The Deubiquitinating Enzyme mUBPy Interacts with the Sperm-Specific Molecular Chaperone MSJ-1: The Relation with the Proteasome, Acrosome, and Centrosome in Mouse Male Germ Cells1

Ubiquitin-Proteasome System-Regulated Protein Degradation in Spermatogenesis

Spermatogenesis is a prolonged and highly ordered physiological process that produces haploid male germ cells through more than 40 steps and experiences dramatic morphological and cellular transformations. The ubiquitin proteasome system (UPS) plays central roles in the precise control of protein homeostasis to ensure the effectiveness of certain protein groups at a given stage and the inactivation of them after this stage. Many UPS components have been demonstrated to regulate the progression of spermatogenesis at different levels. Especially in recent years, novel testis-specific proteasome isoforms have been identified to be essential and unique for spermatogenesis. In this review, we set out to discuss our current knowledge in functions of diverse USP components in mammalian spermatogenesis through: (1) the composition of proteasome isoforms at each stage of spermatogenesis; (2) the specificity of each proteasome isoform and the associated degradation events; (3) the E3 ubiquitin ligases mediating protein ubiquitination in male germ cells; and (4) the deubiquitinases involved in spermatogenesis and male fertility. Exploring the functions of UPS machineries in spermatogenesis provides a global picture of the proteome dynamics during male germ cell production and shed light on the etiology and pathogenesis of human male infertility.

Differential Expression of Kisspeptin System and Kisspeptin Receptor Trafficking during Spermatozoa Transit in the Epididymis

The hypothalamus–pituitary–testis axis controls the production of spermatozoa, and the kisspeptin system, comprising Kiss1 and Kiss1 receptor (Kiss1R), is the main central gatekeeper. The activity of the kisspeptin system also occurs in testis and spermatozoa, but currently the need of peripheral kisspeptin to produce gametes is not fully understood. Hence, we characterized kisspeptin system in rat spermatozoa and epididymis caput and cauda and analyzed the possible presence of Kiss1 in the epididymal fluid. The presence of Kiss1 and Kiss1R in spermatozoa collected from epididymis caput and cauda was evaluated by Western blot; significant high Kiss1 levels in the caput (p < 0.001 vs. cauda) and constant levels of Kiss1R proteins were observed. Immunofluorescence analysis revealed that the localization of Kiss1R in sperm head shifts from the posterior region in the epididymis caput to perforatorium in the epididymis cauda. In spermatozoa-free epididymis, Western blot revealed higher expression of Kiss1 and Kiss1R in caput (p < 0.05 vs. cauda). Moreover, immunohistochemistry revealed that Kiss1 and Kiss1R proteins were mainly localized in the secretory epithelial cell types and in contractile myoid cells, respectively. Finally, both dot blot and Elisa revealed the presence of Kiss1 in the epididymal fluid collected from epididymis cauda and caput, indicating that rat epididymis and spermatozoa possess a complete kisspeptin system. In conclusion, we reported for the first time in rodents Kiss1R trafficking in spermatozoa during the epididymis transit and Kiss1 measure in the epididymal fluid, thus suggesting a possible role for the system in spermatozoa maturation and storage within the epididymis.

The molecular mechanisms underlying acrosome biogenesis elucidated by gene-manipulated mice

Sexual reproduction requires the fusion of two gametes in a multistep and multifactorial process termed fertilization. One of the main steps that ensures successful fertilization is acrosome reaction. The acrosome, a special kind of organelle with a cap-like structure that covers the anterior portion of sperm head, plays a key role in the process. Acrosome biogenesis begins with the initial stage of spermatid development, and it is typically divided into four successive phases: the Golgi phase, cap phase, acrosome phase, and maturation phase. The run smoothly of above processes needs an active and specific coordination between the all kinds of organelles (endoplasmic reticulum, trans-golgi network and nucleus) and cytoplasmic structures (acroplaxome and manchette). During the past two decades, an increasingly genes have been discovered to be involved in modulating acrosome formation. Most of these proteins interact with each other and show a complicated molecular regulatory mechanism to facilitate the occurrence of this event. This Review focuses on the progresses of studying acrosome biogenesis using gene-manipulated mice and highlights an emerging molecular basis of mammalian acrosome formation.

Destruction or Reconstruction: A Subtle Liaison between the Proteolytic and Signaling Role of Protein Ubiquitination in Spermatogenesis

Ubiquitination is one of the most diverse forms of protein post-translational modification that changes the function of the landscape of substrate proteins in response to stimuli, without the need for "de novo" protein synthesis. Ubiquitination is involved in almost all aspects of eukaryotic cell biology, from the best-studied role in promoting the removal of faulty or unnecessary proteins by the way of the ubiquitin proteasome system and autophagy-lysosome pathway to the recruitment of proteins in specific non-proteolytic signaling pathways, as emerged by the more recent discoveries about the protein signature with peculiar types of ubiquitin chains. Spermatogenesis, on its own, is a complex cellular developmental process in which mitosis, meiosis, and cell differentiation coexist so to result in the continuous formation of haploid spermatozoa. Successful spermatogenesis is thus at the same time a mixed result of the precise expression and correct intracellular destination of structural proteins and enzymes, from one hand, and the fine removal by targeted degradation of unfolded or damaged proteins as well as of obsolete, outlived proteins, from the other hand. In this minireview, I will focus on the importance of the ubiquitin system all over the spermatogenic process, discussing both proteolytic and non-proteolytic functions of protein ubiquitination. Alterations in the ubiquitin system have been in fact implicated in pathologies leading to male infertility. Notwithstanding several aspects of the multifaceted world of the ubiquitin system have been clarified, the physiological meaning of the so-called ubiquitin code remains still partially elusive. The studies reviewed in this chapter provide information that could aid the investigators to pursue new promising discoveries in the understanding of human and animal reproductive potential.

Identification of a New QTL Region on Mouse Chromosome 1 Responsible for Male Hypofertility: Phenotype Characterization and Candidate Genes

Male fertility disorders often have their origin in disturbed spermatogenesis, which can be induced by genetic factors. In this study, we used interspecific recombinant congenic mouse strains (IRCS) to identify genes responsible for male infertility. Using ultrasonography, in vivo and in vitro fertilization (IVF) and electron microscopy, the phenotyping of several IRCS carrying mouse chromosome 1 segments of Mus spretus origin revealed a decrease in the ability of sperm to fertilize. This teratozoospermia included the abnormal anchoring of the acrosome to the nucleus and a persistence of residual bodies at the level of epididymal sperm midpiece. We identified a quantitative trait locus (QTL) responsible for these phenotypes and we have proposed a short list of candidate genes specifically expressed in spermatids. The future functional validation of candidate genes should allow the identification of new genes and mechanisms involved in male infertility.

Ubiquitin-specific protease 8 (USP8/UBPy): a prototypic multidomain deubiquitinating enzyme with pleiotropic functions

Protein modification by ubiquitin is one of the most versatile posttranslational regulations and counteracted by almost 100 deubiquitinating enzymes (DUBs). USP8 was originally identified as a growth regulated ubiquitin-specific protease and is like many other DUBs characterized by its multidomain architecture. Besides the catalytic domain, specific protein-protein interaction modules were characterized which contribute to USP8 substrate recruitment, regulation and targeting to distinct protein complexes. Studies in mice and humans impressively showed the physiological relevance and non-redundant function of USP8 within the context of the whole organism. USP8 knockout (KO) mice exhibit early embryonic lethality while induced deletion in adult animals rapidly causes lethal liver failure. Furthermore, T-cell specific ablation disturbs T-cell development and function resulting in fatal autoimmune inflammatory bowel disease. In human patients, somatic mutations in USP8 were identified as the underlying cause of adrenocorticotropic hormone (ACTH) releasing pituitary adenomas causing Cushing's disease (CD). Here we provide an overview of the versatile molecular, cellular and pathology associated function and regulation of USP8 which appears to depend on specific protein binding partners, substrates and the cellular context.

Ubiquitin Carboxy-Terminal HydrolaseL3 Correlates with Human Sperm Count, Motility and Fertilization

Ubiquitin C-terminal hydrolase L3 (UCHL3) belongs to the group of deubiquitinating enzymes and plays a part in apoptosis of germ cells and the differentiation of spermatocytes into spermatids. However, the exact role of UCHL3 in human spermatogenesis and sperm function remains unknown. Here we examined the level and activity of UCHL3 in spermatozoa from men with asthenozoospermia (A), oligoasthenozoospermia (OA) or normozoospermia (N). Immunofluorescence indicated that UCHL3 was mainly localized in the acrosome and throughout the flagella, and western blotting revealed a lower level in A or OA compared with N (p < 0.05). The catalytic activity of UCHL3 was decreased in spermatozoa from A or OA (p < 0.05, p < 0.001, respectively). The level and activity of UCHL3 were positively correlated with sperm count, concentration and motility. The UCHL3 level was positively correlated with the normal fertilization rate (FR) and percentage of embryos suitable for transfer/cryopreservation of in vitro fertilization (IVF). The UCHL3 activity was also positively correlated with FR, the percentage of embryos suitable for transfer/cryopreservation and high-quality embryos rate of IVF. Aforementioned correlations were not manifested in intra-cytoplasmic sperm injection (ICSI). These findings suggest that UCHL3 may play a role in male infertility.

Concise Review: Fate Determination of Stem Cells by Deubiquitinating Enzymes

Post-translational modification by ubiquitin molecules is a key regulatory process for stem cell fate determination. Ubiquitination and deubiquitination are the major cellular processes used to balance the protein turnover of several transcription factors that regulate stem cell differentiation. Deubiquitinating enzymes (DUBs), which facilitate the processing of ubiquitin, significantly influence stem cell fate choices. Specifically, DUBs play a critical regulatory role during development by directing the production of new specialized cells. This review focuses on the regulatory role of DUBs in various cellular processes, including stem cell pluripotency and differentiation, adult stem cell signaling, cellular reprogramming, spermatogenesis, and oogenesis. Specifically, the identification of interactions of DUBs with core transcription factors has provided new insight into the role of DUBs in regulating stem cell fate determination. Thus, DUBs have emerged as key pharmacologic targets in the search to develop highly specific agents to treat various illnesses. Stem Cells 2017;35:9-16.

The role of deubiquitinating enzymes in spermatogenesis

Spermatogenesis is a complex process through which spermatogonial stem cells undergo mitosis, meiosis, and cell differentiation to generate mature spermatozoa. During this process, male germ cells experience several translational modifications. One of the major post-translational modifications in eukaryotes is the ubiquitination of proteins, which targets proteins for degradation; this enables control of the expression of enzymes and structural proteins during spermatogenesis. It has become apparent that ubiquitination plays a key role in regulating every stage of spermatogenesis starting from gonocytes to differentiated spermatids. It is understood that, where there is ubiquitination, deubiquitination by deubiquitinating enzymes (DUBs) also exists to counterbalance the ubiquitination process in a reversible manner. Normal spermatogenesis is dependent on the balanced actions of ubiquitination and deubiquitination. This review highlights the current knowledge of the role of DUBs and their essential regulatory contribution to spermatogenesis, especially during progression into meiotic phase, acrosome biogenesis, quality sperm production, and apoptosis of germ cells.

Expression of Human DNAJ (Heat Shock Protein-40) B3 in Humanized UDP-glucuronosyltransferase 1 Mice

The human DNAJB3 gene encodes a DNAJ (Heat shock protein 40; Hsp40) homolog, subfamily B, member 3 chaperone protein (DNAJB3), which can be down-regulated in disease conditions, as observed in decreased expression of DNAJB3 mRNA in peripheral blood mononuclear cells (PBMC) of obese patients. Recently, humanized UDP-glucuronosyltransferase (UGT) 1 mice (hUGT1 mice) were developed, in which the introduced human UGT1 gene contained a gene encoding human DNAJB3. In the present study, we analyzed the expression of human DNAJB3 mRNA in hUGT1 mice. Among the examined tissues, the testis had the highest expression of human DNAJB3 mRNA, while the lowest expression was observed in the liver. We found that the pattern of tissue-specific expression of mouse Dnajb3 in hUGT1 mice was very similar to that of human DNAJB3. We further demonstrated that the expression of human DNAJB3 in the liver was significantly reduced in high-fat-diet-fed hUGT1 mice compared to the expression level in the control mice, indicating that the expression of human DNAJB3 in hUGT1 mice could be similarly regulated in disease conditions such as obesity. Humanized UGT1 mice might therefore be useful to investigate the physiological role of human DNAJB3 in vivo.

USP8/UBPy-regulated sorting and the development of sperm acrosome: the recruitment of MET

The acrosome is a peculiar vacuole that at fertilization undergoes the acrosome reaction (AR), an event unique in the sperm life. Contents released promote sperm penetration through oocyte's investments; membranous components are involved in sperm–egg interaction/fusion. Therefore, both constituents play a role in fertilization. The biogenesis of this vacuole, however, has not been clarified yet; recently, it has been proposed as a novel lysosome-related organelle (LRO). Our research focuses on the involvement of the endosomal pathway in acrosomogenesis starting from the early phases. The trafficking sorted by USP8/UBPy, an endosomal regulator recently described as a compelling candidate for male fertility gene, was investigated in comparison to that of SP56, a marker of the biosynthetic pathway. Mouse spermatids were double/triple immunolabeled and examined by confocal microscopy. The contribution of the vesicular traffic assisted by the cortical microtubule array was also evaluated in nocodazole-treated spermatids. USP8/UBPy-sorted cargo contributes early to acrosomogenesis and its trafficking is microtubule mediated. It was identified, through co-immunoprecipitation/co-immunolocalization assays, that the membrane receptor MET, described herein for the first time in spermatids, as an USP8/UBPy-target substrate is delivered to the acrosome. MET and USP8/UBPy still colocalize in epididymal spermatozoa. Following the AR, MET and USP8/UBPy show a distinct fate. MET, in particular, translocates at the PAS, the post acrosomal segment known to harbor sperm-borne factors involved in oocyte activation. Overall, our results support the concept of the acrosome as a LRO and provide evidence for the identification of MET as a tyrosine kinase receptor that may play a role in fertilization.

Acrosome biogenesis: Revisiting old questions to yield new insights

The acrosome is a unique membranous organelle located over the anterior part of the sperm nucleus that is highly conserved throughout evolution. This acidic vacuole contains a number of hydrolytic enzymes that, when secreted, help the sperm penetrate the egg's coats. Although acrosome biogenesis is an important aspect of spermiogenesis, the molecular mechanism(s) that regulates this event remains unknown. Active trafficking from the Golgi apparatus is involved in acrosome formation, but experimental evidence indicates that trafficking of vesicles out of the Golgi also occurs during acrosomogenesis. Unfortunately, this second aspect of acrosome biogenesis remains poorly studied. In this article, we briefly discuss how the biosynthetic and endocytic pathways, assisted by a network of microtubules, tethering factors, motor proteins and small GTPases, relate and connect to give rise to the sperm-specific vacuole, with a particular emphasis placed on the endosomal compartment. It is hoped that this information will be useful to engage more studies on acrosome biogenesis by focusing attention towards suggested directions.

Molecular chaperones, cochaperones, and ubiquitination/deubiquitination system: involvement in the production of high quality spermatozoa

Spermatogenesis is a complex process in which mitosis, meiosis, and cell differentiation events coexist. The need to guarantee the production of qualitatively functional spermatozoa has evolved into several control systems that check spermatogenesis progression/sperm maturation and tag aberrant gametes for degradation. In this review, we will focus on the importance of the evolutionarily conserved molecular pathways involving molecular chaperones belonging to the superfamily of heat shock proteins (HSPs), their cochaperones, and ubiquitination/deubiquitination system all over the spermatogenetic process. In this respect, we will discuss the conserved role played by the DNAJ protein Msj-1 (mouse sperm cell-specific DNAJ first homologue) and the deubiquitinating enzyme Ubpy (ubiquitin-specific processing protease-y) during the spermiogenesis in both mammals and nonmammalian vertebrates.

Atg7 is required for acrosome biogenesis during spermatogenesis in mice

The acrosome is a specialized organelle that covers the anterior part of the sperm nucleus and plays an essential role in the process of fertilization. The molecular mechanism underlying the biogenesis of this lysosome-related organelle (LRO) is still largely unknown. Here, we show that germ cell-specific Atg7-knockout mice were infertile due to a defect in acrosome biogenesis and displayed a phenotype similar to human globozoospermia; this reproductive defect was successfully rescued by intracytoplasmic sperm injections. Furthermore, the depletion of Atg7 in germ cells did not affect the early stages of development of germ cells, but at later stages of spermatogenesis, the proacrosomal vesicles failed to fuse into a single acrosomal vesicle during the Golgi phase, which finally resulted in irregular or nearly round-headed spermatozoa. Autophagic flux was disrupted in Atg7-depleted germ cells, finally leading to the failure of LC3 conjugation to Golgi apparatus-derived vesicles. In addition, Atg7 partially regulated another globozoospermia-related protein, Golgi-associated PDZ- and coiled-coil motif-containing protein (GOPC), during acrosome biogenesis. Finally, the injection of either autophagy or lysosome inhibitors into testis resulted in a similar phenotype to that of germ cell-specific Atg7-knockout mice. Altogether, our results uncover a new role for Atg7 in the biogenesis of the acrosome, and we provide evidence to support the autolysosome origination hypothesis for the acrosome.

Ubiquitin-proteasome system in spermatogenesis

Spermatogenesis represents a complex succession of cell division and differentiation events resulting in the continuous formation of spermatozoa. Such a complex program requires precise expression of enzymes and structural proteins which is effected not only by regulation of gene transcription and translation, but also by targeted protein degradation. In this chapter, we review current knowledge about the role of the ubiquitin-proteasome system in spermatogenesis, describing both proteolytic and non-proteolytic functions of ubiquitination. Ubiquitination plays essential roles in the establishment of both spermatogonial stem cells and differentiating spermatogonia from gonocytes. It also plays critical roles in several key processes during meiosis such as genetic recombination and sex chromosome silencing. Finally, in spermiogenesis, we summarize current knowledge of the role of the ubiquitin-proteasome system in nucleosome removal and establishment of key structures in the mature spermatid. Many mechanisms remain to be precisely defined, but present knowledge indicates that research in this area has significant potential to translate into benefits that will address problems in both human and animal reproduction.

Ubiquitination regulates the morphogenesis and function of sperm organelles

It is now understood that protein ubiquitination has diverse cellular functions in eukaryotes. The molecular mechanism and physiological significance of ubiquitin-mediated processes have been extensively studied in yeast, Drosophila and mammalian somatic cells. Moreover, an increasing number of studies have emphasized the importance of ubiquitination in spermatogenesis and fertilization. The dysfunction of various ubiquitin systems results in impaired sperm development with abnormal organelle morphology and function, which in turn is highly associated with male infertility. This review will focus on the emerging roles of ubiquitination in biogenesis, function and stability of sperm organelles in mammals.

The ESCRT-deubiquitinating enzyme USP8 in the cervical spinal cord of wild-type and Vps54-recessive (wobbler) mutant mice

Usp8 is a deubiquitinating enzyme that works as regulator of endosomal trafficking and is involved in cell proliferation. "In vivo" USP8 is predominantly expressed in the central nervous system and testis, two organs with highly polarized cells. Considering that neuronal cell functionality is strictly dependent on vesicular traffic and ubiquitin-mediated sorting of the endocytosed cargo, it could be of relevance to investigate about USP8 in neuronal cells, in particular motor neurons. In this study, we found that USP8 is expressed in the gray and white matter of the spinal cord, labeling neuronal cell bodies, axonal microtubules and synaptic terminals. The glia component is essentially USP8-immunonegative. The partial colocalization of USP8 with EEA1 in motor neurons indicates that USP8 is involved in early endosomal trafficking while that with Vps54 suggests an involvement in the retrograde traffic. The variant Vps54(L967Q) is responsible for the wobbler phenotype, a disorder characterized by motor neuron degeneration. We searched for USP8/Vps54 in wobbler spinal cord. The most worth-mention result was that wobbler oligodendrocytes, in contrast to the wild-type, are heavily USP8-immunoreactive; no significant modification was appreciated about the cellular expression of mutated Vps54. On the other hand, as to the neuronal intracellular localization, both USP8 and Vps54(L967Q) did not show the typical spot-like distribution, but seemed to accumulate in proteinaceous aggregates. Collectively, our study suggests that in neuronal cells USP8 could be involved in endosomal trafficking, retrograde transport and synaptic plasticity. In disorders leading to neurodegeneration USP8 is upregulated and could influence the neuron-oligodendrocyte interactions.

The wobbler mouse, an ALS animal model

This review article is focused on the research progress made utilizing the wobbler mouse as animal model for human motor neuron diseases, especially the amyotrophic lateral sclerosis (ALS). The wobbler mouse develops progressive degeneration of upper and lower motor neurons and shows striking similarities to ALS. The cellular effects of the wobbler mutation, cellular transport defects, neurofilament aggregation, neuronal hyperexcitability and neuroinflammation closely resemble human ALS. Now, 57 years after the first report on the wobbler mouse we summarize the progress made in understanding the disease mechanism and testing various therapeutic approaches and discuss the relevance of these advances for human ALS. The identification of the causative mutation linking the wobbler mutation to a vesicle transport factor and the research focussed on the cellular basis and the therapeutic treatment of the wobbler motor neuron degeneration has shed new light on the molecular pathology of the disease and might contribute to the understanding the complexity of ALS.

Isolation and proteomic characterization of the mouse sperm acrosomal matrix

A critical step during fertilization is the sperm acrosome reaction in which the acrosome releases its contents allowing the spermatozoa to penetrate the egg investments. The sperm acrosomal contents are composed of both soluble material and an insoluble material called the acrosomal matrix (AM). The AM is thought to provide a stable structure from which associated proteins are differentially released during fertilization. Because of its important role during fertilization, efforts have been put toward isolating the AM for biochemical study and to date AM have been isolated from hamster, guinea pig, and bull spermatozoa. However, attempts to isolate AM from mouse spermatozoa, the species in which fertilization is well-studied, have been unsuccessful possibly because of the small size of the mouse sperm acrosome and/or its fusiform shape. Herein we describe a procedure for the isolation of the AM from caput and cauda mouse epididymal spermatozoa. We further carried out a proteomic analysis of the isolated AM from both sperm populations and identified 501 new proteins previously not detected by proteomics in mouse spermatozoa. A comparison of the AM proteome from caput and cauda spermatozoa showed that the AM undergoes maturational changes during epididymal transit similar to other sperm domains. Together, our studies suggest the AM to be a dynamic and functional structure carrying out a variety of biological processes as implied by the presence of a diverse group of proteins including proteases, chaperones, hydrolases, transporters, enzyme modulators, transferases, cytoskeletal proteins, and others.

Differentially expressed genes associated with cisplatin resistance in human ovarian adenocarcinoma cell line A2780

Ovarian cancer cells are usually initially sensitive to platinum-based chemotherapy, such as cisplatin (CDDP), but typically become resistant over time. Such drug resistance is a serious impediment to successful disease treatment, and the molecular mechanisms responsible for resistance are not fully understood. In search of novel mechanisms that may lead to the development of CDDP chemoresistance, we used subtractive hybridization to identify differentially expressed genes in CDDP resistant CP70 and C200 cells vs. CDDP sensitive A2780 human ovarian adenocarcinoma cells. We analyzed 256 randomly selected clones. Subtraction efficiency was determined by dot blot and DNA sequencing. Confirmation of differentially expressed cDNAs was done by virtual northern blot analysis, and 17 genes that were differentially expressed in CDDP resistant cell lines vs. CDDP sensitive A2780 cells were identified. The expression of 10 of these genes was low or undetectable in sensitive A2780 cells in comparison to resistant cells and an additional seven genes were more highly expressed in resistant CP70 and C200 vs. A2780 cells. Our identified genes are involved in numerous and diverse cellular processes, such as inhibition of apoptosis (ARHGDIB), stress response (HSPCA, TRA1), chromatin condensation (CNAP1, RanBP2), invasiveness of cells (MMP10), alteration of Ca(2+) homeostasis (ASPH, ATP2B1) and others. Further characterization of these genes and gene products should yield important insights into the biology of CDDP resistance in ovarian carcinoma.

Failure of acrosome formation and globozoospermia in the wobbler mouse, a Vps54 spontaneous recessive mutant

The acrosome is a unique organelle that plays an important role at fertilization and during sperm morphogenesis and that is absent in globozoospermia, an inherited infertility syndrome in humans. At the light of recent experimental evidence, the acrosome is considered a lysosome-related organelle to whose biogenesis both the endocytic and biosynthetic pathways contribute. Vps54 is a vesicular sorting protein involved in the retrograde traffic; the recessive Vps54(L967Q) mutation in the mouse results in the wobbler phenotype, characterized by motor-neuron degeneration and male infertility. Here we have investigated the spatio-temporal occurrence/progression of the wobbler fertility disorder starting from mice at post-natal day 35, the day of the first event of spermiation. We show that the pathogenesis of wobbler infertility originates at the first spermiogenetic wave, affecting acrosome formation and sperm head elongation. Vps54(L967Q)-labeled vesicles, on the contrary of the wild-type Vps54-labeled ones, are not able to coalesce into a larger vesicle that develops, flattens and shapes to give rise to the acrosome. Evidence that it is the malfunctioning of the endocytic traffic to hamper the development of the acrosome comes out from the study on UBPy. UBPy, a deubiquitinating enzyme, is a marker of acrosome biogenesis from the endocytic pathway. In wobbler spermatids UBPy-positive endosomes remain single, scattered vesicles that do not contribute to acrosome formation. As secondary defect of wobbler spermiogenesis, spermatid mitochondria are misorted; moreover, with the progression of the age/disease also Sertoli-germ cell adhesions are compromised suggesting a derailment in the endocytic route that underlies their restructuring.

The deubiquitinating enzyme USP8 promotes trafficking and degradation of the chemokine receptor 4 at the sorting endosome

Reversible ubiquitination orchestrated by the opposition of ubiquitin ligases and deubiquitinating enzymes mediates endocytic trafficking of cell surface receptors for lysosomal degradation. Ubiquitin-specific protease 8 (USP8) has previously been implicated in endocytosis of several receptors by virtue of their deubiquitination. The present study explores an indirect role for USP8 in cargo trafficking through its regulation of the chemokine receptor 4 (CXCR4). Contrary to the effects of USP8 loss on enhanced green fluorescent protein, we find that USP8 depletion stabilizes CXCR4 on the cell surface and attenuates receptor degradation without affecting its ubiquitination status. In the presence of ligand, diminished CXCR4 turnover is accompanied by receptor accumulation on enlarged early endosomes and leads to enhancement of phospho-ERK signaling. Perturbation in CXCR4 trafficking, resulting from USP8 inactivation, occurs at the ESCRT-0 checkpoint, and catalytic mutation of USP8 specifically targeted to the ESCRT-0 complex impairs the spatial and temporal organization of the sorting endosome. USP8 functionally opposes the ubiquitin ligase AIP4 with respect to ESCRT-0 ubiquitination, thereby promoting trafficking of CXCR4. Collectively, our findings demonstrate a functional cooperation between USP8, AIP4, and the ESCRT-0 machinery at the early sorting phase of CXCR4 and underscore the versatility of USP8 in shaping trafficking events at the early-to-late endosome transition.

A novel testis-specific GTPase serves as a link to proteasome biogenesis: functional characterization of RhoS/RSA-14-44 in spermatogenesis

We functionally characterized RhoS/RSA-14-44 as a new member of Rho GTPase subfamily in spermatogenesis, which provides a direct link between Rho family GTPase and the proteasome biogenesis.

Most Rho family GTPases serve as key molecular switches in a wide spectrum of biological processes. An increasing number of studies have expanded their roles to the spermatogenesis. Several members of Rho family have been confirmed to be essential for mammalian spermatogenesis, but the precise roles of this family in male reproduction have not been well studied yet. Here we report a surprising function of an atypical and testis-specific Rho GTPase, RSA-14-44 in spermatogenesis. Featured by unique structural and expressional patterns, RSA-14-44 is distinguished from three canonical members of Rho cluster. Thus, we define RSA-14-44 as a new member of Rho GTPases family and rename it RhoS (Rho in spermatogenic cells). RhoS associates with PSMB5, a catalytic subunit of the proteasome, in a series of stage-specific spermatogenic cells. More importantly, RhoS does not directly modulate the cellular proteasome activity, but participates in regulating the stability of “unincorporated” PSMB5 precursors. Meanwhile, our data demonstrate that the activation of RhoS is prerequisite for negatively regulating the stability of PSMB5 precursors. Therefore, our finding uncovers a direct and functional connection between the Rho GTPase family and the pathway of proteasome biogenesis and provide new clues for deciphering the secrets of spermatogenesis.

Expression pattern of mUBPy in the brain and sensory organs of mouse during embryonic development

Mouse UBPy (mUBPy) belongs to the family of ubiquitin-specific processing proteases (UBPs). In this study we have investigated the expression of mUBPy in the brain and sensory organs of mouse at different embryonic stages (E9, E11, E13, E15, E17, E19) and during the postnatal stages P0, P1, P2, P4 and P5 using Western blot and immunohistochemistry. mUBPy-immunoreactive cell bodies first appeared at stage E11 in several brain regions, particularly in the walls surrounding the vesicles and the ventricles. Subsequently, at stage E13, new mUBPy-positive cells appeared in the corpus striatum, the caudate nucleus, the thalamus, the epithalamus, the hypothalamus and the pons. At E15 the mUBPy pattern was very similar to that observed at E13, whereas at stage E17 mUBPy-immunoreactivity significantly decreased and a high number of mUBPy-immunoreactive cells was found only to line the third ventricle and within the mantle layer of the fourth ventricle. At E19 and P0, no mUBPy-immunoreactive element was found in the brain. At the postnatal stages P2 and P5, mUBPy-positive cells were detected in all subdivisions of the brain, with high concentrations in several cortex regions. Double labeling with the mUBPy antiserum and antisera against specific cell markers showed that the enzyme is expressed both in neurons and astrocytes. Outside the brain, mUBPy was detected, from stage E11, in the eye, within the lens and the cornea, in the inner ear, at the level of the cochlear and vestibular systems and in the olfactory epithelium. The spatio-temporal expression of mUBPy suggests that the enzyme may be involved in neuroregulatory processes during embryogenesis.

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 3: developmental changes in spermatid flagellum and cytoplasmic droplet and interaction of sperm with the zona pellucida and egg plasma membrane

Spermiogenesis constitutes the steps involved in the metamorphosis of spermatids into spermatozoa. It involves modification of several organelles in addition to the formation of several structures including the flagellum and cytoplasmic droplet. The flagellum is composed of a neck region and middle, principal, and end pieces. The axoneme composed of nine outer microtubular doublets circularly arranged to form a cylinder around a central pair of microtubules is present throughout the flagellum. The middle and principal pieces each contain specific components such as the mitochondrial sheath and fibrous sheath, respectively, while outer dense fibers are common to both. A plethora of proteins are constituents of each of these structures, with each playing key roles in functions related to the fertility of spermatozoa. At the end of spermiogenesis, a portion of spermatid cytoplasm remains associated with the released spermatozoa, referred to as the cytoplasmic droplet. The latter has as its main feature Golgi saccules, which appear to modify the plasma membrane of spermatozoa as they move down the epididymal duct and hence may be partly involved in male gamete maturation. The end product of spermatogenesis is highly streamlined and motile spermatozoa having a condensed nucleus equipped with an acrosome. Spermatozoa move through the female reproductive tract and eventually penetrate the zona pellucida and bind to the egg plasma membrane. Many proteins have been implicated in the process of fertilization as well as a plethora of proteins involved in the development of spermatids and sperm, and these are high lighted in this review.

Expression and localization of the deubiquitinating enzyme mUBPy in wobbler mouse testis during spermiogenesis

Mouse ubiquitin-specific processing protease (mUBPy) is a deubiquitinating enzyme highly expressed in both brain and testis. In testis, it interacts with the DnaJ protein, MSJ-1; both mUBPy and MSJ-1 are located on the cytoplasmic surface of the developing acrosome and in the centrosomal region during spemiogenesis. Present data show the first appearance in testis of mUbpy mRNA and protein at 10 days post-partum (d.p.p.). In addition, to investigate on a possible role of mUBPy in sperm formation, we took advantage of mutant wr/wr (wobbler) mice characterized by male infertility, which is likely due to the lack of a real, functional acrosome. RT-PCR and Northern blot analyses show that mUbpy is up-regulated in adult wobbler testis. Furthermore, in wild-type testis mUBPy protein is primarily detected by Western blot in the soluble (cytosolic/nuclear) fraction during the first round of spermatogenesis and in the adult. By contrast, mUBPy is primarily detected in membranous/insoluble protein fraction when wobbler phenotype is clearly shown (30 d.p.p.) and in adult wobbler testis. By immunohistochemistry, whereas in wild-type animals mUBPy marks the profile of the acrosomic vesicle in differentiating spermatids, in wobbler mice only a detergent pre-treatment procedure allows to detect mUBPy immunoreactivity, which results in diffuse spotted granules inside the cytoplasm and around the nuclear shape. In conclusion, in wobbler testis expression of mUbpy is up-regulated, while a differential sorting of the protein characterizes wobbler spermatids where acrosome formation is impaired.

Structure of msj-1 gene in mice and humans: a possible role in the regulation of male reproduction

Msj-1 gene encodes a DnaJ protein highly expressed in spermatids and spermatozoa of both rodents and amphibians, possibly involved in vesicle fusion and protein quality control by means of interaction with heat shock proteins. We isolated and characterized the entire murine msj-1 gene and searched for putative msj-1-like genes into the human genome. Furthermore, ultrastructural localization of MSJ-1 was analyzed in mouse germ cells by immunogold electron microscopy. The analysis of murine msj-1 genomic sequence reveals that it is an intron less gene. Putative promoter region was predicted within the 600 bp upstream the transcription start site. In mouse, msj-1 maps on chromosome 1, into an intronic region of UDP glucuronosyl-transferase 1 family cluster. At ultrastructural level, MSJ-1 marks the developing acrosomic vesicle and the sperm centriolar region. A blast search against the human genome database revealed two closed regions (Ha and Hb) on human chromosome 2 having high nucleotide identity with murine msj-1 coding region. Similarly to mouse, in human both regions map into an intronic region of UDP glycosyl-transferase 1 family polypeptide A cluster (ugt1a@). A significant ORF encoding a putative DnaJ protein of 145 aa was predicted from Ha. Finally, expression analysis, conducted by RT-PCR in human sperm cells, demonstrated that Ha mRNA is effectively present in humans; by Western blot, a specific MSJ-1 band of approximately 30kDa was detected in human sperm. Taken together, these data suggest that msj-1 gene might be conserved among vertebrates and might exert fundamental functions in reproduction.

Expression of the deubiquitinating enzyme mUBPy in the mouse brain

Mouse UBPy (mUBPy) is an ubiquitin-specific protease which belongs to a family of deubiquitinating enzymes (DUBs) implicated in several cellular processes related to both cell growth and differentiation. Previously, Northern blot analysis revealed an important expression of mUBPy in the testis and brain. However, a more comprehensive map of mUBPy localization in the central nervous system (CNS) is still lacking. In this study, we mapped the distribution of mUBPy in the mouse brain using nonradioactive in situ hybridization and immunohistochemical techniques. In general, transcript and protein showed a similar and widespread distribution. In particular, mUBPy was strongly expressed in the hippocampal formation, septal region, ventral pallidum, preoptic nucleus, periventricular nucleus of hypothalamus, compact part of the substantia nigra, ventral tegmental area, cochlear nucleus and granular cell layer of cerebellum. A moderate expression of mUBPy was found in the amygdaloid complex, supraoptic nucleus, arcuate and ventromedial nuclei of hypothalamus, lateral hypothalamic area and lateral and reticular part of the substantia nigra. Double labelling with the mUBPy antiserum and antisera against specific cell markers showed that the enzyme is generally expressed in neurons and, in specific regions, also in oligodendrocytes. Moreover, by using antisera to TH and mUBPy we found that mUBPy is localized in dopaminergic neurons. The different distribution of mUBPy in the distinct regions of the brain suggests that it could be related to different deubiquitinating processes; in particular, in the areas where it is expressed at high levels, mUBPy could exert a specialized function through its interaction with specific protein substrates.

UBPy/MSJ-1 system during male germ cell progression in the frog, Rana esculenta

mUBPy (mouse ubiquitin specific processing protease) is a de-ubiquitinating enzyme expressed in mouse testis and brain. In testis, it interacts with the DnaJ protein MSJ-1 (mouse sperm cell specific DnaJ first homologue), a molecular chaperone expressed in spermatids and spermatozoa. Since MSJ-1 is conserved among vertebrates, to demonstrate an evolutionarily conserved function of UBPy/MSJ-1 system, we assayed mUBPy presence in the anuran amphibian, the frog, Rana esculenta, during the annual sexual cycle. By Western blot we have detected a specific signal of 126kDa in testis and isolated spermatozoa. During the annual sexual cycle, the signal gradually increases as soon as spermatogenesis resumes after the winter stasis. Using immunocytochemistry, we have localized the protein in spermatids and spermatozoa. In conclusion, UBPy/MSJ-1 system is available in R. esculenta testis suggesting a conserved fundamental function in spermatogenesis and sperm formation.

Centrosomal protein centrin is not detectable during early pre-implantation development but reappears during late blastocyst stage in porcine embryos

Centrin is an evolutionarily conserved 20 kDa, Ca+2-binding, calmodulin-related protein associated with centrioles and basal bodies of phylogenetically diverse eukaryotic cells. Earlier studies have shown that residual centrosomes of non-rodent mammalian spermatozoa retain centrin and, in theory, could contribute this protein for the reconstruction of the zygotic centrosome after fertilization. The present work shows that CEN2 and CEN3 mRNA were detected in germinal vesicle-stage (GV) oocytes, MII oocytes, and pre-implantation embryos from the two-cell through the blastocyst stage, but not in spermatozoa. Boar ejaculated spermatozoa possess centrin as revealed by immunofluorescence microscopy and western blotting. Immature, GV oocytes possess speckles of centrin particles in the perinuclear area, visualized by immunofluorescence microscopy and exhibit a 19 kDa band revealed by western blotting. Mature MII stage oocytes lacked centrin that could be detected by immunofluorescence or western blotting. The sperm centrin was lost in zygotes after in vitro fertilization. It was not detectable in embryos by immunofluorescence microscopy until the late blastocyst stage. Embryonic centrin first appeared as fine speckles in the perinuclear area of some interphase blastocyst cells and as putative centrosomes of the spindle poles of dividing cells. The cells of the hatched blastocysts developed centrin spots comparable with those of the cultured cells. Some blastomeres displayed undefined curved plate-like centrin-labeled structures. Anti-centrin antibody labeled interphase centrosomes of cultured pig embryonic fibroblast cells as distinct spots in the juxtanuclear area. Enucleated pig oocytes reconstructed by electrofusion with pig fibroblasts displayed centrin of the donor cell during the early stages of nuclear decondensation but became undetectable in the late pronuclear or cleavage stages. These observations suggest that porcine zygotes and pre-blastocyst embryonic cells lack centrin and do not retain exogenously incorporated centrin. The early embryonic centrosomes function without centrin. Centrin in the blastocyst stage embryos is likely a result of de novo synthesis at the onset of differentiation of the pluripotent blastomeres.

Identification and characterization of rDJL, a novel member of the DnaJ protein family, in rat testis

Applying the method of segmentation of seminiferous tubules combined with DDRT-PCR and cDNA library screening, a novel DnaJ homologue, rDJL was identified in rat testis. The reading frame encodes a protein of 223 amino acid residues containing J domain in the NH2 terminal region. rDJL gene is expressed mainly in testis and rDJL protein was immunolocalized notably in the acrosome region of spermatozoa. Immunoprecipitation experiments showed that rDJL interacted with Hsc70 and clathrin protein. When CHO cells were treated with EGF, rDJL and clathrin protein were found to be colocalized and be concentrated as endosome vesicles. The present findings suggest that rDJL functions as co-chaperone to Hsc70, participates in vesicular trafficking and may play an important role in acrosomogenesis.