Unique chromatin remodeling and transcriptional regulation in spermatogenesis

Differential expression of protamine 1 and 2 genes in mature spermatozoa of normal and motility impaired semen producing crossbred Frieswal (HF×Sahiwal) bulls

Mature spermatozoa contain thousands of mRNA transcripts. These untranslated mRNA may perhaps serve as a "footprint" of spermatogenesis since many of them might directly or indirectly be involved in fertilization, early embryo cleavage, poor semen quality and fertility. In this study, we tried to isolate high-quality RNA from mature spermatozoa and to monitor the expression profile of protamine 1 (PRM1) and protamine 2 (PRM2) gene in ejaculated spermatozoa of normal (good, % initial progressive motility: 57.61±1.41, n=9) and motility impaired (poor, % initial progressive motility: 18.45±1.61, n=8) crossbred Frieswal (HF×Sahiwal) bulls semen using real time quantitative PCR. Semen samples were subjected to discontinuous (45:90) Percoll gradient centrifugation, specifically to eliminate damaged spermatozoa and contaminating somatic cells. Total RNA was extracted from sperm pellets and cDNA was synthesized. Furthermore, the absence of contamination of germ cells, epithelial cells and leucocytes in all the RNA extractions was tested by RT-PCR targeting specific molecular markers like KIT, CDH1 and CD4, respectively. The presence of transcripts like PRM1, PRM2, DAZL, and PPIA were demonstrated in ejaculated spermatozoa using appropriate PCR primers without RNA amplification. Expression of PRM1 and PRM2 genes were evaluated by real time quantitative PCR using TaqMan chemistry, where PPIA was used as internal control. The cDNA synthesized from normal buffalo testicular tissue was served as positive control. The good quality semen producing group showed significantly higher level of PRM1 mRNAs expression as compared to the poor quality semen producers (P<0.05) indicating putative role of the gene and semen quality parameters especially initial progressive motility. However, PRM2 transcript levels were not significantly different between the groups (P>0.05).

Epigenetics and the transition from acute to chronic pain

OBJECTIVE

The objective of this study was to review the epigenetic modifications involved in the transition from acute to chronic pain and to identify potential targets for the development of novel, individualized pain therapeutics.

BACKGROUND

Epigenetics is the study of heritable modifications in gene expression and phenotype that do not require a change in genetic sequence to manifest their effects. Environmental toxins, medications, diet, and psychological stresses can alter epigenetic processes such as DNA methylation, histone acetylation, and RNA interference. As epigenetic modifications potentially play an important role in inflammatory cytokine metabolism, steroid responsiveness, and opioid sensitivity, they are likely key factors in the development of chronic pain. Although our knowledge of the human genetic code and disease-associated polymorphisms has grown significantly in the past decade, we have not yet been able to elucidate the mechanisms that lead to the development of persistent pain after nerve injury or surgery.

DESIGN

This is a focused literature review of epigenetic science and its relationship to chronic pain.

RESULTS

Significant laboratory and clinical data support the notion that epigenetic modifications are affected by the environment and lead to differential gene expression. Similar to mechanisms involved in the development of cancer, neurodegenerative disease, and inflammatory disorders, the literature endorses an important potential role for epigenetics in chronic pain.

CONCLUSIONS

Epigenetic analysis may identify mechanisms critical to the development of chronic pain after injury, and may provide new pathways and target mechanisms for future drug development and individualized medicine.

The Drosophila Translational Control Element (TCE) is required for high-level transcription of many genes that are specifically expressed in testes

To investigate the importance of core promoter elements for tissue-specific transcription of RNA polymerase II genes, we examined testis-specific transcription in Drosophila melanogaster. Bioinformatic analyses of core promoter sequences from 190 genes that are specifically expressed in testes identified a 10 bp A/T-rich motif that is identical to the translational control element (TCE). The TCE functions in the 5′ untranslated region of Mst(3)CGP mRNAs to repress translation, and it also functions in a heterologous gene to regulate transcription. We found that among genes with focused initiation patterns, the TCE is significantly enriched in core promoters of genes that are specifically expressed in testes but not in core promoters of genes that are specifically expressed in other tissues. The TCE is variably located in core promoters and is conserved in melanogaster subgroup species, but conservation dramatically drops in more distant species. In transgenic flies, short (300–400 bp) genomic regions containing a TCE directed testis-specific transcription of a reporter gene. Mutation of the TCE significantly reduced but did not abolish reporter gene transcription indicating that the TCE is important but not essential for transcription activation. Finally, mutation of testis-specific TFIID (tTFIID) subunits significantly reduced the transcription of a subset of endogenous TCE-containing but not TCE-lacking genes, suggesting that tTFIID activity is limited to TCE-containing genes but that tTFIID is not an obligatory regulator of TCE-containing genes. Thus, the TCE is a core promoter element in a subset of genes that are specifically expressed in testes. Furthermore, the TCE regulates transcription in the context of short genomic regions, from variable locations in the core promoter, and both dependently and independently of tTFIID. These findings set the stage for determining the mechanism by which the TCE regulates testis-specific transcription and understanding the dual role of the TCE in translational and transcriptional regulation.

Transcriptional regulation of human novel gene SPATA12 promoter by AP-1 and HSF

Human SPATA12 is a spermatogenesis associated gene and is supposed to function as an inhibitor during male germ cell development. SPATA12 is specifically expressed in spermatocytes, spermatids, and spermatozoa of human testis. In order to understand the regulation mechanism of SPATA12 gene expression, we identified and characterized the SPATA12 gene core promoter region and transcription factor binding sites by using reporter gene assays. AP-1 is founded to be a potential transcriptional activator of SPATA12. The promoter activity of SPATA12 was drastically declined after AP-1 binding site mutation or deletion. We also demonstrated that AP-1 combined with Smad3/4 contributes to the transcriptional regulation of SPATA12 in response to TGF-β1. The expression of SPATA12 could be induced by TGF-β1 in a dose-dependent manner, suggesting that AP-1 as an activator plays a role in the regulation of SPATA12 promoter. We have also shown that heat shock treatment could activate the expression of SPATA12 and transcription factor HSF binding sites in the SPATA12 promoter might be responsible for this heat-induction. These results suggested that AP-1 and HSF may play an important role in regulating SPATA12 promoter activity.

Bromodomain-dependent stage-specific male genome programming by Brdt

Male germ cell differentiation is a highly regulated multistep process initiated by the commitment of progenitor cells into meiosis and characterized by major chromatin reorganizations in haploid spermatids. We report here that a single member of the double bromodomain BET factors, Brdt, is a master regulator of both meiotic divisions and post-meiotic genome repackaging. Upon its activation at the onset of meiosis, Brdt drives and determines the developmental timing of a testis-specific gene expression program. In meiotic and post-meiotic cells, Brdt initiates a genuine histone acetylation-guided programming of the genome by activating essential genes and repressing a 'progenitor cells' gene expression program. At post-meiotic stages, a global chromatin hyperacetylation gives the signal for Brdt's first bromodomain to direct the genome-wide replacement of histones by transition proteins. Brdt is therefore a unique and essential regulator of male germ cell differentiation, which, by using various domains in a developmentally controlled manner, first drives a specific spermatogenic gene expression program, and later controls the tight packaging of the male genome.

Circadian proteins CLOCK and BMAL1 in the chromatoid body, a RNA processing granule of male germ cells

Spermatogenesis is a complex differentiation process that involves genetic and epigenetic regulation, sophisticated hormonal control, and extensive structural changes in male germ cells. RNA nuclear and cytoplasmic bodies appear to be critical for the progress of spermatogenesis. The chromatoid body (CB) is a cytoplasmic organelle playing an important role in RNA post-transcriptional and translation regulation during the late steps of germ cell differentiation. The CB is also important for fertility determination since mutations of genes encoding its components cause infertility by spermatogenesis arrest. Targeted ablation of the Bmal1 and Clock genes, which encode central regulators of the circadian clock also result in fertility defects caused by problems other than spermatogenesis alterations. We show that the circadian proteins CLOCK and BMAL1 are localized in the CB in a stage-specific manner of germ cells. Both BMAL1 and CLOCK proteins physically interact with the ATP-dependent DEAD-box RNA helicase MVH (mouse VASA homolog), a hallmark component of the CB. BMAL1 is differentially expressed during the spermatogenic cycle of seminiferous tubules, and Bmal1 and Clock deficient mice display significant CB morphological alterations due to BMAL1 ablation or low expression. These findings suggest that both BMAL1 and CLOCK contribute to CB assembly and physiology, raising questions on the role of the circadian clock in reproduction and on the molecular function that CLOCK and BMAL1 could potentially have in the CB assembly and physiology.

Androgen-responsive microRNAs in mouse Sertoli cells

Although decades of research have established that androgen is essential for spermatogenesis, androgen's mechanism of action remains elusive. This is in part because only a few androgen-responsive genes have been definitively identified in the testis. Here, we propose that microRNAs – small, non-coding RNAs – are one class of androgen-regulated trans-acting factors in the testis. Specifically, by using androgen suppression and androgen replacement in mice, we show that androgen regulates the expression of several microRNAs in Sertoli cells. Our results reveal that several of these microRNAs are preferentially expressed in the testis and regulate genes that are highly expressed in Sertoli cells. Because androgen receptor-mediated signaling is essential for the pre- and post-meiotic germ cell development, we propose that androgen controls these events by regulating Sertoli/germ cell-specific gene expression in a microRNA-dependent manner.

C. elegans piRNAs mediate the genome-wide surveillance of germline transcripts

Piwi Argonautes and Piwi-interacting RNAs (piRNAs) mediate genome defense by targeting transposons. However, many piRNA species lack obvious sequence complementarity to transposons or other loci; only one C. elegans transposon is a known piRNA target. Here, we show that, in mutants lacking the Piwi Argonaute PRG-1 (and consequently its associated piRNAs/21U-RNAs), many silent loci in the germline exhibit increased levels of mRNA expression with a concomitant depletion of RNA-dependent RNA polymerase (RdRP)-derived secondary small RNAs termed 22G-RNAs. Sequences depleted of 22G-RNAs are proximal to potential target sites that base pair imperfectly but extensively to 21U-RNAs. We show that PRG-1 is required to initiate, but not to maintain, silencing of transgenes engineered to contain complementarity to endogenous 21U-RNAs. Our findings support a model in which C. elegans piRNAs utilize their enormous repertoire of targeting capacity to scan the germline transcriptome for foreign sequences, while endogenous germline-expressed genes are actively protected from piRNA-induced silencing.

Cell-free seminal mRNA and microRNA exist in different forms

BACKGROUND

The great interest in cell-free mRNA, microRNA (miRNA) as molecular biomarkers for clinical applications, and as 'signaling' molecules for intercellular communication highlights the need to reveal their physical nature. Here this issue was explored in human cell-free seminal mRNA (cfs-mRNA) and miRNA (cfs-miRNA).

METHODOLOGY/PRINCIPAL FINDINGS

Selected male reproductive organ-specific mRNAs, miRNAs, and piRNAs were quantified by quantitative real-time PCR in all experiments. While the stability of cfs-miRNA assessed by time-course analysis (up to 24 h at room temperature) was similar with cfs-mRNA, the reductive changes between cfs-miRNA and cfs-mRNA after filtration and Triton X-100 treatment on seminal plasma were very different, implying their different physical nature. Seminal microvesicles (SMVs) were then recovered and proportions of cfs-mRNA and cfs-miRNA within SMVs were quantified. The amounts of SMVs- sequestered cfs-mRNAs almost were the same as total cfs-mRNA, and were highly variable depending on the different sizes of SMVs. But most of cfs-miRNA was independent of SMVs and existed in the supernatant. The possible form of cfs-miRNA in the supernatant was further explored by filtration and protease K digestion. It passed through the 0.10-µm pore, but was degraded dramatically after intense protease K digestion.

CONCLUSIONS/SIGNIFICANCE

The predominant cfs-mRNA is contained in SMVs, while most cfs-miRNA is bound with protein complexes. Our data explained the stability of extracellular RNAs in human semen, and shed light on their origins and potential functions in male reproduction, and strategy of developing them as biomarkers of male reproductive system.

Characterization of a novel human testis-specific gene: testis developmental related gene 1 (TDRG1)

Spermatogenesis is a highly coordinated physiological process that requires the correct expression and functions of thousands of developmentally regulated genes. The regulation of spermatogenesis is not well defined, since majority of the related genes have neither been identified nor fully characterized. Hence, it is meaningful to identify and characterize these genes to reveal the mechanism underlying spermatogenesis. In this study, using digital differential display, we identified a novel human testis-specific gene, testis developmental related gene 1 (TDRG1, GenBank DQ168992), via electronic subtraction of human testis UniGene databases from those of non-reproductive tissues. The transcript of the TDRG1 gene has an open-reading frame that encodes 100 amino acids. We next prepared the anti-TDRG1 monoclonal antibody 10B6 and confirmed that it specifically recognizes an 11-kDa protein in the tissue extracts from an adult human testicular sample (age 31 years) by Western blot analysis. RT-PCR coupled with immunohistochemistry of human tissues demonstrated that TDRG1 is exclusively expressed in the testis but not in any other non-reproductive tissues. TDRG1 is mainly located in spermatogenic cells in seminiferous tubules of adult testis. Furthermore, TDRG1 shows the highest expression level in human post-puberty testis, with the expression levels decreasing afterwards with aging. Importantly, TDRG1 mRNA is undetectable in the fetal testis, as judged by RT-PCR. In conclusion, TDRG1 is a developmentally regulated testicular-specific gene. We suggest that TDRG1, a newly identified testis-specific gene, may play important roles in human spermatogenesis.

Insights into role of bromodomain, testis-specific (Brdt) in acetylated histone H4-dependent chromatin remodeling in mammalian spermiogenesis

Mammalian spermiogenesis is of considerable biological interest especially due to the unique chromatin remodeling events that take place during spermatid maturation. Here, we have studied the expression of chromatin remodeling factors in different spermatogenic stages and narrowed it down to bromodomain, testis-specific (Brdt) as a key molecule participating in chromatin remodeling during rat spermiogenesis. Our immunocytochemistry experiments reveal that Brdt colocalizes with acetylated H4 in elongating spermatids. Remodeling assays showed an acetylation-dependent but ATP-independent chromatin reorganization property of Brdt in haploid round spermatids. Furthermore, Brdt interacts with Smarce1, a member of the SWI/SNF family. We have studied the genomic organization of smarce1 and identified that it has two splice variants expressed during spermatogenesis. The N terminus of Brdt is involved in the recognition of Smarce1 as well as in the reorganization of hyperacetylated round spermatid chromatin. Interestingly, the interaction between Smarce1 and Brdt increases dramatically upon histone hyperacetylation both in vitro and in vivo. Thus, our results indicate this interaction to be a vital step in the chromatin remodeling process during mammalian spermiogenesis.

A concise review on epigenetic regulation: insight into molecular mechanisms

Epigenetic mechanisms are responsible for the regulation of transcription of imprinted genes and those that induce a totipotent state. Starting just after fertilization, DNA methylation pattern undergoes establishment, reestablishment and maintenance. These modifications are important for normal embryo and placental developments. Throughout life and passing to the next generation, epigenetic events establish, maintain, erase and reestablish. In the context of differentiated cell reprogramming, demethylation and activation of genes whose expressions contribute to the pluripotent state is the crux of the matter. In this review, firstly, regulatory epigenetic mechanisms related to somatic cell nuclear transfer (SCNT) reprogramming are discussed, followed by embryonic development, and placental epigenetic issues.

Sperm development and motility are regulated by PP1 phosphatases in Caenorhabditis elegans

Sperm from different species have evolved distinctive motility structures, including tubulin-based flagella in mammals and major sperm protein (MSP)-based pseudopods in nematodes. Despite such divergence, we show that sperm-specific PP1 phosphatases, which are required for male fertility in mouse, function in multiple processes in the development and motility of Caenorhabditis elegans amoeboid sperm. We used live-imaging analysis to show the PP1 phosphatases GSP-3 and GSP-4 (GSP-3/4) are required to partition chromosomes during sperm meiosis. Postmeiosis, tracking fluorescently labeled sperm revealed that both male and hermaphrodite sperm lacking GSP-3/4 are immotile. Genetic and in vitro activation assays show lack of GSP-3/4 causes defects in pseudopod development and the rate of pseudopodial treadmilling. Further, GSP-3/4 are required for the localization dynamics of MSP. GSP-3/4 shift localization in concert with MSP from fibrous bodies that sequester MSP at the base of the pseudopod, where directed MSP disassembly facilitates pseudopod contraction. Consistent with a role for GSP-3/4 as a spatial regulator of MSP disassembly, MSP is mislocalized in sperm lacking GSP-3/4. Although a requirement for PP1 phosphatases in nematode and mammalian sperm suggests evolutionary conservation, we show PP1s have independently evolved sperm-specific paralogs in separate lineages. Thus PP1 phosphatases are highly adaptable and employed across a broad range of sexually reproducing species to regulate male fertility.

Transition of basic protein during spermatogenesis of Fenneropenaeus chinensis (Osbeck, 1765)

According to the ultrastructural characteristic observation of the developing male germ cells, spermatogenesis of the crustacean shrimp, Fenneropenaeus chinensis, is classified into spermatogonia, primary spermatocytes, secondary spermatocyte, four stages of spermatids, and mature sperm. The basic protein transition during its spermatogenesis is studied by transmission electron microscopy of ammoniacal silver reaction and immunoelectron microscopical distribution of acetylated histone H4. The results show that basic protein synthesized in cytoplasm of spermatogonia is transferred into the nucleus with deposition on new duplicated DNA. In the spermatocyte stage, some nuclear basic protein combined with RNP is transferred into the cytoplasm and is involved in forming the cytoplasmic vesicle clumps. In the early spermatid, most of the basic protein synthesized in the new spermatid cytoplasm is transferred into the nucleus, and the chromatin condensed gradually, and the rest is shifted into the pre-acrosomal vacuole. In the middle spermatid, the nuclear basic protein linked with DNA is acetylated and transferred into the proacrosomal vacuole and assembled into the acrosomal blastema. At the late spermatid, almost all of the basic protein in the nucleus has been removed into the acrosome. During the stage from late spermatid to mature sperm, some de novo basic proteins synthesized in the cytoplasm belt transfer into the nucleus without a membrane and almost all deposit in the periphery to form a supercoating. The remnant histone H4 accompanied by chromatin fibers is acetylated in the center of the nucleus, leading to relaxed DNA and activated genes making the nucleus non-condensed.

An in vitro, short-term culture method for mammalian haploid round spermatids amenable for molecular manipulation

Extensive chromatin remodeling is a characteristic feature of mammalian spermiogenesis. To date, methods for the molecular manipulation of haploid spermatids are not available as there is a lack of a well-established culture system. Biochemical experiments and knockout studies reveal only the final outcome; studying the incremental details of the intricate mechanisms involved is still a challenge. We have established an in vitro culture system for pure haploid round spermatids isolated from rat testes that can be maintained with good viability for up to 72 hr. Changes in cell morphology and flagellar growth were also studied in the cultured spermatids. Further, we have demonstrated that upon treatment of cells with specific histone deacetylase inhibitors, sodium butyrate and trichostatin A, there is an increase in the hyperacetylation status of histone H4, mimicking an important event characteristic of histone replacement process that occurs during later stages of spermiogenesis. We have also tried various methods for introducing DNA and protein into these round spermatids in culture, and report that while DNA transfection is still a challenging task, protein transfection could be achieved using Chariot™ peptide as a transfection reagent. Thus, the method described here sets a stage to study the molecular roles of spermatid-specific proteins and chromatin remodelers in the cellular context.

The evolutionary origin of orphan genes

Gene evolution has long been thought to be primarily driven by duplication and rearrangement mechanisms. However, every evolutionary lineage harbours orphan genes that lack homologues in other lineages and whose evolutionary origin is only poorly understood. Orphan genes might arise from duplication and rearrangement processes followed by fast divergence; however, de novo evolution out of non-coding genomic regions is emerging as an important additional mechanism. This process appears to provide raw material continuously for the evolution of new gene functions, which can become relevant for lineage-specific adaptations.

Immunohistochemical Analysis of Histone H3 Modifications in Germ Cells during Mouse Spermatogenesis

Histone modification has been implicated in the regulation of mammalian spermatogenesis. However, the association of differently modified histone H3 with a specific stage of germ cells during spermatogenesis is not fully understood. In this study, we examined the localization of variously modified histone H3 in paraffin-embedded sections of adult mouse testis immunohistochemically, focusing on acetylation at lysine 9 (H3K9ac), lysine 18 (H3K18ac), and lysine 23 (H3K23ac); tri-methylation at lysine 4 (H3K4me3) and lysine 27 (H3K27me3); and phosphorylation at serine 10 (H3S10phos). As a result, we found that there was a significant fluctuation in the modifications; in spermatogonia, the stainings for H3K9ac, H3K18ac, and H3K23ac were strong while that for H3K4me3 was weak. In spermatocytes, the stainings for H3K9ac, H3K18ac, H3K23ac, and H3K4me3 were reduced in the preleptotene to pachytene stage, but in diplotene stage the stainings for H3K18ac, H3K23ac, and H3K4me3 seemed to become intense again. The staining for H3K27me3 was nearly constant throughout these stages. In the ensuing spermiogenesis, a dramatic acetylation and methylation of histone H3 was found in the early elongated spermatids and then almost all signals disappeared in the late elongated spermatids, in parallel with the replacement from histones to protamines. In addition, we confirmed that the staining of histone H3S10phos was exclusively associated with mitotic and meiotic cell division. Based upon the above results, we indicated that the modification pattern of histone H3 is subject to dynamic change and specific to a certain stage of germ cell differentiation during mouse spermatogenesis.

Foxo1 is required in mouse spermatogonial stem cells for their maintenance and the initiation of spermatogenesis

Spermatogonial stem cells (SSCs) capable of self-renewal and differentiation are the foundation for spermatogenesis. Although several factors important for these processes have been identified, the fundamental mechanisms regulating SSC self-renewal and differentiation remain unknown. Here, we investigated a role for the Foxo transcription factors in mouse spermatogenesis and found that Foxo1 specifically marks mouse gonocytes and a subset of spermatogonia with stem cell potential. Genetic analyses showed that Foxo1 was required for both SSC homeostasis and the initiation of spermatogenesis. Combined deficiency of Foxo1, Foxo3, and Foxo4 resulted in a severe impairment of SSC self-renewal and a complete block of differentiation, indicating that Foxo3 and Foxo4, although dispensable for male fertility, contribute to SSC function. By conditional inactivation of 3-phosphoinositide-dependent protein kinase 1 (Pdk1) and phosphatase and tensin homolog (Pten) in the male germ line, we found that PI3K signaling regulates Foxo1 stability and subcellular localization, revealing that the Foxos are pivotal effectors of PI3K-Akt signaling in SSCs. We also identified a network of Foxo gene targets--most notably Ret--that rationalized the maintenance of SSCs by the Foxos. These studies demonstrate that Foxo1 expression in the spermatogenic lineage is intimately associated with the stem cell state and revealed what we believe to be novel Foxo-dependent mechanisms underlying SSC self-renewal and differentiation, with implications for common diseases, including male infertility and testicular cancer, due to abnormalities in SSC function.

Control of messenger RNA fate by RNA-binding proteins: an emphasis on mammalian spermatogenesis

Posttranscriptional status of messenger RNAs (mRNA) can be affected by many factors, most of which are RNA-binding proteins (RBP) that either bind mRNA in a nonspecific manner or through specific motifs, usually located in the 3' untranslated regions. RBPs can also be recruited by small noncoding RNAs (sncRNA), which have been shown to be involved in posttranscriptional regulations and transposon repression (eg, microRNAs or P-element-induced wimpy testis-interacting RNA) as components of the sncRNA effector complex. Non-sncRNA-binding RBPs have much more diverse effects on their target mRNAs. Some can cause degradation of their target transcripts and/or repression of translation, whereas others can stabilize and/or activate translation. The splicing and exportation of transcripts from the nucleus to the cytoplasm are often mediated by sequence-specific RBPs. The mechanisms by which RBPs regulate mRNA transcripts involve manipulating the 3' poly(A) tail, targeting the transcript to polysomes or to other ribonuclear protein particles, recruiting regulatory proteins, or competing with other RBPs. Here, we briefly review the known mechanisms of posttranscriptional regulation mediated by RBPs, with an emphasis on how these mechanisms might control spermatogenesis in general.

Unique aspects of transcription regulation in male germ cells

Spermatogenesis is a complex and ordered differentiation process in which the spermatogonial stem cell population gives rise to primary spermatocytes that undergo two successive meiotic divisions followed by a major biochemical and structural reorganization of the haploid cells to generate mature elongate spermatids. The transcriptional regulatory programs that orchestrate this process have been intensively studied in model organisms such as Drosophila melanogaster and mouse. Genetic and biochemical approaches have identified the factors involved and revealed mechanisms of action that are unique to male germ cells. In a well-studied example, cofactors and pathways distinct from those used in somatic tissues mediate the action of CREM in male germ cells. But perhaps the most striking feature concerns the paralogs of somatically expressed transcription factors and of components of the general transcription machinery that act in distinct regulatory mechanisms in both Drosophila and murine spermatogenesis.

A polymorphism of the CREB binding protein (CREBBP) gene is a risk factor for addiction

Unequivocal evidences have implicated c-AMP response element binding protein (CREB) in drug addiction. Recent reports indicate that the CREB binding protein (CREBBP), a transcription co-activator, may also be involved in the sensitivity to drugs of abuse. We undertook studies on the single nucleotide polymorphisms (SNP) at selective areas of CREBBP gene in heroin as well as in alcohol addicts and compared them with that in normal population. One hundred fifty healthy controls, one hundred thirty heroin addict and one hundred ten alcohol addicts, all males, Bengali-Hindu, and residing in Kolkata, a city in eastern India, participated in the study. DNA prepared from blood drawn from the subjects was PCR amplified for the regions corresponding to exon 3 and 22 of CREBBP gene followed by sequencing. Three SNPs identified in the population were analyzed to find out the association of these SNPs with addiction. One SNP, rs3025684 in intron 21 having the contig position of 3795363, showed association with addiction. The genotype frequencies of the SNP were significantly different between opioid dependent cases and controls (χ(2)=20.28, p<0.0001) as well as between alcoholics and controls (χ(2)=13.60, p=0.0011). Our studies suggest that rs3025684 polymorphism may be a possible risk factor for developing addiction.

Transcriptional and proteomic profiling of flatfish (Solea senegalensis) spermatogenesis

The Senegalese sole (Solea senegalensis) is a marine flatfish of high economic value and a target species for aquaculture. The efforts to reproduce this species in captivity have been hampered by the fact that farmed males (F1) often show lower sperm production and fertilization capacity than wild-type males (F0). Our knowledge on spermatogenesis is however limited to a few studies. In a previous work, we identified by 2-D DIGE several potential protein markers in testis for the poor reproductive performance of F1 males. Therefore, the objectives of the present study were, first, to investigate changes in genes and proteins expressed in the testis throughout spermatogenesis in F0 males by using a combination of transcriptomic and proteomic approaches and, second, to further compare the testis proteome between late spermatogenic stages of F0 and F1 fish to identify potential indicators of hampered reproductive performance in F1 fish. We identified approximately 400 genes and 49 proteins that are differentially expressed during the progression of spermatogenesis and that participate in processes such as transcriptional activation, the ubiquitin-proteasome system, sperm maturation and motility or cytoskeletal remodeling. Interestingly, a number of these proteins differed in abundance between F0 and F1 fish, pointing toward alterations in cytoskeleton, sperm motility, the ubiquitin-proteasome system and the redox state during spermiogenesis as possible causes for the decreased fertility of F1 fish.

Transcription and post-transcriptional regulation of spermatogenesis

Spermatogenesis in mammals is achieved by multiple players that pursue a common goal of generating mature spermatozoa. The developmental processes acting on male germ cells that culminate in the production of the functional spermatozoa are regulated at both the transcription and post-transcriptional levels. This review addresses recent progress towards understanding such regulatory mechanisms and identifies future challenges to be addressed in this field. We focus on transcription factors, chromatin-associated factors and RNA-binding proteins necessary for spermatogenesis and/or sperm maturation. Understanding the molecular mechanisms that govern spermatogenesis has enormous implications for new contraceptive approaches and treatments for infertility.

Elucidating gene regulatory mechanisms for sperm function through the integration of classical and systems approaches in C. elegans

From worms to mammals, successful spermatogenesis depends on a gene expression profile that balances activating and repressive mechanisms. Besides developmental control of specific spermatogenic genes, male fertility requires temporal shifts in global gene expression and dramatic changes in chromatin structure and condensation. Recent studies are beginning to elucidate the molecular processes that both drive these temporal changes in gene expression and underlie fertility. In this review, we provide an overview of relevant C. elegans studies that have laid the groundwork for modern approaches. Next, we highlight recent studies that investigate how gene expression in C. elegans is modulated during spermatogenesis. These studies use large-scale genomic profiling in combination with bioinformatics, genetics, biochemistry, and in vitro methods to target specific stages or processes during sperm formation. Such studies are beginning to elucidate the multiple layers of gene regulation required during spermatogenesis, i.e., transcriptional, post-transcriptional, and epigenetic. Moreover, knowledge of how C. elegans coordinately regulates gene expression during spermatogenesis promises to provide key insights into parallel processes in mammals that are vital for fertility.

Zmynd15 encodes a histone deacetylase-dependent transcriptional repressor essential for spermiogenesis and male fertility

Spermatogenesis is a complex process through which male germ line stem cells undergo a multi-step differentiation program and sequentially become spermatogonia, spermatocytes, spermatids, and eventually spermatozoa. In this process, transcription factors act as switches that precisely regulate the expression of genes that in turn control the developmental program of male germ cells. Transcription factors identified to be essential for normal haploid gene expression all display transcription-activating effects and thus serve as the "on" switch for haploid gene expression. Here, we report that ZMYND15 acts as a histone deacetylase-dependent transcriptional repressor and controls normal temporal expression of haploid cell genes during spermiogenesis. Inactivation of Zmynd15 results in early activation of transcription of numerous important haploid genes including Prm1, Tnp1, Spem1, and Catpser3; depletion of late spermatids; and male infertility. ZMYND15 represents the first transcriptional repressor identified to be essential for sperm production and male fertility.

Origins, evolution, and phenotypic impact of new genes

Ever since the pre-molecular era, the birth of new genes with novel functions has been considered to be a major contributor to adaptive evolutionary innovation. Here, I review the origin and evolution of new genes and their functions in eukaryotes, an area of research that has made rapid progress in the past decade thanks to the genomics revolution. Indeed, recent work has provided initial whole-genome views of the different types of new genes for a large number of different organisms. The array of mechanisms underlying the origin of new genes is compelling, extending way beyond the traditionally well-studied source of gene duplication. Thus, it was shown that novel genes also regularly arose from messenger RNAs of ancestral genes, protein-coding genes metamorphosed into new RNA genes, genomic parasites were co-opted as new genes, and that both protein and RNA genes were composed from scratch (i.e., from previously nonfunctional sequences). These mechanisms then also contributed to the formation of numerous novel chimeric gene structures. Detailed functional investigations uncovered different evolutionary pathways that led to the emergence of novel functions from these newly minted sequences and, with respect to animals, attributed a potentially important role to one specific tissue--the testis--in the process of gene birth. Remarkably, these studies also demonstrated that novel genes of the various types significantly impacted the evolution of cellular, physiological, morphological, behavioral, and reproductive phenotypic traits. Consequently, it is now firmly established that new genes have indeed been major contributors to the origin of adaptive evolutionary novelties.

Environmental epigenetics

Epigenetics investigates heritable changes in gene expression that occur without changes in DNA sequence. Several epigenetic mechanisms, including DNA methylation and histone modifications, can change genome function under exogenous influence. We review current evidence indicating that epigenetic alterations mediate effects caused by exposure to environmental toxicants. Results obtained from animal models indicate that in utero or early-life environmental exposures produce effects that can be inherited transgenerationally and are accompanied by epigenetic alterations. The search for human equivalents of the epigenetic mechanisms identified in animal models is under way. Recent investigations have identified a number of environmental toxicants that cause altered methylation of human repetitive elements or genes. Some exposures can alter epigenetic states and the same and/or similar epigenetic alterations can be found in patients with the disease of concern. On the basis of current evidence, we propose possible models for the interplay between environmental exposures and the human epigenome. Several investigations have examined the relationship between exposure to environmental chemicals and epigenetics, and have identified toxicants that modify epigenetic states. Whether environmental exposures have transgenerational epigenetic effects in humans remains to be elucidated. In spite of the current limitations, available evidence supports the concept that epigenetics holds substantial potential for furthering our understanding of the molecular mechanisms of environmental toxicants, as well as for predicting health-related risks due to conditions of environmental exposure and individual susceptibility.

Differential contribution of the MTOR and MNK pathways to the regulation of mRNA translation in meiotic and postmeiotic mouse male germ cells

Translation of stored mRNAs accounts for protein synthesis during the transcriptionally inactive stages of spermatogenesis. A key step in mRNA translation is the assembly of the initiation complex EIF4F, which is regulated by the MTOR (mammalian target of rapamycin) and MNK1/2 (MAP kinase-interacting kinase 1 and 2) pathways. We investigated the expression and activity of regulatory proteins of these pathways in male germ cells at different stages of differentiation. All translation factors analyzed were expressed in germ cells throughout spermatogenesis. However, while EIF4G and PABP1 (poly[A]-binding protein 1) were more abundant in postmeiotic cells, MTOR and its target EIF4EBP1 (4E-BP1) decreased steadily during spermatogenesis. In vivo labeling showed that pachytene spermatocytes display higher rates of protein synthesis, which are partially dependent on MTOR and MNK activity. By contrast, haploid spermatids are characterized by lower levels of protein synthesis, which are independent of the activity of these pathways. Accordingly, MTOR and MNK activity enhanced formation of the EIF4F complex in pachytene spermatocytes but not in round spermatids. Moreover, external cues differentially modulated the activity of these pathways in meiotic and haploid cells. Heat shock decreased MTOR and MNK activity in pachytene spermatocytes, whereas round spermatids were much less sensitive. On the other hand, treatment with the phosphatase inhibitor okadaic acid activated MTOR and MNK in both cell types. These results indicate that translational regulation is differentially dependent on the MTOR and MNK pathways in mouse spermatocytes and spermatids and suggest that the late stages of germ cell differentiation display constitutive assembly of the translation initiation complex.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 4: intercellular bridges, mitochondria, nuclear envelope, apoptosis, ubiquitination, membrane/voltage-gated channels, methylation/acetylation, and transcription factors

As germ cells divide and differentiate from spermatogonia to spermatozoa, they share a number of structural and functional features that are common to all generations of germ cells and these features are discussed herein. Germ cells are linked to one another by large intercellular bridges which serve to move molecules and even large organelles from the cytoplasm of one cell to another. Mitochondria take on different shapes and features and topographical arrangements to accommodate their specific needs during spermatogenesis. The nuclear envelope and pore complex also undergo extensive modifications concomitant with the development of germ cell generations. Apoptosis is an event that is normally triggered by germ cells and involves many proteins. It occurs to limit the germ cell pool and acts as a quality control mechanism. The ubiquitin pathway comprises enzymes that ubiquitinate as well as deubiquitinate target proteins and this pathway is present and functional in germ cells. Germ cells express many proteins involved in water balance and pH control as well as voltage-gated ion channel movement. In the nucleus, proteins undergo epigenetic modifications which include methylation, acetylation, and phosphorylation, with each of these modifications signaling changes in chromatin structure. Germ cells contain specialized transcription complexes that coordinate the differentiation program of spermatogenesis, and there are many male germ cell-specific differences in the components of this machinery. All of the above features of germ cells will be discussed along with the specific proteins/genes and abnormalities to fertility related to each topic.

Histone H4 acetylation is essential to proceed from a histone- to a protamine-based chromatin structure in spermatid nuclei of Drosophila melanogaster

In humans, other mammals, and also in Drosophila, the paternal genome in the sperm is highly condensed and organized mainly in a protamine-based chromatin structure. However, the timing and mechanism of the switch from a histone- to the protamine-based chromatin configuration is still poorly understood. We therefore established Drosophila in vitro cultures of cysts with 64 synchronously developing spermatids genetically marked with histone H2AvD-RFP and ProtamineB-eGFP. Live cell imaging showed that the switch from H2AvD-RFP to Protamine-eGFP chromatin takes approximately five hours, with a short but clear overlap of the presence of both histones and protamines. Moreover, cultured pupal testes showed H4 hyperacetylation at the canoe stage shortly before histone removal; a feature previously observed in the intact animal. We then used TSA to inhibit histone deacetylation and found that premature hyperacetylation was already induced at the round nuclei stage of spermatids. However, this premature hyperacetylation did not lead to a premature switch to the protamine-based chromatin structure, showing that histone hyperacetylation is not the sole inducer of the histone to protamine switch. Importantly, we observed that inactivation of histone acetyltransferases by anacardic acid blocks further differentiation and thus prevents the degradation of histones and the switch to a protamine-based chromatin. Thus, we conclude that H4 hyperacetylation is an essential feature but not the sole inducer of the histone to protamine switch during spermiogenesis.

Novel siRNA delivery system to target podocytes in vivo

Podocytes are injured in several glomerular diseases. To alter gene expression specifically in podocytes in vivo, we took advantage of their active endocytotic machinery and developed a method for the targeted delivery of small interfering ribonucleic acids (siRNA). We generated an anti-mouse podocyte antibody that binds to rat and mouse podocytes in vivo. The polyclonal IgG antibody was cleaved into monovalent fragments, while preserving the antigen recognition sites. One Neutravidin molecule was linked to each monovalent IgG via the available sulfohydryl group. Protamine, a polycationic nuclear protein and universal adaptor for anionic siRNA, was linked to the neutravidin via biotin. The delivery system was named shamporter (sheep anti mouse podocyte transporter). Injection of shamporter coupled with either nephrin siRNA or TRPC6 siRNA via tail vein into normal rats substantially reduced the protein levels of nephrin or TRPC6 respectively, measured by western blot analysis and immunostaining. The effect was target specific because other podocyte-specific genes remained unchanged. Shamporter + nephrin siRNA induced transient proteinuria in rats. Control rats injected with shamporter coupled to control-siRNA showed no changes. These results show for the first time that siRNA can be delivered efficiently and specifically to podocytes in vivo using an antibody-delivery system.

Role of RNA-binding proteins in mammalian spermatogenesis

Spermatogenesis is a cell differentiation programme that allows a normally dividing diploid cell to become haploid and to acquire the morphological characteristics required to reach and to fertilize the female gamete. Many of the steps involved in this differentiation programme necessitate profound modifications of the genome, rendering it unable to play its template role for the synthesis of mRNAs. Therefore, de novo transcription is not a continuous process during germ cell differentiation and many mRNAs need to be synthesized and stored at specific times to be available during the transcriptionally inactive stages of spermatogenesis. Germ cells express high levels of RNA-binding proteins that assist these post-transcriptional events. The generation of mouse knockout models has highlighted the essential role played by many of these RNA-binding proteins for the correct progress of spermatogenesis and for the formation of a fertile male gamete. Herein, we review the major findings on the role of RNA-binding proteins in mammalian spermatogenesis.

Inheritance of epigenetic aberrations (constitutional epimutations) in cancer susceptibility

The pathogenic role for heritable mutations in the DNA sequence of tumor suppressor and DNA repair genes has been well established in familial cancer syndromes. These germ line mutations confer a high risk of developing particular types of cancer, according to the gene affected, at a young age of onset when compared to sporadically arising cancers of a similar type. The widespread role for epigenetic dysregulation in the development and progression of sporadic cancers is also well recognized. However, it has only become apparent in recent years that epigenetic aberrations can also occur constitutionally to confer a similar cancer phenotype as a genetic mutation within the same gene. These epigenetic errors are termed "constitutional epimutations" and are characterized by promoter methylation and transcriptional silencing of a single allele of the gene in normal somatic tissues in the absence of a sequence mutation within the affected locus. This is best exemplified in Lynch syndrome, which is an autosomal dominant cancer susceptibility syndrome characterized by the early development of colorectal, uterine, and additional cancers exhibiting microsatellite instability due to impaired mismatch repair. Lynch syndrome is usually caused by heterozygous loss-of-function germ line mutations of the mismatch repair genes, namely MLH1, MSH2, MSH6, and PMS2. Tumors develop following an acquired somatic loss of the remaining functional allele. However, a subset of Lynch syndrome cases without genetic mutations instead has a constitutional epimutation of MLH1 or MSH2. These epimutations are associated with distinct patterns of inheritance depending on the nature of the mechanisms underlying them.

A common haplotype of protamine 1 and 2 genes is associated with higher sperm counts

Sperm chromatin compaction in the sperm head is achieved when histones are replaced by protamines during spermatogenesis. Haploinsufficiency of the protamine 1 (PRM1) or PRM2 gene causes infertility in mice. However, the published data remain inconclusive about a role of PRM1/2 variants in male infertility and their association with semen parameters. By full sequence analysis, we assessed the frequency of sequence variations in PRM1 and PRM2 in three groups of Caucasian patients with idiopathic teratozoospermia and normal (n = 88) or reduced sperm concentration (n = 83) and in men with a high percentage of normal sperm morphology and normal concentrations (n = 77). Two rare (c.54G>A and c.102G>T) and one common SNP (c.230A>C) were identified in PRM1. In PRM2, some rare heterozygous mutations and the two common intronic SNPs 298G>C and 373C>A were detected. None of the PRM1/2 variants was associated with teratozoospermia or individually with other semen parameters. However, significant linkage disequilibrium was detected between the common SNPs of PRM1 and PRM2 which formed haplotypes. Analysis of the pooled group (n = 248) revealed that homozygous carriers of the common haplotype ACC had a twofold higher sperm concentration and count than men lacking this haplotype, with sperm counts of heterozygotes for ACC being midway between the homozygotes. This markedly decreased sperm output might either be caused by spermatozoa lacking the ACC haplotype not being viable, or subject to negative selection. In addition, a significant deviation from Hardy-Weinberg-Equilibrium of these SNPs might indicate natural selection in favour of the ACC allele which leads to higher sperm output and therefore better fertility. In conclusion, for the first time we describe an association of a common haplotype formed by PRM1 and PRM2 with sperm output in a large group of men.

Sperm chromatin-induced ectopic polar body extrusion in mouse eggs after ICSI and delayed egg activation

Meiotic chromosomes in an oocyte are not only a maternal genome carrier but also provide a positional signal to induce cortical polarization and define asymmetric meiotic division of the oocyte, resulting in polar body extrusion and haploidization of the maternal genome. The meiotic chromosomes play dual function in determination of meiosis: 1) organizing a bipolar spindle formation and 2) inducing cortical polarization and assembly of a distinct cortical cytoskeleton structure in the overlying cortex for polar body extrusion. At fertilization, a sperm brings exogenous paternal chromatin into the egg, which induces ectopic cortical polarization at the sperm entry site and leads to a cone formation, known as fertilization cone. Here we show that the sperm chromatin-induced fertilization cone formation is an abortive polar body extrusion due to lack of spindle induction by the sperm chromatin during fertilization. If experimentally manipulating the fertilization process to allow sperm chromatin to induce both cortical polarization and spindle formation, the fertilization cone can be converted into polar body extrusion. This suggests that sperm chromatin is also able to induce polar body extrusion, like its maternal counterpart. The usually observed cone formation instead of ectopic polar body extrusion induced by sperm chromatin during fertilization is due to special sperm chromatin compaction which restrains it from rapid spindle induction and therefore provides a protective mechanism to prevent a possible paternal genome loss during ectopic polar body extrusion.

Spermatogenesis-specific features of the meiotic program in Caenorhabditis elegans

In most sexually reproducing organisms, the fundamental process of meiosis is implemented concurrently with two differentiation programs that occur at different rates and generate distinct cell types, sperm and oocytes. However, little is known about how the meiotic program is influenced by such contrasting developmental programs. Here we present a detailed timeline of late meiotic prophase during spermatogenesis in Caenorhabditis elegans using cytological and molecular landmarks to interrelate changes in chromosome dynamics with germ cell cellularization, spindle formation, and cell cycle transitions. This analysis expands our understanding C. elegans spermatogenesis, as it identifies multiple spermatogenesis-specific features of the meiotic program and provides a framework for comparative studies. Post-pachytene chromatin of spermatocytes is distinct from that of oocytes in both composition and morphology. Strikingly, C. elegans spermatogenesis includes a previously undescribed karyosome stage, a common but poorly understood feature of meiosis in many organisms. We find that karyosome formation, in which chromosomes form a constricted mass within an intact nuclear envelope, follows desynapsis, involves a global down-regulation of transcription, and may support the sequential activation of multiple kinases that prepare spermatocytes for meiotic divisions. In spermatocytes, the presence of centrioles alters both the relative timing of meiotic spindle assembly and its ultimate structure. These microtubule differences are accompanied by differences in kinetochores, which connect microtubules to chromosomes. The sperm-specific features of meiosis revealed here illuminate how the underlying molecular machinery required for meiosis is differentially regulated in each sex.

Male germ cell-specific protein Trs4 binds to multiple proteins

Temperature-related sequence 4 (Trs4) has been identified as a testis-specific gene with expression sensitive to the abdominal temperature changes induced by artificial cryptorchidism. In murine testes, Trs4 mRNA was detected in round spermatids and its protein was localized mainly in the elongating spermatids as well as in the acrosomes and tails of mature spermatozoa. Using a yeast two-hybrid screening system, we identified Rshl-2, Gstmu1, and Ddc8 as putative binding partners of the Trs4 protein in mouse testes. Their interactions were confirmed by in vivo and in vitro binding assays. Further studies demonstrated that Ddc8, a newly identified gene with unknown functions, displayed a similar expression pattern with Trs4 in mouse testes. In particular, Trs4, Ddc8, and Rshl-2 proteins were co-localized to the tails of mature spermatozoa. These results suggested that Trs4 might be involved in diverse processes of spermiogenesis and/or fertilization through interactions with its multiple binding partners.

Loss of histone deacetylase 4 causes segregation defects during mitosis of p53-deficient human tumor cells

We investigated the role of histone deacetylase 4 (HDAC4) using RNA interference (RNAi) and knockout cells to specifically address its role in cell cycle progression in tumor and normal cells. Ablation of HDAC4 led to growth inhibition in human tumor cells but not to detectable effects in normal human dermal fibroblasts (NHDF) or myelopoietic progenitors. HDAC4-/+ or HDAC4-/- murine embryonic fibroblasts showed no detectable growth defects. On the other hand, HDAC4 RNAi in HeLa cells produced mitotic arrest followed by caspase-dependent apoptosis. Mitotically arrested cells showed chromosome segregation defects. Even though the growth of both p53-wild-type and p53-null tumor cells were affected by HDAC4 ablation, segregation defects were observed only in p53-null cells. HDAC4 associates with the PP2A-B56 regulatory subunit, which is known to be involved in chromosome segregation, and RNAi of either the structural subunit A or the regulatory subunit B56 of PP2A also caused chromosome segregation defects. We conclude that HDAC4 is required for cell cycle progression of tumor cells by multiple mechanisms, one of which seems to be specific to p53-deficient cells through chromosome segregation defects. On the contrary, HDAC4 is not required for the progression of NHDF. We therefore suggest that systemic selective interference with the expression or function of HDAC4 is expected to have a significant therapeutic window, in particular, for p53-deficient tumors.

Conservation of the PRM1→PRM2→TNP2 Domain

In mouse and human, the genes encoding protamines PRM1, PRM2 and transition protein TNP2 are found clustered together on chromosome 16. In addition, these three genes lie in the same orientation to one another and are coordinately expressed in a haploid-specific manner during spermatogenesis. Previously, we have shown that the human PRM1 --> PRM2 --> TNP2 locus exists as a single chromatin domain bounded by two male germ cell-specific MARs, i.e. Matrix Attachment Regions. A third, somatic-specific MAR element lies immediately 3' of the PRM1 --> PRM2 --> TNP2 domain. This MAR maps to a conserved CpG island 5' of the human SOCS-1 gene. Similarly, two candidate MARs flank the mouse Prm1 --> Prm2 --> Tnp2 domain. Comparative analysis of the mouse and human promoter regions identified several conserved regulatory motifs for each of the genes of this cluster. This further establishes the synteny of this region. Global structural similarities and the functional relevance of the associated candidate regulatory elements are discussed.

Male infertility caused by spermiogenic defects: lessons from gene knockouts

Spermiogenesis refers to the process by which postmeiotic spermatids differentiate into elongated spermatids and eventually spermatozoa. During spermiogenesis, round spermatids undergo dynamic morphologic changes, which include nuclear condensation and elongation, formation of flagella and acrosome, reorganization of organelles and elimination of cytoplasm upon spermiation. This cellular differentiation process is unique to male haploid germ cells, which may explain why approximately half of the testis-specific genes are exclusively expressed in spermiogenesis. The spermiogenesis-specific expression implies that these genes contribute to either structural or functional aspects of future sperm. Many such genes have been inactivated in mice and some of these gene knockout mice display male infertility due to nonfunctional sperm which display no or various degrees of structural abnormalities. Since the majority of these spermiogenesis-specific genes are highly conserved between mice and humans, findings from knockout mouse studies may be applicable to human infertility. Here, I briefly review some of these spermatid-specific gene knockouts. The mouse studies strongly suggest that sperm quality rather than quantity is a better indicator of male fertility and novel assays should be developed to determine sperm functionality.

Seminiferous tubule transfection in vitro to define post-meiotic gene regulation

BACKGROUND

Post-meiotically expressed genes in the testis are essential for the proper progression of spermatogenesis, and yet, aside from the construction of individual transgenic mice using specific promoters to drive reporter plasmids, there are only very limited possibilities for relevant and quantitative analysis of gene promoters. This is due to the special nature of post-meiotic haploid cells, which to date are not represented in any appropriate cell-lines. This article reports the development of novel methodology using isolated and cultured rat seminiferous tubules in a multiwell format, into which promoter-reporter constructs can be introduced by a combination of microinjection and electroporation.

METHODS

Culture conditions were developed which allowed the continued incubation of isolated rat seminiferous tubules for up to 48 h without obvious cell death and loss of post-meiotic cells. Transfection of intact seminiferous tubules by microinjection and electroporation was optimized to achieve high expression efficiencies of control plasmids, using either fluorescent protein or luciferase as reporters, thereby allowing both morphological as well as quantitative assessment.

RESULTS

Successful transfection was achieved into all cell types except for mature spermatozoa. However, there appeared to be only limited cell-type specificity for the promoters used, even though these had appeared to be specific when used in transgenic animals.

CONCLUSION

We have devised a methodology which allows relatively high throughput analysis of post-meiotic gene promoters into primary cells of intact seminiferous tubules. An apparent lack of cell-type specificity suggests that the gene fragments used do not contain sufficient targeting information, or that the transient episomal expression of the constructs does not encourage appropriate expression specificity. The results also highlight the doubtful interpretation of many studies using heterologous transfection systems to analyse post-meiotically expressed genes.

Role of translation by mitochondrial-type ribosomes during sperm capacitation: an analysis based on a proteomic approach

Mammalian spermatozoa contain a complex population of mRNAs, some of which have been demonstrated to be translated de novo by mitochondrial-type ribosomes using D-chloramphenicol (CP), a specific inhibitor of mitochondrial translation. However, little is known about the functions of these mRNAs in mature sperm. In the present study, differential proteomic approaches were applied to study sperm protein profiles translated by mitochondrial-type ribosomes using the inhibitor CP and 44 proteins were identified with lower expression in CP-treated sperm in comparison to capacitated sperm (ratio >or= 1.5, p<0.05). Results of Western blot and real-time PCR suggest that four proteins were translated by mitochondrial-type ribosomes. Bioinformatics analysis indicated that 26 of 44 proteins were involved in some critical processes correlated to sperm-egg interaction event. In addition, Mups, whose functions in reproduction have never been studied, were chosen for further study. Our results showed that Mups proteins were localized to the acrosome and flagellum of precapacitated sperm, and were also expressed in the equatorial segment of capacitated sperm. The depletion of Mups using neutralizing antibodies significantly inhibited capacitation in a dose-dependent manner, subsequently inhibited acrosome reaction and sperm-egg fusion. In summary, mitochondrial translation during capacitation can store proteins beneficial for sperm-egg interaction.