Gonadotropin-regulated testicular RNA helicase (GRTH/Ddx25) is essential for spermatid development and completion of spermatogenesis

DDX20 is required for cell-cycle reentry of prospermatogonia and establishment of spermatogonial stem cell pool during testicular development in mice

RNA-binding proteins (RBPs), as key regulators of mRNA fate, are abundantly expressed in the testis. However, RBPs associated with human male infertility remain largely unknown. Through bioinformatic analyses, we identified 62 such RBPs, including an evolutionarily conserved RBP, DEAD-box helicase 20 (DDX20). Male germ-cell-specific inactivation of Ddx20 at E15.5 caused T1-propsermatogonia (T1-ProSG) to fail to reenter cell cycle during the first week of testicular development in mice. Consequently, neither the foundational spermatogonial stem cell (SSC) pool nor progenitor spermatogonia were ever formed in the knockout testes. Mechanistically, DDX20 functions to control the translation of its target mRNAs, many of which encode cell-cycle-related regulators, by interacting with key components of the translational machinery in prospermatogonia. Our data demonstrate a previously unreported function of DDX20 as a translational regulator of critical cell-cycle-related genes, which is essential for cell-cycle reentry of T1-ProSG and formation of the SSC pool.

Decreased Ubiquitination and Acetylation of Histones 3 and 4 Are Associated with Obesity-Induced Disorders of Spermatogenesis in Mice

BACKGROUND

Obesity, a chronic metabolic disorder, is related to cardiovascular diseases, diabetes, cancer, and reproductive disorders. The relationship between obesity and male infertility is now well recognized, but the mechanisms involved are unclear. We aimed to observe the effect of obesity on spermatogenesis and to investigate the role of histone ubiquitination and acetylation modifications in obesity-induced spermatogenesis disorders.

METHODS

Thirty male C57BL/6J mice were randomly divided into two groups. The control group was fed with a general maintenance diet (12% fat), while a high-fat diet (HFD) group was fed with 40% fat for 10 weeks; then, they were mated with normal females. The fertility of male mice was calculated, testicular and sperm morphology were observed, and the expression levels of key genes and the levels of histone acetylation and ubiquitination modification during spermatogenesis were detected.

RESULTS

The number of sperm was decreased, as well as the sperm motility, while the number of sperm with malformations was increased. In the testes, the mRNA and protein expression levels of gonadotropin-regulated testicular RNA helicase (GRTH/DDX25), chromosome region maintenance-1 protein (CRM1), high-mobility group B2 (HMGB2), phosphoglycerate kinase 2 (PGK2), and testicular angiotensin-converting enzyme (tACE) were decreased. Furthermore, obesity led to a decrease in ubiquitinated H2A (ubH2A) and reduced levels of histone H3 acetylation K18 (H3AcK18) and histone H4 acetylation K5, K8, K12, and K16 (H4tetraAck), which disrupted protamine 1 (Prm1) deposition in testis tissue.

CONCLUSION

These results suggest that low levels of histone ubiquitination and acetylation are linked with obesity-induced disorders during spermatogenesis, contributing to a better understanding of obesity-induced damage to male reproduction.

P-body-like condensates in the germline

P-bodies are cytoplasmic condensates that accumulate low-translation mRNAs for temporary storage before translation or degradation. P-bodies have been best characterized in yeast and mammalian tissue culture cells. We describe here related condensates in the germline of animal models. Germline P-bodies have been reported at all stages of germline development from primordial germ cells to gametes. The activity of the universal germ cell fate regulator, Nanos, is linked to the mRNA decay function of P-bodies, and spatially-regulated condensation of P-body like condensates in embryos is required to localize mRNA regulators to primordial germ cells. In most cases, however, it is not known whether P-bodies represent functional compartments or non-functional condensation by-products that arise when ribonucleoprotein complexes saturate the cytoplasm. We speculate that the ubiquity of P-body-like condensates in germ cells reflects the strong reliance of the germline on cytoplasmic, rather than nuclear, mechanisms of gene regulation.

Identification of candidate genes for developmental colour agnosia in a single unique family

Colour agnosia is a disorder that impairs colour knowledge (naming, recognition) despite intact colour perception. Previously, we have identified the first and only-known family with hereditary developmental colour agnosia. The aim of the current study was to explore genomic regions and candidate genes that potentially cause this trait in this family. For three family members with developmental colour agnosia and three unaffected family members CGH-array analysis and exome sequencing was performed, and linkage analysis was carried out using DominantMapper, resulting in the identification of 19 cosegregating chromosomal regions. Whole exome sequencing resulted in 11 rare coding variants present in all affected family members with developmental colour agnosia and absent in unaffected members. These variants affected genes that have been implicated in neural processes and functions (CACNA2D4, DDX25, GRINA, MYO15A) or that have an indirect link to brain function, development or disease (MAML2, STAU1, TMED3, RABEPK), and a remaining group lacking brain expression or involved in non-neural traits (DEPDC7, OR1J1, OR8D4). Although this is an explorative study, the small set of candidate genes that could serve as a starting point for unravelling mechanisms of higher level cognitive functions and cortical specialization, and disorders therein such as developmental colour agnosia.

Single-cell RNA-seq uncovers dynamic processes orchestrated by RNA-binding protein DDX43 in chromatin remodeling during spermiogenesis

Mammalian spermatogenesis shows prominent chromatin and transcriptomic switches in germ cells, but it is unclear how such dynamics are controlled. Here we identify RNA helicase DDX43 as an essential regulator of the chromatin remodeling process during spermiogenesis. Testis-specific Ddx43 knockout mice show male infertility with defective histone-to-protamine replacement and post-meiotic chromatin condensation defects. The loss of its ATP hydrolysis activity by a missense mutation replicates the infertility phenotype in global Ddx43 knockout mice. Single-cell RNA sequencing analyses of germ cells depleted of Ddx43 or expressing the Ddx43 ATPase-dead mutant reveals that DDX43 regulates dynamic RNA regulatory processes that underlie spermatid chromatin remodeling and differentiation. Transcriptomic profiling focusing on early-stage spermatids combined with enhanced crosslinking immunoprecipitation and sequencing further identifies Elfn2 as DDX43-targeted hub gene. These findings illustrate an essential role for DDX43 in spermiogenesis and highlight the single-cell-based strategy to dissect cell-state-specific regulation of male germline development.

Regulation of Miwi-mediated mRNA stabilization by Ck137956/Tssa is essential for male fertility

BACKGROUND

Sperm is formed through spermiogenesis, a highly complex process involving chromatin condensation that results in cessation of transcription. mRNAs required for spermiogenesis are transcribed at earlier stages and translated in a delayed fashion during spermatid formation. However, it remains unknown that how these repressed mRNAs are stabilized.

RESULTS

Here we report a Miwi-interacting testis-specific and spermiogenic arrest protein, Ck137956, which we rename Tssa. Deletion of Tssa led to male sterility and absence of sperm formation. The spermiogenesis arrested at the round spermatid stage and numerous spermiogenic mRNAs were down-regulated in Tssa^-/- mice. Deletion of Tssa disrupted the localization of Miwi to chromatoid body, a specialized assembly of cytoplasmic messenger ribonucleoproteins (mRNPs) foci present in germ cells. We found that Tssa interacted with Miwi in repressed mRNPs and stabilized Miwi-interacting spermiogenesis-essential mRNAs.

CONCLUSIONS

Our findings indicate that Tssa is indispensable in male fertility and has critical roles in post-transcriptional regulations by interacting with Miwi during spermiogenesis.

DEAD-box ATPases as regulators of biomolecular condensates and membrane-less organelles

RNA-dependent DEAD-box ATPases (DDXs) are emerging as major regulators of RNA-containing membrane-less organelles (MLOs). On the one hand, oligomerizing DDXs can promote condensate formation 'in cis', often using RNA as a scaffold. On the other hand, DDXs can disrupt RNA-RNA and RNA-protein interactions and thereby 'in trans' remodel the multivalent interactions underlying MLO formation. In this review, we discuss the best studied examples of DDXs modulating MLOs in cis and in trans. Further, we illustrate how this contributes to the dynamic assembly and turnover of MLOs which might help cells to modulate RNA sequestration and processing in a temporal and spatial manner.

miRNA Expression Profiles of Mouse Round Spermatids in GRTH/DDX25-Mediated Spermiogenesis: mRNA-miRNA Network Analysis

GRTH/DDX25 is a testis-specific DEAD-box family of RNA helicase, which plays an essential role in spermatogenesis and male fertility. There are two forms of GRTH, a 56 kDa non-phosphorylated form and a 61 kDa phosphorylated form (pGRTH). GRTH-KO and GRTH Knock-In (KI) mice with R242H mutation (lack pGRTH) are sterile with a spermatogenic arrest at step 8 of spermiogenesis due to failure of round spermatids (RS) to elongate. We performed mRNA-seq and miRNA-seq analysis on RS of WT, KI, and KO to identify crucial microRNAs (miRNAs) and mRNAs during RS development by establishing a miRNA-mRNA network. We identified increased levels of miRNAs such as miR146, miR122a, miR26a, miR27a, miR150, miR196a, and miR328 that are relevant to spermatogenesis. mRNA-miRNA target analysis on these DE-miRNAs and DE-mRNAs revealed miRNA target genes involved in ubiquitination process (Ube2k, Rnf138, Spata3), RS differentiation, and chromatin remodeling/compaction (Tnp1/2, Prm1/2/3, Tssk3/6), reversible protein phosphorylation (Pim1, Hipk1, Csnk1g2, Prkcq, Ppp2r5a), and acrosome stability (Pdzd8). Post-transcriptional and translational regulation of some of these germ-cell-specific mRNAs by miRNA-regulated translation arrest and/or decay may lead to spermatogenic arrest in KO and KI mice. Our studies demonstrate the importance of pGRTH in the chromatin compaction and remodeling process, which mediates the differentiation of RS into elongated spermatids through miRNA-mRNA interactions.

Single-Cell Transcriptomic Profiling of the Mouse Testicular Germ Cells Reveals Important Role of Phosphorylated GRTH/DDX25 in Round Spermatid Differentiation and Acrosome Biogenesis during Spermiogenesis

Gonadotropin-regulated testicular RNA helicase (GRTH)/DDX25 is a member of DEAD-box family of RNA helicase essential for the completion of spermatogenesis and male fertility, as evident from GRTH-knockout (KO) mice. In germ cells of male mice, there are two species of GRTH, a 56 kDa non-phosphorylated form and 61 kDa phosphorylated form (pGRTH). GRTH Knock-In (KI) mice with R242H mutation abolished pGRTH and its absence leads to infertility. To understand the role of the GRTH in germ cell development at different stages during spermatogenesis, we performed single-cell RNA-seq analysis of testicular cells from adult WT, KO and KI mice and studied the dynamic changes in gene expression. Pseudotime analysis revealed a continuous developmental trajectory of germ cells from spermatogonia to elongated spermatids in WT mice, while in both KO and KI mice the trajectory was halted at round spermatid stage indicating incomplete spermatogenesis process. The transcriptional profiles of KO and KI mice were significantly altered during round spermatid development. Genes involved in spermatid differentiation, translation process and acrosome vesicle formation were significantly downregulated in the round spermatids of KO and KI mice. Ultrastructure of round spermatids of KO and KI mice revealed several abnormalities in acrosome formation that includes failure of pro-acrosome vesicles to fuse to form a single acrosome vesicle, and fragmentation of acrosome structure. Our findings highlight the crucial role of pGRTH in differentiation of round spermatids into elongated spermatids, acrosome biogenesis and its structural integrity.

Whole-exome sequencing improves the diagnosis and care of men with non-obstructive azoospermia

Non-obstructive azoospermia (NOA) is a severe and frequent cause of male infertility, often treated by testicular sperm extraction followed by intracytoplasmic sperm injection. The aim of this study is to improve the genetic diagnosis of NOA, by identifying new genes involved in human NOA and to better assess the chances of successful sperm extraction according to the individual's genotype. Exome sequencing was performed on 96 NOA-affected individuals negative for routine genetic tests. Bioinformatics analysis was limited to a panel of 151 genes selected as known causal or candidate genes for NOA. Only highly deleterious homozygous or hemizygous variants were retained as candidates. A likely causal defect was identified in 16 genes in a total of 22 individuals (23%). Six genes had not been described in man (DDX25, HENMT1, MCMDC2, MSH5, REC8, TDRKH) and 10 were previously reported (C14orf39, DMC1, FANCM, GCNA, HFM1, MCM8, MEIOB, PDHA2, TDRD9, TERB1). Seven individuals had defects in genes from piwi or DNA repair pathways, three in genes involved in post-meiotic maturation, and 12 in meiotic processes. Interestingly, all individuals with defects in meiotic genes had an unsuccessful sperm retrieval, indicating that genetic diagnosis prior to TESE could help identify individuals with low or null chances of successful sperm retrieval and thus avoid unsuccessful surgeries.

Chromatoid Bodies in the Regulation of Spermatogenesis: Novel Role of GRTH

Post-transcriptional and translational control of specialized genes play a critical role in the progression of spermatogenesis. During the early stages, mRNAs are actively transcribed and stored, temporarily bound to RNA binding proteins in chromatoid bodies (CBs). CBs are membrane-less dynamic organelles which serve as storehouses and processing centers of mRNAs awaiting translation during later stages of spermatogenesis. These CBs can also regulate the stability of mRNAs to secure the correct timing of protein expression at different stages of sperm formation. Gonadotropin-regulated testicular RNA helicase (GRTH/DDX25) is an essential regulator of spermatogenesis. GRTH transports mRNAs from the nucleus to the cytoplasm and phospho-GRTH transports mRNAs from the cytoplasm to the CBs. During spermiogenesis, there is precise control of mRNAs transported by GRTH from and to the CBs, directing the timing of translation of critical proteins which are involved in spermatid elongation and acrosomal development, resulting in functional sperm formation. This chapter presents our current knowledge on the role of GRTH, phospho-GRTH and CBs in the control of spermiogenesis. In addition, it covers the components of CBs compared to those of stress granules and P-bodies.

The Dynamic Regulation of mRNA Translation and Ribosome Biogenesis During Germ Cell Development and Reproductive Aging

The regulation of mRNA translation, both globally and at the level of individual transcripts, plays a central role in the development and function of germ cells across species. Genetic studies using flies, worms, zebrafish and mice have highlighted the importance of specific RNA binding proteins in driving various aspects of germ cell formation and function. Many of these mRNA binding proteins, including Pumilio, Nanos, Vasa and Dazl have been conserved through evolution, specifically mark germ cells, and carry out similar functions across species. These proteins typically influence mRNA translation by binding to specific elements within the 3′ untranslated region (UTR) of target messages. Emerging evidence indicates that the global regulation of mRNA translation also plays an important role in germ cell development. For example, ribosome biogenesis is often regulated in a stage specific manner during gametogenesis. Moreover, oocytes need to produce and store a sufficient number of ribosomes to support the development of the early embryo until the initiation of zygotic transcription. Accumulating evidence indicates that disruption of mRNA translation regulatory mechanisms likely contributes to infertility and reproductive aging in humans. These findings highlight the importance of gaining further insights into the mechanisms that control mRNA translation within germ cells. Future work in this area will likely have important impacts beyond germ cell biology.

Blockade of GRTH/DDX25 Phosphorylation by Cyclic Peptides Provides an Avenue for Developing a Nonhormonal Male Contraceptive

Gonadotropin-regulated testicular RNA helicase (GRTH)/DDX25 is a DEAD-box RNA helicase essential for the completion of spermatogenesis. Our previous studies indicated that blocking the GRTH phospho-site or perturbing the GRTH/protein kinase A (PKA) interface could provide an avenue for developing a nonhormonal male contraceptive. In this study, cyclic peptides were rationally designed and synthesized as promising therapeutic agents. The peptides showed effective delivery into COS-1 and germ cells and a dose-dependent inhibitory effect on GRTH phosphorylation. The peptides inhibit GRTH phosphorylation in the presence of PKA, and binding to the helicase resulted in thermal stabilization of non-phospho GRTH. Increased efficiency in fluorescence resonance energy transfer (FRET) assay revealed their interaction with GRTH. Cyclic peptide exposure of cultures from mice seminiferous tubules resulted in significant inhibition of phospho GRTH. These peptides did not exhibit toxicity. Effective delivery and targeted decrease of in vitro expression of phospho GRTH by cyclic peptides provide a promising angle to develop effective compounds as a nonhormonal male contraceptive.

Targeted knock-in mice with a human mutation in GRTH/DDX25 reveals the essential role of phosphorylated GRTH in spermatid development during spermatogenesis

Gonadotropin-regulated testicular RNA helicase (GRTH/DDX25) is a testis specific member of the DEAD-box family of RNA helicases expressed in meiotic and haploid germ cells which plays an essential role in spermatogenesis. There are two species of GRTH the 56 kDa non-phospho and 61 kDa phospho forms. Our early studies revealed a missense mutation (R242H) of GRTH in azoospermic men that when expressed in COS1-cells lack the phospho-form of GRTH. To investigate the role of the phospho-GRTH species in spermatogenesis, we generated a GRTH knock-in (KI) transgenic mice with the R242H mutation. GRTH-KI mice are sterile with reduced testis size, lack sperm with spermatogenic arrest at round spermatid stage and loss of the cytoplasmic phospho-GRTH species. Electron microscopy studies revealed reduction in the size of chromatoid bodies (CB) of round spermatids (RS) and germ cell apoptosis. We observed absence of phospho-GRTH in the CB of RS. Complete loss of chromatin remodeling and related proteins such as TP2, PRM2, TSSK6 and marked reduction of their respective mRNAs and half-lives were observed in GRTH-KI mice. We showed that phospho-GRTH has a role in TP2 translation and revealed its occurrence in a 3' UTR dependent manner. These findings demonstrate the relevance of phospho-GRTH in the structure of the chromatoid body, spermatid development and completion of spermatogenesis and provide an avenue for the development of a male contraceptive.

Maintenance DNA methylation in pre-meiotic germ cells regulates meiotic prophase by facilitating homologous chromosome pairing

Heterochromatin-related epigenetic mechanisms, such as DNA methylation, facilitate pairing of homologous chromosomes during the meiotic prophase of mammalian spermatogenesis. In pro-spermatogonia, de novo DNA methylation plays a key role in completing meiotic prophase and initiating meiotic division. However, the role of maintenance DNA methylation in the regulation of meiosis, especially in the adult, is not well understood. Here, we reveal that NP95 (also known as UHRF1) and DNMT1 - two essential proteins for maintenance DNA methylation - are co-expressed in spermatogonia and are necessary for meiosis in male germ cells. We find that Np95- or Dnmt1-deficient spermatocytes exhibit spermatogenic defects characterized by synaptic failure during meiotic prophase. In addition, assembly of pericentric heterochromatin clusters in early meiotic prophase, a phenomenon that is required for subsequent pairing of homologous chromosomes, is disrupted in both mutants. Based on these observations, we propose that DNA methylation, established in pre-meiotic spermatogonia, regulates synapsis of homologous chromosomes and, in turn, quality control of male germ cells. Maintenance DNA methylation, therefore, plays a role in ensuring faithful transmission of both genetic and epigenetic information to offspring.

Role of Phosphorylated Gonadotropin-Regulated Testicular RNA Helicase (GRTH/DDX25) in the Regulation of Germ Cell Specific mRNAs in Chromatoid Bodies During Spermatogenesis

GRTH/DDX25 is a member of the DEAD-box family of RNA helicases that play an essential role in spermatogenesis. GRTH knock-in (KI) mice with the human mutant GRTH gene (R242H) show loss of the phospho-species from cytoplasm with preservation of the non-phospho form in the cytoplasm and nucleus. GRTH KI mice are sterile and lack elongated spermatids and spermatozoa, with spermatogenic arrest at step 8 of round spermatids which contain chromatoid body (CB) markedly reduced in size. We observed an absence of phospho-GRTH in CB of GRTH KI mice. RNA-Seq analysis of mRNA isolated from CB revealed that 1,421 genes show differential abundance, of which 947 genes showed a decrease in abundance and 474 genes showed an increase in abundance in GRTH KI mice. The transcripts related to spermatid development, differentiation, and chromatin remodeling (Tnp1/2, Prm1/2/3, Spem1/2, Tssk 2/3/6, Grth, tAce, and Upf2) were reduced, and the transcripts encoding for factors involved in RNA transport, regulation, and surveillance and transcriptional and translational regulation (Eef1a1, Ppp1cc, Pabpc1, Ybx3, Tent5b, H2al1m, Dctn2, and Dync1h1) were increased in the CB of KI mice and were further validated by qPCR. In the round spermatids of wild-type mice, mRNAs of Tnp2, Prm2, and Grth were abundantly co-localized with MVH protein in the CB, while in GRTH KI mice these were minimally present. In addition, GRTH binding to Tnp1/2, Prm1/2, Grth, and Tssk6 mRNAs was found to be markedly decreased in KI. These results demonstrate the importance of phospho-GRTH in the maintenance of the structure of CB and its role in the storage and stability of germ cell-specific mRNAs during spermiogenesis.

Molecular genetics of infertility: loss-of-function mutations in humans and corresponding knockout/mutated mice

BACKGROUND

Infertility is a major issue in human reproductive health, affecting an estimated 15% of couples worldwide. Infertility can result from disorders of sex development (DSD) or from reproductive endocrine disorders (REDs) with onset in infancy, early childhood or adolescence. Male infertility, accounting for roughly half of all infertility cases, generally manifests as decreased sperm count (azoospermia or oligozoospermia), attenuated sperm motility (asthenozoospermia) or a higher proportion of morphologically abnormal sperm (teratozoospermia). Female infertility can be divided into several classical types, including, but not limited to, oocyte maturation arrest, premature ovarian insufficiency (POI), fertilization failure and early embryonic arrest. An estimated one half of infertility cases have a genetic component; however, most genetic causes of human infertility are currently uncharacterized. The advent of high-throughput sequencing technologies has greatly facilitated the identification of infertility-associated gene mutations in patients over the past 20 years.

OBJECTIVE AND RATIONALE

This review aims to conduct a narrative review of the genetic causes of human infertility. Loss-of-function mutation discoveries related to human infertility are summarized and further illustrated in tables. Corresponding knockout/mutated animal models of causative genes for infertility are also introduced.

SEARCH METHODS

A search of the PubMed database was performed to identify relevant studies published in English. The term 'mutation' was combined with a range of search terms related to the core focus of the review: infertility, DSD, REDs, azoospermia or oligozoospermia, asthenozoospermia, multiple morphological abnormalities of the sperm flagella (MMAF), primary ciliary dyskinesia (PCD), acephalic spermatozoa syndrome (ASS), globozoospermia, teratozoospermia, acrosome, oocyte maturation arrest, POI, zona pellucida, fertilization defects and early embryonic arrest.

OUTCOMES

Our search generated ∼2000 records. Overall, 350 articles were included in the final review. For genetic investigation of human infertility, the traditional candidate gene approach is proceeding slowly, whereas high-throughput sequencing technologies in larger cohorts of individuals is identifying an increasing number of causative genes linked to human infertility. This review provides a wide panel of gene mutations in several typical forms of human infertility, including DSD, REDs, male infertility (oligozoospermia, MMAF, PCD, ASS and globozoospermia) and female infertility (oocyte maturation arrest, POI, fertilization failure and early embryonic arrest). The causative genes, their identified mutations, mutation rate, studied population and their corresponding knockout/mutated mice of non-obstructive azoospermia, MMAF, ASS, globozoospermia, oocyte maturation arrest, POI, fertilization failure and early embryonic arrest are further illustrated by tables. In this review, we suggest that (i) our current knowledge of infertility is largely obtained from knockout mouse models; (ii) larger cohorts of clinical cases with distinct clinical characteristics need to be recruited in future studies; (iii) the whole picture of genetic causes of human infertility relies on both the identification of more mutations for distinct types of infertility and the integration of known mutation information; (iv) knockout/mutated animal models are needed to show whether the phenotypes of genetically altered animals are consistent with findings in human infertile patients carrying a deleterious mutation of the homologous gene; and (v) the molecular mechanisms underlying human infertility caused by pathogenic mutations are largely unclear in most current studies.

WILDER IMPLICATIONS

It is important to use our current understanding to identify avenues and priorities for future research in the field of genetic causes of infertility as well as to apply mutation knowledge to risk prediction, genetic diagnosis and potential treatment for human infertility.

The ubiquitination and acetylation of histones are associated with male reproductive disorders induced by chronic exposure to arsenite

Exposure to arsenic, which occurs via various routes, can cause reproductive toxicity. However, the mechanism for arsenic-induced reproductive disorders in male mice has not been extensively investigated. Here, 6-week-old male mice were dosed to 0, 5, 10, or 20 ppm sodium arsenite (NaAsO₂), an active form of arsenic, in drinking water for six months. For male mice exposed to arsenite, fertility was lower compared to control mice. Moreover, for exposed mice, there were lower sperm counts, lower sperm motility, and higher sperm malformation ratios. Further, the mRNA and protein levels of the gonadotropin-regulated testicular RNA helicase (DDX25) and chromosome region maintenance-1 protein (CRM1), along with proteins associated with high mobility group box 2 (HMGB2), phosphoglycerate kinase 2 (PGK2), and testicular angiotensin-converting enzyme (tACE) were lower. Furthermore, chronic exposure to arsenite led to lower H2A ubiquitination (ubH2A); histone H3 acetylation K18 (H3AcK18); and histone H4 acetylations K5, K8, K12, and K16 (H4tetraAck) in haploid spermatids from testicular tissues. These alterations disrupted deposition of protamine 1 (Prm1) in testes. Overall, the present results indicate that the ubiquitination and acetylation of histones is involved in the spermiogenesis disorders caused by chronic exposure to arsenite, which points to a previously unknown connection between the modification of histones and arsenite-induced male reproductive toxicity.

Critical roles of the ddx5 gene in zebrafish sex differentiation and oocyte maturation

DEAD-box helicase 5 (Ddx5) functions as an ATP-dependent RNA helicase and as a transcriptional coactivator for several transcription factors; however, the developmental function of the ddx5 gene in vertebrates is not fully understood. We found that the zebrafish ddx5 gene was expressed in developing gonads. Using the genome editing technology transcription activator-like effector nuclease, we established a ddx5-disrupted zebrafish and examined the morphological phenotypes of the mutant. We found that the majority of ddx5-deficient mutants developed as fertile males with normal testes and a small number of ddx5-deficient mutants developed as infertile females with small ovaries. Apoptotic cell death at 31 days post fertilization was increased in thick immature gonads (presumptive developing ovaries) of the ddx5-deficient mutant compared to those of heterozygous wild-type fish, while the number of apoptotic cells in thin immature gonads (presumptive developing testes) was comparable between the mutant and wild-type animals. Histological analysis revealed that ovaries of adult ddx5-deficient females had fewer vitellogenic oocytes and a larger number of stage I and II oocytes. The amount of cyclic adenosine monophosphate in the ddx5-deficient ovaries was high compared to that of wild-type ovaries, presumably leading to the mitotic arrest of oocyte maturation. Therefore, the ddx5 gene is dispensable for testis development, but it is essential for female sex differentiation and oocyte maturation in zebrafish.

ADAD1 and ADAD2, testis-specific adenosine deaminase domain-containing proteins, are required for male fertility

Adenosine-to-inosine RNA editing, a fundamental RNA modification, is regulated by adenosine deaminase (AD) domain containing proteins. Within the testis, RNA editing is catalyzed by ADARB1 and is regulated in a cell-type dependent manner. This study examined the role of two testis-specific AD domain proteins, ADAD1 and ADAD2, on testis RNA editing and male germ cell differentiation. ADAD1, previously shown to localize to round spermatids, and ADAD2 had distinct localization patterns with ADAD2 expressed predominantly in mid- to late-pachytene spermatocytes suggesting a role for both in meiotic and post-meiotic germ cell RNA editing. AD domain analysis showed the AD domain of both ADADs was likely catalytically inactive, similar to known negative regulators of RNA editing. To assess the impact of Adad mutation on male germ cell RNA editing, CRISPR-induced alleles of each were generated in mouse. Mutation of either Adad resulted in complete male sterility with Adad1 mutants displaying severe teratospermia and Adad2 mutant germ cells unable to progress beyond round spermatid. However, mutation of neither Adad1 nor Adad2 impacted RNA editing efficiency or site selection. Taken together, these results demonstrate ADAD1 and ADAD2 are essential regulators of male germ cell differentiation with molecular functions unrelated to A-to-I RNA editing.

Linking Phospho-Gonadotropin Regulated Testicular RNA Helicase (GRTH/DDX25) to Histone Ubiquitination and Acetylation Essential for Spermatid Development During Spermiogenesis

GRTH/DDX25 is a testicular RNA helicase expressed in germ cells that plays a crucial role in completion of spermatogenesis. Previously, we demonstrated a missense mutation (R242H) of GRTH gene in Japanese infertile patients (5.8%) with non-obstructive azoospermia. This mutation upon expression in COS-1 cells revealed absence of the 61 kDa phosphorylated GRTH in cytoplasm and the presence of the 56 kDa non-phosphorylated GRTH in the nucleus. GRTH knock-in (KI) mice carrying the human GRTH (R242H) mutation, lack phosphorylated GRTH, and sperm due to failure of round spermatid elongation during spermiogenesis. To determine the impact of phosphorylated GRTH on molecular events/pathways participating in spermatid development during spermiogenesis, we analyzed transcriptome profiles obtained from RNA-Seq of germ cells from KI and WT mice. RNA-Seq analysis of 2624 differentially expressed genes revealed 1404 down-regulated and 1220 up-regulated genes in KI mice. Genes relevant to spermatogenesis, spermatid development and spermatid differentiation were significantly down-regulated. KEGG enrichment analysis showed genes related to ubiquitin-mediated proteolysis and protein processing in endoplasmic reticulum pathway genes were significantly down-regulated while the up-regulated genes were found to be involved in Focal adhesion and ECM-receptor interaction pathways. Real-Time PCR analysis confirmed considerable reduction in transcripts of ubiquitination related genes Ube2j1, Ube2k, Ube2w, Rnf8, Rnf133, Rnf138, Cul3 and increased expression of Ccnd2, Col1a, Lamb1, Cav1, Igf1, Itga9 mRNA's in KI mice compared to WT. Also, marked reduction in protein expression of UBE2J1, RNF8, RNF138 (ubiquitination network), MOF (histone acetyltransferase), their modified Histone substrates (H2AUb, H2BUb) and H4Ac, H4K16Ac were observed in KI mice. GRTH-IP mRNA binding studies revealed that Rnf8 and Ube2J1 mRNAs from WT mice associated with GRTH protein and the binding is greatly impaired in the KI mice. Immunohistochemistry analysis showed significantly reduced expression of RNF8, MOF, H4Ac and H4K16Ac in round spermatids of KI mice. Absence of phosphorylated GRTH impairs UBE2J1, RNF8 and MOF-dependent histone ubiquitination and acetylation essential for histone replacement, chromatin condensation and spermatid elongation during spermiogenesis.

Identification of key genes associated with spermatogenesis arrest in fox hybrids using weighted gene co-expression network analysis

The silver fox and the blue fox represent different genera, but produce viable offspring. Although these hybrids show obvious heterosis, they are completely sterile due to spermatogenic arrest at the early stages of spermatogenesis, especially mitosis and meiosis I; the hybrids produce few spermatogonia and primary spermatocytes, and no secondary spermatocytes. Although the mechanisms of spermatogenic arrest have been well investigated, transcriptomic differences between hybrid and the pure-species testes have not clarified. In the present study, we used RNA sequencing (RNA-Seq) to generate testicular transcriptomic profiles for silver foxes, blue foxes, and reciprocal hybrids during the pre-breeding period and the breeding season. In total, 1,344,022 transcripts (≥200 bp) were generated; 1,057,724 genes were obtained; and 33,423 genes were shown to have fragments per kilobase of transcript per million mapped reads (FPKM) > 0.3. To identify the hub genes associated with spermatogenesis arrest, weighted gene co-expression network analysis (WGCNA) was used. Nine modules were explored. Genes in only a single module were consistently downregulated in the hybrids as compared to the pure species; these genes were significantly associated with fox hybrid male infertility. Six of the genes in this module (CATSPERD, DMRTC2, RNF17, NME5, SPEF2, SPINK2) also play key roles in mitosis and meiosis during spermatogenesis. Therefore, these six genes might be associated with fox hybrid male infertility.

Mitochondria Associated Germinal Structures in Spermatogenesis: piRNA Pathway Regulation and Beyond

Multiple specific granular structures are present in the cytoplasm of germ cells, termed nuage, which are electron-dense, non-membranous, close to mitochondria and/or nuclei, variant size yielding to different compartments harboring different components, including intermitochondrial cement (IMC), piP-body, and chromatoid body (CB). Since mitochondria exhibit different morphology and topographical arrangements to accommodate specific needs during spermatogenesis, the distribution of mitochondria-associated nuage is also dynamic. The most relevant nuage structure with mitochondria is IMC, also called pi-body, present in prospermatogonia, spermatogonia, and spermatocytes. IMC is primarily enriched with various Piwi-interacting RNA (piRNA) proteins and mainly functions as piRNA biogenesis, transposon silencing, mRNA translation, and mitochondria fusion. Importantly, our previous work reported that mitochondria-associated ER membranes (MAMs) are abundant in spermatogenic cells and contain many crucial proteins associated with the piRNA pathway. Provocatively, IMC functionally communicates with other nuage structures, such as piP-body, to perform its complex functions in spermatogenesis. Although little is known about the formation of both IMC and MAMs, its distinctive characters have attracted considerable attention. Here, we review the insights gained from studying the structural components of mitochondria-associated germinal structures, including IMC, CB, and MAMs, which are pivotal structures to ensure genome integrity and male fertility. We discuss the roles of the structural components in spermatogenesis and piRNA biogenesis, which provide new insights into mitochondria-associated germinal structures in germ cell development and male reproduction.

Arsenic influences spermatogenesis by disorganizing the elongation of spermatids in adult male mice

Arsenic (As) has become a major problem in maintaining the environment and human health due to its wide application in the production of agriculture and industry. Many studies indicate that As can affect spermatogenesis process and lower sperm quality. However, the undergoing molecular mechanism is unclear. For this, forty-eight 8-week old adult male mice were divided into four groups of twelve each, which were administrated to 0, 0.2, 2, 20 ppm As₂O₃ in their drinking water respectively for six months. The results showed that As treatment reduced sperm counts and increased the sperm malformation ratio of mice. Interestingly, both the amounts of round and elongated spermatids, and the ratios of spermatids elongation were decreased significantly by As exposure. Furthermore, the structure of Chromatoid Body (CB) which presents a typical nebulous shape in round spermatids after spermatogenesis arrested, and the mRNA expression levels of gene TDRD1, TDRD6 and TDRD7 related to CB were changed by arsenic. Again, the mRNA and protein expression levels of the markers DDX25 and CRM1 in haploid periods of spermatogenesis and the associated proteins HMG2, PGK2, and H4 with DDX25 regulation were declined significantly with As treatment. Taken together; it reveals that As interferes with spermatogenesis by disorganizing the elongation of spermatids. H4, HMG2 and PGK2 are regulated by DDX25 which interacts with CRM1 and may play a vital role in spermatogenesis disorder induced by As exposure, which maybe provides one of the underlying mechanisms for As-induced male reproductive toxicity.

Fluoride-induced unrestored arrest during haploid period of spermatogenesis via the regulation of DDX25 in rats

The effect of fluoride as an ongoing topic has attracted much attentions due to the decline in overall human fertility worldwide. However, whether fluorine causes a temporary stimulus or permanent damage to the male reproductive system, as well as the mechanism of fluoride influencing spermatogenesis remained unclear. 48 adult male rats were randomly divided into four groups (twelve each). Control group received the distilled water, while the other three groups were treated with 25, 50, 100 mg/L NaF via drinking water for 8 weeks. Six rats from each group were selected randomly to detect the levels of various indices related to spermatogenesis. The remaining rats were given only distilled water and left for recovery of a period of 2 weeks. Results showed that the levels of serum CK, ALP, CHE, BUN, UA, and Cr, testis morphology and the ultrastructure of sperm acrosome and chromatoid body (CB) were significantly changed by fluoride. Interestingly, the elongated spermatid counts, spermatids elongation ratio, and mRNA expressions of Prm1/2 and MIWI, TDRD1, TDRD 6, TDRD7, PABP, and Hsp72 related to CB decreased markedly in fluoride treatment groups compared to the control. Furthermore, the expression levels of DDX25 and associated regulatory proteins like CRM1, HMG2, H4, TP2, and PGK2 were down-regulated by fluoride. After 2-weeks withdrawal period, out of the 19 altered spermatogenesis indicators, 15 indicators in 100 mg/L group and 3 indicators in 50 mg/L group still exhibited a significant change, while none showed change in 25 mg/L group. These results proved that the reversibility of fluoride toxicity is dose-dependent on the male reproductive system. Meanwhile, fluoride caused unrestored arrest during the haploid period of spermatogenesis, where reduced DDX25 and associated regulatory proteins play a crucial role in this process, which could provide the underlying insights to the toxic mechanism of fluoride induced male reproductive toxicity.

Characterization of the Phosphorylation Site of GRTH/DDX25 and Protein Kinase A Binding Interface Provides Structural Basis for the Design of a Non-Hormonal Male Contraceptive

Gonadotropin Regulated Testicular Helicase (GRTH/DDX25), expressed in the male gonad, is essential for the completion of spermatogenesis. Our early studies revealed a missense mutation (R242H) of GRTH in 5.8% of Japanese patient population with azoospermia. Transfection of the mutant GRTH construct in COS-1 cells leads to loss of the 61 kDa cytoplasmic phospho-species. Mice with knock-in of the human GRTH mutation are sterile and lack sperm with normal androgen and mating behavior. These findings provide an avenue for the development of a non-hormonal male contraceptive. Using site directed mutagenesis and a site-specific phospho-antibody, we have identified T239, structurally adjacent to the patient’s mutant site as the GRTH phospho-site. Molecular modelling provided structural basis for the role of R242 and other critical solvent-exposed residues at the GRTH/PKA interface (E165/K240/D237), on the control of GRTH phosphorylation at T239. Single or double mutations of these residues caused marked reduction or abolition of the phospho-form. These effects can be ascribed to critical disruptions of intramolecular H-bonds at the GRTH/PKA interface, which leads to modest but consequential structural changes that can affect PKA catalytic efficiency. Inhibition of phosphorylation may be achieved by small, drug-like molecules that bind to GRTH and reconfigure the GRTH/PKA interface.

Gonadotropin Regulation Testicular RNA Helicase, Two Decades of Studies on Its Structure Function and Regulation From Its Discovery Opens a Window for Development of a Non-hormonal Oral Male Contraceptive

Gonadotropin Regulated Testicular Helicase (GRTH/DDX25) is member of the DEAD-box family of RNA helicases present in Leydig and germ cells. GRTH is the only family member regulated by hormones, luteinizing hormone, through androgen action. Male mice with knock-out of the GRTH gene are sterile, lack sperm with arrest at round spermatids. GRTH participates on the nuclear export and transport of specific mRNAs, the structural integrity of Chromatoid Bodies of round spermatids, where mRNAs are processed and stored, and in their transit to polyribosomes, where it may regulate translation of relevant genes. GRTH has a central role in the control of germ cell apoptosis and acts as negative regulator of miRNAs which regulate expression of genes involved in the progress of spermatogenesis. In Leydig cells, GRTH gene transcription is regulated by LH via autocrine actions of androgen/androgen receptor and has regulatory effects in steroidogenesis. In germ cells, androgen actions are indirect via receptors in Sertoli cells. Transgenic mice carrying GRTH 5' flanking region-GFP permitted to discern regions in the gene which directs its expression upstream, in germ cells, and downstream in Leydig cells, and the androgen-regulated transcription at interstitial (autocrine), and germ cell (paracrine) compartments. Further evidence for paracrine actions of androgen/androgen receptor is their transcriptional induction of Germ Cell Nuclear Factor as requisite up-regulator of GRTH gene transcription in round spermatids, linking androgen action to two relevant germ cell genes essential for the progress of spermatogenesis. A missense mutation of R to H at amino acid 242 of GRTH found in 5.8% of a patient population with azoospermia causes loss of the cytoplasmic phospho-GRTH species with preservation of the non-phospho form in transfected cells. Mice with knock-in of the human mutation, lack sperm due to arrest at round spermatids. This model permits to discern the function of phospho-GRTH. The GRTH phospho-site resides at a Threonine structurally adjacent to the mutant site found in patients. Molecular modeling of this site elucidated the amino acids that form the GRTH/PKA interphase and provide the basis for drug design for use as male contraceptive.

The transcription factor SOX30 is a key regulator of mouse spermiogenesis

The postmeiotic development of male germ cells, also known as spermiogenesis, features the coordinated expression of a large number of spermatid-specific genes. However, only a limited number of key transcription factors have been identified and the underlying regulatory mechanisms remain largely unknown. Here, we report that SOX30, the most-divergent member of the Sry-related high-motility group box (SOX) family of transcription factors, is essential for mouse spermiogenesis. The SOX30 protein was predominantly expressed in spermatids, while its transcription was regulated by retinoic acid and by MYBL1 before and during meiosis. Sox30 knockout mice arrested spermiogenesis at step 3 round spermatids, which underwent apoptosis and abnormal chromocenter formation. We also determined that SOX30 regulated the expression of hundreds of spermatid-specific protein-coding and long non-coding RNA genes. SOX30 bound to the proximal promoter of its own gene and activated its transcription. These results reveal SOX30 as a novel key regulator of spermiogenesis that regulates its own transcription to enforce and activate this meiotic regulatory pathway.

PL10 DEAD-Box Protein is Expressed during Germ Cell Differentiation in the Reptile Podarcis sicula (Family Lacertidae)

Among genes involved in the regulation of germ cell differentiation, those of DDX4/Vasa and the Ded1/DDX3 subfamilies encode for DEAD-box ATP-dependent RNA helicases, proteins involved in many mechanisms related to RNA processing. For the first time in reptiles, using specific antibodies at confocal microscopy, we analysed the localization pattern of a Ded1/DDX3 subfamily member in testis and ovary of Podarcis sicula (Ps-PL10) during the reproductive cycle. In testis, Ps-PL10 is expressed in the cytoplasm of spermatocytes and it is not detected in spermatogonia. Differently from Ps-VASA, in round spermatids, Ps-PL10 is not segregated in the chromatoid body but it accumulates in the cytoplasm of residual bodies, and mature spermatozoa are unstained. These observations suggest that in males, Ps-PL10 (1) is involved in spermatogenesis and (2) is then eliminated with residual bodies. In the ovary, Ps-PL10 is present with granules in the cytoplasm of early meiotic cells of the germinal bed (GB), while it is not present in oogonia and somatic cells of the GB stroma. In follicular cells of ovarian follicles, Ps-PL10 expression starts after their fusion with the oocyte. Numerous Ps-PL10 spots are visible in pyriform (nurse-like) cells concomitantly with the protein accumulation in the cytoplasm of differentiating oocyte. In pyriform cells, Ps-PL10 spots are present in the cytoplasm and nuclei, as observed for Ps-VASA, and in the nucleoli, suggesting for Ps-PL10 a role in rRNA processing and in the transport of molecules from the nucleus to cytoplasm and from nurse cells to the oocyte.

Germ granule-mediated RNA regulation in male germ cells

Germ cells have exceptionally diverse transcriptomes. Furthermore, the progress of spermatogenesis is accompanied by dramatic changes in gene expression patterns, the most drastic of them being near-to-complete transcriptional silencing during the final steps of differentiation. Therefore, accurate RNA regulatory mechanisms are critical for normal spermatogenesis. Cytoplasmic germ cell-specific ribonucleoprotein (RNP) granules, known as germ granules, participate in posttranscriptional regulation in developing male germ cells. Particularly, germ granules provide platforms for the PIWI-interacting RNA (piRNA) pathway and appear to be involved both in piRNA biogenesis and piRNA-targeted RNA degradation. Recently, other RNA regulatory mechanisms, such as the nonsense-mediated mRNA decay pathway have also been associated to germ granules providing new exciting insights into the function of germ granules. In this review article, we will summarize our current knowledge on the role of germ granules in the control of mammalian male germ cell's transcriptome and in the maintenance of fertility.

Differential regulation of spermatogenic process by Lkb1 isoforms in mouse testis

Liver serine/threonine kinase B1 (LKB1) is a tumor suppressor associated with the pathogenesis of Peutz-Jeghers syndrome. Affected males are at increased risk of developing Sertoli cell tumors and display defective spermatogenesis. Male mice lacking the short isoform (Lkb1_S) of Lkb1 were sterile and exhibited abnormal spermiogenesis. In addition to the short isoform, the long isoform of Lkb1 (Lkb1_L) is also expressed in testis; however, the requirement of the long isoform for fertility and the functional difference between the isoforms remain unknown. Herein, different from the spermiation failure reported in Lkb1_S knockout mice, conditional deletion (cKO) of both isoforms of Lkb1 in germ cells resulted in male sterility stemming from defects in acrosome formation, as well as nuclear elongation and condensation during spermatid differentiation. Additionally, cKO mice showed a progressive germ cell loss that was never reported in mice with Lkb1_S deletion. Further experiments revealed that the defect resulted from the failure of spermatogonial stem/progenitor cells (SPCs) maintenance. Although increased mTORC1 activity in postnatal cKO testes was consistent with a tendency toward germline stem cell differentiation, in vivo inhibition of the pathway by rapamycin treatment failed to rescue the phenotype. Concurrently, we detected a significant reduction of mitochondrial activity in Lkb1deficient SPCs. The results suggest that the regulation of LKB1 on SPCs' maintenance is associated with mitochondrial functions but not through the mTOR signaling pathway. In summary, our study supports different roles of Lkb1 isoforms in spermatogenesis with Lkb1_L directing SPCs maintenance, and Lkb1_L and Lkb1_S coordinately regulating spermatid differentiation.

Characterization of mechanisms underlying degradation of sclerotia of Sclerotinia sclerotiorum by Aspergillus aculeatus Asp-4 using a combined qRT-PCR and proteomic approach

Background

The biological control agent Aspergillus aculeatus Asp-4 colonizes and degrades sclerotia of Sclerotinia sclerotiorum resulting in reduced germination and disease caused by this important plant pathogen. Molecular mechanisms of mycoparasites underlying colonization, degradation, and reduction of germination of sclerotia of this and other important plant pathogens remain poorly understood.

Results

An RNA-Seq screen of Asp-4 growing on autoclaved, ground sclerotia of S. sclerotiorum for 48 h identified 997 up-regulated and 777 down-regulated genes relative to this mycoparasite growing on potato dextrose agar (PDA) for 48 h. qRT-PCR time course experiments characterized expression dynamics of select genes encoding enzymes functioning in degradation of sclerotial components and management of environmental conditions, including environmental stress. This analysis suggested co-temporal up-regulation of genes functioning in these two processes. Proteomic analysis of Asp-4 growing on this sclerotial material for 48 h identified 26 up-regulated and 6 down-regulated proteins relative to the PDA control. Certain proteins with increased abundance had putative functions in degradation of polymeric components of sclerotia and the mitigation of environmental stress.

Conclusions

Our results suggest co-temporal up-regulation of genes involved in degradation of sclerotial compounds and mitigation of environmental stress. This study furthers the analysis of mycoparasitism of sclerotial pathogens by providing the basis for molecular characterization of a previously uncharacterized mycoparasite-sclerotial interaction.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-4016-8) contains supplementary material, which is available to authorized users.

DEAD-Box Helicase DDX25 Is a Negative Regulator of Type I Interferon Pathway and Facilitates RNA Virus Infection

Dengue is a mosquito-borne viral disease that rapidly spread in tropic and subtropic area in recent years. DEAD (Glu-Asp-Ala-Glu)-box RNA helicases have been reported to play important roles in viral infection, either as cytosolic sensors of viral nucleic acids or as essential host factors for the replication of different viruses. In this study, we reported that DDX25, a DEAD-box RNA helicase, plays a proviral role in DENV infection. The expression levels of DDX25 mRNA and protein were upregulated in DENV infected cells. During DENV infection, the intracellular viral loads were significantly lower in DDX25 silenced cells and higher in DDX25 overexpressed cells. Meanwhile, the expression level of type I interferon (IFN) was increased in DDX25 siRNA treated cells during viral infection. Consistent with the in vitro findings, the Ddx25-transgenic mice have an increased susceptibility to lethal vesicular stomatitis virus (VSV) virus challenge. The viremia was significantly higher while the anti-viral cytokine levels were lower in Ddx25-transgenic mice. Further, DDX25 modulated RIG-I signaling pathway and blocked IFNβ production, by interrupting IFN regulatory factor 3 (IRF3) and NFκB activation. Thus, DDX25 is a novel negative regulator of IFN pathway and facilitates RNA virus infection.

NRF1 coordinates with DNA methylation to regulate spermatogenesis

Spermatogenesis is a highly coordinated process that requires tightly regulated gene expression programmed by transcription factors and epigenetic modifiers. In this study, we found that nuclear respiratory factor (NRF)-1, a key transcription factor for mitochondrial biogenesis, cooperated with DNA methylation to directly regulate the expression of multiple germ cell-specific genes, including Asz1 In addition, conditional ablation of NRF1 in gonocytes dramatically down-regulated these germline genes, blocked germ cell proliferation, and subsequently led to male infertility in mice. Our data highlight a precise crosstalk between transcriptional regulation by NRF1 and epigenetic modulation during germ cell development and unequivocally demonstrate a novel role of NRF1 in spermatogenesis.-Wang, J., Tang, C., Wang, Q., Su, J., Ni, T., Yang, W., Wang, Y., Chen, W., Liu, X., Wang, S., Zhang, J., Song, H., Zhu, J., Wang, Y. NRF1 coordinates with DNA methylation to regulate spermatogenesis.

Synthesis of β-tubulin occurs within chromatoid body of round spermatids

mRNAs for proteins required in elongated spermatids are considered to be transcribed at an early stage and stored in cytoplasm, presumably in chromatoid body (CB), one type of nuage component (a unique structure that appears and disappears during spermatogenesis), because transcription of genes does not occur at late stages. In elongated spermatids, a large amount of tubulin molecules is required to form microtubules of manchette and flagellum. To investigate the possible role of CB in translation of tubulin mRNA, we performed immunofluorescence and immunoelectron microscopic localization studies of α- and β-tubulin in rat spermatogenic cells. β-tubulin was detected in CB, but α-tubulin was not. Other nuage components present in pachytene spermatocytes (ISPG, IMC, SB) were negative for both α- and β-tubulin. Our findings suggest that: (i) β-tubulin in round spermatids is translated within the CB, whereas α-tubulin is not; (ii) αβ-heterodimers are formed outside CB and incorporated into microtubules of manchette and flagellum.

Prorenin receptor controls renal branching morphogenesis via Wnt/β-catenin signaling

The prorenin receptor (PRR) is a receptor for renin and prorenin, and an accessory subunit of the vacuolar proton pump H⁺-ATPase. Renal branching morphogenesis, defined as growth and branching of the ureteric bud (UB), is essential for mammalian kidney development. Previously, we demonstrated that conditional ablation of the PRR in the UB in PRR^UB-/- mice causes severe defects in UB branching, resulting in marked kidney hypoplasia at birth. Here, we investigated the UB transcriptome using whole genome-based analysis of gene expression in UB cells, FACS-isolated from PRR^UB-/-, and control kidneys at birth (P0) to determine the primary role of the PRR in terminal differentiation and growth of UB-derived collecting ducts. Three genes with expression in UB cells that previously shown to regulate UB branching morphogenesis, including Wnt9b, β-catenin, and Fgfr2, were upregulated, whereas the expression of Wnt11, Bmp7, Etv4, and Gfrα1 was downregulated. We next demonstrated that infection of immortalized UB cells with shPRR in vitro or deletion of the UB PRR in double-transgenic PRR^UB-/-/BatGal⁺ mice, a reporter strain for β-catenin transcriptional activity, in vivo increases β-catenin activity in the UB epithelia. In addition to UB morphogenetic genes, the functional groups of differentially expressed genes within the downregulated gene set included genes involved in molecular transport, metabolic disease, amino acid metabolism, and energy production. Together, these data demonstrate that UB PRR performs essential functions during UB branching and collecting duct morphogenesis via control of a hierarchy of genes that control UB branching and terminal differentiation of the collecting duct cells.

Position-dependent interactions of Y-box protein 2 (YBX2) with mRNA enable mRNA storage in round spermatids by repressing mRNA translation and blocking translation-dependent mRNA decay

Many mRNAs encoding proteins needed for the construction of the specialized organelles of spermatozoa are stored as translationally repressed, free messenger ribonucleoproteins in round spermatids, to be actively translated in elongating and elongated spermatids. The factors that repress translation in round spermatids, however, have been elusive. Two lines of evidence implicate the highly abundant and well-known translational repressor, Y-box protein 2 (YBX2), as a critical factor: First, protamine 1 (Prm1) and sperm-mitochondria cysteine-rich protein (Smcp) mRNAs are prematurely recruited onto polysomes in Ybx2-knockout mouse round spermatids. Second, mutations in 3' untranslated region (3'UTR) cis-elements that abrogate YBX2 binding activate translation of Prm1 and Smcp mRNAs in round spermatids of transgenic mice. The abundance of YBX2 and its affinity for variable sequences, however, raise questions of how YBX2 targets specific mRNAs for repression. Mutations to the Prm1 and Smcp mRNAs in transgenic mice reveal that strong repression in round spermatids requires YBX2 binding sites located near the 3' ends of their 3'UTRs as locating the same sites in upstream positions produce negligible repression. This location-dependence implies that the assembly of repressive complexes is nucleated by adjacent cis-elements that enable cooperative interactions of YBX2 with co-factors. The available data suggest that, in vertebrates, YBX2 has the important role of coordinating the storage of translationally repressed mRNAs in round spermatids by inhibiting translational activity and the degradation of transcripts via translation-dependent deadenylation. These insights should facilitiate future experiments designed to unravel how YBX2 targets mRNAs for repression in round spermatids and how mutations in the YBX2 gene cause infertility in humans. Mol. Reprod. Dev. 83: 190-207, 2016. © 2016 Wiley Periodicals, Inc.

Transcription Factor RFX2 Is a Key Regulator of Mouse Spermiogenesis

The regulatory factor X (RFX) family of transcription factors is crucial for ciliogenesis throughout evolution. In mice, Rfx1-4 are highly expressed in the testis where flagellated sperm are produced, but the functions of these factors in spermatogenesis remain unknown. Here, we report the production and characterization of the Rfx2 knockout mice. The male knockout mice were sterile due to the arrest of spermatogenesis at an early round spermatid step. The Rfx2-null round spermatids detached from the seminiferous tubules, forming large multinucleated giant cells that underwent apoptosis. In the mutants, formation of the flagellum was inhibited at its earliest stage. RNA-seq analysis identified a large number of cilia-related genes and testis-specific genes that were regulated by RFX2. Many of these genes were direct targets of RFX2, as revealed by chromatin immunoprecipitation-PCR assays. These findings indicate that RFX2 is a key regulator of the post-meiotic development of mouse spermatogenic cells.

RNA-binding proteins in mouse male germline stem cells: a mammalian perspective

Adult stem cells that reside in particular types of tissues are responsible for tissue homeostasis and regeneration. Cellular functions of adult stem cells are intricately related to the gene expression programs in those cells. Past research has demonstrated that regulation of gene expression at the transcriptional level can decisively alter cell fate of stem cells. However, cellular contents of mRNAs are sometimes not equivalent to proteins, the functional units of cells. It is increasingly realized that post-transcriptional and translational regulation of gene expression are also fundamental for stem cell functions. Compared to differentiated somatic cells, effects on cellular status manifested by varied expression of RNA-binding proteins and global protein synthesis have been demonstrated in several stem cell systems. Through the cooperation of both cis-elements of mRNAs and trans-acting RNA-binding proteins that are intimately associated with them, regulation of localization, stability, and translational status of mRNAs directly influences the self-renewal and differentiation of stem cells. Previous studies have uncovered some of the molecular mechanisms that underlie the functions of RNA-binding proteins in stem cells in invertebrate species. However, their roles in adult stem cells in mammals are just beginning to be unveiled. This review highlights some of the RNA-binding proteins that play important functions during the maintenance and differentiation of mouse male germline stem cells, the adult stem cells in the male reproductive organ.

Germ Cell Nuclear Factor (GCNF/RTR) Regulates Transcription of Gonadotropin-Regulated Testicular RNA Helicase (GRTH/DDX25) in Testicular Germ Cells--The Androgen Connection

Gonadotropin-regulated testicular RNA helicase (GRTH) (GRTH/DDX25), is a testis-specific protein essential for completion of spermatogenesis. Transgenic mice carrying 5'-flanking regions of the GRTH gene/green fluorescence protein (GFP) reporter revealed a region (-6.4/-3.6 kb) which directs its expression in germ cells (GCs) via androgen action. This study identifies a functional cis-binding element on the GRTH gene for GC nuclear factor (GCNF) (GCNF/RTR) required to regulate GRTH gene expression in postmeiotic testis GCs and explore the action of androgen on GCNF and GRTH transcription/expression. GCNF expression decreased in mice testis upon flutamide (androgen receptor antagonist) treatment, indicating the presence of an androgen/GCNF network to direct GRTH expression in GC. Binding studies and chromatin immunoprecipitation demonstrated specific association of GCNF to a consensus half-site (-5270/-5252) of the GRTH gene in both round spermatids and spermatocytes, which was abolished by flutamide treatment in round spermatids. Moreover, flutamide treatment of wild-type mice caused selective reduction of GCNF and GRTH in round spermatids. GCNF knock-down in seminiferous tubules from GRTH-transgenic mice (dark zone, round spermatid rich) caused decreased GFP expression. Exposure of tubules to flutamide caused decrease in GCNF and GFP expression, whereas androgen exposure induced significant increase. Our studies provide evidence for actions of androgen on GCNF cell-specific regulation of GRTH expression in GC. GRTH associates with GCNF mRNA, its absence caused increase on GCNF expression and mRNA stability indicative of a negative autocrine regulation of GCNF by GRTH. These in vivo/in vitro models link androgen actions to GC through GCNF, as regulated transfactor that controls transcription/expression of GRTH.

Prolonged in vivo administration of testosterone-enanthate, the widely used and abused anabolic androgenic steroid, disturbs prolactin and cAMP signaling in Leydig cells of adult rats

This study was designed to systematically analyze and define the effects of 1-day, 2-weeks, 10-weeks intramuscular administration of testosterone-enanthate, widely used and abused anabolic androgenic steroid (AAS), on main regulators of steroidogenesis and steroidogenic genes expression in testosterone-producing Leydig cells of adult rats. The results showed that prolonged (10-weeks) intramuscular administration of testosterone-enanthate, in clinically relevant dose, significantly increased prolactin, but decreased Prlr2 and Gnrhr in pituitary of adult rat. The levels of testosterone, Insl3, cAMP and mitochondrial membrane potential of Leydig cells were significantly reduced. This was followed by decreased expression of some steroidogenic enzymes and regulatory proteins such as Lhcgr, Prlr1/2, Tspo, Star, Cyp11a1, Cyp17a1, Dax1. Oppositely, Hsd3b1/2, Hsd3b5, Hsd17b4, Ar, Arr19 increased. In the same cells, transcriptional milieu of cAMP signaling elements was disturbed with remarkable up-regulation of PRKA (the main regulator of steroidogenesis). Increased prolactin together with stimulated transcription of Jak2/Jak3 could account for increased Hsd3b1/2 and Hsd3b5 in Leydig cells following 10-weeks in vivo treatment with testosterone-enanthate. In vitro studies revealed that testosterone is capable to increase level of Prlr1, Prlr2, Hsd3b1/2, Hsd3b5 in Leydig cells. Accordingly, testosterone-induced changes in prolactin receptor signaling together with up-regulation of PRKA, Hsd3b1/2, Hsd3b5, Ar in Leydig cells, could be the possible mechanism that contribute to the establishment of a new adaptive response to maintain homeostasis and prevent loss of steroidogenic function. Presented data provide new molecular insights into the relationship between disturbed testosterone homeostasis and mammalian reproduction and are important in terms of wide use and abuse of AASs and human reproductive health.

Ddx1 knockout results in transgenerational wild-type lethality in mice

DEAD box 1 (DDX1) is a member of the DEAD box family of RNA helicases which are involved in all aspects of RNA metabolism. DDX1 has been implicated in a variety of biological processes, including 3’-end processing of mRNA, DNA repair, microRNA processing, tRNA maturation and mRNA transport. To study the role of DDX1 during development, we have generated mice carrying a constitutive Ddx1 knock-out allele. Ddx1^+/− mice have no obvious phenotype and express similar levels of DDX1 as wild-type mice indicating compensation from the intact Ddx1 allele. Heterozygote matings produce no viable Ddx1^−/− progeny, with Ddx1^−/− embryos dying prior to embryonic day (E) 3.5. Intriguingly, the number of wild-type progeny is significantly decreased in heterozygote crosses, with two different heterozygote populations identified based on parental genotype: (i) normal Ddx1^+/− mice which generate the expected number of wild-type progeny and (ii) Ddx1*^/− mice (with * signifying a non-genetically altered allele) which generate a significantly reduced number of wild-type mice. The transgenerational inheritance of wild-type lethality observed upon crossing Ddx1*^/− mice is independent of parental sex and occurs in cis through a mechanism that is different from other types of previously reported transgenerational epigenetic inheritance.

Piwi-pathway alteration induces LINE-1 transposon derepression and infertility development in cryptorchidism

Spermatogonia contain processing bodies that harbor P-element-induced wimpy testis (Piwi) proteins. Piwi proteins are associated specifically with Piwi-interacting RNAs to silence transposable DNA elements. Loss-of-function mutations in the Piwi pathway lead to derepression of transposable elements, resulting in defective spermatogenesis. Furthermore, deletion of gametocyte-specific factor 1 (GTSF1), a factor involved in Piwi-mediated transcriptional repression, causes male-specific sterility and derepression of LINE-1 (L1) retrotransposons. No previous studies have examined GTSF1, L1 and PIWIL4 expression in cryptorchidism. We examined transposon-silencing genes and L1 transposon expression in testicular biopsies with Affymetrix microarrays and immunohistology. Seven members of the Tudor gene family, 3 members of the DEAD-box RNA helicase family, and the GTSF1 gene were found to show significantly lower RNA signals in the high-infertility-risk group. In the immunohistochemical analysis, patients from the low-infertility-risk group showed coherently stronger staining for GTSF1 and PIWIL4 proteins and weaker staining for L1 transposon when compared to the high-infertility-risk samples. These new findings provide first evidence consistent with the idea that infertility in cryptorchidism is a consequence of alterations in the Piwi pathway and transposon derepression induced by the impaired function of mini-puberty.

Mechanisms of translational repression of the Smcp mRNA in round spermatids

The protamine 1 (Prm1) and sperm mitochondria-associated, cysteine-rich protein (Smcp) mRNAs exemplify a widespread pattern of mRNA-specific regulation of mRNA translation in post-meiotic spermatogenic cells, spermatids. Both mRNAs are transcribed and initially stored in free-mRNPs in early spermatids, and translated on polysomes in late spermatids. In this study, we demonstrate that the 5' and 3'-UTRs and the 3' terminus of the Smcp 3'-UTR are required for normal repression of the Smcp mRNA in transgenic mice. RNA affinity chromatography and mass spectrometry sequencing identified Y-box protein 2 (YBX2/MSY2) as the major protein that interacts with the 3' terminus of the Smcp 3'-UTR and a Y-box recognition sequence, GCCACCU, in the translation control element that is necessary for Prm1 mRNA repression. Depletion of YBX2 in Ybx2-null mice prematurely activates Prm1 and Smcp mRNA translation in early spermatids. Fluorescent in situ hybridization reveals that the Smcp intron, the Smcp mRNA, and both Smcp-Gfp transgenic mRNAs are strongly concentrated in the chromatoid body, and that theYbx2-null mutation does not eliminate the Smcp mRNA from the chromatoid body. This and previous findings suggest that the Smcp pre-mRNA is spliced and associates with YBX2 in the chromatoid body, and that repressed free-mRNPs are stored in the general cytoplasm. As YBX2 is the predominant protein in testis free-mRNPs, it likely represses many mRNAs in early spermatids. The mechanisms by which YBX2 represses the Smcp and Prm1 mRNAs are relevant to reproductive medicine because mutations in the human YBX2 gene correlate with abnormal protamine expression and male infertility.

Molecular adaptations of testosterone-producing Leydig cells during systemic in vivo blockade of the androgen receptor

This study systematically evaluates the effects of androgen receptor (AR) blockade on molecular events in Leydig cells. Results showed that intramuscular administration of testosterone-enanthate, at clinically relevant dose, decreased testosterone in interstitial fluid and Leydig cells from adult rats. AR-blocker (Androcur) prevented this effect and testosterone-reduced Leydig cells steroidogenic capacity/activity. Testosterone-reduced expression of some steroidogenic enzymes/proteins (Tspo,StAR,Hsd3b1/2) and transcription factors (Nur77,Gata4,Dax1) was completely abrogated, while decreased expression of Star,Cyp11a1,Cyp17a1,Hsd17b4,Creb1a was partially prevented. In the same cells, increased expression of Hsd3b5/HSD3B and Ar/AR was abolished. Androcur-treatment abolished testosterone-reduced cAMP, coupled with a changed expressional milieu of cAMP signaling elements. Results from in vitro experiments suggest that some of these effects are testosterone-AR dependent, while others could be due to disturbed LH and/or other signals. Presented data provide new molecular insight into Leydig cells function and are important in terms of human reproductive health and the wide-spread use of Androcur as well as use/abuse of testosterone-enanthate.