Detection of protamine 2 in bovine spermatozoa and testicles

New approaches in bovine spermatozoa evaluation and their relationship with male fertility

Male fertility potential depends on physical, endocrine, and genetic factors responsible for producing functional male gametes. Although the main function of the male gamete, the spermatozoon, is to deliver its genetic material to the oocyte, this premise has been modified over the past few years. It is believed that the spermatozoon provides essential factors for fertilization and pre-implantation embryo development. A viable/healthy spermatozoon has functional subcellular compartments (nucleus, acrosome, midpiece, and flagellum) due to the actions of proteins, transcripts, and epigenetic marks in the organelles present in them that have important roles in reproductive biology. Male fertility potential reflects viable spermatozoa with proper function. Therefore, new approaches to functional sperm analysis are essential. Additionally, intrinsic factors and sperm molecules constitute potential biomarkers of viable spermatozoa and male fertility. Among these factors are proteins, the genome, and coding and non-coding RNAs, such as microRNAs, that act during fertilization and early embryo development. Research has been seeking increasingly efficient tools to predict fertility and functional studies of these molecules through gene and protein expression. Thus, analytical tools are essential to identify and classify viable and functional spermatozoa, to evaluate assisted reproductive male potential.

Biomarker-based human and animal sperm phenotyping: the good, the bad and the ugly†

Conventional, brightfield-microscopic semen analysis provides important baseline information about sperm quality of an individual; however, it falls short of identifying subtle subcellular and molecular defects in cohorts of "bad," defective human and animal spermatozoa with seemingly normal phenotypes. To bridge this gap, it is desirable to increase the precision of andrological evaluation in humans and livestock animals by pursuing advanced biomarker-based imaging methods. This review, spiced up with occasional classic movie references but seriously scholastic at the same time, focuses mainly on the biomarkers of altered male germ cell proteostasis resulting in post-testicular carryovers of proteins associated with ubiquitin-proteasome system. Also addressed are sperm redox homeostasis, epididymal sperm maturation, sperm-seminal plasma interactions, and sperm surface glycosylation. Zinc ion homeostasis-associated biomarkers and sperm-borne components, including the elements of neurodegenerative pathways such as Huntington and Alzheimer disease, are discussed. Such spectrum of biomarkers, imaged by highly specific vital fluorescent molecular probes, lectins, and antibodies, reveals both obvious and subtle defects of sperm chromatin, deoxyribonucleic acid, and accessory structures of the sperm head and tail. Introduction of next-generation image-based flow cytometry into research and clinical andrology will soon enable the incorporation of machine and deep learning algorithms with the end point of developing simple, label-free methods for clinical diagnostics and high-throughput phenotyping of spermatozoa in humans and economically important livestock animals.

Aberrant protamination in sperm correlates to anomalous nuclear and cytoplasmic architectures in infertile males with sperm dysmorphology

Aberrant sperm protamination is linked to sperm dysmorphology and nuclear chromatin condensation. Yet, its effects on sperm cytoplasmic maturation remain largely unexplored. The relationships of protamines, sperm morphology, DNA damage, and cytoplasmic remodeling were illustrated in this study to provide fresh perspectives on the mechanisms of male infertility. A total of 205 infertile males were allocated into 5 groups according to the percentage of spermatozoa exhibiting abnormal morphology within their samples. Sperm concentration, motility, abnormal sperm morphology, cytoplasmic droplets (CDs), and excess residual cytoplasm (ERC) were analyzed according to the World Health Organization manual (2010). Sperm nuclear vacuoles (NVs) were determined by propidium iodide (PI) staining. Sperm protamine expressions (P1 and P2) were detected by western blot. DNA damage was measured by acridine orange test (AOT) to calculate the proportion of sperm with single-strand DNA breaks (SSBs). Our data showed that sperm concentration and motility in infertile males significantly decreased with the severity of abnormal sperm morphology (both P < 0.01). P1 level, P1/P2 ratio, and SSB rate increased with the severity of sperm dysmorphology, whilst the P2 level decreased (all P < 0.01). NVs, CDs, and ERC were more common in males with sperm dysmorphology and positively correlated with the SSB rate (all P < 0.01). The relationships between the SSB rate and the P1/P2 ratio were also significant ( P < 0.01). Aberrant protamination may cause sperm dysmorphology and compromise male fertility by impairing sperm's nucleus and cytoplasm maturation, with the P1/P2 ratio potentially serving as a valuable indicator of sperm quality and male fertility.

Comparative Transcriptomic Analyses for the Optimization of Thawing Regimes during Conventional Cryopreservation of Mature and Immature Human Testicular Tissue

Cryopreservation of human testicular tissue, as a key element of anticancer therapy, includes the following stages: saturation with cryoprotectants, freezing, thawing, and removal of cryoprotectants. According to the point of view existing in "classical" cryobiology, the thawing mode is the most important consideration in the entire process of cryopreservation of any type of cells, including cells of testicular tissue. The existing postulate in cryobiology states that any frozen types of cells must be thawed as quickly as possible. The technologically maximum possible thawing temperature is 100 °C, which is used in our technology for the cryopreservation of testicular tissue. However, there are other points of view on the rate of cell thawing, according to how thawing should be carried out at physiological temperatures. In fact, there are morphological and functional differences between immature (from prepubertal patients) and mature testicular tissue. Accordingly, the question of the influence of thawing temperature on both types of tissues is relevant. The purpose of this study is to explore the transcriptomic differences of cryopreserved mature and immature testicular tissue subjected to different thawing methods by RNA sequencing. Collected and frozen testicular tissue samples were divided into four groups: quickly (in boiling water at 100 °C) thawed cryopreserved mature testicular tissue (group 1), slowly (by a physiological temperature of 37 °C) thawed mature testicular tissue (group 2), quickly thawed immature testicular tissue (group 3), and slowly thawed immature testicular tissue (group 4). Transcriptomic differences were assessed using differentially expressed genes (DEG), the Kyoto Encyclopedia of Genes and Genomes (KEGG), gene ontology (GO), and protein-protein interaction (PPI) analyses. No fundamental differences in the quality of cells of mature and immature testicular tissue after cryopreservation were found. Generally, thawing of mature and immature testicular tissue was more effective at 100 °C. The greatest difference in the intensity of gene expression was observed in ribosomes of cells thawed at 100 °C in comparison with cells thawed at 37 °C. In conclusion, an elevated speed of thawing is beneficial for frozen testicular tissue.

Review: Evaluation of bull fertility. Functional and molecular approaches

With the term "assisted reproduction technologies" in modern cattle farming, one could imply the collection of techniques that aim at the optimal use of bovine gametes to produce animals of high genetic value in a time- and cost-efficient manner. The accurate characterisation of sperm quality plays a critical role for the efficiency of several assisted reproduction-related procedures, such as sperm processing, in vitro embryo production and artificial insemination. Bull fertility is ultimately a collective projection of the ability of a series of ejaculates to endure sperm processing stress, and achieve fertilisation of the oocyte and production of a viable and well-developing embryo. In this concept, the assessment of sperm functional and molecular characteristics is key to bull fertility diagnostics and prognostics. Among others, functional features linked to sperm plasma membrane, acrosome and DNA integrity are usually assessed as a measure of the ability of sperm to express the phenotypes that will allow them to maintain their homeostasis and orchestrate-in a strict temporal manner-the course of events that will enable the delivery of their genetic content to the oocyte upon fertilisation. Nevertheless, measures of sperm functionality are not always adequate indicators of bull fertility. Nowadays, advancements in the field of molecular biology have facilitated the profiling of several biomolecules in male gametes. The molecular profiling of bovine sperm offers a deeper insight into the mechanisms underlying sperm physiology and, thus, can reveal novel candidate markers for bull fertility prognosis. In this review, the importance of three organelles (the nucleus, the plasma membrane and the acrosome) for the characterisation of sperm fertilising capacity and bull fertility is discussed at functional and molecular levels. In particular, information about sperm head morphometry, chromatin structure, viability as well as the ability of sperm to capacitate and undergo the acrosome reaction are presented in relation to the cryotolerance of male gametes and bull fertility. Finally, major spermatozoal coding and non-coding RNAs, and proteins that are involved in the above-mentioned aspects of sperm functionality are also summarised.

CDKN2AIP is critical for spermiogenesis and germ cell development

Background

As a member of RNA-binding protein, CDKN2AIP has been shown to play a critical role in stem cell pluripotency and somatic differentiation. Recent studies indicate that Cdkn2aip is essential for spermatogonial self-renewal and proliferation through the activating Wnt-signaling pathway. However, the mechanisms of how Cdkn2aip regulate spermatogenesis is poorly characterized.

Results

We discovered that the CDKN2AIP was expressed in spermatocyte as well as spermatids and participated in spermiogenesis. Cdkn2aip^−/− mice exhibited multiple sperm head defects accompanied by age dependent germ cell loss that might be result of protamine replacement failure and impaired SUN1 expression. Loss of Cdkn2aip expression in male mice resulted in synapsis failure in 19% of all spermatocytes and increased apoptosis due to damaged DNA double-strand break (DSB) repair and crossover formation. In vitro, knockdown of Cdkn2aip was associated with extended S phase, increased DNA damage and apoptosis.

Conclusions

Our findings not only identified the importance of CDKN2AIP in spermiogenesis and germ cell development, but also provided insight upon the driving mechanism.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00861-z.

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 potential of sperm bovine protamine as a protein marker of semen production and quality at the National Artificial Insemination Center of Indonesia

Background and Aim:

Protamine (PRM) is the major protein in the sperm nucleus and plays an essential role in its normal function. Moreover, PRM has great potential as a protein marker of semen production and quality. This study aimed to assess the potential of sperm bovine PRM as a protein marker of semen production and quality in bulls at the National Artificial Insemination (AI) Center of Indonesia.

Materials and Methods:

The semen production capacity of each bull was collected from frozen semen production data at the Singosari AI Center for 6 months, and was then divided into two groups (high and low). A total of 440 frozen semen straws from six Limousin (LIM), six Friesian Holstein (FH), six Peranakan Ongole (PO), and four Aceh bulls aged 4-5 years were used in the study. The frozen semen was used to measure the concentration of PRM1, PRM2, and PRM3 using the enzyme immunoassay method. The frozen semen was also used to assess the quality of the semen, including progressive motility (PM) through computer-assisted semen analysis, sperm viability through eosin–nigrosin analysis, and the DNA fragmentation index through Acridine Orange staining.

Results:

PRM1 was significantly higher in all bull breeds included in the study (p<0.00), followed by PRM2 (p<0.00) and PRM3 (p<0.00). PRM1 significantly affected semen production in LIM, FH, PO, and Aceh bulls (p<0.05). Moreover, PRM2 significantly affected semen production only in FH and Aceh bulls (p<0.05), whereas PRM3 affected this parameter in PO and Aceh bulls exclusively (p<0.05). Consistently and significantly, PRM1 was positively correlated with the PM and viability of sperm and negatively associated with its DNA fragmentation in LIM, FH, PO, and Aceh bulls (p<0.05; p<0.01). The correlation analysis between PRM2 and PRM3 and semen quality parameters varied across all bull breeds; some were positively and negatively correlated (p<0.05; p<0.01), and some were not correlated at all.

Conclusion:

PRM1 has excellent potential as a protein marker of semen production and quality in bulls at the National AI Center of Indonesia.

An improved acetic acid-urea polyacrylamide electrophoresis method to evaluate bovine sperm protamines

The acetic acid-urea polyacrylamide gel electrophoresis system could separate very similar basic proteins on differences in size and effective charge. This system has been used for many years to analyse histones and their post-translational modifications and widely used in the study of mammal protamines. Two types of protamine have been described, the protamine 1 (P1) and the protamine 2 (P2) family members, which are synthetized by PRM1 and PRM2 genes. The ratio of P1 and P2 is important for predicting fertility in humans and mice. Therefore, the quantification of protamines is a fundamental step in order to establish the ratio between P1 and P2 in these species. In other mammals, studies linking sperm protamination and the protamine ratio with fertility are increasing. So, the use of an effective technique to separate and quantify protamines is important to study sperm P1/P2 ratio. Therefore, this article describes in detail a feasible and useful procedure to isolate bovine sperm protamines, to perform pre-electrophoresis with PEG solution and finally to carry out acid-urea polyacrylamide gel electrophoresis in reverse polarity. This technique allows a clear separation and efficient detection of bovine sperm protamines.

Paternal epigenetics: Mammalian sperm provide much more than DNA at fertilization

The spermatozoon is a highly differentiated cell with unique characteristics: it is mobile, thanks to its flagellum, and is very compact. The sperm cytoplasm is extremely reduced, containing no ribosomes, and therefore does not allow translation, and its nucleus contains very closed chromatin, preventing transcription. This DNA compaction is linked to the loss of nucleosomes and the replacement of histones by protamines. Based on these characteristics, sperm was considered to simply deliver paternal DNA to the oocyte. However, some parts of the sperm DNA remain organized in a nucleosomal format, and bear epigenetic information. In addition, the nucleus and the cytoplasm contain a multitude of RNAs of different types, including non-coding RNAs (ncRNAs) which also carry epigenetic information. For a long time, these RNAs were considered residues of spermatogenesis. After briefly describing the mechanisms of compaction of sperm DNA, we focus this review on the origin and function of the different ncRNAs. We present studies demonstrating the importance of these RNAs in embryonic development and transgenerational adaptation to stress. We also look at other epigenetic marks, such as DNA methylation or post-translational modifications of histones, and show that they are sensitive to environmental stress and transmissible to offspring. The post-fertilization role of certain sperm-borne proteins is also discussed.

Sperm DNA fragmentation: causes and identification

Sperm DNA fragmentation is referred to as one of the main causes of male infertility. Failures in the protamination process, apoptosis and action of reactive oxygen species (ROS) are considered the most important causes of DNA fragmentation. Action of ROS or changes in sperm protamination would increase the susceptibility of sperm DNA to fragmentation. Routine semen analysis is unable to estimate sperm chromatin damage. Sperm DNA integrity influences sperm functional capability, therefore tests that measure sperm DNA fragmentation are important to assess fertility disorders. Actually, there is a considerable number of methods for assessing sperm DNA fragmentation and chromatin integrity, sperm chromatin stability assay (SCSA modified), sperm chromatin dispersion (SCD), comet assay, transferase dUTP nick end labelling (TUNEL); and protamine evaluation in sperm chromatin assay, such as toluidine blue, CMA3, protamine expression and evaluation of cysteine radicals. This review aims to describe the main causes of sperm DNA fragmentation and the tests commonly used to evaluate sperm DNA fragmentation.