulators. In addition, transcriptomes in porcine male germ cells could be subjected to the m6A modification. Our data show that m6A plays the regulatory roles during spermatogenesis in pigs, which is similar to that in mice. Illustrations of this point are three genes (SETDB1, FOXO1, and FOXO3) that are crucial to the determination of the fate of SSCs. To the best of our knowledge, this study for the first time uncovers the expression profile and role of m6A during spermatogenesis in large animals and provides insights into the intricate transcriptional regulation underlying the lifelong male fertility in non-rodent mammalian species.

Developmental regulators moonlighting as transposons defense factors

BACKGROUND

The germline perpetuates genetic information across generations. To maintain the integrity of the germline, transposable elements in the genome must be silenced, as these mobile elements would otherwise engender widespread mutations passed on to subsequent generations. There are several well-established mechanisms that are dedicated to providing defense against transposable elements, including DNA methylation, RNA interference, and the PIWI-interacting RNA pathway.

OBJECTIVES

Recently, several studies have provided evidence that transposon defense is not only provided by factors dedicated to this purpose but also factors with other roles, including in germline development. Many of these are transcription factors. Our objective is to summarize what is known about these "bi-functional" transcriptional regulators.

MATERIALS AND METHODS

Literature search.

RESULTS AND CONCLUSION

We summarize the evidence that six transcriptional regulators-GLIS3, MYBL1, RB1, RHOX10, SETDB1, and ZBTB16-are both developmental regulators and transposable element-defense factors. These factors act at different stages of germ cell development, including in pro-spermatogonia, spermatogonial stem cells, and spermatocytes. Collectively, the data suggest a model in which specific key transcriptional regulators have acquired multiple functions over evolutionary time to influence developmental decisions and safeguard transgenerational genetic information. It remains to be determined whether their developmental roles were primordial and their transposon defense roles were co-opted, or vice versa.

Multi-Omics Approaches for Revealing the Epigenetic Regulation of Histone H3.1 during Spermatogonial Stem Cell Differentiation In Vitro

Epigenetic regulation, particularly post-translational modifications (PTMs) of histones, participates in spermatogonial stem cell (SSCs) differentiation. However, there is a lack of systemic studies of histone PTM regulation during the differentiation of SSCs due to its low number in vivo. Herein, we quantified dynamic changes of 46 different PTMs on histone H3.1 by targeted quantitative proteomics using mass spectrometry during SSCs differentiation in vitro, in combination with our RNA-seq data. We identified seven histone H3.1 modifications to be differentially regulated. In addition, we selected H3K9me2 and H3S10ph for subsequent biotinylated peptide pull-down experiments and identified 38 H3K9me2-binding proteins and 42 H3S10ph-binding proteins, which contain several transcription factors, such as GTF2E2 and SUPT5H, which appear to be crucial for epigenetic regulation of SSC differentiation.

METTL21A, a Non-Histone Methyltransferase, Is Dispensable for Spermatogenesis and Male Fertility in Mice

Protein methyltransferases play various physiological and pathological roles through methylating histone and non-histone targets. Many histone methyltransferases have been reported to regulate the development of spermatogenic cells. However, the specific function of non-histone methyltransferases during spermatogenesis remains unclear. In this study, we found that METTL21A, a non-histone methyltransferase, is highly expressed in mouse testes. In order to elucidate the role of METTL21A in spermatogenesis, we generated a Mettl21a global knockout mouse model using CRISPR/Cas9 technology. Unexpectedly, our results showed that knockout males are fertile without apparent defects in the processes of male germ cell development, including spermatogonial differentiation, meiosis, and sperm maturation. Furthermore, the ablation of METTL21A does not affect the expression and localization of its known targeting proteins in testes. Together, our data demonstrated that METTL21A is not essential for mouse spermatogenesis and male fertility.

SETDB1 Regulates Porcine Spermatogonial Adhesion and Proliferation through Modulating MMP3/10 Transcription

The transition from gonocytes into spermatogonia takes place during the homing process. A subpopulation of undifferentiated spermatogonia in niche then shifts to spermatogonial stem cells (SSCs), accompanied by the self-renewal ability to maintain life-long fertility in males. Enormous changes in cell morphology, gene expression, and epigenetic features have been reported during spermatogenesis. However, little is known about the difference of these features in SSCs during aging. Here, we examined the dynamics of SET domain bifurcated 1 (SETDB1) expression in porcine testes. SETDB1 was expressed in postnatal undifferentiated spermatogonia, while gradually disappeared after being packed within the basal compartment of seminiferous tubules. In addition, the cell-adhesion ability, proliferative activity, and trimethylation of the histone H3 lysine 9 (H3K9me3) level were significantly altered in SETDB1-deficient porcine SSCs. Moreover, the matrix metalloproteinases 3/10 (MMP3/10) was upregulated at both mRNA and protein levels. These results illustrate the significance of SETDB1 in modulating early male germ cell development.

Identifying regulators of parental imprinting by CRISPR/Cas9 screening in haploid human embryonic stem cells

In mammals, imprinted genes are regulated by differentially methylated regions (DMRs) that are inherited from germ cells, leading to monoallelic expression in accordance with parent-of-origin. Yet, it is largely unknown how imprinted DMRs are maintained in human embryos despite global DNA demethylation following fertilization. Here, we explored the mechanisms involved in imprinting regulation by employing human parthenogenetic embryonic stem cells (hpESCs), which lack paternal alleles. We show that although global loss of DNA methylation in hpESCs affects most imprinted DMRs, many paternally-expressed genes (PEGs) remain repressed. To search for factors regulating PEGs, we performed a genome-wide CRISPR/Cas9 screen in haploid hpESCs. This revealed ATF7IP as an essential repressor of a set of PEGs, which we further show is also required for silencing sperm-specific genes. Our study reinforces an important role for histone modifications in regulating imprinted genes and suggests a link between parental imprinting and germ cell identity.

Genetic imprinting ensures monoallelic gene expression critical for normal embryonic development. Here the authors take advantage of human haploid parthenogenic embryonic stem cells lacking paternal alleles to identify, by genome-wide screening, factors involved in the regulation of imprinted genes.

Mitochondrial Dynamics Markers and Related Signaling Molecules Are Important Regulators of Spermatozoa Number and Functionality

Here, we study possible mechanisms of (in/sub)fertility related to the acute or repeated psychological stresses (the most common stresses in human society) by following the transcriptional profile of 22 mitochondrial dynamics/function markers and 22 signaling molecules regulating both mitochondrial dynamics and spermatozoa number/functionality. An in vivo study mimicking acute (once for 3 h) and repeated (3 h for 10 consecutive days) psychophysical stress was performed on adult rats. The analysis of hormones, the number/functionality of spermatozoa, and 44 transcriptional markers were performed on individual samples from up to 12 animals per group. Results showed that both types of stress reduced spermatozoa functionality (acute by 4.4-fold, repeated by 3.3-fold) and ATP production (acute by 2.3-fold, repeated by 14.5-fold), while only repeated stress reduces the number of spermatozoa (1.9-fold). Stress significantly disturbed transcription of 34-out-of-44 markers (77%). Mitochondrial dynamics and functionality markers: 18-out-of-22 =>82% (mitochondrial-biogenesis-markers –>6-out-of-8 =>75%; mitochondrial-fusion-markers –>3-out-of-3 =>100%; mitochondrial-fission-markers –>1-out-of-2 =>50%; mitochondrial-autophagy-markers –>3-out-of-3 =>100%; mitochondrial-functionality-markers –>5-out-of-6 =>83%). Markers of signaling pathways regulating both mitochondrial dynamics/functionality and spermatozoa number/functionality important for male (in/sub)fertility –>16-out-of-22 =>73% (cAMP-signaling-markers –>8-out-of-12 =>67%; MAPK-signaling-markers –>8-out-of-10 =>80%). Accordingly, stress-triggered changes of transcriptional profile of mitochondrial dynamics/functionality markers as well as signaling molecules regulating both mitochondrial dynamics and spermatozoa number and functionality represent adaptive mechanisms.

The Histone Methyltransferase SETDB1 Modulates Survival of Spermatogonial Stem/Progenitor Cells Through NADPH Oxidase

SETDB1, a histone H3 lysine 9 (H3K9) methyltransferase, is crucial in meiosis and embryo development. This study aimed to investigate whether SETDB1 was associated with spermatogonial stem cells (SSC) homeostasis. We found that knockdown of Setdb1 impaired cell proliferation, led to an increase in reactive oxygen species (ROS) level through NADPH oxidase, and Setdb1 deficiency activated ROS downstream signaling pathways, including JNK and p38 MAPK, which possibly contributed to SSC apoptosis. Melatonin scavenged ROS and rescued the phenotype of Setdb1 KD. In addition, we demonstrated that SETDB1 regulated NADPH oxidase 4 (Nox4) and E2F1. Therefore, this study uncovers the new roles of SETDB1 in mediating intracellular ROS homeostasis for the survival of SSC.

Epigenetic Regulation of Spermatogonial Stem Cell Homeostasis: From DNA Methylation to Histone Modification

Spermatogonial stem cells(SSCs)are the ultimate germline stem cells with the potential of self-renewal and differentiation, and a dynamic balance of SSCs play an essential role in spermatogenesis. During the gene expression process, genomic DNA and nuclear protein, working together, contribute to SSC homeostasis. Recently, emerging studies have shown that epigenome-related molecules such as chromatin modifiers play an important role in SSC homeostasis through regulating target gene expression. Here, we focus on two types of epigenetic events, including DNA methylation and histone modification, and summarize their function in SSC homeostasis. Understanding the molecular mechanism during SSC homeostasis will promote the recognition of epigenetic biomarkers in male infertility, and bring light into therapies of infertile patients.Graphical Abstract.

SETDB1-Mediated Silencing of Retroelements

SETDB1 (SET domain bifurcated histone lysine methyltransferase 1) is a protein lysine methyltransferase and methylates histone H3 at lysine 9 (H3K9). Among other H3K9 methyltransferases, SETDB1 and SETDB1-mediated H3K9 trimethylation (H3K9me3) play pivotal roles for silencing of endogenous and exogenous retroelements, thus contributing to genome stability against retroelement transposition. Furthermore, SETDB1 is highly upregulated in various tumor cells. In this article, we describe recent advances about how SETDB1 activity is regulated, how SETDB1 represses various types of retroelements such as L1 and class I, II, and III endogenous retroviruses (ERVs) in concert with other epigenetic factors such as KAP1 and the HUSH complex and how SETDB1-mediated H3K9 methylation can be maintained during replication.

Histone Post-Translational Modifications and CircRNAs in Mouse and Human Spermatozoa: Potential Epigenetic Marks to Assess Human Sperm Quality

Spermatozoa (SPZ) are motile cells, characterized by a cargo of epigenetic information including histone post-translational modifications (histone PTMs) and non-coding RNAs. Specific histone PTMs are present in developing germ cells, with a key role in spermatogenic events such as self-renewal and commitment of spermatogonia (SPG), meiotic recombination, nuclear condensation in spermatids (SPT). Nuclear condensation is related to chromatin remodeling events and requires a massive histone-to-protamine exchange. After this event a small percentage of chromatin is condensed by histones and SPZ contain nucleoprotamines and a small fraction of nucleohistone chromatin carrying a landascape of histone PTMs. Circular RNAs (circRNAs), a new class of non-coding RNAs, characterized by a nonlinear back-spliced junction, able to play as microRNA (miRNA) sponges, protein scaffolds and translation templates, have been recently characterized in both human and mouse SPZ. Since their abundance in eukaryote tissues, it is challenging to deepen their biological function, especially in the field of reproduction. Here we review the critical role of histone PTMs in male germ cells and the profile of circRNAs in mouse and human SPZ. Furthermore, we discuss their suggested role as novel epigenetic biomarkers to assess sperm quality and improve artificial insemination procedure.

Distinct H3K9me3 and DNA methylation modifications during mouse spermatogenesis

DNA methylation and histone modifications critically regulate the expression of many genes and repeat regions during spermatogenesis. However, the molecular details of these processes in male germ cells remain to be addressed. Here, using isolated murine sperm cells, ultra-low-input native ChIP-Seq (ULI-NChIP-Seq), and whole genome bisulfite sequencing (WGBS), we investigated genome-wide DNA methylation patterns and histone 3 Lys-9 trimethylation (H3K9me3) modifications during mouse spermatogenesis. We found that DNA methylation and H3K9me3 have distinct sequence preferences and dynamics in promoters and repeat elements during spermatogenesis. H3K9me3 modifications in histones at gene promoters were highly enriched in round spermatids. H3K9me3 modification on long terminal repeats (LTRs) and long interspersed nuclear elements (LINEs) was involved in silencing active transcription from these regions in conjunction with reestablishment of DNA methylation. Furthermore, H3K9me3 remodeling on the X chromosome was involved in meiotic sex chromosome inactivation and in partial transcriptional reactivation of sex chromosomes in spermatids. Our findings also revealed the DNA methylation patterns and H3K9me3 modification profiles of paternal and maternal germline imprinting control regions (gICRs) during spermatogenesis. Taken together, our results provide a genome-wide map of H3K9me3 modifications during mouse spermatogenesis that may be helpful for understanding male reproductive disorders.

SETDB1 Links the Meiotic DNA Damage Response to Sex Chromosome Silencing in Mice

Meiotic synapsis and recombination ensure correct homologous segregation and genetic diversity. Asynapsed homologs are transcriptionally inactivated by meiotic silencing, which serves a surveillance function and in males drives meiotic sex chromosome inactivation. Silencing depends on the DNA damage response (DDR) network, but how DDR proteins engage repressive chromatin marks is unknown. We identify the histone H3-lysine-9 methyltransferase SETDB1 as the bridge linking the DDR to silencing in male mice. At the onset of silencing, X chromosome H3K9 trimethylation (H3K9me3) enrichment is downstream of DDR factors. Without Setdb1, the X chromosome accrues DDR proteins but not H3K9me3. Consequently, sex chromosome remodeling and silencing fail, causing germ cell apoptosis. Our data implicate TRIM28 in linking the DDR to SETDB1 and uncover additional factors with putative meiotic XY-silencing functions. Furthermore, we show that SETDB1 imposes timely expression of meiotic and post-meiotic genes. Setdb1 thus unites the DDR network, asynapsis, and meiotic chromosome silencing.

Noncoding RNAs: Potential players in the self-renewal of mammalian spermatogonial stem cells

Spermatogonial stem cells (SSCs), a unique population of male germ cells with self-renewal ability, are the foundation for maintenance of spermatogenesis throughout the life of the male. Although many regulatory molecules essential for SSC self-renewal have been identified, the fundamental mechanism underlying how SSCs acquire and maintain their self-renewal activity remains largely to be elucidated. In recent years, many types of noncoding RNAs (ncRNAs) have been suggested to regulate the SSC self-renewal through multiple ways, indicating ncRNAs play crucial roles in SSC self-renewal. In this paper, we mainly focus on four types of ncRNAs including microRNA, long ncRNA, piwi-interacting RNA, as well as circular RNAs, and reviewed their potential roles in SSC self-renewal that discovered recently to help us gain a better understanding of molecular mechanisms by which ncRNAs perform their function in regulating SSC self-renewal.

The histone methyltransferase SETD2 is required for expression of acrosin-binding protein 1 and protamines and essential for spermiogenesis in mice

Spermatogenesis is precisely controlled by complex gene expression programs and involves epigenetic reprogramming, including histone modification and DNA methylation. SET domain-containing 2 (SETD2) is the predominant histone methyltransferase catalyzing the trimethylation of histone H3 lysine 36 (H3K36me3) and plays key roles in embryonic stem cell differentiation and somatic cell development. However, its role in male germ cell development remains elusive. Here, we demonstrate an essential role of Setd2 for spermiogenesis, the final stage of spermatogenesis. Using RNA-seq, we found that, in postnatal mouse testes, Setd2 mRNA levels dramatically increase in 14-day-old mice. Using a germ cell-specific Setd2 knockout mouse model, we also found that targeted Setd2 knockout in germ cells causes aberrant spermiogenesis with acrosomal malformation before step 8 of the round-spermatid stage, resulting in complete infertility. Furthermore, we noted that the Setd2 deficiency results in complete loss of H3K36me3 and significantly decreases expression of thousands of genes, including those encoding acrosin-binding protein 1 (Acrbp1) and protamines, required for spermatogenesis. Our findings thus reveal a previously unappreciated role of the SETD2-dependent H3K36me3 modification in spermiogenesis and provide clues to the molecular mechanisms in epigenetic disorders underlying male infertility.

SETDB1 plays an essential role in maintenance of gonocyte survival in pigs

Histone methyltransferase SETDB1 suppresses gene expression and modulates heterochromatin formation through H3K9me2/3. Previous studies have revealed that SETDB1 catalyzes lysine 9 of histone H3 tri-methylation and plays essential roles in maintaining the survival of embryonic stem cells and spermatogonial stem cells in mice. However, the function of SETDB1 in porcine male germ cells remains unclear. The aim of the present study was to reveal the expression profile and function of SETDB1 in porcine germ cells. SETDB1 expression gradually increased during testis development. SETDB1 was strongly localized in gonocytes. Knockdown of SETDB1 gene expression led to gonocyte apoptosis and a decrease in H3K27me3, but no significant change in H3K9me3. These observations suggested that SETDB1 is a novel epigenetic regulator of porcine male germ cells, and contributes to the maintenance of gonocyte survival in pigs, probably due to the regulation of H3K27me3 rather than H3K9me3. These findings will provide a theoretical basis for the future study of epigenetic regulation of spermatogenesis.

Canonical Wnt signalling regulates nuclear export of Setdb1 during skeletal muscle terminal differentiation

The histone 3 lysine 9 methyltransferase Setdb1 is essential for both stem cell pluripotency and terminal differentiation of different cell types. To shed light on the roles of Setdb1 in these mutually exclusive processes, we used mouse skeletal myoblasts as a model of terminal differentiation. Ex vivo studies on isolated single myofibres showed that Setdb1 is required for adult muscle stem cells expansion following activation. In vitro studies in skeletal myoblasts confirmed that Setdb1 suppresses terminal differentiation. Genomic binding analyses showed a release of Setdb1 from selected target genes upon myoblast terminal differentiation, concomitant to a nuclear export of Setdb1 to the cytoplasm. Both genomic release and cytoplasmic Setdb1 relocalisation during differentiation were dependent on canonical Wnt signalling. Transcriptomic assays in myoblasts unravelled a significant overlap between Setdb1 and Wnt3a regulated genetic programmes. Together, our findings revealed Wnt-dependent subcellular relocalisation of Setdb1 as a novel mechanism regulating Setdb1 functions and myogenesis.

Spermatogonial stem cell autotransplantation and germline genomic editing: a future cure for spermatogenic failure and prevention of transmission of genomic diseases

BACKGROUND

Subfertility affects approximately 15% of all couples, and a severe male factor is identified in 17% of these couples. While the etiology of a severe male factor remains largely unknown, prior gonadotoxic treatment and genomic aberrations have been associated with this type of subfertility. Couples with a severe male factor can resort to ICSI, with either ejaculated spermatozoa (in case of oligozoospermia) or surgically retrieved testicular spermatozoa (in case of azoospermia) to generate their own biological children. Currently there is no direct treatment for azoospermia or oligozoospermia. Spermatogonial stem cell (SSC) autotransplantation (SSCT) is a promising novel clinical application currently under development to restore fertility in sterile childhood cancer survivors. Meanwhile, recent advances in genomic editing, especially the clustered regulatory interspaced short palindromic repeats-associated protein 9 (CRISPR-Cas9) system, are likely to enable genomic rectification of human SSCs in the near future.

OBJECTIVE AND RATIONALE

The objective of this review is to provide insights into the prospects of the potential clinical application of SSCT with or without genomic editing to cure spermatogenic failure and to prevent transmission of genetic diseases.

SEARCH METHODS

We performed a narrative review using the literature available on PubMed not restricted to any publishing year on topics of subfertility, fertility treatments, (molecular regulation of) spermatogenesis and SSCT, inherited (genetic) disorders, prenatal screening methods, genomic editing and germline editing. For germline editing, we focussed on the novel CRISPR-Cas9 system. We included papers written in English only.

OUTCOMES

Current techniques allow propagation of human SSCs in vitro, which is indispensable to successful transplantation. This technique is currently being developed in a preclinical setting for childhood cancer survivors who have stored a testis biopsy prior to cancer treatment. Similarly, SSCT could be used to restore fertility in sterile adult cancer survivors. In vitro propagation of SSCs might also be employed to enhance spermatogenesis in oligozoospermic men and in azoospermic men who still have functional SSCs albeit in insufficient numbers. The combination of SSCT with genomic editing techniques could potentially rectify defects in spermatogenesis caused by genomic mutations or, more broadly, prevent transmission of genomic diseases to the offspring. In spite of the promising prospects, SSCT and germline genomic editing are not yet clinically applicable and both techniques require optimization at various levels.

WIDER IMPLICATIONS

SSCT with or without genomic editing could potentially be used to restore fertility in cancer survivors to treat couples with a severe male factor and to prevent the paternal transmission of diseases. This will potentially allow these couples to have their own biological children. Technical development is progressing rapidly, and ethical reflection and societal debate on the use of SSCT with or without genomic editing is pressing.

Herp depletion arrests the S phase of the cell cycle and increases estradiol synthesis in mouse granulosa cells

The endoplasmic reticulum (ER) stress response has been implicated in the development, atresia and luteinization of ovarian follicles. However, there have been few reports concerning the role of Herp, an ER stress-induced protein, in follicular development. The present study aims to detect the distribution and cyclic variations of Herp during the estrous cycle and to reveal the roles of Herp in regulating the cell cycle, apoptosis and steroid hormone biosynthesis in mouse granulosa cells. In this study, immunohistochemistry staining showed that Herp expression was primarily in the granulosa cells and oocytes. Furthermore, we constructed recombinant lentiviral vectors for Herp short hairpin interfering RNA (shRNA) expression; immunofluorescence staining, real-time quantitative PCR (RT-qPCR) and western blot analysis revealed that Herp was successfully knocked down. Flow cytometry showed that knockdown of Herp arrested granulosa cells at the S phase of the cell cycle. More importantly, ELISA analysis revealed that Herp knockdown significantly upregulated the concentration of estradiol (E2) in the culture supernatants. RT-qPCR was performed to determine the regulatory mechanism of Herp knockdown in the cell cycle, and in steroid synthesis, RT-qPCR analysis revealed that Herp knockdown upregulated the mRNA expression of steroidogenic enzymes (Cyp19a1) and downregulated metabolic enzymes (Cyp1b1) and cell cycle factors (cyclin A1, cyclin B1 and cyclin D2). These results suggest that Herp may regulate the cell cycle and hormone secretions in mouse granulosa cells. The present study helps to elucidate the physiological functions of Herp as they relate to reproduction.

An efficient strategy for generation of transgenic mice by lentiviral transduction of male germline stem cells in vivo

Background

Male germline stem cells (MGSCs) are a subpopulation of germ cells in the testis tissue. MGSCs are capable of differentiation into spermatozoa and thus are perfect targets for genomic manipulation to generate transgenic animals.

Method

The present study was to optimize a protocol of production of transgenic mice through transduction of MGSCs in vivo using lentiviral-based vectors. The recombinant lentiviral vectors with either EF-1 or CMV promoter to drive the expression of enhanced green fluorescent protein (eGFP) transgene were injected into seminiferous tubules or inter-tubular space of 7-day-old and 28-day-old mouse testes. At 5 or 6 wk post-surgery, these pre-founders were mated with wild-type C57BL/6J female mice (1.5 to 2.0-month-old).

Results

Sixty-seven percent of F1 generation and 55.56 % of F2 offspring were positive for eGFP transgene under the control of EF-1 promoter via PCR analysis. The transgenic pups were generated in an injection site-and age-independent manner. The expression of transgene was displayed in the progeny derived from lentiviral vector containing CMV promoter to drive transgene, but it was silenced or undetectable in the offspring derived from lentiviral vector with transgene under EF-1 promoter. The methylation level of gDNA in the promoter region of transgene was much higher in the samples derived lentiviral vectors with EF-1 promoter than that with CMV promoter, suggesting eGFP transgene was suppressed by DNA methylation in vivo.

Conclusion

This research reported here an effective strategy for generation of transgenic mice through transduction of MGSCs in vivo using lentivirus vectors with specific promoters, and the transgenic offspring were obtained in an injection site-and age-independent manner. This protocol could be applied to other animal species, leading to advancement of animal transgenesis in agricultural and biomedical fields.

Electronic supplementary material

The online version of this article (doi:10.1186/s40104-015-0058-4) contains supplementary material, which is available to authorized users.

Knockout of the Histone Demethylase Kdm3b Decreases Spermatogenesis and Impairs Male Sexual Behaviors

Kdm3b is a JmjC domain-containing histone H3 (H3) demethylase and its physiological functions are largely unknown. In this study, we found that Kdm3b protein is highly expressed in multiple cell types in the mouse testes, including Leydig cells, Sertoli cells, spermatogonia and spermatocytes at different differentiation stages. We also observed Kdm3b protein in the epithelial cells of the caput epididymis, prostate and seminal vesicle. Breeding tests revealed that the number of pups produced by the breeding pairs with Kdm3b knockout (Kdm3bKO) males and wild type (WT) females was reduced 68% because of the decreased number of litters when compared with the breeding pairs with WT males and females. Further analysis demonstrated that Kdm3bKO male mice produced 44% fewer number of mature sperm in their cauda epididymides, displaying significantly reduced sperm motility. No significant differences in the circulating concentration of testosterone and the expression levels of androgen receptor and its representative target genes in the testis were observed. However, the circulating levels of 17β-estradiol, a modulator of sperm maturation and male sexual behaviors, was markedly reduced in Kdm3bKO male mice. Strikingly, abrogation of Kdm3b in male mice significantly increased the latencies to mount, intromit and ejaculate and decreased the number of mounts and intromissions, largely due to their loss of interest in female odors. These findings indicate that Kdm3b is required for normal spermatogenesis and sexual behaviors in male mice.

The histone methyltransferase SETDB1 represses endogenous and exogenous retroviruses in B lymphocytes

Genome stability relies on epigenetic mechanisms that enforce repression of endogenous retroviruses (ERVs). Current evidence suggests that distinct chromatin-based mechanisms repress ERVs in cells of embryonic origin (histone methylation dominant) vs. more differentiated cells (DNA methylation dominant). However, the latter aspect of this model has not been tested. Remarkably, and in contrast to the prevailing model, we find that repressive histone methylation catalyzed by the enzyme SETDB1 is critical for suppression of specific ERV families and exogenous retroviruses in committed B-lineage cells from adult mice. The profile of ERV activation in SETDB1-deficient B cells is distinct from that observed in corresponding embryonic tissues, despite the loss of repressive chromatin modifications at all ERVs. We provide evidence that, on loss of SETDB1, ERVs are activated in a lineage-specific manner depending on the set of transcription factors available to target proviral regulatory elements. These findings have important implications for genome stability in somatic cells, as well as the interface between epigenetic repression and viral latency.

Setdb1 is required for germline development and silencing of H3K9me3-marked endogenous retroviruses in primordial germ cells

Transcription of endogenous retroviruses is inhibited by de novo DNA methylation during gametogenesis, and DNA methylation reaches a low point in E13.5 primordial germ cells (PGCs) of both sexes. Liu et al. find that germline-specific conditional knockout of the H3K9 methyltransferase SETDB1 yields a decrease of H3K9me3 and H3K27me3 marks and DNA methylation at H3K9me3-enriched retrotransposon families. Setdb1 deficiency is associated with a reduced number of male E13.5 PGCs and postnatal hypogonadism in both sexes. Therefore, SETDB1 is an essential guardian against proviral expression prior to the onset of de novo DNA methylation in the germline.

Transcription of endogenous retroviruses (ERVs) is inhibited by de novo DNA methylation during gametogenesis, a process initiated after birth in oocytes and at approximately embryonic day 15.5 (E15.5) in prospermatogonia. Earlier in germline development, the genome, including most retrotransposons, is progressively demethylated. Young ERVK and ERV1 elements, however, retain intermediate methylation levels. As DNA methylation reaches a low point in E13.5 primordial germ cells (PGCs) of both sexes, we determined whether retrotransposons are marked by H3K9me3 and H3K27me3 using a recently developed low-input ChIP-seq (chromatin immunoprecipitation [ChIP] combined with deep sequencing) method. Although these repressive histone modifications are found predominantly on distinct genomic regions in E13.5 PGCs, they concurrently mark partially methylated long terminal repeats (LTRs) and LINE1 elements. Germline-specific conditional knockout of the H3K9 methyltransferase SETDB1 yields a decrease of both marks and DNA methylation at H3K9me3-enriched retrotransposon families. Strikingly, Setdb1 knockout E13.5 PGCs show concomitant derepression of many marked ERVs, including intracisternal A particle (IAP), ETn, and ERVK10C elements, and ERV-proximal genes, a subset in a sex-dependent manner. Furthermore, Setdb1 deficiency is associated with a reduced number of male E13.5 PGCs and postnatal hypogonadism in both sexes. Taken together, these observations reveal that SETDB1 is an essential guardian against proviral expression prior to the onset of de novo DNA methylation in the germline.

Construction and expression of lentiviral vectors encoding recombinant mouse CREBZF in NIH 3T3 cells

CREBZF, also known as Zhangfei or SMILE, is a member of the CREB/ATF protein family. CREBZF has mainly been considered as a basic region-leucine zipper transcription factor that functions in coordination with other transcription factors and plays a role in latent HSV-1 infection, apoptosis and the mammalian endoplasmic reticulum stress and unfolded protein response. In this study, we constructed recombinant lentiviral vectors for CREBZF short hairpin RNA (shRNA) expression and over-expression to improve understanding of the mechanisms regulating CREBZF. The CREBZF ORF sequence was cloned into the lentiviral shuttle plasmid pCD513B-1, and various shRNA oligonucleotides and one negative control (shN) were cloned into the pCD513B-U6 expression vector. The recombinant lentivirus was packaged and transduced into NIH 3T3 cells. CREBZF mRNA and protein expression were examined using real-time reverse transcription-polymerase chain reaction (RT-qPCR) and western blotting, respectively. The over-expression vector and the most effective shRNA vector significantly affected the expression of CREBZF mRNA and protein. Both of the CREBZF recombinant lentiviral vectors were successfully constructed. The over-expression vector significantly increased the expression of exogenous CREBZF and inhibited the growth of NIH 3T3 cells compared to controls. The most effective shRNA lentiviral vector, pCD513B-U6-CREBZF-shRNA-3, was transformed, leading to significant knockdown of the CREBZF gene. We conclude that CREBZF the recombinant lentiviral vectors are promising tools for regulating the expression of CREBZF in NIH 3T3 cells.