SUMO-1, human male germ cell development, and the androgen receptor in the testis of men with normal and abnormal spermatogenesis

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.

SUMO1 and Defective Spermatozoa Correlate with Endogenous Hydrogen Peroxide and Live Birth Outcome in Intrauterine Insemination Cycles for Unexplained Infertility

This study aimed to investigate the correlation between hydrogen peroxide (H2O2), small ubiquitin-like modifier molecules (SUMO), and pregnancy outcomes in couples with unexplained infertility (UI) undergoing intrauterine insemination (IUI) treatment. We prospectively collected semen samples from 56 couples with UI and divided the spermatozoa into motile and immotile fractions by density gradient centrifugation (DSC). Immunofluorescence staining was used to examine the immunostaining and localization of nuclear pore complex (NPC), SUMO1, and SUMO2/3 in spermatozoa. We detected H2O2 levels by chemiluminescence methods. We found that H2O2 levels correlated with NPC (neck) (r = 0.400) and NPC (tail) (r = 0.473) in motile sperm fractions. In immotile fractions, H2O2 positively correlated with NPC (tail) (r = 0.431) and SUMO1 (neck) (r = 0.282). Furthermore, the positive NPC (tail) group had a significantly lower live birth rate than the negative NPC group (17.9% = 5/28 vs. 42.9% = 12/28). In conclusion, H2O2 positively correlated with SUMO1 (neck) and NPC (tail) in human spermatozoa. The DSC may partially eliminate defective spermatozoa (positive NPC staining); however, if defective spermatozoa remain in the motile fraction, this scenario is associated with a low live birth rate following IUI treatment.

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.

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.

Analysis of lncRNA Expression Profile during the Formation of Male Germ Cells in Chickens

Simple Summary

The differentiation of germ cells plays an important role in sex differentiation in poultry. Therefore, it is necessary for us to explore the potential regulators in the process of germ cell development. In this study, RNA-seq was used to detect the expression profile of long non-coding RNAs (lncRNAs) in chicken embryonic stem cells (ESCs), primordial germ cells (PGCs) and spermatogonial stem cells (SSCs). The results showed that a total of 296, 280 and 357 differentially expressed lncRNAs (DELs) were screened in ESCs vs. PGCs, ESCs vs. SSCs and PGCs vs. SSCs, respectively. Functional analysis of the target genes of DELs showed that autophagy, Wnt/β-catenin, TGF-β, Notch and ErbB signaling pathways were involved in the differentiation process of male germ cells and, moreover, XLOC_612026, XLOC_612029, XLOC_240662, XLOC_362463, XLOC_023952, XLOC_674549, XLOC_160716, ALDBGALG0000001810, ALDBGALG0000002986, XLOC_657380674549, XLOC_022100 and XLOC_657380 were predicted to be the key lncRNAs in this process. Our findings could not only supply scientific data for constructing the gene regulatory network of germ cell development, but also provide new ideas for further optimizing the induction efficiency of germ cells in vitro.

Abstract

Germ cells have an irreplaceable role in transmitting genetic information from one generation to the next, and also play an important role in sex differentiation in poultry, while little is known about epigenetic factors that regulate germ cell differentiation. In this study, RNA-seq was used to detect the expression profiles of long non-coding RNAs (lncRNAs) during the differentiation of chicken embryonic stem cells (ESCs) into spermatogonial stem cells (SSCs). The results showed that a total of 296, 280 and 357 differentially expressed lncRNAs (DELs) were screened in ESCs vs. PGCs, ESCs vs. SSCs and PGCs vs. SSCs, respectively. Gene Ontology (GO) and KEGG enrichment analysis showed that DELs in the three cell groups were mainly enriched in autophagy, Wnt/β-catenin, TGF-β, Notch and ErbB and signaling pathways. The co-expression network of 37 candidate DELs and their target genes enriched in the biological function of germ cell development showed that XLOC_612026, XLOC_612029, XLOC_240662, XLOC_362463, XLOC_023952, XLOC_674549, XLOC_160716, ALDBGALG0000001810, ALDBGALG0000002986, XLOC_657380674549, XLOC_022100 and XLOC_657380 were the key lncRNAs in the process of male germ cell formation and, moreover, the function of these DELs may be related to the interaction of their target genes. Our findings preliminarily excavated the key lncRNAs and signaling pathways in the process of male chicken germ cell formation, which could be helpful to construct the gene regulatory network of germ cell development, and also provide new ideas for further optimizing the induction efficiency of germ cells in vitro.

Mouse testicular transcriptome after modulation of non-canonical oestrogen receptor activity

The aims of this study were to shed light on the role of G-protein-coupled membrane oestrogen receptor (GPER) and oestrogen-related receptor (ERR) in mouse testis function at the gene expression level, as well as the involvement of GPER and ERR in cellular and molecular processes. Male mice were injected (50µg kg-1,s.c.) with the GPER antagonist G-15, the ERRα inverse agonist XCT790 or the ERRβ/ERRγ agonist DY131. Next-generation sequencing (RNA-Seq) was used to evaluate gene expression. Bioinformatic analysis of read abundance revealed that 50, 86 and 171 transcripts were differentially expressed in the G-15-, XCT790- and DY131-treated groups respectively compared with the control group. Annotated genes and their protein products were categorised regarding their associated biological processes and molecular functions. In the XCT790-treated group, genes involved in immunological processes were upregulated. In the DY131-treated group, genes with increased expression were primarily engaged in protein modification (protein folding and small protein conjugation). In addition, the expression of genes recognised as oncogenes, such as BMI1 proto-oncogene, polycomb ring finger (Bmi1) and nucleophosphin 1 (Npm1), was significantly increased in all experimental groups. This study provides detailed information regarding the genetic changes in the testicular transcriptome of the mouse in response to modulation of non-canonical oestrogen receptor activity.

Post-translational modifications of seminal proteins and their importance in male fertility potential

Introduction: The seminal proteome has been shown to directly influence the male fertile potential. Post-translational modifications (PTMs) are significant changes that play a role in the biological regulation of proteins. Sperm cells are transcriptionally and translationally inactive and these modifications are essential to control protein function.Areas covered: Here we reviewed seven PTMs which importance for male reproductive function investigated in the past decade, namely S-nitrosylation and tyrosine nitration (both occurring by the action of NO), glycosylation, ubiquitination, acetylation, methylation, and SUMOylation. Since they were previously identified in human semen, we focus on their role in sperm function, as well as in physiological and pathophysiological processes which could contribute to the fertility potential. The following keywords were applied: 'post-translational modification', 'sperm', 'semen', 'seminal plasma', 'male infertility', 'nitrosylation', 'nitration', 'histone methylation', 'SUMOylation', 'ubiquitination', 'ubiquitilation', 'glycosylation', and 'acetylation'.Expert opinion: Most biological processes orchestrated by proteins require PTMs for their activation or inhibition. Most of them are dynamic and occur in mature sperm, modulating protein function, thus exerting a significant role in sperm function and fertility. Finally, the study of PTMs should be also addressed in pathophysiological processes, as different clinical conditions are known to alter the proteome.

Fish SUMO3 functions as a critical antiviral molecule against iridovirus and nodavirus

Protein SUMOylation (SUMO is small ubiquitin-related modifier) is a dynamic process that is strictly regulated under physiological and pathological conditions. We previously cloned and characterized two SUMO homologue genes (EcSUMO1 and EcSUMO2) from orange-spotted grouper (Epinephelus coioides). In the present study, the SUMO3 homologue from E. coioides (EcSUMO3) was cloned and its possible roles in fish immunity were analyzed. The open reading frame of EcSUMO3 contains 285 base pairs encoding a 94 amino acid protein with a predicted molecular mass of 10.73 kDa. The protein sequence of EcSUMO3 revealed similar domains with mammals, including the UBQ (ubiquitin-like proteins) domain, the hydrophobic surface, the Ulp1-Smt3 interaction sites, a VKTE motif and the C-terminal Gly residues. EcSUMO3 shares 46.83% and 89.58% identity with EcSUMO1 and EcSUMO2, respectively, and it shares 94%, 98%, and 98% identity with SUMO3 from Oreochromis niloticus, Danio rerio, and Homo sapiens, respectively. Quantitative real-time polymerase chain reaction analysis indicated that EcSUMO3 was constitutively expressed in all of the analyzed tissues in healthy grouper. EcSUMO3 expression levels were remarkably (p < 0.01) up-regulated in grouper spleen (GS) cells in response to stimulation with red-spotted grouper nervous necrosis virus (RGNNV) and Singapore grouper iridovirus (SGIV). EcSUMO3 was distributed in both the cytoplasm and nucleus in GS cells. EcSUMO3 enhanced SGIV and RGNNV replication during viral infection in vitro. These results are important for better understanding of the SUMO pathway in fish and provide insights into the regulatory mechanism of viral infection in E. coioides under farmed conditions.

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.

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.

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.

Spermatogenesis in humans and its affecting factors

Spermatogenesis is an extraordinary complex process. The differentiation of spermatogonia into spermatozoa requires the participation of several cell types, hormones, paracrine factors, genes and epigenetic regulators. Recent researches in animals and humans have furthered our understanding of the male gamete differentiation, and led to clinical tools for the better management of male infertility. There is still much to be learned about this intricate process. In this review, the critical steps of human spermatogenesis are discussed together with its main affecting factors.

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.

Roles of ubiquitination and SUMOylation on prostate cancer: mechanisms and clinical implications

The initiation and progression of human prostate cancer are highly associated with aberrant dysregulations of tumor suppressors and proto-oncogenes. Despite that deletions and mutations of tumor suppressors and aberrant elevations of oncogenes at the genetic level are reported to cause cancers, emerging evidence has revealed that cancer progression is largely regulated by posttranslational modifications (PTMs) and epigenetic alterations. PTMs play critical roles in gene regulation, cellular functions, tissue development, diseases, malignant progression and drug resistance. Recent discoveries demonstrate that ubiquitination and SUMOylation are complicated but highly-regulated PTMs, and make essential contributions to diseases and cancers by regulation of key factors and signaling pathways. Ubiquitination and SUMOylation pathways can be differentially modulated under various stimuli or stresses in order to produce the sustained oncogenic potentials. In this review, we discuss some new insights about molecular mechanisms on ubiquitination and SUMOylation, their associations with diseases, oncogenic impact on prostate cancer (PCa) and clinical implications for PCa treatment.

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.

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.

SUMO: a multifaceted modifier of chromatin structure and function

A major challenge in nuclear organization is the packaging of DNA into dynamic chromatin structures that can respond to changes in the transcriptional requirements of the cell. Posttranslational protein modifications, of histones and other chromatin-associated factors, are essential regulators of chromatin dynamics. In this Review, we summarize studies demonstrating that posttranslational modification of proteins by small ubiquitin-related modifiers (SUMOs) regulates chromatin structure and function at multiple levels and through a variety of mechanisms to influence gene expression and maintain genome integrity.

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.

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.

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.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 2: changes in spermatid organelles associated with development of spermatozoa

Spermiogenesis is a long process whereby haploid spermatids derived from the meiotic divisions of spermatocytes undergo metamorphosis into spermatozoa. It is subdivided into distinct steps with 19 being identified in rats, 16 in mouse and 8 in humans. Spermiogenesis extends over 22.7 days in rats and 21.6 days in humans. In this part, we review several key events that take place during the development of spermatids from a structural and functional point of view. During early spermiogenesis, the Golgi apparatus forms the acrosome, a lysosome-like membrane bound organelle involved in fertilization. The endoplasmic reticulum undergoes several topographical and structural modifications including the formation of the radial body and annulate lamellae. The chromatoid body is fully developed and undergoes structural and functional modifications at this time. It is suspected to be involved in RNA storing and processing. The shape of the spermatid head undergoes extensive structural changes that are species-specific, and the nuclear chromatin becomes compacted to accommodate the stream-lined appearance of the sperm head. Microtubules become organized to form a curtain or manchette that associates with spermatids at specific steps of their development. It is involved in maintenance of the sperm head shape and trafficking of proteins in the spermatid cytoplasm. During spermiogenesis, many genes/proteins have been implicated in the diverse dynamic events occurring at this time of development of germ cells and the absence of some of these have been shown to result in subfertility or infertility.

SUMO proteins are involved in the stress response during spermatogenesis and are localized to DNA double-strand breaks in germ cells

Small ubiquitin-like modifiers (SUMO) proteins have been implicated in cellular stress response in different tissues, but whether sumoylation has a similar role during spermatogenesis is currently unknown. In this study, changes in the levels of both free SUMO isoforms and high-molecular weight (HMW) SUMO conjugates were monitored before and after the induction of different types of cellular stresses. Using cell lines and primary cells freshly isolated from mouse testes, significant changes were detected in the levels of SUMO1 and SUMO2/3 conjugates following short exposure of the cells to heat stress and oxidative stress. While high concentrations of H(2)O(2) caused an increase in protein sumoylation, low concentrations of H(2)O(2) mostly caused protein desumoylation. Immunofluorescence studies localized SUMO to the sites of DNA double-strand breaks in stressed germ cells and during meiotic recombination. To study the effect of oxidative stress in vivo, animals exposed to tobacco smoke for 12 weeks were used. Changes in sumoylation of HMW proteins were consistent with their oxidative damage in the tobacco-exposed mice. Our results are consistent with the important roles of different SUMO isoforms in stress responses in germ cells. Furthermore, this study identified topoisomerase 2 alpha as one of the targets of sumoylation during normal spermatogenesis and under stress.

The forkhead transcription factor Foxl2 is sumoylated in both human and mouse: sumoylation affects its stability, localization, and activity

The FOXL2 forkhead transcription factor is expressed in ovarian granulosa cells, and mutated FOXL2 causes the blepharophimosis, ptosis and epicanthus inversus syndrome (BPES) and predisposes to premature ovarian failure. Inactivation of Foxl2 in mice demonstrated its indispensability for female gonadal sex determination and ovary development and revealed its antagonism of Sox9, the effector of male testis development. To help to define the regulatory activities of FOXL2, we looked for interacting proteins. Based on yeast two-hybrid screening, we found that FOXL2 interacts with PIAS1 and UBC9, both parts of the sumoylation machinery. We showed that human FOXL2 is sumoylated in transfected cell lines, and that endogenous mouse Foxl2 is comparably sumoylated. This modification changes its cellular localization, stability and transcriptional activity. It is intriguing that similar sumoylation and regulatory consequences have also been reported for SOX9, the male counterpart of FOXL2 in somatic gonadal tissues.

Spermatogenesis associated retrogenes are expressed in the human ovary and ovarian cancers

Background

Ovarian cancer is the second most prevalent gynecologic cancer in women. However, it is by far the most lethal. This is generally attributed to the absence of easily detectable markers specific to ovarian cancers that can be used for early diagnosis and specific therapeutic targets.

Methodology/Principal Findings

Using end point PCR we have found that a family of retrogenes, previously thought to be expressed only in the male testis during spermatogenesis in man, are also expressed in normal ovarian tissue and a large percentage of ovarian cancers. In man there are at least eleven such autosomal retrogenes, which are intronless copies of genes on the X chromosome, essential for normal spermatogenesis and expressed specifically in the human testis. We tested for the expression of five of the known retrogenes, UTP14C, PGK2, RPL10L, RPL39L and UBL4B in normal human ovary and ovarian cancers.

Conclusions/Significance

We propose that the activation of the testis specific retrogenes in the ovary and ovarian cancers is of biological significance in humans. Because these retrogenes are specifically expressed in the ovary and ovarian cancers in the female they may prove useful in developing new diagnostic and/or therapeutic targets for ovarian cancer.

Detection of proteins sumoylated in vivo and in vitro

Small ubiquitin-related modifier (SUMO) is an ubiquitin-like protein that is covalently attached to a variety of target proteins. Unlike ubiquitination, sumoylation does not target proteins for proteolytic breakdown, but is instead involved in regulating multiple protein functional properties including protein-protein interactions and subcellular targeting, to name a few. Protein sumoylation has been particularly well characterized as a regulator of many nuclear processes as well as nuclear structure, making the characterization of this modification vital for understanding nuclear structure and function. Consequently, there has been intense interest in identifying new proteins that are targets of this modification and determining what role it plays in regulating their functions. This chapter presents methodologies for determining whether a particular protein is a substrate of sumoylation, and for identifying the lysine residue(s) where the modification occurs.

Small ubiquitin-related modifier (SUMO)-1, SUMO-2/3 and SUMOylation are involved with centromeric heterochromatin of chromosomes 9 and 1 and proteins of the synaptonemal complex during meiosis in men

BACKGROUND

Post-transcriptional modification by SUMOylation is involved in numerous cellular processes including human spermatogenesis. For human male meiosis, we previously showed that the small ubiquitin-related modifier-1 (SUMO-1) protein localizes to chromatin axes in early pachytene spermatocytes, then to kinetochores as meiosis progresses. Here, we delineate possible functional roles based on subcellular localization for SUMO-1 and SUMO-2/3.

METHODS

Western and immunoprecipitation analyses were conducted on proteins isolated from the testis of two normal adult fertile men. Combinatorial immunofluorescence and chromosome-specific fluorescence in situ hybridization analyses were performed on male meiocytes obtained during testicular biopsy from four patients undergoing testicular sperm extraction for assisted reproduction technologies.

RESULTS

The synaptonemal complex (SC) and SC proteins (SCP)-1 and SCP2, but not SCP3, are SUMOylated by SUMO-1 during the pachytene substage. Likewise, two distinct localization patterns for SUMO-1 are identified: a linear pattern co-localized with autosomal SCs and isolated SUMO-1 near the centromeric heterochromatin of chromosomes 9 and 1. In contrast to SUMO-1, which is not detectable prior to pachytene in normal tissue, SUMO-2/3 is identified as early as leptotene and zygotene and in some, but not all, pachytene cells; no linear patterns were detected. Similar to SUMO-1, SUMO-2/3 localizes in two predominant subnuclear patterns: a single, dense signal near the centromere of human chromosome 9 and small, individual foci co-localized with autosomal centromeres.

CONCLUSIONS

Our data suggest that SUMO-1 may be involved in maintenance and/or protection of the autosomal SC. SUMO-2/3, though expressed similarly, may function separately and independently during pachytene in men.

In human pachytene spermatocytes, SUMO protein is restricted to the constitutive heterochromatin

SUMO-1, a ubiquitin-like protein, is covalently bound to many proteins, leading to chromatin inactivation and transcriptional repression. The high concentration of SUMO-1 on the XY body in rodents suggests that this protein has an important role in facultative heterochromatin organization. In human, the precise role of SUMO in chromatin/heterochromatin organization remains to be defined. Here we describe the SUMO-1 distribution, during human male meiosis, in relation to the formation of the different types of heterochromatin. We show that, during late pachynema, SUMO-1 appears on the constitutive heterochromatin, but is excluded from the XY body facultative heterochromatin. At the SUMO-1 labelled areas, the presence of HP1alpha protein, as well as of trimethylated H3-K9 and H4-K20 histone modifications, supports a role for SUMO-1 in constitutive heterochromatin organization. We also establish that, on the constitutive heterochromatin, H4-K20me3 staining progressively decreases as SUMO-1 staining increases, suggesting that core histone(s), and histone H4 in particular, are direct targets for sumoylation. Our results also suggest that, in the context of global histone H4 hyperacetylation that precedes the histone-to-protamine transition at postmeiotic stages of spermatogenesis, histone H4 sumoylation may represent an important epigenetic marker replacing methylation on the constitutive heterochromatin.

Developmental control of sumoylation pathway proteins in mouse male germ cells

Protein sumoylation regulates a variety of nuclear functions and has been postulated to be involved in meiotic chromosome dynamics as well as other processes of spermatogenesis. Here, the expression and distribution of sumoylation pathway genes and proteins were determined in mouse male germ cells, with a particular emphasis on prophase I of meiosis. Immunofluorescence microscopy revealed that SUMO1, SUMO2/3 and UBE2I (also known as UBC9) were localized to the XY body in pachytene and diplotene spermatocytes, while only SUMO2/3 and UBE2I were detected near centromeres in metaphase I spermatocytes. Quantitative RT-PCR and Western blotting were used to examine the expression of sumoylation pathway genes and proteins in enriched preparations of leptotene/zygotene spermatocytes, prepubertal and adult pachytene spermatocytes, as well as round spermatids. Two general expression profiles emerged from these data. The first profile, where expression was more prominent during meiosis, identified sumoylation pathway participants that could be involved in meiotic chromosome dynamics. The second profile, elevated expression in post-meiotic spermatids, suggested proteins that could be involved in spermiogenesis-related sumoylation events. In addition to revealing differential expression of protein sumoylation mediators, which suggests differential functioning, these data demonstrate the dynamic nature of SUMO metabolism during spermatogenesis.

Ecm11 protein of yeastSaccharomyces cerevisiaeis regulated by sumoylation during meiosis

Damaged regulation of the small ubiquitin-like modifier (SUMO) system contributes to some human diseases; therefore, it is very important to identify the SUMO targets and to determine the function of their sumoylation. In this study, it is shown that Ecm11 protein in Saccharomyces cerevisiae is modified by SUMO during meiosis. It is known that Ecm11 is required in the early stages of yeast meiosis where its function is related to DNA replication and crossing over. Here it is shown that the level of Ecm11 protein is low in mitosis, but high in meiosis. The highest level of Ecm11 is in the early-middle phase of sporulation. A specific site of sumoylation was identified in Ecm11 at Lys5 and evidence is provided that sumoylation at this site directly regulates Ecm11 function in meiosis. On the other hand, no relationship was observed between sumoylation of Ecm11 and its role during vegetative growth. It was shown that Ecm11 interacts with Siz2 SUMO ligase in a two-hybrid system; although Siz2 is not essential for the Ecm11 sumoylation.

Meiosis and small ubiquitin-related modifier (SUMO)-conjugating enzyme, Ubc9

In this review, we describe the role of a small ubiquitin-like protein modifier (SUMO)-conjugating protein, Ubc9, in synaptonemal complex formation during meiosis in a basidiomycete, Coprinus cinereus. Because its meiotic cell cycle is long and naturally synchronous, it is suitable for molecular biological, biochemical and genetic studies of meiotic prophase events. In yeast two-hybrid screening using the meiotic-specific cDNA library of C. cinereus, we found that the meiotic RecA homolog CcLim15 interacted with CcUbc9, CcTopII and CcPCNA. Moreover, both TopII and PCNA homologs were known as Ubc9 interactors and the targets of sumoylation. Immunocytochemistry demonstrates that CcUbc9, CcTopII and CcPCNA localize with CcLim15 in meiotic nuclei during leptotene to zygotene when synaptonemal complex is formed and when homologous chromosomes pair. We discuss the relationships between Lim15/Dmc1 (CcLim15), TopII (CcTopII), PCNA (CcPCNA) and CcUbc9, and subsequently, the role of sumoylation in the stages. We speculate that CcLim15 and CcTopII work in cohesion between homologous chromatins initially and then, in the process of the zygotene events, CcUbc9 works with factors including CcLim15 and CcTopII as an inhibitor of ubiquitin-mediated degradation and as a metabolic switch in the meiotic prophase cell cycle. After CcLim15-CcTopII dissociation, CcLim15 remains on the zygotene DNA and recruits CcUbc9, Rad54B, CcUbc9, Swi5-Sfr1, CcUbc9 and then CcPCNA in rotation on the C-terminus. Finally during zygotene, CcPCNA replaces CcLim15 on the DNA and the free-CcLim15 is probably ubiquitinated and disappears. CcPCNA may recruit the polymerase. The idea that CcUbc9 intervenes in every step by protecting CcLim15 and by switching several factors at the C-terminus of CcLim15 is likely. At the boundary of the zygotene and pachytene stages, CcPCNA would be sumoylated. CcUbc9 may also be involved with CcPCNA in the switch from the replicative polymerase being recruited at zygotene to the repair-type DNA polymerases being recruited at pachytene.

Sumoylation dynamics during keratinocyte differentiation

SUMO modification regulates the activity of numerous transcription factors that have a direct role in cell-cycle progression, apoptosis, cellular proliferation, and development, but its role in differentiation processes is less clear. Keratinocyte differentiation requires the coordinated activation of a series of transcription factors, and as several crucial keratinocyte transcription factors are known to be SUMO substrates, we investigated the role of sumoylation in keratinocyte differentiation. In a human keratinocyte cell line model (HaCaT cells), Ca2+-induced differentiation led to the transient and coordinated transcriptional activation of the genes encoding crucial sumoylation system components, including SAE1, SAE2, Ubc9, SENP1, Miz-1 (PIASx beta), SUMO2 and SUMO3. The increased gene expression resulted in higher levels of the respective proteins and changes in the pattern of sumoylated substrate proteins during the differentiation process. Similarly to the HaCaT results, stratified human foreskin keratinocytes showed an upregulation of Ubc9 in the suprabasal layers. Abrogation of sumoylation by Gam1 expression severely disrupted normal HaCaT differentiation, consistent with an important role for sumoylation in the proper progression of this biological process.