Exogenous Expression of Human Protamine 1 (hPrm1) Remodels Fibroblast Nuclei into Spermatid-like Structures

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.

SPAG17 mediates nuclear translocation of protamines during spermiogenesis

Protamines (PRM1 and PRM2) are small, arginine-rich, nuclear proteins that replace histones in the final stages of spermiogenesis, ensuring chromatin compaction and nuclear remodeling. Defects in protamination lead to increased DNA fragmentation and reduced male fertility. Since efficient sperm production requires the translocation of protamines from the cytoplasm to the nucleus, we investigated whether SPAG17, a protein crucial for intracellular protein trafficking during spermiogenesis, participates in protamine transport. Initially, we assessed the protein-protein interaction between SPAG17 and protamines using proximity ligation assays, revealing a significant interaction originating in the cytoplasm and persisting within the nucleus. Subsequently, immunoprecipitation and mass spectrometry (IP/MS) assays validated this initial observation. Sperm and spermatids from Spag17 knockout mice exhibited abnormal protamination, as revealed by chromomycin A3 staining, suggesting defects in protamine content. However, no differences were observed in the expression of Prm1 and Prm2 mRNA or in protein levels between testes of wild-type and Spag17 knockout mice. Conversely, immunofluorescence studies conducted on isolated mouse spermatids unveiled reduced nuclear/cytoplasm ratios of protamines in Spag17 knockout spermatids compared to wild-type controls, implying transport defects of protamines into the spermatid nucleus. In alignment with these findings, in vitro experiments involving somatic cells, including mouse embryonic fibroblasts, exhibited compromised nuclear translocation of PRM1 and PRM2 in the absence of SPAG17. Collectively, our results present compelling evidence that SPAG17 facilitates the transport of protamines from the cytoplasm to the nucleus.

Nucleosomes in mammalian sperm: conveying paternal epigenetic inheritance or subject to reprogramming between generations?

The genome of mammalian sperm is largely packaged by sperm-specific proteins termed protamines. The presence of some residual nucleosomes has, however, emerged as a potential source of paternal epigenetic inheritance between generations. Sperm nucleosomes bear important regulatory histone marks and locate at gene-regulatory regions, functional elements, and intergenic regions. It is unclear whether sperm nucleosomes are retained at specific genomic locations in a deterministic manner or are randomly preserved due to inefficient exchange of histones by protamines. Recent studies indicate heterogeneity in chromatin packaging within sperm populations and an extensive reprogramming of paternal histone marks post fertilization. Obtaining single-sperm nucleosome distributions is fundamental to estimating the potential of sperm-borne nucleosomes in instructing mammalian embryonic development and in the transmission of acquired phenotypes.

Insights into the sperm chromatin and implications for male infertility from a protein perspective

Male germ cells undergo an extreme but fascinating process of chromatin remodeling that begins in the testis during the last phase of spermatogenesis and continues through epididymal sperm maturation. Most of the histones are replaced by small proteins named protamines, whose high basicity leads to a tight genomic compaction. This process is epigenetically regulated at many levels, not only by posttranslational modifications, but also by readers, writers, and erasers, in a context of a highly coordinated postmeiotic gene expression program. Protamines are key proteins for acquiring this highly specialized chromatin conformation, needed for sperm functionality. Interestingly, and contrary to what could be inferred from its very specific DNA-packaging function across protamine-containing species, human sperm chromatin contains a wide spectrum of protamine proteoforms, including truncated and posttranslationally modified proteoforms. The generation of protamine knock-out models revealed not only chromatin compaction defects, but also collateral sperm alterations contributing to infertile phenotypes, evidencing the importance of sperm chromatin protamination toward the generation of a new individual. The unique features of sperm chromatin have motivated its study, applying from conventional to the most ground-breaking techniques to disentangle its peculiarities and the cellular mechanisms governing its successful conferment, especially relevant from the protein point of view due to the important epigenetic role of sperm nuclear proteins. Gathering and contextualizing the most striking discoveries will provide a global understanding of the importance and complexity of achieving a proper chromatin compaction and exploring its implications on postfertilization events and beyond. This article is categorized under: Reproductive System Diseases > Genetics/Genomics/Epigenetics Reproductive System Diseases > Molecular and Cellular Physiology.

Protamine 1 as a secreted colorectal cancer-specific antigen facilitating G1/S phase transition under nutrient stress conditions

PURPOSE

Cancer testis antigens (CTAs) are optimal tumor diagnostic markers and involved in carcinogenesis. However, colorectal cancer (CRC) related CTAs are less reported with impressive diagnostic capability or relevance with tumor metabolism rewiring. Herein, we demonstrated CRC-related CTA, Protamine 1 (PRM1), as a promising diagnostic marker and involved in regulation of cellular growth under nutrient deficiency.

METHODS

Transcriptomics of five paired CRC tissues was used to screen CRC-related CTAs. Capability of PRM1 to distinguish CRC was studied by detection of clinical samples through enzyme linked immunosorbent assay (ELISA). Cellular functions were investigated in CRC cell lines through in vivo and in vitro assays.

RESULTS

By RNA-seq and detection in 824 clinical samples from two centers, PRM1 expression were upregulated in CRC tissues and patients` serum. Serum PRM1 showed impressive accuracy to diagnose CRC from healthy controls and benign gastrointestinal disease patients, particularly more sensitive for early-staged CRC. Furthermore, we reported that when cells were cultured in serum-reduced medium, PRM1 secretion was upregulated, and secreted PRM1 promoted CRC growth in culture and in mice. Additionally, G1/S phase transition of CRC cells was facilitated by PRM1 protein supplementation and overexpression via activation of PI3K/AKT/mTOR pathway in serum deficient medium.

CONCLUSIONS

In general, our research presented PRM1 as a specific CRC antigen and illustrated the importance of PRM1 in CRC metabolism rewiring. The new vulnerability of CRC cells was also provided with the potential to be targeted in future. Diagnostic value and grow factor-like biofunction of PRM1 A represents the secretion process of PRM1 regulated by nutrient deficiency. B represents activation of PI3K/AKT/mTOR pathway of secreted PRM1.

Somatic Cell Nuclear Transfer Using Freeze-Dried Protaminized Donor Nuclei

Somatic cell nuclear transfer (SCNT) is the only nuclear reprogramming method that allows rewinding an adult nucleus into a totipotent state. As such, it offers excellent opportunities for the multiplication of elite genotypes or endangered animals, whose number have shrunk to below the threshold of safe existence. Disappointingly, SCNT efficiency is still low. Hence, it would be wise to store somatic cells from threatened animals in biobanks. We were the first to show that freeze-dried cells allow generating blastocysts upon SCNT. Only a few papers have been published on the topic since then, and viable offspring have not been produced. On the other hand, lyophilization of mammalian spermatozoa has made considerable progress, partially due to the physical stability that protamines provide to the genome. In our previous work, we have demonstrated that a somatic cell could be made more amenable to the oocyte reprogramming by the exogenous expression of human Protamine 1. Given that the protamine also provides natural protection against dehydration stress, we have combined the cell protaminization and lyophilization protocols. This chapter comprehensively describes the protocol for somatic cell protaminization, lyophilization, and its application in SCNT. We are confident that our protocol will be relevant for establishing somatic cells stocks amenable to reprogramming at low cost.

Production of mouse offspring from zygotes fertilized with freeze-dried spermatids

Mouse cloning by nuclear transfer using freeze-drying (FD) somatic cells is now possible, but the success rate is significantly lower than that of FD spermatozoa. Because spermatozoa, unlike somatic cells, are haploid cells with hardened nuclei due to protamine, the factors responsible for their tolerance to FD treatment remain unclear. In this study, we attempt to produce offspring from FD spermatid, a haploid sperm progenitor cell whose nuclei, like somatic cells, have not yet been replaced by protamine. We developed a method for collecting FD spermatids from testicular suspension. Despite the significantly lower success rate than that of FD spermatozoa, healthy offspring were obtained when FD spermatids were injected into oocytes. Offspring were also obtained from FD spermatids derived from immature male mice that had not yet produced spermatozoa. These results suggest that nuclear protaminization, rather than haploid nuclei, is one of the key processes responsible for tolerance to FD treatment.

Embryo biotechnologies in sheep: Achievements and new improvements

To date, large-scale use of multiple ovulation and embryo transfer (MOET) programmes in ovine species is limited due to unpredictable results and high costs of hormonal stimulation and treatment. Therefore, even if considered reliable, they are not fully applicable in large-scale systems. More recently, the new prospects offered by in vitro embryo production (IVEP) through collection of oocytes post-mortem or by repeated ovum pick-up from live females suggested an alternative to MOET programmes and may be more extensively used, moving from the exclusive research in the laboratory to field application. The possibility to perform oocytes recovery from juvenile lambs to obtain embryos (JIVET) offers the great advantage to significantly reduce the generation interval, speeding the rate of genetic improvement. Although in the past decades several studies implemented novel protocols to enhance embryo production in sheep, the conditions of every single stage of IVEP can significantly affect embryo yield and successful transfer into the recipients. Moreover, the recent progresses on embryo production and freezing technologies might allow wider propagation of valuable genes in small ruminants populations and may be used for constitution of flocks without risks of disease. In addition, they can give a substantial contribution in preserving endangered breeds. The new era of gene editing might offer innovative perspectives in sheep breeding, but the application of such novel techniques implies involvement of specialized operators and is limited by relatively high costs for embryo manipulation and molecular biology analysis.

Protamines: lessons learned from mouse models

In brief

Protamines package and shield the paternal DNA in the sperm nucleus and have been studied in many mouse models over decades. This review recapitulates and updates our knowledge about protamines and reveals a surprising complexity in protamine function and their interactions with other sperm nuclear proteins.

Abstract

The packaging and safeguarding of paternal DNA in the sperm cell nucleus is a critical feature of proper sperm function. Histones cannot mediate the necessary hypercondensation and shielding of chromatin required for motility and transit through the reproductive tracts. Paternal chromatin is therefore reorganized and ultimately packaged by protamines. In most mammalian species, one protamine is present in mature sperm (PRM1). In rodents and primates among others, however, mature sperm contain a second protamine (PRM2). Unlike PRM1, PRM2 is cleaved at its N-terminal end. Although protamines have been studied for decades due to their role in chromatin hypercondensation and involvement in male infertility, key aspects of their function are still unclear. This review updates and integrates our knowledge of protamines and their function based on lessons learned from mouse models and starts to answer open questions. The combined insights from recent work reveal that indeed both protamines are crucial for the production of functional sperm and indicate that the two protamines perform distinct functions beyond simple DNA compaction. Loss of one allele of PRM1 leads to subfertility whereas heterozygous loss of PRM2 does not. Unprocessed PRM2 seems to play a distinct role related to the eviction of intermediate DNA-bound proteins and the incorporation of both protamines into chromatin. For PRM1, on the other hand, heterozygous loss leads to strongly reduced sperm motility as the main phenotype, indicating that PRM1 might be important for processes ensuring correct motility, apart from DNA compaction.

Sperm-borne proteins improve rabbit cloning efficiency via regulating embryonic cleavage and epigenetics

Somatic cell nuclear transfer (SCNT) shows great application value in the generation of transgenic animals, protection of endangered species, and therapeutic cloning. However, the cloning efficiency is still very low, which greatly restricts its application. Compared to fertilized embryos, cloned embryos lack the sperm proteins, which are considered to play an important role in embryonic development. Here we compared the sperm proteome, with that of donor fibroblasts and oocytes, and identified 342 proteins unique to sperm, with 42 being highly expressed. The 384 proteins were mainly enriched in the categories of post-translational modification and cytoskeletal arrangement. Extracts of soluble sperm or fibroblast proteins were injected into cloned embryos, and the result showed that injection of sperm protein significantly inhibited abnormal embryonic cleavage, significantly decreased the level of trimethylated histone H3Lys9 (H3K9me3) and the apoptotic index, and increased the inner cell mass (ICM)-to-trophectoderm (TE) ratio. More importantly, the sperm proteins also significantly enhanced the birthrate. The results of in vitro and in vivo experiments demonstrate that sperm-derived proteins improve embryo cloning efficiency. Our findings not only provide new insights into ways to overcome low cloning efficiency, but also add to the understanding of sperm protein function. This article is protected by copyright. All rights reserved.

The Activation of Protamine 1 Using Epigenome Editing Decreases the Proliferation of Tumorigenic Cells

DNA methyltransferases (DNMT) and histone deacetylases (HDAC) inhibitors are used as cancer epigenome drugs. However, these epigenetic drugs lack targeting specificity and could risk inducing genome instability and the expression of oncogenes. Therefore, there is a need to develop new therapeutic strategies where specific cancer genes can be targeted for silencing or activation. The CRISPR/dCas9 system represents a promising, powerful therapeutic tool because of its simplicity and specificity. Protamine 1 (PRM1) is exclusively expressed in sperm and has a vital role in the tight packaging of DNA, thus inducing transcriptional silencing in sperm cells. We hypothesized that the activation of the PRM1 gene in tumorigenic cells would lead to DNA condensation and reduce the proliferation of these cells. To test our hypothesis, we transfected human embryonic kidney cells 293T with a dCas9-P300 plasmid that adds acetyl groups to the promoter region of PRM1 via specific gRNAs plasmids. RNA-Seq analysis of transfected cells revealed high specificity of targeted gene activation. PRM1 expression resulted in a significant decrease in cell proliferation as measured by the BrdU ELISA assay. To confirm that the activation of PRM1 was due to acetyl groups deposited to H3K27, a ChIP-qPCR was performed. The acetylation of the PRM1 promoter region targeted by dCas9-p300 in transfected cells was higher than that of the control cells. Interestingly, the targeted promoter region for acetylation showed reduced DNA methylation. These findings demonstrate the efficacy of epigenome editing in activating PRM1 in non-expressing tumorigenic cells, which could be used as a promising therapeutic strategy in cancer treatment.

Sperm chromatin condensation: epigenetic mechanisms to compact the genome and spatiotemporal regulation from inside and outside the nucleus

Sperm chromatin condensation is a critical step in mammalian spermatogenesis to protect the paternal DNA from external damaging factors and to acquire fertility. During chromatin condensation, various events proceed in a chronological order, independently or in sequence, interacting with each other both inside and outside the nucleus to support the dramatic chromatin changes. Among these events, histone-protamine replacement, which is concomitant with acrosome biogenesis and cytoskeletal alteration, is the most critical step associated with nuclear elongation. Failures of not only intranuclear events but also extra-nuclear events severely affect sperm shape and chromatin state and are subsequently linked to infertility. This review focuses on nuclear and non-nuclear factors that affect sperm chromatin condensation and its effects, and further discusses the possible utility of sperm chromatin for clinical applications.

Loss of the cleaved-protamine 2 domain leads to incomplete histone-to-protamine exchange and infertility in mice

Protamines are unique sperm-specific proteins that package and protect paternal chromatin until fertilization. A subset of mammalian species expresses two protamines (PRM1 and PRM2), while in others PRM1 is sufficient for sperm chromatin packaging. Alterations of the species-specific ratio between PRM1 and PRM2 are associated with infertility. Unlike PRM1, PRM2 is generated as a precursor protein consisting of a highly conserved N-terminal domain, termed cleaved PRM2 (cP2), which is consecutively trimmed off during chromatin condensation. The carboxyterminal part, called mature PRM2 (mP2), interacts with DNA and together with PRM1, mediates chromatin-hypercondensation. The removal of the cP2 domain is believed to be imperative for proper chromatin condensation, yet, the role of cP2 is not yet understood. We generated mice lacking the cP2 domain while the mP2 is still expressed. We show that the cP2 domain is indispensable for complete sperm chromatin protamination and male mouse fertility. cP2 deficient sperm show incomplete protamine incorporation and a severely altered protamine ratio, retention of transition proteins and aberrant retention of the testis specific histone variant H2A.L.2. During epididymal transit, cP2 deficient sperm seem to undergo ROS mediated degradation leading to complete DNA fragmentation. The cP2 domain therefore seems to be a key aspect in the complex crosstalk between histones, transition proteins and protamines during sperm chromatin condensation. Overall, we present the first step towards understanding the role of the cP2 domain in paternal chromatin packaging and open up avenues for further research.

Protamines are small sperm-specific proteins crucial to packaging and protecting the paternal genome on its way to the fertilization site. Most mammalian species express only protamine 1. However, primates and rodents additionally express protamine 2. Protamine 2 differs mainly in its N-terminal domain (cP2), which is sequentially cleaved off during paternal chromatin packaging. Alteration in this process has been associated with infertility. However, the precise role of cP2 is still a mystery. We generated cP2 deficient mice and demonstrate, that loss of cP2 results in incomplete histone-to-protamine transition, resulting in sperm DNA degradation and infertility. Evidently, cP2 helps in orchestrating the fine-tuned dynamics of DNA-hypercondensation while protecting DNA integrity and aiding removal of DNA-bound transition proteins.

Current Progress and Prospects in Rabbit Cloning

Somatic cell nuclear transfer (SCNT) shows great value in the generation of transgenic animals, protection of endangered animals, and stem cell therapy. The combination of SCNT and gene editing has produced a variety of genetically modified animals for life science and medical research. Rabbits have unique advantages as transgenic bioreactors and human disease models; however, the low SCNT efficiency severely impedes the application of this technology. The difficulty in SCNT may be attributable to the abnormal reprogramming of somatic cells in rabbits. This review focuses on the abnormal reprogramming of cloned mammalian embryos and evaluates the progress and prospects of rabbit somatic cell cloning.

The expression, function, and utilization of Protamine1: a literature review

Objective

Protamine 1 (PRM1) is specific in sperm and plays essential roles in fertilization, also a member of cancer testis antigen (CTA) family. This study aims to summarize the expression and function of PRM1 in spermatogenesis, and to broaden the current knowledge and inspire future development of PRM1-based therapeutic strategies in cancer treatment and nanomedicine.

Background

The protamine proteins, are characterized by an arginine-rich core and cysteine residues. Humans express two types of protamine: PRM1 and PRM2. The abnormal expression or proportion of PRM1 and PRM2 is known to be associated with subfertility and infertility, especially for PRM1 which is highly evolutionary conserved in mammalians and expressed in all vertebrates. Biological functions of PRM1 have been unveiled in diverse cellular processes, such as tumorigenesis, somatic cell nucleus transfer, and drug delivery systems. Moreover, PRM1 is identified as a CTA in chronic leukemia (CLL) and colorectal cancer (CRC).

Methods

Literature was obtained using PubMed and the keywords protamine 1, PRM1, or P1, from January 1, 1980, through July 20, 2021. We also collect the additional evidence through screening references of articles identified through the PubMed searches.

Conclusions

PRM1 is well-studied in male infertility, and further researches and attempts to develop PRM1 as novel tumor marker, as well as drug delivery vector, will be of important clinical significance.

Technical, Biological and Molecular Aspects of Somatic Cell Nuclear Transfer – A Review

Since the announcement of the birth of the first cloned mammal in 1997, Dolly the sheep, 24 animal species including laboratory, farm, and wild animals have been cloned. The technique for somatic cloning involves transfer of the donor nucleus of a somatic cell into an enucleated oocyte at the metaphase II (MII) stage for the generation of a new individual, genetically identical to the somatic cell donor. There is increasing interest in animal cloning for different purposes such as rescue of endangered animals, replication of superior farm animals, production of genetically engineered animals, creation of biomedical models, and basic research. However, the efficiency of cloning remains relatively low. High abortion, embryonic, and fetal mortality rates are frequently observed. Moreover, aberrant developmental patterns during or after birth are reported. Researchers attribute these abnormal phenotypes mainly to incomplete nuclear remodeling, resulting in incomplete reprogramming. Nevertheless, multiple factors influence the success of each step of the somatic cloning process. Various strategies have been used to improve the efficiency of nuclear transfer and most of the phenotypically normal born clones can survive, grow, and reproduce. This paper will present some technical, biological, and molecular aspects of somatic cloning, along with remarkable achievements and current improvements.

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.

Effect of Khat (Catha edulis Forsk) extract on testicular maturation in pre-pubertal and pubertal rats: A morphological and biochemical study

The present study aimed at analysing the effect of Khat plant extract on rat testicular development. Thirty-two weaned male albino rats (4 weeks old) were divided into four groups consisting of eight animals each. While control animals received normal saline, rats of groups I, II and III received 100, 200 and 300 mg Khat extract per kg body weight dissolved in distilled water by oral gavage daily for 8 weeks, respectively. Blood samples were collected in separate heparinized tubes by cardiac puncture from each rat and processed for measuring plasma levels of reproductive hormones LH, FSH, testosterone and prolactin. Five-µm sections were stained with haematoxylin and eosin and examined by light microscope. Some sections were immunostained for protamine-1 representing a biomarker for intact sperm differentiation. The present study clearly demonstrated that Khat extract has a pronounced effect on testicular maturation of developing albino rats at both the morphological and functional levels. Khat-treated groups revealed a significantly low serum testosterone level and severe impairment of spermatogenesis when compared with control animals. The current findings also verified, for the first time, that the final stages of sperm maturation (spermiogenesis) were strongly impaired after administration of Khat extract to experimental rats particularly at a higher dose (300 mg/kg body weight). This was proved by the very weak, if any, expression of protamine-1 in the maturing spermatids in Khat-treated rats.

Cytogenetic Characterization of a Small Evolutionary Rearrangement Involving Chromosomes BTA21 and OAR18

Both cattle (Bos taurus) and sheep (Ovis aries) belong to the Bovidae family but to different subfamilies, Bovinae and Caprinae, respectively. From a chromosomal point of view, apart from the already known centric fusions (that occurred during the evolutionary process in the Bovidae family) and the small differences in the chromosome classification, the 2 karyotypes are very similar in banding patterns. In this study, the combination of bioinformatics techniques and physical mapping of DNA markers enabled the identification of a micro-rearrangement, a small inversion involving bovine chromosome 21 (BTA21) and the corresponding sheep chromosome 18 (OAR18). The aim of this study was the cytogenetic characterization of this difference in genomic assemblies between cattle and sheep in this single chromosome region. To verify the inversion in FISH experiments, we used the BACs 442H08 and 222H03 from the INRA library and BACs 134H22 and 436P08 from the sheep-specific CHORI library. The results confirmed the presence of the inverted fragment in sheep compared to the cattle genome. Genomic rearrangements may have consequences depending on their influence on gene activity, but in this case no gene or transcribed DNA portion seemed to be involved. In conclusion, we showed for the first time, concerning autosomes, that besides the already known centric fusions also other differences exist between the bovine and sheep karyotypes. Furthermore, we demonstrated that the combination of a bioinformatics approach and physical mapping is a valid tool for the identification of currently unknown rearrangements between related species.

Epigenetic Reprogramming During Somatic Cell Nuclear Transfer: Recent Progress and Future Directions

Somatic cell nuclear transfer (SCNT) has broad applications but is limited by low cloning efficiency. In this review, we mainly focus on SCNT-mediated epigenetic reprogramming in livestock and also describe mice data for reference. This review presents the factors contributing to low cloning efficiency, demonstrates that incomplete epigenetic reprogramming leads to the low developmental potential of cloned embryos, and further describes the regulation of epigenetic reprogramming by long non-coding RNAs, which is a new research perspective in the field of SCNT-mediated epigenetic reprogramming. In conclusion, this review provides new insights into the epigenetic regulatory mechanism during SCNT-mediated nuclear reprogramming, which could have great implications for improving cloning efficiency.

Effects of recipient oocyte source, number of transferred embryos and season on somatic cell nuclear transfer efficiency in sheep

To improve the efficiency of somatic cell nuclear transfer (SCNT) in sheep, we investigated the effects of recipient oocyte source, number of transferred embryos and season on the pregnancy and live lamb rates for sheep somatic cell nuclear transfer embryos. Follicle-stimulating hormone (FSH)-stimulated ovaries produced significantly more oocytes both in total and of suitable quality for maturation culture than those without FSH treatment (from slaughterhouse). However, their in vitro maturation rates were similar. Embryos were reconstructed using adult fibroblast cells into enucleated MII oocytes. The pregnancy and term rates were significantly higher in the FSH-stimulated group than in the slaughterhouse one. Oocytes from FSH-stimulated ovaries were enucleated as recipient cytoplasm for nuclear transfer in the following experiments. The transfer of 7-9 and 11-13 embryos produced significantly higher pregnancy rates than that of six embryos. However, the former groups exhibited similar live lamb rates. FSH-stimulated ovaries produced significantly more oocytes in November and December (winter) than in May to July (summer), but the associated maturation rate did not increase. Pregnancy and term rates were significantly higher when transfer occurred in winter than in summer. In conclusion, FSH treatment produced significant benefit regarding the number and quality of collected oocytes and also for the pregnancy and live lamb rates for reconstructed embryos. However, the transfer of an appropriate number of embryos (7-13) and at an appropriate season (winter) increased pregnancy and term rates.

Histone variants: critical determinants in tumour heterogeneity

Malignant cell transformation could be considered as a series of cell reprogramming events driven by oncogenic transcription factors and upstream signalling pathways. Chromatin plasticity and dynamics are critical determinants in the control of cell reprograming. An increase in chromatin dynamics could therefore constitute an essential step in driving oncogenesis and in generating tumour cell heterogeneity, which is indispensable for the selection of aggressive properties, including the ability of cells to disseminate and acquire resistance to treatments. Histone supply and dosage, as well as histone variants, are the best-known regulators of chromatin dynamics. By facilitating cell reprogramming, histone under-dosage and histone variants should also be crucial in cell transformation and tumour metastasis. Here we summarize and discuss our knowledge of the role of histone supply and histone variants in chromatin dynamics and their ability to enhance oncogenic cell reprogramming and tumour heterogeneity.

Cloning: A Sleeping Beauty Awaiting the Kiss?

The first 20 years of somatic cell nuclear transfer can hardly be described as a success story. Controversially, many factors leading to the fiasco are not intrinsic features of the technique itself. Misunderstandings and baseless accusations alongside with unsupported fears and administrative barriers hampered cloners to overcome the initial challenging period with obvious difficulties that are common features of a radically new approach. In spite of some promising results of mostly sporadic and small-scale experiments, the future of cloning is still uncertain. On the other hand, a reincarnation, just like the idea of electric cars, may result in many benefits in various areas of science and economy. One can only hope that-in contrast to electric cars-the ongoing paralyzed phase will not last for 100 years, and breakthroughs achieved in some promising areas will provide enough evidence to intensify research and large-scale application of cloning in the next decade.

Nuclear quiescence and histone hyper-acetylation jointly improve protamine-mediated nuclear remodeling in sheep fibroblasts

Recently we have demonstrated the possibility to replace histones with protamine, through the heterologous expression of human protamine 1 (hPrm1) gene in sheep fibroblasts. Here we have optimized protaminization of somatic nucleus by adjusting the best concentration and exposure time to trichostatin A (TSA) in serum-starved fibroblasts (nuclear quiescence), before expressing Prm1 gene. To stop cell proliferation, we starved cells in 0.5% FBS in MEM ("starved"-ST group), whereas in the Control group (CTR) the cells were cultured in 10% FBS in MEM. To find the most effective TSA concentration, we treated the cells with increasing concentrations of TSA in MEM + 10% FBS. Our results show that combination of cell culture conditions in 50 nM TSA, is more effective in terminating cell proliferation than ST and CTR groups (respectively 8%, 17.8% and 90.2% p<0.0001). Moreover, nuclear quiescence marker genes expression (Dicer1, Smarca 2, Ezh1 and Ddx39) confirmed that our culture conditions kept the cells in a nuclear quiescent state. Finally, ST and 50 nM TSA jointly increased the number of spermatid-like cell (39.4%) at higher rate compared to 25 nM TSA (20.4%, p<0.05) and 100 nM TSA (13.7%, p<0.05). To conclude, we have demonstrated that nuclear quiescence in ST cells and the open nuclear structure conferred by TSA resulted in an improved Prm1-mediated conversion of somatic nuclei into spermatid-like structures. This finding might improve nuclear reprogramming of somatic cells following nuclear transfer.

Live Cell Imaging of Chromosome Segregation During Mitosis

Chromosomes must be reliably and uniformly segregated into daughter cells during mitotic cell division. Fidelity of chromosomal segregation is controlled by multiple mechanisms that include the Spindle Assembly Checkpoint (SAC). The SAC is part of a complex feedback system that is responsible for prevention of a cell progress through mitosis unless all chromosomal kinetochores have attached to spindle microtubules. Chromosomal lagging and abnormal chromosome segregation is an indicator of dysfunctional cell cycle control checkpoints and can be used to measure the genomic stability of dividing cells. Deregulation of the SAC can result in the transformation of a normal cell into a malignant cell through the accumulation of errors during chromosomal segregation. Implementation of the SAC and the formation of the kinetochore complex are tightly regulated by interactions between kinases and phosphatase such as Protein Phosphatase 2A (PP2A). This protocol describes live cell imaging of lagging chromosomes in mouse embryonic fibroblasts isolated from mice that had a knockout of the PP2A-B56γ regulatory subunit. This method overcomes the shortcomings of other cell cycle control imaging techniques such as flow cytometry or immunocytochemistry that only provide a snapshot of a cell cytokinesis status, instead of a dynamic spatiotemporal visualization of chromosomes during mitosis.

Histone variants: essential actors in male genome programming

Prior to its transmission to the offspring, the male genome has to be tightly compacted. A genome-scale histone eviction and the subsequent repackaging of DNA by protamines (Prms) direct this essential genome condensation step. The requirement for male germ cells to undergo such a dramatic and unique genome reorganization explains why these cells express the largest number of histone variants, including many testis-specific ones. Indeed, an open chromatin, nucleosome instability and a facilitated process of histone disassembly are direct consequences of the presence of these histone variants in the chromatin of male germ cells. These histone-induced changes in chromatin first control a stage-specific gene expression program and then directly mediate the histone-to-Prm transition process. This review aims at summarizing and discussing a series of recent functional studies of male germ cell histone variants with a focus on their impact on the process of histone eviction and male genome compaction.

Remodeling somatic nuclei via exogenous expression of protamine 1 to create spermatid-like structures for somatic nuclear transfer

This protocol describes how to convert the chromatin structure of sheep and mouse somatic cells into spermatid-like nuclei through the heterologous expression of the protamine 1 gene (Prm1). Furthermore, we also provide step-by-step instructions for somatic cell nuclear transfer (SCNT) of Prm1-remodeled somatic nuclei in sheep oocytes. There is evidence that changing the organization of a somatic cell nucleus with that which mirrors the spermatozoon nucleus leads to better nuclear reprogramming. The protocol may have further potential application in determining the protamine and histone footprints of the whole genome; obtaining 'gametes' from somatic cells; and furthering understanding of the molecular mechanisms regulating the maintenance of DNA methylation in imprinted control regions during male gametogenesis. The protocol is straightforward, and it requires 4 weeks from the establishment of the cell lines to their transfection and the production of cloned blastocysts. It is necessary for researchers to have experience in cell biology and embryology, with basic skills in molecular biology, to carry out the protocol.

Synergies between assisted reproduction technologies and functional genomics

This review, is a synopsis of advanced reproductive technologies in farm animals, including the discussion of their limiting factors as revealed by the study of offspring derived from embryos produced in vitro and through cloning. These studies show that the problems of epigenetic mis-programming, which were reported in the initial stages of assisted reproduction, still persist. The importance of whole-genome analyses, including the methylome and transcriptome, in improving embryo biotechnologies in farm animals, are discussed. Genome editing approaches for the improvement of economically-relevant traits in farm animals are also described. Efficient farm animal embryo biotechnologies, including cloning and the most recent technologies such as genome editing, will effectively complement the latest strategies to accelerate genetic improvement of farm animals.

A New, Dynamic Era for Somatic Cell Nuclear Transfer?

Cloning animals by somatic cell nuclear transfer (SCNT) has remained an uncontrollable process for many years. High rates of embryonic losses, stillbirths, and postnatal mortality have been typical outcomes. These developmental problems arise from abnormal genomic reprogramming: the capacity of the oocyte to reset the differentiated memory of a somatic cell. However, effective reprogramming strategies are now available. These target the whole genome or single domains such as the Xist gene, and their effectiveness has been validated with the ability of experimental animals to develop to term. Thus, SCNT has become a controllable process that can be used to 'rescue' endangered species, and for biomedical research such as therapeutic cloning and the isolation of induced pluripotent stem cells (iPSCs).