A walk though vertebrate and invertebrate protamines

Structural insights into instability of the nucleosome driven by histone variant H3T

The testis-specific histone variant H3T plays a crucial role in chromatin reorganization during spermatogenesis by destabilizing nucleosomes. However, the structure basis for the nucleosome instability driven by H3T is not fully understand. In this study, we determinate the crystal structure of H3T-H4 in complex with histone chaperone ASF1a at 2.8 Å resolution. Our findings reveal that H3T-H4 binds ASF1a similarly to the conventional H3.1-H4 complex. However, significant structural differences are observed in the H3 α1 helix, the N- and C-terminal region of α2, and N-terminal region of L2. These differences are driven by H3T-specific residues, particularly Val111. Unlike the smaller Ala111 in H3.1, we find that bulkier residue Val111 fits well within the ASF1-H3T-H4 complex, but is difficult to arrange in nucleosome structure. Given that H3.1-Ala111/H3T-Val111 is located at the DNA binding and tetramerization interface of H3-H4, it is likely that Ala111Val substitution will lead to the instability of the corresponding area in nucleosome, contributing to instability of H3T-containing nucleosome. These structural findings may elucidate the role of H3T in chromatin reorganization during spermatogenesis.

The protamines of the noble false widow spider Steatoda nobilis provide an example of liquid-liquid phase separation chromatin transitions during spermiogenesis

While there is extensive information about sperm nuclear basic proteins (SNBP) in vertebrates, there is very little information about Arthropoda by comparison. This paper aims to contribute to filling this gap by analyzing these proteins in the sperm of the noble false widow spider Steatoda nobilis (Order Araneae, Family Theridiidae). To this end, we have developed a protein extraction method that allows the extraction of cysteine-containing protamines suitable for the preparation and analysis of SNBPs from samples where the amount of starting tissue material is limited. We carried out top-down mass spectrometry sequencing and molecular phylogenetic analyses to characterize the protamines of S. nobilis and other spiders. We also used electron microscopy to analyze the chromatin organization of the sperm, and we found it to exhibit liquid-liquid phase spinodal decomposition during the late stages of spermiogenesis. These studies further our knowledge of the distribution of SNBPs within the animal kingdom and provide additional support for a proposed evolutionary origin of many protamines from a histone H1 (H5) replication-independent precursor.

Protamines and the sperm nuclear basic proteins Pandora's Box of insects

Insects are the largest group of animals when it comes to the number and diversity of species. Yet, with the exception of Drosophila, no information is currently available on the primary structure of their sperm nuclear basic proteins (SNBPs). This paper represents the first attempt in this regard and provides information about six species of Neoptera: Poecillimon thessalicus, Graptosaltria nigrofuscata, Apis mellifera, Nasonia vitripennis, Parachauliodes continentalis, and Tribolium castaneum. The SNBPs of these species were characterized by acetic acid urea gel electrophoresis (AU-PAGE) and high-performance liquid chromatography fractionated. Protein sequencing was obtained using a combination of mass spectrometry sequencing, Edman N-terminal degradation sequencing and genome mining. While the SNBPs of several of these species exhibit a canonical arginine-rich protamine nature, a few of them exhibit a protamine-like composition. They appear to be the products of extensive cleavage processing from a precursor protein which are sometimes further processed by other post-translational modifications that are likely involved in the chromatin transitions observed during spermiogenesis in these organisms.

H2BFWT Variations in Sperm DNA and Its Correlation to Pregnancy

Abnormalities in sperm nuclei and chromatin can interfere with normal fertilization, embryonic development, implantation, and pregnancy. We aimed to study the impact of H2BFWT gene variants in sperm DNA on ICSI outcomes in couples undergoing ART treatment. One hundred and nineteen partners were divided into pregnant (G1) and non-pregnant (G2) groups. After semen analysis, complete DNA was extracted from purified sperm samples. The sequence of the H2BFWT gene was amplified by PCR and then subjected to Sanger sequencing. The results showed that there are three mutations in this gene: rs7885967, rs553509, and rs578953. Significant differences were shown in the distribution of alternative and reference alleles between G1 and G2 (p = 0.0004 and p = 0.0020, respectively) for rs553509 and rs578953. However, there was no association between these SNPs and the studied parameters. This study is the first to shed light on the connection between H2BFWT gene variants in sperm DNA and pregnancy after ICSI therapy. This is a pilot study, so further investigations about these gene variants at the transcriptional and translational levels will help to determine its functional consequences and to clarify the mechanism of how pregnancy can be affected by sperm DNA.

Probing the hierarchical dynamics of DNA-sperm nuclear transition protein complexes through fuzzy interaction and mesoscale condensation

Nuclear transition protein TNP1 is a crucial player mediating histone-protamine exchange in condensing spermatids. A unique combination of intrinsic disorder and multivalent properties turns TNP1 into an ideal agent for orchestrating the formation of versatile TNP-DNA assemblies. Despite its significance, the physicochemical property and the molecular mechanism followed by TNP1 for histone replacement and DNA condensation are still poorly understood. This study reports the first-time in vitro expression and purification of human TNP1 and investigates the hierarchical dynamics of TNP1-DNA interaction using a combination of computational simulations, biochemical assays, fluorescence imaging, and atomic force microscopy. We explored three crucial facets of TNP1-DNA interactions. Initially, we delve into the molecular binding process that entails fuzzy interactions between TNP1 and DNA at the atomistic scale. Subsequently, we analyze how TNP1 binding affects the electrostatic and mechanical characteristics of DNA and influences its morphology. Finally, we study the biomolecular condensation of TNP1-DNA when subjected to high concentrations. The findings of our study set the foundation for comprehending the potential involvement of TNP1 in histone replacement and DNA condensation in spermatogenesis.

Computational Approach to Elucidating Insulin-Protamine Binding Interactions and Dynamics in Insulin NPH Formulations

Insulin NPH is an intermediate-acting insulin. Its protracted action profile is due to the formation of microcrystalline suspensions when insulin is complexed with a basic peptide protamine, zinc ion, and phenolic ligands. Despite advancements in analytical techniques, the binding epitope and binding mode of the protamine in the insulin-protamine complex are still unknown. In this study, we used bioinformatics tools such as molecular docking and molecular dynamics (MD) simulations to compute the binding sites and energetics of the insulin-protamine complex. We have taken four naturally occurring protamine peptides that are independently docked with the insulin R6 hexamer and subjected them to 200 ns MD simulations to observe the dynamics of the complexes and estimate the binding energies. The arginine-rich protamine peptides were found to bind on the surface of the insulin hexamer through hydrogen bonding, hydrophobic, and electrostatic interactions well supported by the calculated negative binding energies. The overall structure of the insulin hexamer was retained upon binding, highlighting its dynamic stability in the complex. Furthermore, the residues at the termini of the protamine peptides in the complex were seen to be highly dynamic, which stabilize toward the end of the simulation.

Histone removal in sperm protects paternal chromosomes from premature division at fertilization

The global replacement of histones with protamines in sperm chromatin is widespread in animals, including insects, but its actual function remains enigmatic. We show that in the Drosophila paternal effect mutant paternal loss (pal), sperm chromatin retains germline histones H3 and H4 genome wide without impairing sperm viability. However, after fertilization, pal sperm chromosomes are targeted by the egg chromosomal passenger complex and engage into a catastrophic premature division in synchrony with female meiosis II. We show that pal encodes a rapidly evolving transition protein specifically required for the eviction of (H3-H4)2 tetramers from spermatid DNA after the removal of H2A-H2B dimers. Our study thus reveals an unsuspected role of histone eviction from insect sperm chromatin: safeguarding the integrity of the male pronucleus during female meiosis.

DNA-protamine condensates under low salt conditions: molecular dynamics simulation with a simple coarse-grained model focusing on electrostatic interactions

Protamine, a small, strongly positively-charged protein, plays a key role in achieving chromatin condensation inside sperm cells and is also involved in the formulation of nanoparticles for gene therapy and packaging of mRNA-based vaccines against viral infection and cancer. The detailed mechanisms of such condensations are still poorly understood especially under low salt conditions where electrostatic interaction predominates. Our previous study, with a refined coarse-grained model in full consideration of the long-range electrostatic interactions, has demonstrated the crucial role of electrostatic interaction in protamine-controlled reversible DNA condensation. Therefore, we herein pay our attention only to the electrostatic interaction and devise a coarser-grained bead-spring model representing the right linear charge density on protamine and DNA chains but treating other short-range interactions as simply as possible, which would be suitable for real-scale simulations. Effective pair potential calculations and large-scale molecular dynamics simulations using this extremely simple model reproduce the phase behaviour of DNA in a wide range of protamine concentrations under low salt conditions, again revealing the importance of the electrostatic interaction in this process and providing a detailed nanoscale picture of bundle formation mediated by a charge disproportionation mechanism. Our simulations also show that protamine length alters DNA overcharging and in turn redissolution thresholds of DNA condensates, revealing the important role played by entropies and correlated fluctuations of condensing agents and thus offering an additional opportunity to design tailored nanoparticles for gene therapy. The control mechanism of DNA-protamine condensates will also provide a better microscopic picture of biomolecular condensates, i.e., membraneless organelles arising from liquid-liquid phase separation, that are emerging as key principles of intracellular organization. Such condensates controlled by post-translational modification of protamine, in particular phosphorylation, or by variations in protamine length from species to species may also be responsible for the chromatin-nucleoplasm patterning observed during spermatogenesis in several vertebrate and invertebrate species.

Sperm chromatin structure and reproductive fitness are altered by substitution of a single amino acid in mouse protamine 1

Conventional dogma presumes that protamine-mediated DNA compaction in sperm is achieved by electrostatic interactions between DNA and the arginine-rich core of protamines. Phylogenetic analysis reveals several non-arginine residues conserved within, but not across species. The significance of these residues and their post-translational modifications are poorly understood. Here, we investigated the role of K49, a rodent-specific lysine residue in protamine 1 (P1) that is acetylated early in spermiogenesis and retained in sperm. In sperm, alanine substitution (P1(K49A)) decreases sperm motility and male fertility-defects that are not rescued by arginine substitution (P1(K49R)). In zygotes, P1(K49A) leads to premature male pronuclear decompaction, altered DNA replication, and embryonic arrest. In vitro, P1(K49A) decreases protamine-DNA binding and alters DNA compaction and decompaction kinetics. Hence, a single amino acid substitution outside the P1 arginine core is sufficient to profoundly alter protein function and developmental outcomes, suggesting that protamine non-arginine residues are essential for reproductive fitness.

Biophysical ordering transitions underlie genome 3D re-organization during cricket spermiogenesis

Spermiogenesis is a radical process of differentiation whereby sperm cells acquire a compact and specialized morphology to cope with the constraints of sexual reproduction while preserving their main cargo, an intact copy of the paternal genome. In animals, this often involves the replacement of most histones by sperm-specific nuclear basic proteins (SNBPs). Yet, how the SNBP-structured genome achieves compaction and accommodates shaping remain largely unknown. Here, we exploit confocal, electron and super-resolution microscopy, coupled with polymer modeling to identify the higher-order architecture of sperm chromatin in the needle-shaped nucleus of the emerging model cricket Gryllus bimaculatus. Accompanying spermatid differentiation, the SNBP-based genome is strikingly reorganized as ~25nm-thick fibers orderly coiled along the elongated nucleus axis. This chromatin spool is further found to achieve large-scale helical twisting in the final stages of spermiogenesis, favoring its ultracompaction. We reveal that these dramatic transitions may be recapitulated by a surprisingly simple biophysical principle based on a nucleated rigidification of chromatin linked to the histone-to-SNBP transition within a confined nuclear space. Our work highlights a unique, liquid crystal-like mode of higher-order genome organization in ultracompact cricket sperm, and establishes a multidisciplinary methodological framework to explore the diversity of non-canonical modes of DNA organization.

DOT1L promotes spermatid differentiation by regulating expression of genes required for histone-to-protamine replacement

Unique chromatin remodeling factors orchestrate dramatic changes in nuclear morphology during differentiation of the mature sperm head. A crucial step in this process is histone-to-protamine exchange, which must be executed correctly to avoid sperm DNA damage, embryonic lethality and male sterility. Here, we define an essential role for the histone methyltransferase DOT1L in the histone-to-protamine transition. We show that DOT1L is abundantly expressed in mouse meiotic and postmeiotic germ cells, and that methylation of histone H3 lysine 79 (H3K79), the modification catalyzed by DOT1L, is enriched in developing spermatids in the initial stages of histone replacement. Elongating spermatids lacking DOT1L fail to fully replace histones and exhibit aberrant protamine recruitment, resulting in deformed sperm heads and male sterility. Loss of DOT1L results in transcriptional dysregulation coinciding with the onset of histone replacement and affecting genes required for histone-to-protamine exchange. DOT1L also deposits H3K79me2 and promotes accumulation of elongating RNA Polymerase II at the testis-specific bromodomain gene Brdt. Together, our results indicate that DOT1L is an important mediator of transcription during spermatid differentiation and an indispensable regulator of male fertility.

Gradient Nanoconfinement Facilitates Binding of Transcriptional Factor NF-κB to Histone- and Protamine-DNA Complexes

Mechanically induced chromosome reorganization plays important roles in transcriptional regulation. However, the interplay between chromosome reorganization and transcription activities is complicated, such that it is difficult to decipher the regulatory effects of intranuclear geometrical cues. Here, we simplify the system by introducing DNA, packaging proteins (i.e., histone and protamine), and transcription factor NF-κB into a well-defined fluidic chip with changing spatical confinement ranging from 100 to 500 nm. It is uncovered that strong nanoconfinement suppresses higher-order folding of histone- and protamine-DNA complexes, the fracture of which exposes buried DNA segments and causes increased quantities of NF-κB binding to the DNA chain. Overall, these results reveal a pathway of how intranuclear geometrical cues alter the open/closed state of a DNA-protein complex and therefore affect transcription activities: i.e., NF-κB binding.

Snf2 Proteins Are Required to Generate Gamete Pronuclei in Tetrahymena thermophila

During sexual reproduction/conjugation of the ciliate Tetrahymena thermophila, the germinal micronucleus undergoes meiosis resulting in four haploid micronuclei (hMICs). All hMICs undergo post-meiotic DNA double-strand break (PM-DSB) formation, cleaving their genome. DNA lesions are subsequently repaired in only one ‘selected’ hMIC, which eventually produces gametic pronuclei. DNA repair in the selected hMIC involves chromatin remodeling by switching from the heterochromatic to the euchromatic state of its genome. Here, we demonstrate that, among the 15 Tetrahymena Snf2 family proteins, a core of the ATP-dependent chromatin remodeling complex in Tetrahymena, the germline nucleus specific Iswi in Tetrahymena IswiGTt and Rad5Tt is crucial for the generation of gametic pronuclei. In either gene knockout, the selected hMIC which shows euchromatin markers such as lysine-acetylated histone H3 does not appear, but all hMICs in which markers for DNA lesions persist are degraded, indicating that both IswiGTt and Rad5Tt have important roles in repairing PM-DSB DNA lesions and remodeling chromatin for the euchromatic state in the selected hMIC.

Direct visualization of pre-protamine 2 detects protamine assembly failures and predicts ICSI success

Histone-to-protamine transition is an essential step in the generation of fully functional spermatozoa in various mammalian species. In human and mouse, one of the two protamine-encoding genes produces a precursor pre-protamine 2 (pre-PRM2) protein, which is then processed and assembled. Here we design an original approach based on the generation of pre-PRM2-specific antibodies to visualize the unprocessed pre-PRM2 by microscopy, flow cytometry and immunoblotting. Using mouse models with characterized failures in histone-to-protamine replacement, we show that pre-Prm2 retention is tightly linked to nucleosome disassembly. Additionally, in elongating/condensing spermatids, we observe that pre-Prm2 and transition protein are co-expressed spatiotemporally, and their physical interaction suggests that these proteins act simultaneously rather than successively during histone replacement. By using our anti-human pre-PRM2 antibody we also measured pre-PRM2 retention rates in the spermatozoa from 49 men of a series of infertile couples undergoing ICSI, which shed new light on the debated relation between pre-PRM2 retention and sperm parameters. Finally, by monitoring 2-pronuclei (2PN) embryo formation following ICSI, we evaluated the fertilization ability of the sperm in these 49 patients. Our results suggest that the extent of pre-PRM2 retention in sperm, rather than pre-PRM2 accumulation per se, is associated with fertilization failure. Hence, anti-pre-PRM2/pre-Prm2 antibodies are valuable tools which could be used in routine monitoring of sperm parameters in fertility clinics, as well as in experimental research programmes to better understand the obscure process of histone-to-protamine transition.

The Art of Packaging the Sperm Genome: Molecular and Structural Basis of the Histone-To-Protamine Exchange

Male fertility throughout life hinges on the successful production of motile sperm, a developmental process that involves three coordinated transitions: mitosis, meiosis, and spermiogenesis. Germ cells undergo both mitosis and meiosis to generate haploid round spermatids, in which histones bound to the male genome are replaced with small nuclear proteins known as protamines. During this transformation, the chromatin undergoes extensive remodeling to become highly compacted in the sperm head. Despite its central role in spermiogenesis and fertility, we lack a comprehensive understanding of the molecular mechanisms underlying the remodeling process, including which remodelers/chaperones are involved, and whether intermediate chromatin proteins function as discrete steps, or unite simultaneously to drive successful exchange. Furthermore, it remains largely unknown whether more nuanced interactions instructed by protamine post-translational modifications affect chromatin dynamics or gene expression in the early embryo. Here, we bring together past and more recent work to explore these topics and suggest future studies that will elevate our understanding of the molecular basis of the histone-to-protamine exchange and the underlying etiology of idiopathic male infertility.

Sperm bauplan and function and underlying processes of sperm formation and selection

The spermatozoon is a highly differentiated and polarized cell, with two main structures: the head, containing a haploid nucleus and the acrosomal exocytotic granule, and the flagellum, which generates energy and propels the cell; both structures are connected by the neck. The sperm's main aim is to participate in fertilization, thus activating development. Despite this common bauplan and function, there is an enormous diversity in structure and performance of sperm cells. For example, mammalian spermatozoa may exhibit several head patterns and overall sperm lengths ranging from ∼30 to 350 µm. Mechanisms of transport in the female tract, preparation for fertilization, and recognition of and interaction with the oocyte also show considerable variation. There has been much interest in understanding the origin of this diversity, both in evolutionary terms and in relation to mechanisms underlying sperm differentiation in the testis. Here, relationships between sperm bauplan and function are examined at two levels: first, by analyzing the selective forces that drive changes in sperm structure and physiology to understand the adaptive values of this variation and impact on male reproductive success and second, by examining cellular and molecular mechanisms of sperm formation in the testis that may explain how differentiation can give rise to such a wide array of sperm forms and functions.

Spermiogenic chromatin condensation patterning in several hexapods may involve phase separation dynamics by spinodal decomposition or microemulsion inversion (nucleation)

We have examined published transmission electron microscopy (TEM). photomicrographs of chromatin condensation patterning in developing sperm nuclei from five species of entognathous hexapods within the Classes Protura, Collembola, Diplura and five species of ancestral wingless insects in the Orders Archaeognatha and Zygentoma as well as in fifteen species of the winged insects. Each species reproduces by internal fertilization. Spatially quantitative analysis indicates that spermiogenic chromatin condensation patterning in several of these species may be due to spinodal decomposition (SD) or to microemulsion inversion (chromatin-in-nucleoplasm → nucleoplasm-in-chromatin), also known as nucleation (Nc). These are two different dynamic mechanisms of liquid-liquid phase separation (LLPS). They might either occur independently or co-exist during the chromatin condensation associated with insect spermiogenesis. For example, the chromatin condensation pattern such as that observed in transverse sections of developing sperm nuclei from the wingless insect Anurida maritima (Collembola) is: granules → fibers → lamellae (SD) → nucleation (Nc) → condensed nuclei. Similar transitions are also observed in other more recently evolved species within the Class Insecta. From the limited but comprehensive sample of entognathus and ectognathus hexapods analyzed here, it appears that LLPS of sperm chromatin during spermiogenesis has occurred quite pervasively within the subphylum Hexapoda, including insects.

Distinct spermiogenic phenotypes underlie sperm elimination in the Segregation Distorter meiotic drive system

Segregation Distorter (SD) is a male meiotic drive system in Drosophila melanogaster. Males heterozygous for a selfish SD chromosome rarely transmit the homologous SD+ chromosome. It is well established that distortion results from an interaction between Sd, the primary distorting locus on the SD chromosome and its target, a satellite DNA called Rsp, on the SD+ chromosome. However, the molecular and cellular mechanisms leading to post-meiotic SD+ sperm elimination remain unclear. Here we show that SD/SD+ males of different genotypes but with similarly strong degrees of distortion have distinct spermiogenic phenotypes. In some genotypes, SD+ spermatids fail to fully incorporate protamines after the removal of histones, and degenerate during the individualization stage of spermiogenesis. In contrast, in other SD/SD+ genotypes, protamine incorporation appears less disturbed, yet spermatid nuclei are abnormally compacted, and mature sperm nuclei are eventually released in the seminal vesicle. Our analyses of different SD+ chromosomes suggest that the severity of the spermiogenic defects associates with the copy number of the Rsp satellite. We propose that when Rsp copy number is very high (> 2000), spermatid nuclear compaction defects reach a threshold that triggers a checkpoint controlling sperm chromatin quality to eliminate abnormal spermatids during individualization.

The evolution of insulin therapy

Evolution in medicine is generally driven by clinical need, hand in hand with opportunities generated by novel chemical and mechanical engineering technologies. Since 1921 that has been a continuing paradigm for insulin therapy, some advances being a continual process, and others arising from external scientific or engineering developments. Purification of insulin preparations was an early issue, resolved in the 1970s, then challenged by the switch to manufacture in microorganisms. The nature of insulin was established serially, in 1928 as a polypeptide, in 1955 by amino acid sequence, and later by 3-dimensional structure (1969), laying foundations for understandings on routes of administration, and later the engineering of novel insulins. Insulin was the first, and remains the predominant, pharmaceutical therapy to benefit from scientific advances underlying the genetic code, and thus recombinant DNA technology. Advances in mechanical and chemical engineering have contributed to important changes in insulin delivery devices. Biological science, including both cellular mechanisms and whole organism physiology, has led to considerable understandings of clinical defects in insulin action, but currently has been disappointing in its applicability to the insulins available for clinical practice, something perhaps now changing. The pathways of these changes are reviewed here.

Global Methylation and Protamine Deficiency in Ram Spermatozoa Correlate with Sperm Production and Quality but Are Not Influenced by Melatonin or Season

Simple Summary

Though environmental factors can alter the epigenome of mammalian spermatozoa, it is currently unclear whether these epigenetic changes are linked to sperm production, quality and fertility. This study aimed to identify whether the hormone melatonin, responsible for upregulating ram reproductive function, is able to alter broad epigenetic markers in spermatozoa, namely sperm global methylation and protamine deficiency. It was also investigated whether these parameters corresponded to ram endocrinology, semen production and quality. Though no effects of season or melatonin were found, both sperm global methylation and protamine deficiency correlated with several semen production and quality parameters. These moderate associations with sperm production and quality support that sperm protamine deficiency and global methylation are broadly indicative of testicular function.

Abstract

This study assessed whether the seasonal effects of melatonin that upregulate ram reproductive function alter sperm global methylation or protamine deficiency and whether these parameters corresponded to ram endocrinology, semen production and quality. Ejaculates were assessed from rams that received melatonin implants (n = 9) or no implants (n = 9) during the non-breeding season. Ejaculates (n = 2/ram/week) were collected prior to implantation (week 0), 1, 6 and 12 weeks post implantation and during the following breeding season (week 30). Flow cytometry was used to assess the sperm global methylation and protamine deficiency in each ejaculate, which had known values for sperm concentration, motility, morphology, DNA fragmentation, seminal plasma levels of melatonin, anti-Mullerian hormone and inhibin A. Serum levels of testosterone and melatonin were also evaluated. Though there was no effect of melatonin or season, sperm protamine deficiency was negatively correlated with sperm production and seminal plasma levels of anti-Mullerian hormone and positively correlated with sperm DNA fragmentation and morphology. Global methylation of spermatozoa was positively correlated with sperm DNA fragmentation, morphology and serum testosterone and negatively correlated with sperm motility. These moderate associations with sperm production and quality suggest that sperm protamine deficiency and global methylation are indicative of ram testicular function.

Photobiomodulation preconditioned human semen protects sperm cells against detrimental effects of cryopreservation

The biological consequences of semen samples preconditioning with photobiomodulation (PBM) were studied on human sperm cells post cryopreservation. Donated semen samples were collected from 22 married men with normal sperm parameters according to World Health Organization (WHO) criteria. Included samples were divided into control and PBM-preconditioning (one session, 810 nm, diode laser, and 0.6 J/cm²) groups before cryopreservation procedure. Progressive sperm motility (PSM), morphology, viability, sperm mitochondrial membrane potential(MMP), intracellular reactive oxygen species (ROS) and lipid peroxidation of sperm cells were assessed post thawing. PBM preconditioning of cryopreserved semen samples most prominently increased the PSM percentage 30 min post thawing (p = 0.000).Application of PBM before cryopreservation significantly increased the number of viable spermatozoa (p = 0.000), increased significantly the number of spermatozoa with high MMP (p = 0.004) and decreased significantly the number of spermatozoa with low MMP post-thawing(P = 0. 007)compared to control group. Cryopreserved human sperm cells with PBM preconditioning showed significant decrease in the levels of intracellular ROS (47.66 ± 2.14 versus 60.42 ± 3.16, p = 0.002) and lipid peroxidation (3.06 ± 0.13 versus 3.68 ± 0.27, p = 0.05)compared to control group. Our findings, as the first evidence, indicated that PBM-preconditioning of human semen before cryopreservation provides a real and substantial advantage. This might lead to a novel strategy in improving PBM application in the procedures of assisted reproductive technologies.

Freezing-thawing induces deprotamination, cryocapacitation-associated changes; DNA fragmentation; and reduced progesterone sensitivity in buck spermatozoa

In the present study, there was evaluation of cryocapacitation-associated changes, apoptotic-like changes, deprotamination, total antioxidant capacity (TAC), and in vitro sperm functional attributes in Barbari bucks after freezing-thawing. The correlation between deprotamination and sperm functional characteristics was established. Using immunoblotting procedures, there was detection of the presence of a single 28-kDa protein band corresponding to protamine-1. The localization in the head region of the spermatozoa was further validated by an immunofluorescence test. Capacitated (B-) and acrosome-reacted (AR-) pattern spermatozoa, spermatozoa with the externalization of phosphatidylserine and a relatively lesser mitochondrial transmembrane potential, and deprotamination and DNA fragmentation was greater (P < 0.05) after freezing-thawing and indicated there were cryocapacitation- and apoptotic-like changes, respectively. Furthermore, the detection of phosphorylation of tyrosine-containing proteins with use of immunoblotting and immunofluorescence procedures confirmed there were cryocapacitation-like changes in the buck spermatozoa after freezing-thawing. Total antioxidant capacity (TAC), in vitro thermal resistance response, Vanguard distance, progesterone sensitivity, and in vitro capacitation response were less (P < 0.05) in the spermatozoa after freezing-thawing compared with spermatozoa after initial dilution and equilibration. Deprotamination (chromomycin A3-positive cells, CMA3+) and DNA fragmentation (TUNEL+ve) were positively correlated with B- and AR-pattern spermatozoa, while other values for other variables were negatively correlated. In conclusion, the results of this study indicated there was protamine-1 in buck spermatozoa and after freezing-thawing there was a loss of protamine-1 combined with cryocapacitation-associated changes and apoptotic-like changes in buck spermatozoa. Spermatozoa deprotamination might be attributed to increased DNA fragmentation, resulting in compromised fertilizing capacity of buck spermatozoa.

Histone Variants: The Nexus of Developmental Decisions and Epigenetic Memory

Nucleosome dynamics and properties are central to all forms of genomic activities. Among the core histones, H3 variants play a pivotal role in modulating nucleosome structure and function. Here, we focus on the impact of H3 variants on various facets of development. The deposition of the replicative H3 variant following DNA replication is essential for the transmission of the epigenomic information encoded in posttranscriptional modifications. Through this process, replicative H3 maintains cell fate while, in contrast, the replacement H3.3 variant opposes cell differentiation during early embryogenesis. In later steps of development, H3.3 and specialized H3 variants are emerging as new, important regulators of terminal cell differentiation, including neurons and gametes. The specific pathways that regulate the dynamics of the deposition of H3.3 are paramount during reprogramming events that drive zygotic activation and the initiation of a new cycle of development.

Sequencing a Bispecific Antibody by Controlling Chain Concentration Effects When Using an Immobilized Nonspecific Protease

Complete sequence coverage of monospecific antibodies was previously achieved using immobilized aspergillopepsin I in a single LC-MS/MS analysis. Bispecific antibodies are asymmetrical compared to their monospecific antibody counterparts, resulting in a decrease in the concentration of individual subunits. Four standard proteins were used to characterize the effect of a decrease in concentration when using this immobilized enzyme reactor. Low concentration samples resulted in the elimination of large peptide products due to a greater number of enzymatic cleavages. A competitive inhibitor rich in arginine residues reduced the number of enzymatic cleavages to the protein and retained large molecular weight products. The digestion of a bispecific antibody with competitive inhibition of aspergillopepsin I maintained large peptide products better suited for sequence reconstruction, resulting in complete sequence coverage from a single LC-MS/MS analysis.

Sperm cellular and nuclear dynamics associated with bull fertility

The objective of this study was to ascertain cellular characteristics and the dynamics of the sperm chromatin proteins protamine 1 (PRM1) and protamine 2 (PRM2) in the sperm of Holstein bulls having a different fertility status. Important sperm variables were analyzed using computer-assisted sperm analysis (CASA). Sperm membrane, acrosome status, DNA integrity were also assessed using propidium iodide (PI), fluorescein isothiocyanate conjugated to Arachis hypogaea (FITC-PNA), and acridine orange (AO) followed by flow cytometry. In addition, abundances of PRM1 and PRM2 were analyzed using flow cytometry experiments. Differences in sperm decondensation capacity were assessed in bulls of varying fertility using a decondensation assay. As determined using CASA, average pathway velocity, amplitude of lateral head displacement and straightness were different (P < 0.05) for sperm from high and low fertility bulls. There, however, were no differences between the high and low fertility bulls for characteristics of sperm plasma membrane, acrosome, and DNA integrity (P >  0.05). Relative abundances of PRM1 and PRM2 in sperm from the high and low fertility bulls were inversely related (P <  0.0001). Percentages of decondensed sperm were different between high and low fertility bulls (P < 0.0001) and total numbers of decondensed sperm were greater in low fertility bulls than high fertility bulls (R² = 0.72). Results of the present study are significant because molecular and morphological phenotypes of sperm that were detected affect fertility in livestock species.

Expression patterns of male germ cell markers in cryptorchid pig testes

Male germ cell apoptosis has been described in heat-damaged testes by cryptorchidism. In the present study, wild type pig testes were compared with cryptorchid testes via histological and immunohistological analyses. Spermatozoa were not detected in two cryptorchid testes and the diameters of seminiferous tubules were significantly reduced in cryptorchid pig testes compared with wild type pig testes. Cells expressing marker genes for undifferentiated spermatogonia, such as protein gene product 9.5 was significantly decreased in cryptochid pig testes. In addition, the numbers of cells expressing DEAD-box polypeptide 4 (VASA), synaptonemal complex protein 3, protamine, and acrosin (a biomarker of spermatocyte, spermatid, and spermatozoa) were significantly reduced in cryptochid pig testes. However, the number of vimentin-expressing Sertoli cells was not changed or was significantly increased in cryptorchid pig testes. This result indicates that male germ cells are specifically damaged by heat in cryptorchid pig testes and not Sertoli cells. These findings will facilitate the further study of spermatogenesis and the specific mechanisms by which cryptorchidism causes male infertility.

Protamines from liverwort are produced by post-translational cleavage and C-terminal di-aminopropanelation of several male germ-specific H1 histones

Protamines are small, highly-specialized, arginine-rich, and intrinsically-disordered chromosomal proteins that replace histones during spermiogenesis in many organisms. Previous evidence supports the notion that, in the animal kingdom, these proteins have evolved from a primitive replication-independent histone H1 involved in terminal cell differentiation. Nevertheless, a direct connection between the two families of chromatin proteins is missing. Here, we primarily used electron transfer dissociation MS-based analyses, revealing that the protamines in the sperm of the liverwort Marchantia polymorpha result from post-translational cleavage of three precursor H1 histones. Moreover, we show that the mature protamines are further post-translationally modified by di-aminopropanelation, and previous studies have reported that they condense spermatid chromatin through a process consisting of liquid-phase assembly likely involving spinodal decomposition. Taken together, our results reveal that the interesting evolutionary ancestry of protamines begins with histone H1 in both the animal and plant kingdoms.

The c.-190 C>A transversion in promoter region of protamine 1 gene as a genetic risk factor in Egyptian men with idiopathic infertility

Protamines are considered the most important structure in the sperm nucleus, and they are proteins with a significantly large amount of amino acids carrying a positive charge, which allows the formation of the tight package of the genomic DNA in the spermatozoa. Many authors studied the abnormalities in the protamine 1 (PRM1) and/or protamine 2 (PRM2) genes and reported their possible association with male infertility. The chromosome 16 (16p13.2) carries these genes containing multiple undiscovered single nucleotide polymorphisms. The aim of the present study was to investigate the association of c.-190 C>A transversions that occur in PRM1 with idiopathic infertility in a sample of Egyptian men. It was a case-control study, and blood samples were collected from sixty male patients complaining of idiopathic infertility and forty healthy fertile males. The c.-190 C>A transversion in promotor region protamine 1 gene (rs2301365) was assessed by 5' nuclease assay, using Rotor-Gene Q real-time PCR system. The results of the present study revealed that CA and AA genotypes in PRM1 gene were associated significantly with low sperm concentration and decreased sperm motility (p = 0.001). Cases carrying A allele had a 6.05-fold increased risk for idiopathic infertility than cases carrying the C allele (OR: 6.05, 95% CI: 2.038-17.98 p statistically significant ≤0.05). Analysis of the results revealed that the c.-190 C>A transversion may be involved in the development of male infertility.

Sperm nuclear protamines: A checkpoint to control sperm chromatin quality

Protamines are nuclear proteins which are specifically expressed in haploid male germ cells. Their replacement of histones and binding to DNA is followed by chromatin hypercondensation that protects DNA from negative influences by environmental factors. Mammalian sperm contain two types of protamines: PRM1 and PRM2. While the proportion of the two protamines is highly variable between different species, abnormal ratios within a species are known to be associated with male subfertility. Therefore, it is more than likely that correct protamine expression represents a kind of chromatin checkpoint during sperm development rendering protamines as suitable biomarkers for the estimation of sperm quality. This review presents an overview of our current knowledge on protamines comparing gene and protein structures between different mammalian species with particular consideration given to man, mouse and stallion. At last, recent insights into the possible role of inherited sperm histones for early embryo development are provided.

Nucleotide variability of protamine genes influencing bull sperm motility variables

Protamines (PRMs), important proteins of chromatin condensation in spermiogenesis, are promising candidate genes to explore markers of sperm motility. The coding and in-silico predicted promoter regions of these genes were investigated in 102 crossbred and 32 purebred cattle. Also, mRNA quantification was done to explore its possibility as diagnostic tool of infertility. The PCR-SSCP analysis indicated there were two band patterns only in fragment I of the PRM1 and fragment II of the PRM2 gene. The sequence analysis revealed A152G and G179A transitions in the PRM1 gene. Similarly, G35A, A49G and A64G transitions were identified in the PRM2 gene which resulted in altered amino acid sequences from arginine (R) to glutamine (Q), from arginine (R) to glycine (G) and from arginine (R) to glycine (G), respectively. This caused the reduction in molecular weight of PRM2 from 2157.66 to 1931.33 Da due to reduction in the number of basic amino acids. These altered properties of the PRM2 protein led to the reduction in Mass Motility (MM: P < 0.01), Initial Progressive Motility (IPM; P < 0.05) and Post Thaw Motility (PTM; P < 0.05) in crossbred bulls. The least squares analysis of variance indicated there was an effect of PRM2 haplotypes on MM (P = 0.0069), IPM (P = 0.0306) and PTM (P = 0.0500) in crossbred cattle and on PTM (P = 0.0408) in the overall cattle population. Based on the RT-qPCR analysis, however, there was not any significant variation of PRM1 and PRM2 gene expression among sperm of Vrindavani bulls with relatively lesser and greater sperm motility.

Sperm Nuclear Basic Proteins of Marine Invertebrates

In this chapter, a short evolutionary history and comparative analysis of sperm nuclear basic proteins (SNBPs) in marine invertebrates are presented based on some of the most recent publications in the field and building upon previously published reviews on the topic. Putative functions of SNBPs in sperm chromatin beyond DNA packaging will also be discussed with a primary focus on outstanding research questions.In somatic cells of all metazoans, DNA is packaged into tightly folded and dynamically accessible chromatin by canonical histones H2A, H2B, H3 and H4. Sperm chromatin of many animals, on the other hand, is organised by small yet structurally highly heterogeneous proteins called SNBPs, which can package sperm DNA on their own or in combination with each other. In extreme cases, sperm chromatin is condensed into a volume 6-10 times smaller than that of a somatic nucleus. SNBPs are classified into three major groups: H1 histone-type proteins (H-type SNBPs), protamines (P-type SNBPs) and protamine-like proteins (PL-type SNBPs). P-type SNBPs are mostly found in vertebrates, while PL-type SNBPs are ubiquitous in many invertebrate phyla. PL-type and P-type SNBPs evolved from histone H-type SNBP precursors through vertical evolution. Porifera, Ctenophora and Crustacea, Echinoidea (phylum Echinodermata) and Hydrozoa (phylum Hydrozoa) lack SNBPs. Echinoidea and Hydrozoa, however, evolved novel nucleosomal histone variants with specific roles during spermatogenesis. Seemingly, chromatin condensation plays a critical role in the silencing and tight packing of the genome within the sperm nucleus of most animals. However, the question of what necessitates the compaction of some sperm DNA beyond classical nucleosomal packaging while other sperm function using 'normal' histones remains unanswered to date.

Collapse of DNA in packaging and cellular transport

The dawn of molecular biology and recombinant DNA technology arose from our ability to manipulate DNA, including the process of collapse of long extended DNA molecules into nanoparticles of approximately 100 nm diameter. This condensation process is important for the packaging of DNA in the cell and for transporting DNA through the cell membrane for gene therapy. Multivalent cations, such as natural polyamines (spermidine and spermine), were initially recognized for their ability to provoke DNA condensation. Current research is targeted on molecules such as linear and branched polymers, oligopeptides, polypeptides and dendrimers that promote collapse of DNA to nanometric particles for gene therapy and on the energetics of DNA packaging.

Role of Disulfide Bonds on DNA Packaging Forces in Bull Sperm Chromatin

Short arginine-rich proteins called protamines mediate the near crystalline DNA packaging in most vertebrate sperm cells. Protamines are synthesized during spermiogenesis and condense the paternal genome into a transcriptionally inactive state in late-stage spermatids. Protamines from eutherian mammals, including bulls and humans, also contain multiple cysteine residues that form intra- and interprotamine sulfur-sulfur bonds during the final stages of sperm maturation. Although the cross-linked protamine network is known to stabilize the resulting nucleoprotamine structure, little is known about the role of disulfide bonds on DNA condensation in the mammalian sperm. Using small angle x-ray scattering, we show that isolated bull nuclei achieve slightly lower DNA packing densities compared to salmon nuclei despite salmon protamine lacking cysteine residues. Surprisingly, reduction of the intermolecular sulfur-sulfur bonds of bull protamine results in tighter DNA packing. Complete reduction of the intraprotamine disulfide bonds ultimately leads to decondensation, suggesting that disulfide-mediated secondary structure is also critical for proper protamine function. Lastly, comparison of multiple bull collections showed some to have aberrant x-ray scattering profiles consistent with incorrect disulfide bond formation. Together, these observations shed light on the biological functions of disulfide linkages for in vivo DNA packaging in sperm chromatin.

The Drosophila chromosomal protein Mst77F is processed to generate an essential component of mature sperm chromatin

In most animals, the bulk of sperm DNA is packaged with sperm nuclear basic proteins (SNBPs), a diverse group of highly basic chromosomal proteins notably comprising mammalian protamines. The replacement of histones with SNBPs during spermiogenesis allows sperm DNA to reach an extreme level of compaction, but little is known about how SNBPs actually function in vivo. Mst77F is a Drosophila SNBP with unique DNA condensation properties in vitro, but its role during spermiogenesis remains unclear. Here, we show that Mst77F is required for the compaction of sperm DNA and the production of mature sperm, through its cooperation with protamine-like proteins Mst35Ba/b. We demonstrate that Mst77F is incorporated in spermatid chromatin as a precursor protein, which is subsequently processed through the proteolysis of its N-terminus. The cleavage of Mst77F is very similar to the processing of protamine P2 during human spermiogenesis and notably leaves the cysteine residues in the mature protein intact, suggesting that they participate in the formation of disulfide cross-links. Despite the rapid evolution of SNBPs, sperm chromatin condensation thus involves remarkably convergent mechanisms in distantly related animals.

Histone Variant H2A.L.2 Guides Transition Protein-Dependent Protamine Assembly in Male Germ Cells

Histone replacement by transition proteins (TPs) and protamines (Prms) constitutes an essential step for the successful production of functional male gametes, yet nothing is known on the underlying functional interplay between histones, TPs, and Prms. Here, by studying spermatogenesis in the absence of a spermatid-specific histone variant, H2A.L.2, we discover a fundamental mechanism involved in the transformation of nucleosomes into nucleoprotamines. H2A.L.2 is synthesized at the same time as TPs and enables their loading onto the nucleosomes. TPs do not displace histones but rather drive the recruitment and processing of Prms, which are themselves responsible for histone eviction. Altogether, the incorporation of H2A.L.2 initiates and orchestrates a series of successive transitional states that ultimately shift to the fully compacted genome of the mature spermatozoa. Hence, the current view of histone-to-nucleoprotamine transition should be revisited and include an additional step with H2A.L.2 assembly prior to the action of TPs and Prms.

Unlocking sperm chromatin at fertilization requires a dedicated egg thioredoxin in Drosophila

In most animals, the extreme compaction of sperm DNA is achieved after the massive replacement of histones with sperm nuclear basic proteins (SNBPs), such as protamines. In some species, the ultracompact sperm chromatin is stabilized by a network of disulfide bonds connecting cysteine residues present in SNBPs. Studies in mammals have established that the reduction of these disulfide crosslinks at fertilization is required for sperm nuclear decondensation and the formation of the male pronucleus. Here, we show that the Drosophila maternal thioredoxin Deadhead (DHD) is specifically required to unlock sperm chromatin at fertilization. In dhd mutant eggs, the sperm nucleus fails to decondense and the replacement of SNBPs with maternally-provided histones is severely delayed, thus preventing the participation of paternal chromosomes in embryo development. We demonstrate that DHD localizes to the sperm nucleus to reduce its disulfide targets and is then rapidly degraded after fertilization.

Dynamics of histone H2A, H4 and HS1ph during spermatogenesis with a focus on chromatin condensation and maturity of spermatozoa

Histones and histone phosphorylation play vital roles during animal spermatogenesis and spermatozoa maturation. The dynamic distribution of histones H2A and H4 and phosphorylated H2A and H4 at serine 1 (HS1ph) was explored in mammalian and Decapoda germ cells, with a special focus on the distribution of H2A, H4 and HS1ph between mouse condensed spermatozoa chromatin and crab non-condensed spermatozoa chromatin. The distribution of histone marks was also analysed in mature spermatozoa with different chromatin structures. Histone H2A and H4 marks were closely associated with the relatively loose chromatin structure in crab spermatozoa. The significant decrease in the HS1ph signal during spermatogenesis suggests that eliminating most of these epigenetic marks in the nucleusis closely associated with spermatozoa maturity.

Comparison of Protamine 1 to Protamine 2 mRNA Ratio and YBX2 gene mRNA Content in Testicular Tissue of Fertile and Azoospermic Men

Background

Although aberrant protamine (PRM) ratios have been observed in infertile men, the mechanisms that implicit the uncoupling of PRM1 and PRM2 expression remain unclear. To uncover these mechanisms, in this observational study we have compared the PRM1/PRM2 mRNA ratio and mRNA contents of two regulatory factors of these genes.

Materials and Methods

In this experimental study, sampling was performed by a multi-step method from 50 non-obstructive azoospermic and 12 normal men. After RNA extraction and cDNA synthesis, real-time quantitative polymerase chain reaction (RT- QPCR) was used to analyze the PRM1, PRM2, Y box binding protein 2 (YBX2) and JmjC-containing histone demethylase 2a (JHDM2A) genes in testicular biopsies of the studied samples.

Results

The PRM1/PRM2 mRNA ratio differed significantly among studied groups, namely 0.21 ± 0.13 in azoospermic samples and -0.8 ± 0.22 in fertile samples. The amount of PRM2 mRNA, significantly reduced in azoospermic patients. Azoospermic men exhibited significant under expression of YBX2 gene compared to controls (P<0.001). mRNA content of this gene showed a positive correlation with PRM mRNA ratio (R=0.6, P=0.007). JHDM2A gene expression ratio did not show any significant difference between the studied groups (P=0.3). We also observed no correlation between JHDM2A mRNA content and the PRM mRNA ratio (R=0.2, P=0.3).

Conclusion

We found significant correlation between the aberrant PRM ratio (PRM2 under expression) and lower YBX2 mRNA content in testicular biopsies of azoospermic men compared to controls, which suggested that downregulation of the YBX2 gene might be involved in PRM2 under expression. These molecules could be useful biomarkers for predicting male infertility.

Two arginine residues suppress the flexibility of nucleosomal DNA in the canonical nucleosome core

The dynamics of nucleosomes containing either canonical H3 or its centromere-specific variant CENP-A were investigated using molecular dynamics simulations. The simulations showed that the histone cores were structurally stable during simulation periods of 100 ns and 50 ns, while DNA was highly flexible at the entry and exit regions and partially dissociated from the histone core. In particular, approximately 20–25 bp of DNA at the entry and exit regions of the CENP-A nucleosome exhibited larger fluctuations than DNA at the entry and exit regions of the H3 nucleosome. Our detailed analysis clarified that this difference in dynamics was attributable to a difference in two basic amino acids in the αN helix; two arginine (Arg) residues in H3 were substituted by lysine (Lys) residues at the corresponding sites in CENP-A. The difference in the ability to form hydrogen bonds with DNA of these two residues regulated the flexibility of nucleosomal DNA at the entry and exit regions. Our exonuclease III assay consistently revealed that replacement of these two Arg residues in the H3 nucleosome by Lys enhanced endonuclease susceptibility, suggesting that the DNA ends of the CENP-A nucleosome are more flexible than those of the H3 nucleosome. This difference in the dynamics between the two types of nucleosomes may be important for forming higher order structures in different phases.

Protamines and spermatogenesis in Drosophila and Homo sapiens : A comparative analysis

The production of mature and motile sperm is a detailed process that utilizes many molecular players to ensure the faithful execution of spermatogenesis. In most species that have been examined, spermatogenesis begins with a single cell that undergoes dramatic transformation, culminating with the hypercompaction of DNA into the sperm head by replacing histones with protamines. Precise execution of the stages of spermatogenesis results in the production of motile sperm. While comparative analyses have been used to identify similarities and differences in spermatogenesis between species, the focus has primarily been on vertebrate spermatogenesis, particularly mammals. To understand the evolutionary basis of spermatogenetic variation, however, a more comprehensive comparison is needed. In this review, we examine spermatogenesis and the final packaging of DNA into the sperm head in the insect Drosophila melanogaster and compare it to spermatogenesis in Homo sapiens.