Keratins: unraveling the coordinated construction of scaffolds in spermatogenic cells

Dietary Arginine Supplementation Modulates the Proteome of Boar Seminal Plasma

This study investigated the impact of an increased arginine (ARG) level in a boar diet on semen production, sperm quality, and seminal plasma proteome. Adult Nebraska Index Line boars were assigned to two groups, one receiving a control diet with 0.77% arginine (n = 4) and the other a high-arginine diet with 1.77% arginine (n = 5). Semen was collected twice a week over the whole experiment, including one week before, six weeks during, and six weeks after the supplementation. Parameters such as semen volume and concentration were assessed immediately after collection, alongside sperm motility and morphology. Centrifugation of raw semen samples yielded seminal plasma for a gel-based proteome analysis. The seminal plasma proteins were extracted, quantified, and separated via 2D gel electrophoresis, allowing protein identification through mass spectrometry. Data analysis involved two-way ANOVA for comparisons (p < 0.05). Results showed that arginine supplementation improved semen volume and total sperm counts, with averages of 21 ± 3 doses in the control group versus 24 ± 2 in the ARG group (p = 0.05). Although sperm motility and morphology remained unaffected (p > 0.05), dietary arginine upregulated ten proteins and downregulated two. In summary, increased dietary arginine did not significantly alter key parameters of semen output or sperm quality but significantly impacted seminal plasma proteome, warranting further research on sperm viability.

Human papillomavirus and male infertility correlation analysis following World Health Organization 2021 guidelines

Male infertility is a complex issue influenced by multiple environmental and pathological factors. In this context, the impact of Human papillomavirus (HPV) infection on male fertility remains controversial. The introduction of new WHO 2021 evaluation criteria, included in the 6th ed. of Laboratory Manual for the examination and processing of human semen, i.e. DNA fragmentation index (DFI), slow and rapid progressive motility, could provide additional information about this correlation. 121 semen samples of male partners of HPV-positive women attending In Vitro Fertilization (IVF) were evaluated following WHO 2021 and HPV-DNA test. Comparing HPV-negative and positive samples for rapid and slow progressive motility showed significantly different results (p = 0.0018, p = 0.0004), contrary to what was observed for total progressive motility. Regarding sperm DFI, only high-risk HPV infections affected DNA integrity. In addition, the correlation between the different semen parameters revealed a significant correlation between midpiece morphological defects and rapid progressive motility in the HPV-positive group (rho = 0.43, p = 0.0006). In conclusion, WHO 2021 provides additional information regarding HPV's impact on seminal parameters. The correlation between HPV positivity, midpiece defects and a higher rapid progressive motility opens new research perspectives that may help unravel the issues surrounding the role of HPV in compromising sperm quality.

The antioxidant effects of butylated hydroxytoluene on cryopreserved goat sperm from a proteomic perspective

At present, there are few reports about the proteomics changes provoked by butylated hydroxytoluene (BHT) supplementation on cryopreserved semen in mammals. Thus, we aimed to evaluate the effects of different concentrations of BHT on goat sperm and to investigate the proteomics changes of adding BHT to cryopreserved goat (Capra hircus) sperm. Firstly, semen samples were collected from four goats, and frozen in the basic extenders containing different concentrations of BHT (0.5 mM, 1.0 mM, 2.0 mM) and a control without BHT, respectively. After thawing, the protective effects of dose-dependent replenished BHT to the freezing medium on post-thaw sperm motility, integrities of plasma membrane and acrosome, reactive oxygen species levels were confirmed, with 0.5 mM BHT being the best (B group) as compared to the control (without BHT, C group). Afterwards, TMT-based quantitative proteomic technique was performed to profile proteome of the goat sperm between C group and B group. Parallel reaction monitoring was used to confirm reliability of the data. Overall, 2,476 proteins were identified and quantified via this approach. Comparing the C and B groups directly (C vs. B), there were 17 differentially abundant proteins (DAPs) po-tentially associated with sperm characteristics and functions were identified, wherein three were upregulated and 14 were downregulated, respectively. GO annotation analysis demonstrated the potential involvement of the identified DAPs in metabolic process, multi-organism process, reproduction, reproductive process, and cellular process. KEGG enrichment analysis further indicated their potential roles in renin-angiotensin system and glutathione metabolism pathways. Together, this novel study clearly shows that BHT can effectively improve quality parameters and fertility potential of post-thawed goat sperm at the optimal concentration, and its cryoprotection may be realized through regulation of sperm metabolism and antioxidative capability from the perspective of sperm proteomic modification.

In vitro proliferation of Mytilus edulis male germ cell progenitors

Our understanding of basic cellular processes has mostly been provided by mammalian cell culture, and by some non-mammalian vertebrate and few invertebrate cell culture models. Developing reliable culture conditions for non-model organisms is essential to allow investigation of more unusual cellular processes. Here, we investigate how cells isolated from different tissues of the marine mussel Mytilus edulis thrive and survive in vitro in the hope of establishing a suitable laboratory model for the investigation of cellular mechanisms specific to these bivalve mollusks. We found that cells dissociated from mantle tissue attached to the culture vessels and proliferated well in vitro, whereas cells isolated from gills, although remaining viable, did not maintain divisions over three to four weeks in culture. We used antibodies against the germ-line marker DEAD-box helicase 4 (DDX4), also known as VASA, and the epithelial cell marker cytokeratin to distinguish different cell types in culture. DDX4-positive cells were predominant in 25-day-old cultures from male mantles. Cells from other tissues remained in low numbers and did not seem to change in composition over time. Overall, the culture conditions described here allow an efficient selection of male germ cells that could be used to study specific cellular mechanisms in vitro.

Integrative analyses of potential biomarkers and pathways for non-obstructive azoospermia

Background: Non-obstructive azoospermia (NOA) is the most severe form of male infertility. Currently, the molecular mechanisms underlying NOA pathology have not yet been elucidated. Hence, elucidation of the mechanisms of NOA and exploration of potential biomarkers are essential for accurate diagnosis and treatment of this disease. In the present study, we aimed to screen for biomarkers and pathways involved in NOA and reveal their potential molecular mechanisms using integrated bioinformatics. Methods: We downloaded two gene expression datasets from the Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) in NOA and matched the control group tissues were identified using the limma package in R software. Subsequently, Gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), gene set enrichment analysis (GSEA), protein-protein interaction (PPI) network, gene-microRNAs network, and transcription factor (TF)-hub genes regulatory network analyses were performed to identify hub genes and associated pathways. Finally, we conducted immune infiltration analysis using CIBERSORT to evaluate the relationship between the hub genes and the NOA immune infiltration levels. Results: We identified 698 common DEGs, including 87 commonly upregulated and 611 commonly downregulated genes in the two datasets. GO analysis indicated that the most significantly enriched gene was protein polyglycylation, and KEGG pathway analysis revealed that the DEGs were most significantly enriched in taste transduction and pancreatic secretion signaling pathways. GSEA showed that DEGs affected the biological functions of the ribosome, focaladhesion, and protein_expor. We further identified the top 31 hub genes from the PPI network, and friends analysis of hub genes in the PPI network showed that NR4A2 had the highest score. In addition, immune infiltration analysis found that CD8⁺ T cells and plasma cells were significantly correlated with ODF3 expression, whereas naive B cells, plasma cells, monocytes, M2 macrophages, and resting mast cells showed significant variation in the NR4A2 gene expression group, and there were differences in T cell regulatory immune cell infiltration in the FOS gene expression groups. Conclusion: The present study successfully constructed a regulatory network of DEGs between NOA and normal controls and screened three hub genes using integrative bioinformatics analysis. In addition, our results suggest that functional changes in several immune cells in the immune microenvironment may play an important role in spermatogenesis. Our results provide a novel understanding of the molecular mechanisms of NOA and offer potential biomarkers for its diagnosis and treatment.

A single amino acid mutation in the mouse MEIG1 protein disrupts a cargo transport system necessary for sperm formation

Mammalian spermatogenesis is a highly coordinated process that requires cooperation between specific proteins to coordinate diverse biological functions. For example, mouse Parkin coregulated gene (PACRG) recruits meiosis-expressed gene 1 (MEIG1) to the manchette during normal spermiogenesis. Here we mutated Y68 of MEIG1 using the CRISPR/cas9 system and examined the biological and physiological consequences in mice. All homozygous mutant males examined were completely infertile, and sperm count was dramatically reduced. The few developed sperm were immotile and displayed multiple abnormalities. Histological staining showed impaired spermiogenesis in these mutant mice. Immunofluorescent staining further revealed that this mutant MEIG1 was still present in the cell body of spermatocytes, but also that more MEIG1 accumulated in the acrosome region of round spermatids. The mutant MEIG1 and a cargo protein of the MEIG1/PACRG complex, sperm-associated antigen 16L (SPAG16L), were no longer found to be present in the manchette; however, localization of the PACRG component was not changed in the mutants. These findings demonstrate that Y68 of MEIG1 is a key amino acid required for PACRG to recruit MEIG1 to the manchette to transport cargo proteins during sperm flagella formation. Given that MEIG1 and PACRG are conserved in humans, small molecules that block MEIG1/PACRG interaction are likely ideal targets for the development of male contraconception drugs.

Thiols of flagellar proteins are essential for progressive motility in human spermatozoa

Male infertility is a disorder of the reproductive system defined by the failure to achieve a clinical pregnancy after 12 months or more of regular unprotected sexual intercourse. The presence of low-motile or immotile spermatozoa is one of many causes of infertility; however, this observation provides little or no information regarding the pathogenesis of the malfunction. Good sperm motility depends on correct assembly of the sperm tail in the testis and efficient maturation during epididymal transit. Thiols of flagellar proteins, such as outer dense fibre protein 1 (ODF1), are oxidised to form disulfides during epididymal transit and the spermatozoa become motile. This study was designed to determine how oxidative changes in protein thiol status affect progressive motility in human spermatozoa. Monobromobimane (mBBr) was used as a specific thiol marker and disruptor of sperm progressive motility. When mBBr was blocked by dithiothreitol it did not promote motility changes. The analysis of mBBr-treated spermatozoa revealed a reduction of progressive motility and an increased number of spermatozoa with non-progressive motility without affecting ATP production. Laser confocal microscopy and western blot analysis showed that one of the mBBr-positive proteins reacted with an antibody to ODF1. Monobromobimane fluorescence intensity of the sperm tail was lower in normozoospermic than asthenozoospermic men, suggesting that thiol oxidation in spermatozoa of asthenozoospermic men is incomplete. Our findings indicate that mBBr affects the thiol status of ODF1 in human spermatozoa and interferes with progressive motility.

Role of non-receptor protein tyrosine kinases in spermatid transport during spermatogenesis

Non-receptor protein tyrosine kinases are cytoplasmic kinases that activate proteins by phosphorylating tyrosine residues, which in turn affect multiple functions in eukaryotic cells. Herein, we focus on the role of non-receptor protein tyrosine kinases, most notably, FAK, c-Yes and c-Src, in the transport of spermatids across the seminiferous epithelium during spermatogenesis. Since spermatids, which are formed from spermatocytes via meiosis, are immotile haploid cells, they must be transported by Sertoli cells across the seminiferous epithelium during the epithelial cycle of spermatogenesis. Without the timely transport of spermatids across the epithelium, the release of sperms at spermiation fails to occur, leading to infertility. Thus, the molecular event pertinent to spermatid transport is crucial to spermatogenesis. We provide a critical discussion based on recent findings in this review. We also provide a hypothetical model on spermatid transport, and the role of non-receptor protein tyrosine kinases in this event. We also highlight areas of research that deserve attention by investigators in the field.

KIF3A is essential for sperm tail formation and manchette function

KIF3A motor protein is responsible for intraflagellar transport, which is required for protein delivery during axoneme formation in ciliated cells. The function of KIF3A during spermatogenesis is not known. In this study, we show that depletion of KIF3A causes severe impairments in sperm tail formation and interestingly, it also affects manchette organization and the shaping of sperm heads. Our results demonstrate the analogy between the mechanisms governing the formation of cilia in somatic cells and the formation of spermatozoa-specific flagella. Furthermore, this study reveals KIF3A as an important regulator of spermatogenesis and emphasizes the crucial role of KIF3A in maintaining male fertility. We also identified several novel interacting partners for KIF3A, including meiosis-specific nuclear structural protein 1 (MNS1) that colocalizes with KIF3A in the manchette and principal piece of the sperm tail. This study highlights the essential role of KIF3A-mediated microtubular transport in the development of spermatozoa and male fertility.

The blood-testis barrier and its implications for male contraception

The blood-testis barrier (BTB) is one of the tightest blood-tissue barriers in the mammalian body. It divides the seminiferous epithelium into the basal and the apical (adluminal) compartments. Meiosis I and II, spermiogenesis, and spermiation all take place in a specialized microenvironment behind the BTB in the apical compartment, but spermatogonial renewal and differentiation and cell cycle progression up to the preleptotene spermatocyte stage take place outside of the BTB in the basal compartment of the epithelium. However, the BTB is not a static ultrastructure. Instead, it undergoes extensive restructuring during the seminiferous epithelial cycle of spermatogenesis at stage VIII to allow the transit of preleptotene spermatocytes at the BTB. Yet the immunological barrier conferred by the BTB cannot be compromised, even transiently, during the epithelial cycle to avoid the production of antibodies against meiotic and postmeiotic germ cells. Studies have demonstrated that some unlikely partners, namely adhesion protein complexes (e.g., occludin-ZO-1, N-cadherin-β-catenin, claudin-5-ZO-1), steroids (e.g., testosterone, estradiol-17β), nonreceptor protein kinases (e.g., focal adhesion kinase, c-Src, c-Yes), polarity proteins (e.g., PAR6, Cdc42, 14-3-3), endocytic vesicle proteins (e.g., clathrin, caveolin, dynamin 2), and actin regulatory proteins (e.g., Eps8, Arp2/3 complex), are working together, apparently under the overall influence of cytokines (e.g., transforming growth factor-β3, tumor necrosis factor-α, interleukin-1α). In short, a "new" BTB is created behind spermatocytes in transit while the "old" BTB above transiting cells undergoes timely degeneration, so that the immunological barrier can be maintained while spermatocytes are traversing the BTB. We also discuss recent findings regarding the molecular mechanisms by which environmental toxicants (e.g., cadmium, bisphenol A) induce testicular injury via their initial actions at the BTB to elicit subsequent damage to germ-cell adhesion, thereby leading to germ-cell loss, reduced sperm count, and male infertility or subfertility. Moreover, we also critically evaluate findings in the field regarding studies on drug transporters in the testis and discuss how these influx and efflux pumps regulate the entry of potential nonhormonal male contraceptives to the apical compartment to exert their effects. Collectively, these findings illustrate multiple potential targets are present at the BTB for innovative contraceptive development and for better delivery of drugs to alleviate toxicant-induced reproductive dysfunction in men.

Expression of two testis-specific genes, SPATA19 and LEMD1, in prostate cancer

BACKGROUND AND AIMS

Screening methods for early detection of prostate cancer have some limitations regarding specificity and sensitivity, so there is a continuing search to find new cancer biomarkers. Cancer-testis genes are a group of genes with expression almost limited to testis and different kinds of tumors. Since testis is an immune privileged site, if these genes are expressed in tumors, they can be immunogenic. We undertook this study to find new members of the cancer-testis gene family appropriate for cancer immunotherapy

METHODS

We analyzed the expression of six testis-specific genes called ODF1, ODF2, ODF3, ODF4, LEMD1 and SPATA19 in 30 prostate cancer and 25 benign prostate hyperplasia (BPH) samples by RT-PCR and restriction fragment length polymorphism (RFLP).

RESULTS

Of the prostate cancer samples, 10, 10, 23 and 40% showed ODF1, ODF2, LEMD1 and SPATA19 specific bands, respectively, but none of the BPH samples expressed any of these genes. The difference between prostate cancer and BPH groups for LEMD1 and SPATA19 expression was significant. Mean serum PSA level was significantly higher in patients expressing ODF2 than in the other patients.

CONCLUSIONS

ODF1, ODF2, SPATA19 and LEMD1 are members of cancer-testis gene family. In addition, LEMD1 and SPATA19 are putative cancer biomarkers and promising targets for active immunotherapy.

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.

Structure and functions of keratin proteins in simple, stratified, keratinized and cornified epithelia

Historically, the term 'keratin' stood for all of the proteins extracted from skin modifications, such as horns, claws and hooves. Subsequently, it was realized that this keratin is actually a mixture of keratins, keratin filament-associated proteins and other proteins, such as enzymes. Keratins were then defined as certain filament-forming proteins with specific physicochemical properties and extracted from the cornified layer of the epidermis, whereas those filament-forming proteins that were extracted from the living layers of the epidermis were grouped as 'prekeratins' or 'cytokeratins'. Currently, the term 'keratin' covers all intermediate filament-forming proteins with specific physicochemical properties and produced in any vertebrate epithelia. Similarly, the nomenclature of epithelia as cornified, keratinized or non-keratinized is based historically on the notion that only the epidermis of skin modifications such as horns, claws and hooves is cornified, that the non-modified epidermis is a keratinized stratified epithelium, and that all other stratified and non-stratified epithelia are non-keratinized epithelia. At this point in time, the concepts of keratins and of keratinized or cornified epithelia need clarification and revision concerning the structure and function of keratin and keratin filaments in various epithelia of different species, as well as of keratin genes and their modifications, in view of recent research, such as the sequencing of keratin proteins and their genes, cell culture, transfection of epithelial cells, immunohistochemistry and immunoblotting. Recently, new functions of keratins and keratin filaments in cell signaling and intracellular vesicle transport have been discovered. It is currently understood that all stratified epithelia are keratinized and that some of these keratinized stratified epithelia cornify by forming a Stratum corneum. The processes of keratinization and cornification in skin modifications are different especially with respect to the keratins that are produced. Future research in keratins will provide a better understanding of the processes of keratinization and cornification of stratified epithelia, including those of skin modifications, of the adaptability of epithelia in general, of skin diseases, and of the changes in structure and function of epithelia in the course of evolution. This review focuses on keratins and keratin filaments in mammalian tissue but keratins in the tissues of some other vertebrates are also considered.

Proteomic analysis of the spermatogonial stem cell compartment in dogfish Scyliorhinus canicula L

In the dogfish (Scyliorhinus canicula L.) the testicular germinative zone (GZ), composed of large isolated spermatogonia surrounded by elongating pre-Sertoli cells, is located between the albuginea and the ventrolateral intratesticular vessel. During the spermatogenic wave, cysts radiate in maturational order forming distinct testicular zones. In this study, soluble proteins of the GZ and of the zone containing cysts with spermatocytes were separated by two-dimensional electrophoresis. Gel images were matched and then evaluated for GZ-specific proteins. From the1400 protein spots identified, 680 were found to be apparently specific to this zone. Using MALDI-TOF/TOF mass spectrometry, de novo sequences were obtained for 33 proteins out of the 169 selected for identification by mass spectrometry, but only 16 of these 169 proteins were identified. One of them, proteasome subunit alpha-6, was analyzed further by immunohistochemistry. This study demonstrates the utility of the dogfish as a model for proteome analysis of the spermatogonial stem cell niche, even if it remains restricted by the lack of genomic data available on Elasmobranchs.

Mammalian transcription in support of hybrid mRNA and protein synthesis in testis and lung

Post-transcriptional mechanisms including differential splicing expand the protein repertoire beyond that provided by the one gene-one protein model. Trans-splicing has been observed in mammalian systems but is low level (sometimes referred to as noise), and a contribution to hybrid protein expression is unclear. In the study of rat sperm tail proteins a cDNA, called 1038, was isolated representing a hybrid mRNA derived in part from the ornithine decarboxylase antizyme 3 (Oaz3) gene located on rat chromosome 2 fused to sequences encoded by a novel gene on chromosome 4. Cytoplasmic Oaz3 mRNA is completely testis specific. However, in several tissues Oaz3 is transcribed and contributes to hybrid 1038 mRNA synthesis, without concurrent Oaz3 mRNA synthesis. 1038 mRNA directs synthesis of a hybrid 14-kDa protein, part chromosome 2- and part chromosome 4-derived as shown in vitro and in transfected cells. Antisera that recognize a chromosome 4-encoded C-terminal peptide confirm the hybrid character of endogenous 14-kDa protein and its presence in sperm tail structures and 1038-positive tissue. Our data suggest that the testis-specific OAZ3 gene may be an example of a mammalian gene that in several tissues is transcribed to contribute to a hybrid mRNA and protein. This finding expands the repertoire of known mechanisms available to cells to generate proteome diversity.

Rat Spag5 associates in somatic cells with endoplasmic reticulum and microtubules but in spermatozoa with outer dense fibers

The leucine zipper motif has been identified as an important and specific interaction motif used by various sperm tail proteins that localize to the outer dense fibers. We had found that rat Odf1, a major integral ODF protein, utilizes its leucine zipper to associate with Odf2, another major ODF protein, Spag4 which localizes to the interface between ODF and axonemal microtubule doublets, and Spag5. The rat Spag5 sequence indicated a close relationship with human Astrin, a microtubule-binding spindle protein suggesting that Spag5, like Spag4, may associate with the sperm tail axoneme. RT PCR assays indicated expression of Spag5 in various tissues and in somatic cells Spag5 localizes to endoplasmic reticulum and microtubules, as expected for an Astrin orthologue. MT binding was confirmed both in vivo and in in vitro MT-binding assays: somatic cells contain a 58 kDa MT-associated Spag5 protein. Western blotting assays of rat somatic cells and male germ cells at different stages of development using anti-Spag5 antibodies demonstrated that the protein expression pattern changes during spermatogenesis and that sperm tails contain a 58 kDa Spag5 protein. Use of affinity-purified anti-Spag5 antibodies in immuno electron microscopy shows that in rat elongated spermatids and epididymal sperm the Spag5 protein associates with ODF, but not with the axonemal MTs. This observation is in contrast to that for the other Odf1-binding, MT-binding protein Spag4, which is present between ODF and axoneme. Our data demonstrate that Spag5 has different localization in somatic versus male germ cells suggesting the possibility of different function.

Proteome analysis of chicken embryonic gonads: identification of major proteins from cultured gonadal primordial germ cells

The domestic chicken (Gallus gallus) is an important model for research in developmental biology because its embryonic development occurs in ovo. To examine the mechanism of embryonic germ cell development, we constructed proteome map of gonadal primordial germ cells (gPGCs) from chicken embryonic gonads. Embryonic gonads were collected from 500 embryos at 6 days of incubation, and the gPGCs were cultured in vitro until colony formed. After 7-10 days in culture, gPGC colonies were separated from gonadal stroma cells (GSCs). Soluble extracts of cultured gPGCs were then fractionated by two-dimensional gel electrophoresis (pH 4-7). A number of protein spots, including those that displayed significant expression levels, were then identified by use of matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry and LC-MS/MS. Of the 89 gPGC spots examined, 50 yielded mass spectra that matched avian proteins found in on-line databases. Proteome map of this type will serve as an important reference for germ cell biology and transgenic research.

The novel protein PTPIP51 exhibits tissue- and cell-specific expression

The expression patterns of both mRNA and protein of the novel protein tyrosine phosphatase interacting protein 51 (PTPIP51) were studied in various organs by in situ hybridization, immunoblotting, and immunocytochemistry. The protein was found in all mammalian species investigated: guinea pig, rat, mouse, pig, and human. The presence of the protein was, however, restricted to specific organs. High levels of PTPIP51 were found in epidermis and seminiferous epithelium. The expression appears to be associated with distinct stages of differentiation. While basal cells in the epidermis and spermatogonia showed no perceptible amount of PTPIP51, keratinocytes of suprabasal layers and differentiating first-order spermatocytes up to spermatids exhibited high expression. In skeletal muscle, the presence of PTPIP51 was restricted to fibers of the fast twitch type. In surface epithelia containing ciliated cells, the protein was associated with the microtubular structures responsible for ciliary movement. Furthermore, specific structures of the central nervous system, for example, neurons of the hippocampal region, ganglion cells of the autonomic nervous system, and axons of the peripheral nervous system showed a distinct staining pattern with the antibody to PTPIP51. Our data suggest that PTPIP51 might be involved in the regulation of cellular processes associated with differentiation, movement, or cytoskeletal organization.

Transcription in haploid male germ cells

Major modifications in chromatin organization occur in spermatid nuclei, resulting in a high degree of DNA packaging within the spermatozoon head. However, before arrest of transcription during midspermiogenesis, high levels of mRNA are found in round spermatids. Some transcripts are the product of genes expressed ubiquitously, whereas some are generated from male germ cell-specific gene homologs of somatic cell genes. Others are transcript variants derived from genes with expression regulated in a testis-specific fashion. The haploid genome of spermatids also initiates the transcription of testis-specific genes. Various general transcription factors, distinct promoter elements, and specific transcription factors are involved in transcriptional regulation. After meiosis, spermatids are genetically but not phenotypically different, because of transcript and protein sharing through cytoplasmic bridges connecting spermatids of the same generation. Interestingly, different types of mRNAs accumulate in the sperm cell nucleus, raising the question of their origin and of a possible role after fertilization.

Association of kinesin light chain with outer dense fibers in a microtubule-independent fashion

Conventional kinesin I motor molecules are heterotetramers consisting of two kinesin light chains (KLCs) and two kinesin heavy chains. The interaction between the heavy and light chains is mediated by the KLC heptad repeat (HR), a leucine zipper-like motif. Kinesins bind to microtubules and are involved in various cellular functions, including transport and cell division. We recently isolated a novel KLC gene, klc3. klc3 is the only known KLC expressed in post-meiotic male germ cells. A monoclonal anti-KLC3 antibody was developed that, in immunoelectron microscopy, detects KLC3 protein associated with outer dense fibers (ODFs), unique structural components of sperm tails. No significant binding of KLC3 with microtubules was observed with this monoclonal antibody. In vitro experiments showed that KLC3-ODF binding occurred in the absence of kinesin heavy chains or microtubules and required the KLC3 HR. ODF1, a major ODF protein, was identified as the KLC3 binding partner. The ODF1 leucine zipper and the KLC3 HR mediated the interaction. These results identify and characterize a novel interaction between a KLC and a non-microtubule macromolecular structure and suggest that KLC3 could play a microtubule-independent role during formation of sperm tails.

New insights into the rat spermatogonial proteome: identification of 156 additional proteins

Despite the essential role played by spermatogonia in testicular function, little is known about these cells. To improve our understanding of their biology, our group recently identified a set of 53 spermatogonial proteins using two-dimensional (2-D) gel electrophoresis and mass spectrometry. To continue this work, we investigated a subset of the spermatogonial proteome using narrow range immobilized pH gradients to favor the detection of less abundant proteins. A 2-D reference map of spermatogonia in the pH range 4-9 was created, and protein entities fractionated in a pH 5-6 2-D gel were further processed for protein identification. A new set of 156 polypeptides was identified by peptide mass fingerprinting and tandem mass spectrometry. These polypeptides corresponded to 102 different proteins, which reflect the complexity of post-translational modifications. Seventy-nine of these proteins were identified for the first time in spermatogonia. All identified proteins were classified into functional groups. This work represents a first step toward the establishment of a systematic spermatogonia protein database.

Novel RING finger protein OIP1 binds to conserved amino acid repeats in sperm tail protein ODF1

Outer dense fibers (ODFs) and the fibrous sheath (FS) are unique structures of the mammalian sperm tail. Recently, progress has been made in the molecular cloning of ODF and FS proteins, and because of this, questions addressing the morphogenesis and underlying protein network that make up sperm tail structures and their function can now be addressed. Using the N-terminal leucine zipper motif of the major ODF protein ODF1, we had previously isolated interacting proteins Odf2, Spag4, and Spag5. We report here a yeast two-hybrid strategy to isolate a novel rat testicular protein, OIP1, that binds to the evolutionarily conserved Cys-Gly-Pro repeats in the C-terminus of ODF1. OIP1 is expressed in round spermatids as well as in spermatocytes and several somatic tissues, albeit at a lower level. No expression was detectable in epididymis, heart, and smooth muscle. OIP1 protein localizes to the sperm tail in a pattern expected for an ODF1-interacting protein. OIP1 belongs to the family of RING finger proteins of the H2 subclass. Deletion of the putative RING motif significantly decreased binding to ODF1. Genomic analysis of rat Oip1 and Oip1 homologs indicates that Oip1 is highly conserved. Oip1 is subject to differential splicing and alternative polyadenylation events. It is interesting that Oip1 mRNAs have been reported that lack the exon encoding the putative RING finger.

Translational repression by MSY4 inhibits spermatid differentiation in mice

In developing male germ cells, newly synthesized protamine mRNAs are stored for up to 7 days before translational activation. Translational repression of protamine 1 (Prm1) mRNA requires sequences present in its 3′ untranslated region (UTR) and substantial evidence suggests a role for the murine Y-box protein MSY4 in this process. To determine if MSY4 can mediate translational repression in vivo, we generated transgenic mice in which the temporal window of MSY4 expression was extended during spermatogenesis. Expression of MSY4 disrupted the normal completion of spermatogenesis and caused dominant sterility. Immunocytochemical analysis of several markers, including the protamines, indicated that MSY4 prevented normal activation of translation. mRNAs whose translation was inhibited contained at least one MSY4 RNA recognition site, suggesting sequence-dependent translational repression. Altered translational activation resulted in defective processing of protamine 2 and severe defects in sperm morphogenesis. These results suggest that MSY4 plays an active role in translational repression of several mRNAs in differentiating spermatids.