Testicular expression of small ubiquitin-related modifier-1 (SUMO-1) supports multiple roles in spermatogenesis: silencing of sex chromosomes in spermatocytes, spermatid microtubule nucleation, and nuclear reshaping

Caloric Restriction and Sirtuins as New Players to Reshape Male Fertility

Over the years, caloric intake has remained a subject of profound scrutiny. Within the scientific community, there has been rigorous debate to ascertain which path is most ideal for enhancing quality of life and extending the human lifespan. Caloric restriction has been shown to be a promising contributor towards longevity and delaying the onset of age-related diseases. This diet consists of a reduction in caloric intake while maintaining essential energy and nutritional requirements to achieve optimal health while avoiding malnutrition. However, the effects of this nutritional regimen on male reproductive health have not yet been comprehensively studied. Nevertheless, such a complex process will certainly be regulated by a variety of metabolic sensors, likely sirtuins. Evidence has been gathered regarding this group of enzymes, and their ability to regulate processes such as chromatin condensation, the cell cycle, insulin signaling, and glucose and lipid metabolism, among many others. Concerning testicular function and male fertility, sirtuins can modulate certain metabolic processes through their interaction with the hypothalamic-pituitary-gonadal axis and mitochondrial dynamics, among many others, which remain largely unexplored. This review explores the impact of caloric restriction on male fertility, highlighting the emerging role of sirtuins as key regulators of male reproductive health through their influence on cellular metabolism.

Reduced SIRT1 and SIRT3 and Lower Antioxidant Capacity of Seminal Plasma Is Associated with Shorter Sperm Telomere Length in Oligospermic Men

Infertility affects millions of couples worldwide and has a profound impact not only on their families, but also on communities. Telomere attrition has been associated with infertility, DNA damage and fragmentation. Oxidative stress has been shown to affect sperm DNA integrity and telomere length. Sirtuins such as SIRT1 and SIRT3 are involved in aging and oxidative stress response. The aim of the present study is to determine the role of SIRT1 and SIRT3 in regulating oxidative stress, telomere shortening, and their association with oligospermia. Therefore, we assessed the protein levels of SIRT1 and SIRT3, total antioxidant capacity (TAC), superoxide dismutase (SOD), malondialdehyde (MDA) and catalase activity (CAT) in the seminal plasma of 272 patients with oligospermia and 251 fertile men. We also measured sperm telomere length (STL) and leukocyte telomere length (LTL) using a standard real-time quantitative PCR assay. Sperm chromatin and protamine deficiency were also measured as per standard methods. Our results for oligospermic patients demonstrate significant reductions in semen parameters, shorter STL and LTL, lower levels of SOD, TAC, CAT, SIRT1 and SIRT3 levels, and also significant protamine deficiency and higher levels of MDA and DNA fragmentation. We conclude that a shorter TL in sperms and leukocytes is associated with increased oxidative stress that also accounts for high levels of DNA fragmentation in sperms. Our results support the hypothesis that various sperm parameters in the state of oligospermia are associated with or caused by reduced levels of SIRT1 and SIRT3 proteins.

Broad phosphorylation mediated by testis-specific serine/threonine kinases contributes to spermiogenesis and male fertility

Genetic studies elucidate a link between testis-specific serine/threonine kinases (TSSKs) and male infertility in mammals, but the underlying mechanisms are unclear. Here, we identify a TSSK homolog in Drosophila, CG14305 (termed dTSSK), whose mutation impairs the histone-to-protamine transition during spermiogenesis and causes multiple phenotypic defects in nuclear shaping, DNA condensation, and flagellar organization in spermatids. Genetic analysis demonstrates that kinase catalytic activity of dTSSK, which is functionally conserved with human TSSKs, is essential for male fertility. Phosphoproteomics identify 828 phosphopeptides/449 proteins as potential substrates of dTSSK enriched primarily in microtubule-based processes, flagellar organization and mobility, and spermatid differentiation and development, suggesting that dTSSK phosphorylates various proteins to orchestrate postmeiotic spermiogenesis. Among them, the two substrates, protamine-like protein Mst77F/Ser⁹ and transition protein Mst33A/Ser²³⁷, are biochemically validated to be phosphorylated by dTSSK in vitro, and are genetically demonstrated to be involved in spermiogenesis in vivo. Collectively, our findings demonstrate that broad phosphorylation mediated by TSSKs plays an indispensable role in spermiogenesis.

Post-ovulatory aging is associated with altered patterns for small ubiquitin-like modifier (SUMO) proteins and SUMO-specific proteases

Mammalian oocytes are ovulated arrested at metaphase of the second meiotic division. If they are not fertilized within a short period, the oocyte undergoes several progressive morphological, structural, and molecular changes during a process called oocyte aging. Herein, we focused on those functional events associated with proper cytoskeleton organization and those that correlate with spindle displacement and chromosome misalignment or scatter. Post-translational modifications by Small Ubiquitin-like Modifier (SUMO) proteins are involved in spindle organization and here we demonstrate that the SUMO pathway is involved in spindle morphology changes and chromosome movements during oocyte aging. SUMO-2/3 as well as the SUMO-specific proteases SENP-2 localization are affected by postovulatory aging in vitro. Consistent with these findings, UBC9 decreases during oocyte aging while differential ubiquitination patterns also correlate with in vitro oocyte aging. These results are consistent with postovulatory aging-related alterations in the posttranslational modifications of the spindle apparatus by SUMO and its SENP proteases. These findings are suggestive that such age-related changes in SUMOylation and the deSUMOylation of key target proteins in the spindle apparatus and kinetochore may be involved with spindle and chromosome alignment defects during mammalian oocyte postovulatory aging. Such findings may have implications for ART-related human oocyte aging in vitro regarding the activities of the SUMO pathway and fertilization success.

SIRT1: A Key Player in Male Reproduction

Reproduction is the way to immortality for an individual, and it is essential to the continuation of the species. Sirtuins are involved in cellular homeostasis, energy metabolism, apoptosis, age-related problems, and sexual reproduction. Sirtuin 1 (SIRT1) belongs to the sirtuin family of deacetylases, and it is a nicotinamide adenine dinucleotide (NAD)-dependent deacetylase. It removes the acetyl group from a variety of substrates. SIRT1 regulates endocrine/metabolic, reproductive, and placental development by deacetylating histone, different transcription factors, and signal transduction molecules in a variety of cellular processes. It also plays a very important role in the synthesis and secretion of sex hormones via regulating the hypothalamus-pituitary-gonadal (HPG) axis. Moreover, SIRT1 participates in several key stages of spermatogenesis and sperm maturation. The current review will give a thorough overview of SIRT1's functions in male reproductive processes, thus paving the way for more research on restorative techniques and their uses in reproductive medicine.

Sumoylation and its regulation in testicular Sertoli cells

The molecular regulation of Sertoli cells and their crosstalk with germ cells has not been fully characterized. SUMO proteins are essential for normal development and are expressed in mouse and human Sertoli cells; However, the cell-specific role of sumoylation in those cells has only started to be elucidated. In other cell types, including granulosa cells, sumoylation is regulated by a SUMO ligase KAP1/Trim28. Deletion of KAP1 in Sertoli cells causes testicular degeneration; However, the role of KAP1 in those cells has not been identified. Here we show that both mouse and human Sertoli undergo apoptosis upon inhibition of sumoylation with a chemical inhibitor or via a siRNA technology. We have additionally detected changes in the Sertoli cell proteome upon the inhibition of sumoylation, and our data suggest that among others, the expression of ER/stress-related proteins is highly affected by this inhibition. Sumoylation may also regulate the NOTCH signaling which is important for the maintenance of the developing germ cells. Furthermore, we show that a siRNA-down-regulation of KAP1 in a Sertoli-derived cell line causes an almost complete inactivation of sumoylation. In conclusion, sumoylation regulates important survival and signaling pathways in Sertoli cells, and KAP1 can be a major regulator of sumoylation in these cells.

The Role of Protein SUMOylation in Human Hepatocellular Carcinoma: A Potential Target of New Drug Discovery and Development

Small ubiquitin-like modifier (SUMO) is a highly conserved post-translational modification protein, mainly found in eukaryotes. They are widely expressed in different tissues, including the liver. As an essential post-translational modification, SUMOylation is involved in many necessary regulations in cells. It plays a vital role in DNA repair, transcription regulation, protein stability and cell cycle progression. Increasing shreds of evidence show that SUMOylation is closely related to Hepatocellular carcinoma (HCC). The high expression of SUMOs in the inflammatory hepatic tissue may lead to the carcinogenesis of HCC. At the same time, SUMOs will upregulate the proliferation and survival of HCC, migration, invasion and metastasis of HCC, tumour microenvironment as well as drug resistance. This study reviewed the role of SUMOylation in liver cancer. In addition, it also discussed natural compounds that modulate SUMO and target SUMO drugs in clinical trials. Considering the critical role of SUMO protein in the occurrence of HCC, the drug regulation of SUMOylation may become a potential target for treatment, prognostic monitoring and adjuvant chemotherapy of HCC.

Mechanisms of doxorubicin-mediated reproductive toxicity - A review

The anticancer drug doxorubicin has been associated with several adverse side-effects including reproductive toxicity in both genders. The current review has complied the mechanisms of doxorubicin induced reproductive toxicity. The articles cited in the review were searched using Google Scholar, PubMed, Scopus, Science Direct. Doxorubicin treatment has been found to cause a decrease in testicular mass along with histopathological deformities, oligospermia and abnormalities in sperm morphology. Apart from severely affecting the normal physiological role of both Leydig cells and Sertoli cells, doxorubicin also causes chromosome abnormalities and affects DNA methylase enzyme. Testicular lipid metabolism has been found to be negatively affected by doxorubicin treatment resulting in altered profile of sphingolipids glycerophospholipids and neutral lipids. Dysregulation of 3β-hydroxysteroid dehydrogenase (3β-HSD) and 17β- hydroxysteroid dehydrogenase (17β-HSD) are strongly linked to testicular exposure to doxorubicin. Further, oxidative stress along with endoplasmic reticulum stress are also found to aggravate the male reproductive functioning in doxorubicin treated conditions. Several antioxidant enzymes such as superoxide dismutase, catalase, glutathione peroxidase (GPx) are downregulated by doxorubicin. It also disturbs the hormones of the hypothalamic-pituitary-gonadal (HPG)-axis including testosterone, luteinizing hormone, follicle stimulating hormone etc. In females, the drug disturbs folliculogenesis and oogenesis leading to failure of ovulation and uterine cycle. In rodent model the drug shortens pro-estrous and estrous phases. It was also found that doxorubicin causes mitochondrial dysfunction in oocytes with impaired calcium signaling along with ER stress. The goal of the present review is to comprehends various pathways due to which doxorubicin treatment promotes toxicity in male and female reproductive system.

The role of SUMOylation during development

During the development of multicellular organisms, transcriptional regulation plays an important role in the control of cell growth, differentiation and morphogenesis. SUMOylation is a reversible post-translational process involved in transcriptional regulation through the modification of transcription factors and through chromatin remodelling (either modifying chromatin remodelers or acting as a ‘molecular glue’ by promoting recruitment of chromatin regulators). SUMO modification results in changes in the activity, stability, interactions or localization of its substrates, which affects cellular processes such as cell cycle progression, DNA maintenance and repair or nucleocytoplasmic transport. This review focuses on the role of SUMO machinery and the modification of target proteins during embryonic development and organogenesis of animals, from invertebrates to mammals.

Identification of sumoylated targets in proliferating mouse spermatogonia and human testicular seminomas

Spermatogenesis is regulated by a complex network of posttranslation modifications. Sumoylation (a modification by small ubiquitin-like modifiers, or SUMO proteins) was identified as an important cellular event in different cell types. SUMO proteins are highly expressed in the testis, and their role during spermatogenesis has begun to be elucidated. Given the important role of sumoylation in the regulation of mitosis and cancer progression in other tissues, the aim of the current study was to identify the targets of SUMO in proliferating mouse spermatogonia and human seminoma tissues and to initially examine the level of sumoylation in relation to the proliferative activity of the tissues. Using freshly purified spermatogonia and C18-4 spermatogonia cell line, mass spectrometry analysis identified several SUMO targets implicated into the proliferation of spermatogonia (such as heat shock protein 60 [HSP60] and prohibitin). Tissue array and western blot approaches showed that SUMO expression is a prominent feature of human seminomas and that the proliferative activity of the tumor tissues was positively correlated with the level of SUMO expression. Downregulation of sumoylation with si-RNA was not sufficient to significantly affect the proliferation of C18-4 spermatogonia; however, SUMO overexpression increased the proliferation rate of the cells. These data suggest that cells are more sensitive to an elevated level of SUMO, and that this situation may lead to an upregulated cellular proliferation and, possibly, cancer. Mass spectrometry analysis identified around a hundred SUMO targets in seminoma samples. Notably, many of the identified proteins (such as proliferating cell nuclear antigen [PCNA], DNA topoisomerase 2-alpha [Top2A], prohibitin, 14-3-3 protein, and others) were implicated in oncogenic transformation and cancer progression.

Programmed DNA Elimination in Vertebrates

Over the last few decades, an increasing number of vertebrate taxa have been identified that undergo programmed genome rearrangement, or programmed DNA loss, during development. In these organisms, the genome of germ cells is often reproducibly different from the genome of all other cells within the body. Although we clearly have not identified all vertebrate taxa that undergo programmed genome loss, the list of species known to undergo loss now represents ∼10% of vertebrate species, including several basally diverging lineages. Recent studies have shed new light on the targets and mechanisms of DNA loss and their association with canonical modes of DNA silencing. Ultimately, expansion of these studies into a larger collection of taxa will aid in reconstructing patterns of shared/independent ancestry of programmed DNA loss in the vertebrate lineage, as well as more recent evolutionary events that have shaped the structure and content of eliminated DNA.

Filamentous actin disorganization and absence of apical ectoplasmic specialization disassembly during spermiation upon interference with retinoid signaling†

Spermiation is a multiple-step process involving profound cellular changes in both spermatids and Sertoli cells. We have observed spermiation defects, including abnormalities in spermatid orientation, translocation and release, in mice deficient in the retinoic acid receptor alpha (RARA) and upon treatment with a pan-RAR antagonist. To elucidate the role of retinoid signaling in regulating spermiation, we first characterized the time course of appearance of spermiogenic defects in response to treatment with the pan-RAR antagonist. The results revealed that defects in spermiation are indeed among the earliest abnormalities in spermatogenesis observed upon inhibition of retinoid signaling. Using fluorescent dye-conjugated phalloidin to label the ectoplasmic specialization (ES), we showed for the first time that these defects involved improper formation of filamentous actin (F-actin) bundles in step 8–9 spermatids and a failure of the actin-surrounded spermatids to move apically to the lumen and to disassemble the ES. The aberrant F-actin organization is associated with diminished nectin-3 expression in both RARA-deficient and pan-RAR antagonist-treated testes. An abnormal localization of both tyrosinated and detyrosinated tubulins was also observed during spermatid translocation in the seminiferous epithelium in drug-treated testes. These results highlight a crucial role of RAR receptor-mediated retinoid signaling in regulating microtubules and actin dynamics in the cytoskeleton rearrangements, required for proper spermiation. This is critical to understand in light of ongoing efforts to inhibit retinoid signaling as a novel approach for male contraception and may reveal spermiation components that could also be considered as new targets for male contraception.

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

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

Nuclear localization of EIF4G3 suggests a role for the XY body in translational regulation during spermatogenesis in mice

Eukaryotic translation initiation factor 4G (EIF4G) is an important scaffold protein in the translation initiation complex. In mice, mutation of the Eif4g3 gene causes male infertility, with arrest of meiosis at the end of meiotic prophase. This study documents features of the developmental expression and subcellular localization of EIF4G3 that might contribute to its highly specific role in meiosis and spermatogenesis. Quite unexpectedly, EIF4G3 is located in the nucleus of spermatocytes, where it is highly enriched in the XY body, the chromatin domain formed by the transcriptionally inactive sex chromosomes. Moreover, many other, but not all, translation-related proteins are also localized in the XY body. These unanticipated observations implicate roles for the XY body in controlling mRNA metabolism and/or "poising" protein translation complexes before the meiotic division phase in spermatocytes.

Deciphering the molecular mechanism during doxorubicin-mediated oxidative stress, apoptosis through Nrf2 and PGC-1α in a rat testicular milieu

Doxorubicin is an extensively applied anti-cancerous drug since 1950's and its usage is constrained because of its accumulation in a non-cancerous organ. Many studies have proven that doxorubicin causes reproductive toxicity depends on its dosage, particularly due to increased oxidative stress and apoptosis. A number of the researches have been carried out concerning its prevention. But there is a need to recognize the mechanism at the back of its toxicity to get better and improved method of treatment. To clarify the feasible mechanism of doxorubicin-mediated reproductive toxicity in rats, we have administrated doxorubicin at distinct dosages inclusive of low dosage (male rats that are at 230-250 g acquired cumulatively 1.5 mg/kg; ip; once per week for five weeks) and high dosage (male rats which are at 230-250 grams obtained cumulatively 15 mg/kg; ip; once every week for five weeks). Doxorubicin decreases antioxidant level such as GSH, Cu/Zn SOD, Mn SOD both in serum and testes. Increased oxidative stress is considered via elevated MDA level both in serum and testes. The level of ROS is measured via the DCFDA method in testes. Apoptosis become found through DNA fragmentation assay and quantification of Caspase 3, Caspase 9, Bcl2 and Cytochrome C. Doxorubicin mediated oxidative stress and apoptosis in testicular milieu is through deregulation of Nrf2, PGC-1α, AHR, ARNT, PXR, SUMO-1, UCP2, UCP3, ANX A5, Caspase 3, Caspase 9, Bcl2, Cytochrome C, GR, and GPX. In end, doxorubicin-mediated oxidative stress and apoptosis is through diverse transcriptional factors and genes with respect to decreased antioxidant level, augmented ROS level and Annexin A5 in the testicular milieu.

Characterization of MAGEG2 with testis-specific expression in mice

Male germ cell development is a well-defined process occurring in numerous seminiferous tubules of the testis. Uncovering testicular novel genes related to intrinsic regulation of spermatogenesis is essential for the understanding of spermatogenesis. In the present study, we investigated mouse Mageg2, which belongs to a group of melanoma-associated antigens (MAGEs). Mageg2 is transcribed in the testis specifically, and its expression level is increased at the pachytene spermatocyte stage, indicating that Mageg2 is expressed predominantly in germ cells. We generated an antibody against mouse MAGEG2 for further characterization at the protein level. Immunoblot analysis suggested that MAGEG2 has specific testicular expression and the expression primarily occurred in pachytene spermatocytes. Proteomic analyses demonstrated that mouse MAGEG2 binded to testicular germ cell-specific serine/threonine-protein kinase 31 (STK31) and heat shock protein 9 (HSPA9). Direct binding with both interaction partners was confirmed by co-immunoprecipitation. We found that STK31 and HSPA9 bind MAGEG2 directly but not with each other. Interestingly, MAGEG2 reduced the kinase activity of STK31. Our study suggests that mouse MAGEG2 has at least two functions, including chaperone activity related to HSPA9 and regulation of pachytene spermatocyte-specific kinase, STK31. Altogether, our results provide the first information about MAGEG2 at the transcript and protein levels and suggest its potential molecular functions.

SUMOylation regulates germinal vesicle breakdown and the Akt/PKB pathway during mouse oocyte maturation

SUMOylation, a process of posttranslational modification of proteins by the small ubiquitin-related modifier (SUMO) family of proteins, is known to be involved in yeast and mammalian somatic cell-cycle regulation. However, the identities of the SUMO-modified oocyte targets are largely unknown and the functional role(s) for SUMOylation during mammalian oocyte maturation remains unclear. On the basis of studies in non-germline cells, protein kinase B/Akt is a potential SUMOylation target in the mouse oocyte, where it plays an essential role in cell-cycle resumption and progression during maturation. This study investigated the temporal patterns and prospective role(s) for interactions between SUMOylation and Akt serine-phosphorylation during oocyte meiotic resumption. Pharmacological inhibition of SUMOylation significantly decreased follicular fluid meiosis-activating sterol-induced cell-cycle resumption in oocytes matured in vitro and negatively affected the phosphorylation and nuclear translocation of Akt. Similarly, nuclear localization of cyclin D1, a downstream target of Akt activation, was significantly decreased following SUMOylation inhibition. Together these data show that SUMO and the posttranslational process of SUMOylation are involved in cell-cycle resumption during murine oocyte maturation and exert a regulatory influence on the Akt pathway during germinal vesicle breakdown.

Temporal and SUMO-specific SUMOylation contribute to the dynamics of Polo-like kinase 1 (PLK1) and spindle integrity during mouse oocyte meiosis

During mammalian meiosis, Polo-like kinase 1 (PLK1) is essential during cell cycle progression. In oocyte maturation, PLK1 expression is well characterized but timing of posttranslational modifications regulating its activity and subcellular localization are less clear. Small ubiquitin-related modifier (SUMO) posttranslational modifier proteins have been detected in mammalian gametes but their precise function during gametogenesis is largely unknown. In the present paper we report for mouse oocytes that both PLK1 and phosphorylated PLK1 undergo SUMOylation in meiosis II (MII) oocytes using immunocytochemistry, immunoprecipitation and in vitro SUMOylation assays. At MII, PLK1 is phosphorylated at threonine-210 and serine-137. MII oocyte PLK1 and phosphorylated PLK1 undergo SUMOylation by SUMO-1, -2 and -3 as shown by individual in vitro assays. Using these assays, forms of phosphorylated PLK1 normalized to PLK1 increased significantly and correlated with SUMOylated PLK1 levels. During meiotic progression and maturation, SUMO-1-SUMOylation of PLK1 is involved in spindle formation whereas SUMO-2/3-SUMOylation may regulate PLK1 activity at kinetochore-spindle attachment sites. Microtubule integrity is required for PLK1 localization with SUMO-1 but not with SUMO-2/3. Inhibition of SUMOylation disrupts proper meiotic bipolar spindle organization and spindle-kinetochore attachment. The data show that both temporal and SUMO-specific-SUMOylation play important roles in orchestrating functional dynamics of PLK1 during mouse oocyte meiosis, including subcellular compartmentalization.

DNA damage response protein TOPBP1 regulates X chromosome silencing in the mammalian germ line

Meiotic synapsis and recombination between homologs permits the formation of cross-overs that are essential for generating chromosomally balanced sperm and eggs. In mammals, surveillance mechanisms eliminate meiotic cells with defective synapsis, thereby minimizing transmission of aneuploidy. One such surveillance mechanism is meiotic silencing, the inactivation of genes located on asynapsed chromosomes, via ATR-dependent serine-139 phosphorylation of histone H2AFX (γH2AFX). Stimulation of ATR activity requires direct interaction with an ATR activation domain (AAD)-containing partner. However, which partner facilitates the meiotic silencing properties of ATR is unknown. Focusing on the best-characterized example of meiotic silencing, meiotic sex chromosome inactivation, we reveal this AAD-containing partner to be the DNA damage and checkpoint protein TOPBP1. Conditional TOPBP1 deletion during pachynema causes germ cell elimination associated with defective X chromosome gene silencing and sex chromosome condensation. TOPBP1 is essential for localization to the X chromosome of silencing "sensors," including BRCA1, and effectors, including ATR, γH2AFX, and canonical repressive histone marks. We present evidence that persistent DNA double-strand breaks act as silencing initiation sites. Our study identifies TOPBP1 as a critical factor in meiotic sex chromosome silencing.

Expression, Localization of SUMO-1, and Analyses of Potential SUMOylated Proteins in Bubalus bubalis Spermatozoa

Mature spermatozoa have highly condensed DNA that is essentially silent both transcriptionally and translationally. Therefore, post translational modifications are very important for regulating sperm motility, morphology, and for male fertility in general. Protein sumoylation was recently demonstrated in human and rodent spermatozoa, with potential consequences for sperm motility and DNA integrity. We examined the expression and localization of small ubiquitin-related modifier-1 (SUMO-1) in the sperm of water buffalo (Bubalus bubalis) using immunofluorescence analysis. We confirmed the expression of SUMO-1 in the acrosome. We further found that SUMO-1 was lost if the acrosome reaction was induced by calcium ionophore A23187. Proteins modified or conjugated by SUMO-1 in water buffalo sperm were pulled down and analyzed by mass spectrometry. Sixty proteins were identified, including proteins important for sperm morphology and motility, such as relaxin receptors and cytoskeletal proteins, including tubulin chains, actins, and dyneins. Forty-six proteins were predicted as potential sumoylation targets. The expression of SUMO-1 in the acrosome region of water buffalo sperm and the identification of potentially SUMOylated proteins important for sperm function implicates sumoylation as a crucial PTM related to sperm function.

Cross-talk between sumoylation and phosphorylation in mouse spermatocytes

The meiotic G2/M1 transition is mostly regulated by posttranslational modifications, however, the cross-talk between different posttranslational modifications is not well-understood, especially in spermatocytes. Sumoylation has emerged as a critical regulatory event in several developmental processes, including reproduction. In mouse oocytes, inhibition of sumoylation caused various meiotic defects and led to aneuploidy. However, the role of sumoylation in male reproduction has only begun to be elucidated. Given the important role of several SUMO targets (including kinases) in meiosis, in this study, the role of sumoylation was addressed by monitoring the G2/M1 transition in pachytene spermatocytes in vitro upon inhibition of sumoylation. Furthermore, to better understand the cross-talk between sumoylation and phosphorylation, the activity of several kinases implicated in meiotic progression was also assessed upon down-regulation of sumoylation. The results of the analysis demonstrate that inhibition of sumoylation with ginkgolic acid (GA) arrests the G2/M1 transition in mouse spermatocytes preventing chromosome condensation and disassembling of the synaptonemal complex. Our results revealed that the activity of PLK1 and the Aurora kinases increased during the G2/M1 meiotic transition, but was negatively regulated by the inhibition of sumoylation. In the same experiment, the activity of c-Abl, the ERKs, and AKT were not affected or increased after GA treatment. Both the AURKs and PLK1 appear to be "at the right place, at the right time" to at least, in part, explain the meiotic arrest obtained in the spermatocyte culture.

Epigenetic: A new approach to etiology of infertility

Infertility is a complex disease which could be caused by male and female factors. The etiology from both factors needs further study. There are some approaches to understanding the etiology of infertility, one of them is epigenetic. Epigenetic modifications consist of DNA methylation, histone modifications, and chromatin remodelling. Male and female germinal cells undergo epigenetic modifications dynamically during differentiation into matured sperm and oocyte cells. In a male, the alteration of DNA methylation in spermatogenesis will cause oligo/asthenozoospermia. In addition, the histone methylation, acetylation, or other histone modification may lead sperm lose its ability to fertilize oocyte. Similarly, in a female, the alteration of DNA methylation and histone modification affects oogenesis, created aneuploidy in fertilized oocytes and resulted in embryonic death in the uterus. Alteration of these epigenetic modification patterns will cause infertility, both in male and female.

Wrestling with Chromosomes: The Roles of SUMO During Meiosis

Meiosis is a specialized form of cell division required for the formation of haploid gametes and therefore is essential for successful sexual reproduction. Various steps are exquisitely coordinated to ensure accurate chromosome segregation during meiosis, thereby promoting the formation of haploid gametes from diploid cells. Recent studies are demonstrating that an important form of regulation during meiosis is exerted by the post-translational protein modification known as sumoylation. Here, we review and discuss the various critical steps of meiosis in which SUMO-mediated regulation has been implicated thus far. These include the maintenance of meiotic centromeric heterochromatin , meiotic DNA double-strand break repair and homologous recombination, centromeric coupling, and the assembly of a proteinaceous scaffold between homologous chromosomes known as the synaptonemal complex.

Identification of cell-specific targets of sumoylation during mouse spermatogenesis

Recent findings suggest diverse and potentially multiple roles of small ubiquitin-like modifier (SUMO) in testicular function and spermatogenesis. However, SUMO targets remain uncharacterized in the testis due to the complex multicellular nature of testicular tissue, the inability to maintain and manipulate spermatogenesis in vitro, and the technical challenges involved in identifying low-abundance endogenous SUMO targets. In this study, we performed cell-specific identification of sumoylated proteins using concentrated cell lysates prepared with de-sumoylation inhibitors from freshly purified spermatocytes and spermatids. One-hundred and twenty proteins were uniquely identified in the spermatocyte and/or spermatid fractions. The identified proteins are involved in the regulation of transcription, stress response, microRNA biogenesis, regulation of major enzymatic pathways, nuclear-cytoplasmic transport, cell-cycle control, acrosome biogenesis, and other processes. Several proteins with important roles during spermatogenesis were chosen for further characterization by co-immunoprecipitation, co-localization, and in vitro sumoylation studies. GPS-SUMO Software was used to identify consensus and non-consensus sumoylation sites within the amino acid sequences of the proteins. The analyses confirmed the cell-specific sumoylation and/or SUMO interaction of several novel, previously uncharacterized SUMO targets such as CDK1, RNAP II, CDC5, MILI, DDX4, TDP-43, and STK31. Furthermore, several proteins that were previously identified as SUMO targets in somatic cells (KAP1 and MDC1) were identified as SUMO targets in germ cells. Many of these proteins have a unique role in spermatogenesis and during meiotic progression. This research opens a novel avenue for further studies of SUMO at the level of individual targets.

Meiotic Silencing in Mammals

Meiosis is essential for reproduction in sexually reproducing organisms. A key stage in meiosis is the synapsis of maternal and paternal homologous chromosomes, accompanied by exchange of genetic material to generate crossovers. A decade ago, studies found that when chromosomes fail to synapse, the many hundreds of genes housed within them are transcriptionally inactivated. This process, meiotic silencing, is conserved in all mammals studied to date, but its purpose is not yet defined. Here, I review the molecular genetics of meiotic silencing and consider the many potential functions that it could serve in the mammalian germ line. In addition, I discuss how meiotic silencing influences sex differences in meiotic infertility and the profound impact that meiotic silencing has had on the evolution of mammalian sex chromosomes.

The enigmatic meiotic dense body and its newly discovered component, SCML1, are dispensable for fertility and gametogenesis in mice

Meiosis is a critical phase in the life cycle of sexually reproducing organisms. Chromosome numbers are halved during meiosis, which requires meiosis-specific modification of chromosome behaviour. Furthermore, suppression of transposons is particularly important during meiosis to allow the transmission of undamaged genomic information between generations. Correspondingly, specialized genome defence mechanisms and nuclear structures characterize the germ line during meiosis. Survival of mammalian spermatocytes requires that the sex chromosomes form a distinct silenced chromatin domain, called the sex body. An enigmatic spherical DNA-negative structure, called the meiotic dense body, forms in association with the sex body. The dense body contains small non-coding RNAs including microRNAs and PIWI-associated RNAs. These observations gave rise to speculations that the dense body may be involved in sex body formation and or small non-coding RNA functions, e.g. the silencing of transposons. Nevertheless, the function of the dense body has remained mysterious because no protein essential for dense body formation has been reported yet. We discovered that the polycomb-related sex comb on midleg-like 1 (SCML1) is a meiosis-specific protein and is an essential component of the meiotic dense body. Despite abolished dense body formation, Scml1-deficient mice are fertile and proficient in sex body formation, transposon silencing and in timely progression through meiosis and gametogenesis. Thus, we conclude that dense body formation is not an essential component of the gametogenetic program in the mammalian germ line.

Molecular cloning and expression analysis of small ubiquitin-like modifier (SUMO) genes from grouper (Epinephelus coioides)

Small ubiquitin-like modifier (SUMO) is a group of proteins binding to lysine residues of target proteins and thereby modifying their stability, activity and subcellular localization. In the present study, two SUMO homolog genes (EcSUMO1 and EcSUMO2) from grouper (Epinephelus coioides) were cloned and characterized. The full-length sequence of EcSUMO1 was 749 bp in length and contained a predicted open reading frame of 306 bp encoding 101 amino acids with a molecular mass of 11.34 kDa. The full-length sequence of EcSUMO2 was 822 bp in length and contained a predicted open reading frame of 291 bp encoding 96 amino acids with a molecular mass of 10.88 kDa EcSUMO1 shares 44.55% identity with EcSUMO2. EcSUMO1 shares 99%, 90%, and 88% identity with those from Oreochromis niloticus, Danio rerio, and Homo sapiens, respectively. EcSUMO2 shares 98%, 93%, and 96% identity with those from Anoplopoma fimbria, D.rerio, and H. sapiens, respectively. Quantitative real-time PCR analysis indicated that EcSUMO1 and EcSUMO2 were constitutively expressed in all of the analyzed tissues in healthy grouper, but the expression of EcSUMO2 was higher than that of EcSUMO1. EcSUMO1 and EcSUMO2 were identified as a remarkably (P < 0.01) up-regulated responding to poly(I:C) and Singapore grouper iridovirus (SGIV) stimulation in head kidney of groupers. EcSUMO1 and EcSUMO2 were distributed in both cytoplasm and nucleus in GS cells. Over-expressed EcSUMO1 and EcSUMO2 enhanced SGIV and Red-spotted grouper nervous necrosis virus (RGNNV) replication during viral infection in vitro. Our study was an important attempt to understand the SUMO pathway in fish, which may provide insights into the regulatory mechanism of viral infection in E.coioides under farmed conditions.

Mammalian meiotic silencing exhibits sexually dimorphic features

During mammalian meiotic prophase I, surveillance mechanisms exist to ensure that germ cells with defective synapsis or recombination are eliminated, thereby preventing the generation of aneuploid gametes and embryos. Meiosis in females is more error-prone than in males, and this is in part because the prophase I surveillance mechanisms are less efficient in females. A mechanistic understanding of this sexual dimorphism is currently lacking. In both sexes, asynapsed chromosomes are transcriptionally inactivated by ATR-dependent phosphorylation of histone H2AFX. This process, termed meiotic silencing, has been proposed to perform an important prophase I surveillance role. While the transcriptional effects of meiotic silencing at individual genes are well described in the male germ line, analogous studies in the female germ line have not been performed. Here we apply single- and multigene RNA fluorescence in situ hybridization (RNA FISH) to oocytes from chromosomally abnormal mouse models to uncover potential sex differences in the silencing response. Notably, we find that meiotic silencing in females is less efficient than in males. Within individual oocytes, genes located on the same asynapsed chromosome are silenced to differing extents, thereby generating mosaicism in gene expression profiles across oocyte populations. Analysis of sex-reversed XY female mice reveals that the sexual dimorphism in silencing is determined by gonadal sex rather than sex chromosome constitution. We propose that sex differences in meiotic silencing impact on the sexually dimorphic prophase I response to asynapsis.

Regulation of germ cell function by SUMOylation

Oogenesis and spermatogenesis are tightly regulated complex processes that are critical for fertility. Germ cells undergo meiosis to generate haploid cells necessary for reproduction. Errors in meiosis, including the generation of chromosomal abnormalities, can result in reproductive defects and infertility. Meiotic proteins are regulated by post-translational modifications including SUMOylation, the covalent attachment of small ubiquitin-like modifier (SUMO) proteins. Here, we review the role of SUMO proteins in controlling germ cell development and maturation based on recent findings from mouse models. Several studies have characterized the localization of SUMO proteins in male and female germ cells. However, a deeper understanding of how SUMOylation regulates proteins with essential roles in oogenesis and spermatogenesis will provide useful insight into the underlying mechanisms of germ cell development and fertility.

Polycomb protein SCML2 associates with USP7 and counteracts histone H2A ubiquitination in the XY chromatin during male meiosis

Polycomb group proteins mediate transcriptional silencing in diverse developmental processes. Sex chromosomes undergo chromosome-wide transcription silencing during male meiosis. Here we report that mouse SCML2 (Sex comb on midleg-like 2), an X chromosome-encoded polycomb protein, is specifically expressed in germ cells, including spermatogonia, spermatocytes, and round spermatids. SCML2 associates with phosphorylated H2AX and localizes to the XY body in spermatocytes. Loss of SCML2 in mice causes defective spermatogenesis, resulting in sharply reduced sperm production. SCML2 interacts with and recruits a deubiquitinase, USP7, to the XY body in spermatocytes. In the absence of SCML2, USP7 fails to accumulate on the XY body, whereas H2A monoubiquitination is dramatically augmented in the XY chromatin. Our results demonstrate that the SCML2/USP7 complex constitutes a novel molecular pathway in modulating the epigenetic state of sex chromosomes during male meiosis.

Transcriptome analysis of red swamp crawfish Procambarus clarkii reveals genes involved in gonadal development

Background

The red swamp crawfish, Procambarus clarkii, has become one of the most economically important cultured species in China. Currently, little is known about the gonadal development of this species. Isolation and characterization of genes are an initial step towards understanding gonadal development of P. clarkii.

Results

Using the 454 pyrosequencing technology, we obtained a total of 1,134,993 high quality sequence reads from the crawfish testis and ovary libraries. We aimed to identify different genes with a potential role in gonad development. The assembly formed into 22,652 isotigs, distributed by GO analysis across 55 categories in the three ontologies, ‘molecular function’, ‘cellular component’, and ‘biological processes’. Comparative transcript analysis showed that 1,720 isotigs in the ovary were up-regulated and 2138 isotigs were down-regulated. Several gonad development related genes, such as vitellogenin, cyclin B, cyclin-dependent kinases 2, Dmc1 and ubiquitin were identified. Quantitative real-time PCR verified the expression profiles of 14 differentially expressed genes, and confirmed the reliability of the 454 pyrosequencing.

Conclusions

Our findings provide an archive for future research on gonadal development at a molecular level in P. clarkii and other crustacean. This data will be helpful to develop new ideas for artificial regulation of the reproductive process in crawfish aquaculture.

SUMO1 in human sperm: new targets, role in motility and morphology and relationship with DNA damage

In studies carried out previously, we demonstrated that small ubiquitin-like modifier 1 (SUMO1) is associated with poor sperm motility when evaluated with a protocol that reveals mostly SUMO1-ylated live sperm. Recently, with another protocol, it has been demonstrated that SUMO is expressed in most sperm and is related to poor morphology and motility, suggesting that sumoylation may have multiple roles depending on its localisation and targets. We show herein, by confocal microscopy and co-immunoprecipitation, that dynamin-related protein 1 (DRP1), Ran GTPase-activating protein 1 (RanGAP1) and Topoisomerase IIα, SUMO1 targets in somatic and/or germ cells, are SUMO1-ylated in mature human spermatozoa. DRP1 co-localises with SUMO1 in the mid-piece, whereas RanGAP1 and Topoisomerase IIα in the post-acrosomal region of the head. Both SUMO1 expression and co-localisation with the three proteins were significantly higher in morphologically abnormal sperm, suggesting that sumoylation represents a marker of defective sperm. DRP1 sumoylation at the mid-piece level was higher in the sperm of asthenospermic men. As in somatic cells, DRP1 sumoylation is associated with mitochondrial alterations, this protein may represent the link between SUMO and poor motility. As SUMO pathways are involved in responses to DNA damage, another aim of our study was to investigate the relationship between sumoylation and sperm DNA fragmentation (SDF). By flow cytometry, we demonstrated that SUMO1-ylation and SDF are correlated (r=0.4, P<0.02, n=37) and most sumoylated sperm shows DNA damage in co-localisation analysis. When SDF was induced by stressful conditions (freezing and thawing and oxidative stress), SUMO1-ylation increased. Following freezing and thawing, SUMO1-Topoisomerase IIα co-localisation and co-immunoprecipitation increased, suggesting an involvement in the formation/repair of DNA breakage.

Evidence Implicating CCNB1IP1, a RING Domain-Containing Protein Required for Meiotic Crossing Over in Mice, as an E3 SUMO Ligase

The RING domain-containing protein CCNB1IP1 (Cyclin B1 Interacting Protein 1) is a putative ubiquitin E3 ligase that is essential for chiasmata formation, and hence fertility, in mice. Previous studies in cultured cells indicated that CCNB1IP1 targets Cyclin B for degradation, thus playing a role in cell cycle regulation. Mice homozygous for a mutant allele (mei4) of Ccnb1ip1 display no detectable phenotype other than meiotic failure from an absence of chiasmata. CCNB1IP1 is not conserved in key model organisms such as yeast and Drosophila, and there are no features of the protein that implicate clear mechanisms for a role in recombination. To gain insight into CCNB1IP1’s function in meiotic cells, we raised a specific antibody and determined that the protein appears in pachynema. This indicates that CCNB1IP1 is involved with crossover intermediate maturation, rather than early (leptotene) specification of a subset of SPO11-induced double strand breaks towards the crossover pathway. Additionally, a yeast 2-hybrid (Y2H) screen revealed that CCNB1IP1 interacts with SUMO2 and a set of proteins enriched for consensus sumoylation sites. The Y2H studies, combined with scrutiny of CCNB1IP1 domains, implicate this protein as an E3 ligase of the sumoylation cascade. We hypothesize CCNB1IP1 represents a novel meiosis-specific SUMO E3 ligase critical to resolution of recombination intermediates into mature chiasmata.

The role of E3 ligases in the ubiquitin-dependent regulation of spermatogenesis

The ubiquitination of proteins is a post-translational modification that was first described as a means to target misfolded or unwanted proteins for degradation by the proteasome. It is now appreciated that the ubiquitination of proteins also serves as a mechanism to modify protein function and cellular functions such as protein trafficking, cell signaling, DNA repair, chromatin modifications, cell-cycle progression and cell death. The ubiquitination of proteins occurs through the hierarchal transfer of ubiquitin from an E1 ubiquitin-activating enzyme to an E2 ubiquitin-conjugating enzyme and finally to an E3 ubiquitin ligase that transfers the ubiquitin to its target protein. It is the final E3 ubiquitin ligase that confers the substrate specificity for ubiquitination and is the focus of this review. Spermatogenesis is a complex and highly regulated process by which spermatogonial stem cells undergo mitotic proliferation and expansion of the diploid spermatogonial population, differentiate into spermatocytes and progress through two meiotic divisions to produce haploid spermatids that proceed through a final morphogenesis to generate mature spermatozoa. The ubiquitination of proteins in the cells of the testis occurs in many of the processes required for the progression of mature spermatozoa. Since it is the E3 ubiquitin ligase that recognizes the target protein and provides the specificity and selectivity for ubiquitination, this review highlights known examples of E3 ligases in the testis and the differing roles that they play in maintaining functional spermatogenesis.

The potential role of As-sumo-1 in the embryonic diapause process and early embryo development of Artemia sinica

During embryonic development of Artemia sinica, environmental stresses induce the embryo diapause phenomenon, required to resist apoptosis and regulate cell cycle activity. The small ubiquitin-related modifier-1 (SUMO), a reversible post-translational protein modifier, plays an important role in embryo development. SUMO regulates multiple cellular processes, including development and other biological processes. The molecular mechanism of diapause, diapause termination and the role of As-sumo-1 in this processes and in early embryo development of Artemia sinica still remains unknown. In this study, the complete cDNA sequences of the sumo-1 homolog, sumo ligase homolog, caspase-1 homolog and cyclin B homolog from Artemia sinica were cloned. The mRNA expression patterns of As-sumo-1, sumo ligase, caspase-1, cyclin B and the location of As-sumo-1 were investigated. SUMO-1, p53, Mdm2, Caspase-1, Cyclin B and Cyclin E proteins were analyzed during different developmental stages of the embryo of A. sinica. Small interfering RNA (siRNA) was used to verify the function of sumo-1 in A. sinica. The full-length cDNA of As-sumo-1 was 476 bp, encoding a 92 amino acid protein. The As-caspases-1 cDNA was 966 bp, encoding a 245 amino-acid protein. The As-sumo ligase cDNA was 1556 bp encoding, a 343 amino acid protein, and the cyclin B cDNA was 739 bp, encoding a 133 amino acid protein. The expressions of As-sumo-1, As-caspase-1 and As-cyclin B were highest at the 10 h stage of embryonic development, and As-sumo ligase showed its highest expression at 0 h. The expression of As-SUMO-1 showed no tissue or organ specificity. Western blotting showed high expression of As-SUMO-1, p53, Mdm2, Caspase-1, Cyclin B and Cyclin E at the 10 h stage. The siRNA caused abnormal development of the embryo, with increased malformation and mortality. As-SUMO-1 is a crucial regulation and modification protein resumption of embryonic diapause and early embryo development of A. sinica.

Meiotic cohesin SMC1β provides prophase I centromeric cohesion and is required for multiple synapsis-associated functions

Cohesin subunit SMC1β is specific and essential for meiosis. Previous studies showed functions of SMC1β in determining the axis-loop structure of synaptonemal complexes (SCs), in providing sister chromatid cohesion (SCC) in metaphase I and thereafter, in protecting telomere structure, and in synapsis. However, several central questions remained unanswered and concern roles of SMC1β in SCC and synapsis and processes related to these two processes. Here we show that SMC1β substantially supports prophase I SCC at centromeres but not along chromosome arms. Arm cohesion and some of centromeric cohesion in prophase I are provided by non-phosphorylated SMC1α. Besides supporting synapsis of autosomes, SMC1β is also required for synapsis and silencing of sex chromosomes. In absence of SMC1β, the silencing factor γH2AX remains associated with asynapsed autosomes and fails to localize to sex chromosomes. Microarray expression studies revealed up-regulated sex chromosome genes and many down-regulated autosomal genes. SMC1β is further required for non-homologous chromosome associations observed in absence of SPO11 and thus of programmed double-strand breaks. These breaks are properly generated in Smc1β^−/− spermatocytes, but their repair is delayed on asynapsed chromosomes. SMC1α alone cannot support non-homologous associations. Together with previous knowledge, three main functions of SMC1β have emerged, which have multiple consequences for spermatocyte biology: generation of the loop-axis architecture of SCs, homologous and non-homologous synapsis, and SCC starting in early prophase I.

The generation of mammalian gametes through meiosis comprises two subsequent cell divisions. The first division, meiosis I, features highly specific chromosome structures, and behavior, and requires distinct sets of chromosome-associated proteins. Cohesin proteins, of which some are meiosis-specific, are essential for meiosis, but their particular roles in meiosis are incompletely understood. We show here that SMC1β, a meiosis-specific cohesin, serves key functions already in prophase of meiosis I: SMC1β contributes to keeping sister chromatids in cohesion at their centromeres and supports synapsis of the four sister chromatids present in these cells. SMC1β is required for the synapsis of the X and Y sex chromosomes. The failure of autosomes to properly synapse in absence of SMC1β causes extensive alterations in gene expression. This leads to expression of sex chromosome-linked genes, which are lethal at this stage, explaining the death of spermatocytes in mid-prophase I. Together with the analyses of other cohesin proteins and of phosphorylated forms of SMC3 and SMC1α, this paper describes hitherto undescribed properties and functions of meiotic cohesin in sister chromatid cohesion and synapsis.

ATR acts stage specifically to regulate multiple aspects of mammalian meiotic silencing

In mammals, homologs that fail to synapse during meiosis are transcriptionally inactivated. This process, meiotic silencing, drives inactivation of the heterologous XY bivalent in male germ cells (meiotic sex chromosome inactivation [MSCI]) and is thought to act as a meiotic surveillance mechanism. The checkpoint protein ATM and Rad3-related (ATR) localizes to unsynapsed chromosomes, but its role in the initiation and maintenance of meiotic silencing is unknown. Here we show that ATR has multiple roles in silencing. ATR first regulates HORMA (Hop1, Rev7, and Mad2) domain protein HORMAD1/2 phosphorylation and localization of breast cancer I (BRCA1) and ATR cofactors ATR-interacting peptide (ATRIP)/topoisomerase 2-binding protein 1 (TOPBP1) at unsynapsed axes. Later, it acts as an adaptor, transducing signaling at unsynapsed axes into surrounding chromatin in a manner that requires interdependence with mediator of DNA damage checkpoint 1 (MDC1) and H2AFX. Finally, ATR catalyzes histone H2AFX phosphorylation, the epigenetic event leading to gene inactivation. Using a novel genetic strategy in which MSCI is used to silence a chosen gene in pachytene, we show that ATR depletion does not disrupt the maintenance of silencing and that silencing comprises two phases: The first is dynamic and reversible, and the second is stable and irreversible. Our work identifies a role for ATR in the epigenetic regulation of gene expression and presents a new technique for ablating gene function in the germline.

Localization and identification of sumoylated proteins in human sperm: excessive sumoylation is a marker of defective spermatozoa

BACKGROUND

Sumoylation is a type of post-translational modification that is implicated in the regulation of numerous cellular events. However, its role in the function of human sperm has not yet been characterized.

METHODS AND RESULTS

In this study, both immunofluorescence and electron microscopy revealed that small ubiquitin-like modifiers (SUMO) SUMO1 and SUMO2/3 were highly enriched in the neck area of human sperm that is associated with the redundant nuclear envelope and were also detectable in the flagella and some head regions. Similar localization patterns of SUMO were also observed in mouse and fly sperm. Nonmotile, two-tailed, curled tailed, misshapen, microcephalic (small head) and aciphalic (no head) sperm exhibited abnormally high levels of sumoylation in their neck and tail regions relative to normal sperm. Numerous sumoylated proteins, ranging from 20 to 260 kDa, were detected via western blotting and identified by mass spectrometry, and 55 SUMO targets that were present specifically in human sperm, and not in the control fraction, corresponded to flagella proteins, proteins involved in the maturation and differentiation of sperm, heat shock proteins and important glycolytic and mitochondrial enzymes. The targets that were identified included proteins with specific functions in germ cells and sperm, such as heat shock-related 70-kDa protein 2, outer dense fiber protein 3, A-kinase anchor proteins 3 and 4, L-lactate dehydrogenase C, sperm protein associated with the nucleus on the X chromosome B/F, valosin-containing protein, seminogelins, histone H4 and ubiquitin. Coimmunoprecipitation experiments confirmed the sumoylation of semenogelin and indicated that some sperm proteins are modified by sumoylation and ubiquitination simultaneously.

CONCLUSIONS

Numerous proteins are modified by sumoylation in human sperm; excessive sumoylation is a marker of defective spermatozoa.

Proteomic changes in rat spermatogenesis in response to in vivo androgen manipulation; impact on meiotic cells

The production of mature sperm is reliant on androgen action within the testis, and it is well established that androgens act on receptors within the somatic Sertoli cells to stimulate male germ cell development. Mice lacking Sertoli cell androgen receptors (AR) show late meiotic germ cell arrest, suggesting Sertoli cells transduce the androgenic stimulus co-ordinating this essential step in spermatogenesis. This study aimed to identify germ cell proteins responsive to changes in testicular androgen levels and thereby elucidate mechanisms by which androgens regulate meiosis. Testicular androgen levels were suppressed for 9 weeks using testosterone and estradiol-filled silastic implants, followed by a short period of either further androgen suppression (via an AR antagonist) or the restoration of intratesticular testosterone levels. Comparative proteomics were performed on protein extracts from enriched meiotic cell preparations from adult rats undergoing androgen deprivation and replacement in vivo. Loss of androgenic stimulus caused changes in proteins with known roles in meiosis (including Nasp and Hsp70–2), apoptosis (including Diablo), cell signalling (including 14-3-3 isoforms), oxidative stress, DNA repair, and RNA processing. Immunostaining for oxidised DNA adducts confirmed spermatocytes undergo oxidative stress-induced DNA damage during androgen suppression. An increase in PCNA and an associated ubiquitin-conjugating enzyme (Ubc13) suggested a role for PCNA-mediated regulation of DNA repair pathways in spermatocytes. Changes in cytoplasmic SUMO1 localisation in spermatocytes were paralleled by changes in the levels of free SUMO1 and of a subunit of its activating complex, suggesting sumoylation in spermatocytes is modified by androgen action on Sertoli cells. We conclude that Sertoli cells, in response to androgens, modulate protein translation and post-translational events in spermatocytes that impact on their metabolism, survival, and completion of meiosis.

Drosophila spermiogenesis: Big things come from little packages

Drosophila melanogaster spermatids undergo dramatic morphological changes as they differentiate from small round cells approximately 12 μm in diameter into highly polarized, 1.8 mm long, motile sperm capable of participating in fertilization. During spermiogenesis, syncytial cysts of 64 haploid spermatids undergo synchronous differentiation. Numerous changes occur at a subcellular level, including remodeling of existing organelles (mitochondria, nuclei), formation of new organelles (flagellar axonemes, acrosomes), polarization of elongating cysts and plasma membrane addition. At the end of spermatid morphogenesis, organelles, mitochondrial DNA and cytoplasmic components not needed in mature sperm are stripped away in a caspase-dependent process called individualization that results in formation of individual sperm. Here, we review the stages of Drosophila spermiogenesis and examine our current understanding of the cellular and molecular mechanisms involved in shaping male germ cell-specific organelles and forming mature, fertile sperm.

SUMO-1 of mud crab (Scylla paramamosain) in gametogenesis

The small ubiquitin-related modifier-1 (SUMO-1) is a member of a family of ubiquitin-related proteins. SUMO pathway, which is involved in gene expression in eukaryotic posttranslational processing, plays important roles in gene expression, genomic stability and the occurrence of cells, development and other biological processes. Scylla paramamosain is one of the important economic breeding crabs in the southeast coast of China. To date, little is known about the distinct roles of SUMO in crustacean, especially in crabs. In the present study, we report the identification and characterization of mud crab, S. paramamosain SUMO-1 (SpSUMO-1) gene using an approach which combines expressed sequence tag (EST) and rapid amplification cDNA end (RACE). The full length cDNA of SpSUMO-1 gene (GenBank: HM581660) is of 732 bp, including a 282 bp open reading frame which encodes a protein of 93 amino acids. Tissue distribution analysis showed that SpSUMO-1 was expressed more abundantly in the ovary than in other tissues (P<0.01). And the expression profiles of SpSUMO-1 in the different gonad developing stages revealed that the highest expression of SpSUMO-1 occurred at proliferation stage, and then decreased gradually as the ovarian development progressed, while in the testis, the expression level of SpSUMO-1 was relatively stable at different stages of testis development. The distribution of SpSUMO-1 mRNA and its protein was observed in the crab gametogenesis by in situ hybridization and immunocytochemical method respectively. In oogenesis, SpSUMO-1 transcripts presented at the cytoplasm and nucleus of oocytes from proliferation stage to primary vitellogenesis stage, but only appeared in the nucleus of oocytes in secondary and tertiary vitellogenesis stages. Meanwhile, SpSUMO-1 protein was localized in the cytoplasm of oogonia and different developing oocytes. On the other hand, the SpSUMO-1 transcript was detected throughout the spermatogenesis, with the strong positive signals of SpSUMO-1 presented at the nuclei of primary and secondary spermatocytes, spermatids and spermatozoa. Interestingly, the positive signals of acrosomal tubules of spermatozoa were also detected. SpSUMO-1 protein was localized in spermatogonium, primary spermatocyte, secondary spermatocyte and spermatid, but the positive signal was only detected in the nucleus of spermatozoa. All these results suggested that SUMO-1 may play essential roles in the gametogenesis of the crustacea.

Emerging roles of the SUMO pathway in development

Sumoylation is a reversible post-translational modification that targets a variety of proteins mainly within the nucleus, but also in the plasma membrane and cytoplasm of the cell. It controls diverse cellular mechanisms such as subcellular localization, protein-protein interactions, or transcription factor activity. In recent years, the use of several developmental model systems has unraveled many critical functions for the sumoylation system in the early life of diverse species. In particular, detailed analyses of mutant organisms in both the components of the SUMO pathway and their targets have established the importance of the SUMO system in early developmental processes, such as cell division, cell lineage commitment, specification, and/or differentiation. In addition, an increasing number of developmental proteins, including transcription factors and epigenetic regulators, have been identified as sumoylation substrates. Sumoylation acts on these targets through various mechanisms. For example, this modification has been involved in converting a transcription factor from an activator to a repressor or in regulating the localization and/or stability of numerous transcription factors. This review will summarize current information on the function of sumoylation in embryonic development in different species from yeast to mammals.

Function of the sex chromosomes in mammalian fertility

The sex chromosomes play a highly specialized role in germ cell development in mammals, being enriched in genes expressed in the testis and ovary. Sex chromosome abnormalities (e.g., Klinefelter [XXY] and Turner [XO] syndrome) constitute the largest class of chromosome abnormalities and the commonest genetic cause of infertility in humans. Understanding how sex-gene expression is regulated is therefore critical to our understanding of human reproduction. Here, we describe how the expression of sex-linked genes varies during germ cell development; in females, the inactive X chromosome is reactivated before meiosis, whereas in males the X and Y chromosomes are inactivated at this stage. We discuss the epigenetics of sex chromosome inactivation and how this process has influenced the gene content of the mammalian X and Y chromosomes. We also present working models for how perturbations in sex chromosome inactivation or reactivation result in subfertility in the major classes of sex chromosome abnormalities.

The SUMO pathway functions in mouse oocyte maturation

Sumoylation is an important post-translational modification in which SUMO (small ubiquitin-related modifier) proteins are bonded covalently to their substrates. Studies on the roles of sumoylation in cell cycle regulation have been emerging in both mitosis from yeast to mammals and meiosis in budding yeast, but the functions of sumoylation in mammalian meiosis, especially in oocyte meiotic maturation are not well known. Here, we examined the localization and expression of SUMO-1 and SUMO-2/3, the two basic proteins in the sumoylation pathway and investigated their roles through over-expression of Senp2 during mouse oocyte maturation. Immunofluorescent staining revealed differential patterns of SUMO-1 and SUMO-2/3 localization: SUMO-1 was localized to the spindle poles in prometaphase I, MI and MII stages, around the separating homologues in anaphase I and telophase I stages of first meiosis, while SUMO-2/3 was mainly concentrated near centromeres during mouse oocyte maturation. Immunoblot analysis uncovered the different expression profiles of SUMO-1 and SUMO-2/3 modified proteins during mouse oocyte maturation. Over-expression of Senp2, a SUMO-specific isopeptidase, caused changes of SUMO-modified proteins and led to defects in MII spindle organization in mature eggs. These results suggest that the SUMO pathway may play an indispensable role during mouse oocyte meiotic maturation.