The interaction of sperm cells with exogenous DNA: a role of CD4 and major histocompatibility complex class II molecules

Multiple transcriptome analyses reveal mouse testis developmental dynamics

The testes are the organs of gamete production and testosterone synthesis. Up to date, no model system is available for mammalian testicular development, and only few studies have characterized the mouse testis transcriptome from no more than three postnatal ages. To describe the transcriptome landscape of the developing mouse testis and identify the potential molecular mechanisms underlying testis maturation, we examined multiple RNA-seq data of mouse testes from 3-week-old (puberty) to 11-week-old (adult). Sperm cells appeared as expected in 5-week-old mouse testis, suggesting the proper sample collection. The principal components analysis revealed the genes from 3w to 4w clustered away from other timepoints, indicating they may be the important nodes for testicular development. The pairwise comparisons at two adjacent timepoints identified 7,612 differentially expressed genes (DEGs), resulting in 58 unique mRNA expression patterns. Enrichment analysis identified functions in tissue morphogenesis (3-4w), regulation of peptidase activity (4-5w), spermatogenesis (7-8w), and antigen processing (10-11w), suggesting distinct functions in different developmental periods. 50 hub genes and 10 gene cluster modules were identified in the testis maturation process by protein-protein interaction (PPI) network analysis, and the miRNA-lncRNA-mRNA, miRNA-circRNA-mRNA and miRNA-circRNA-lncRNA-mRNA competing endogenous RNA (ceRNA) networks were constructed. The results suggest that testis maturation is a complex developmental process modulated by various molecules, and that some potential RNA-RNA interactions may be involved in specific developmental stages. In summary, this study provides an update on the molecular basis of testis development, which may help to understand the molecular mechanisms of mouse testis development and provide guidance for mouse reproduction.

Tale of Viruses in Male Infertility

Male infertility is a condition where the males either become sterile or critically infertile. The World Health Organisation assessed that approximately 9% of the couple have fertility issues where the contribution of the male partner was estimated to be 50%. There are several factors that can amalgamate to give rise to male infertility. Among them are lifestyle factors, genetic factors and as well as several environmental factors. The causes of male infertility may be acquired, congenital or sometimes idiopathic. All these factors adversely affect the spermatogenesis process as well as they impart serious threats to male genital organs thus resulting in infertility. Viruses are submicroscopic pathogenic agents that rely on host for their replication and survival. They enter the host cell, hijack the host cell machinery to aid their own replication and exit the cell for a new round of infection. With the growing abundance of different types of viruses and the havoc they have stirred in the form of pandemics, it is very essential to decipher their route of entry inside the human body and understand their diverse functional roles in order to combat them. In this chapter, we will review how viruses invade the male genital system thus in turn leading to detrimental consequence on male fertility. We will discuss the tropism of various viruses in the male genital organs and explore their sexual transmissibility. This chapter will summarise the functional and mechanistic approaches employed by the viruses in inducing oxidative stress inside spermatozoa thus leading to male infertility. Moreover, we will also highlight the various antiviral therapies that have been studied so far in order to ameliorate viral infection in order to combat the harmful consequences leading to male infertility.

The effect of methyl-beta-cyclodextrin on DNA absorption and quality of posttransfected sperm

Sperm can be selected as a natural vector for the production of transgenic animals. Methyl-beta-cyclodextrin (MBCD) removes cholesterol from the phospholipid membrane of sperm and improves the efficiency of DNA uptake by sperm. In experiment 1, fresh sperm was treated with various concentrations of MBCD. The direct effects of MBCD on sperm parameters were monitored. In experiment 2, different concentrations of MBCD (0, 1, 2, and 4 mmol) were assessed for the transfection of genetically exogenous construction to rooster sperm. Washed semen was divided into 5 equal groups for the incubation and transfection with a pcDNA3.1+/hG-CSF vector (exogenous DNA) as follows; Treatment I-Control (washed semen without DNA); Treatment II-Control (washed semen with DNA); Treatment III-(washed semen incubated with DNA and 1 mmol MBCD); Treatment IV-(washed semen incubated with DNA and 2 mmol MBCD); and Treatment V-(washed semen incubated with DNA and 4 mmol MBCD). We demonstrated that rooster spermatozoa spontaneously can uptake exogenous DNA; this was assessed using exogenous DNA amplification (sperm genomic DNA used as a template for PCR reaction) after DNase I treatment. In addition, total motility (TM), progressive motility (PM), velocity parameters [curvilinear velocity (VCL), straight linear velocity (VSL), sperm track straightness (STR), linearity (LIN)], membrane integrity (MI), and membrane functionality were posttransfectionally evaluated. The concentrations of 1 and 2 mmol MBCD significantly (P < 0.05) improved the motion characteristics and membrane integrity of fresh sperm. The presence of hG-CSF in rooster sperm was detected by PCR and based on sperm analyses MBCD (1 mmol) improved the percentage of motility (98.9 ± 0.81), membrane functionality (64 ± 1.64), and MI (76.2 ± 1.65) after transfection when compared with the other groups (P < 0.05). For the production of transgenic chicken, hens were inseminated (AI) by transfected sperm treated with 1 and 0 mmol MBCD. A PCR analysis of the blood samples and dead embryo tissues of chicks did not reveal the transgene integration.

A novel pathway for the induction of DNA damage in human spermatozoa involving extracellular cell-free DNA

DNA damage is a common feature of human spermatozoa associated with an impaired capacity to fertilize the oocyte and an increased mutational load in the offspring. However, the etiology of this damage remains poorly defined. In this study we demonstrate that a major pathway for the induction of DNA damage in mammalian spermatozoa is triggered by exposure to exogenous cell free DNA (cfDNA). Exposure of human and mouse spermatozoa to cfDNA (calf thymus, mouse liver and salmon testes) in vitro induced a dose-dependent increase in sperm DNA damage that could be effectively suppressed by the concomitant presence of DNase. The induction of such damage was not accompanied by any concomitant change in sperm motility or vitality and was not directly associated with the induction of oxidative stress. In vivo the injection of exogenous DNA again precipitated an increase in sperm DNA fragmentation that could be reversed by the prior administration of DNase. Similarly, the induction of a transient unilateral testicular ischemia induced an increase in DNA fragmentation that was evident within 24 h and sustained for at least 14 days via mechanisms that could be completely suppressed by the prior administration of DNase. We conclude that exogenous cfDNA activates a defensive response in human spermatozoa associated with the nuclease-mediated induction of DNA fragmentation, possibly involving the participation of TLR9 and CD4. These novel insights have significant implications for our understanding of DNA fragmentation in the male germ line and open up new pathways for the remediation of this condition.

The active role of spermatozoa in transgenerational inheritance

The active uptake of exogenous nucleic acids by spermatozoa of virtually all animal species is a well-established phenomenon whose significance has long been underappreciated. A growing body of published data demonstrates that extracellular vesicles released from mammalian somatic tissues pass an RNA-based flow of information to epididymal spermatozoa, thereby crossing the Weismann barrier. That information is delivered to oocytes at fertilization and affects the fate of the developing progeny. We propose that this essential process of epigenetic transmission depends upon the documented ability of epididymal spermatozoa to bind and internalize foreign nucleic acids in their nuclei. In other words, spermatozoa are not passive vectors of exogenous molecules but rather active participants in essential somatic communication across generations.

The effects of IAM38 blocking or CD4 blocking on the binding of exogenous DNA in rabbit sperm

The binding of exogenous DNA to sperm is a key process for sperm-mediated gene transfer; however, the underlying molecular mechanisms have yet to be elucidated. In the present study, we aimed to identify the DNA binding proteins (DBPs) in rabbit sperm and to gain further understanding of the molecular mechanism of sperm and exogenous DNA interaction. Native polyacrylamide gel electrophoresis was used for separating free sperm proteins and complexes of DNA fragment/sperm proteins. A distinct band was found after Coomassie blue staining, and seven potential proteins were identified by mass spectrometry analysis. An analysis of the physical/chemical properties of the seven proteins revealed that the sperm inner acrosomal membrane protein IAM38 (IAM38) matched the features of the DBPs. Western blotting analysis showed that the IAM38 and CD4 were present in the sperm but not in the seminal plasma. Blocking of the IAM38 impaired the DNA-binding capacity of the sperm. Blocking the CD4 decreased the DNA-uptake capacity of the sperm but did not influence the DNA-binding capacity of the sperm. Moreover, the EGFP-positive embryos and EGFP-positive blastocysts were also decreased after IAM38 blocking or CD4 blocking in comparison with the control group. In conclusion, our results imply that foreign DNA first binds to the transmembrane IAM38 of the sperm plasma membrane and then forms the complex of DNA/IAM38/CD4 with CD4 to complete the transportation of exogenous DNA into the nucleus of sperm.

Dimethyl sulphoxide and electrolyte-free medium improve exogenous DNA uptake in mouse sperm and subsequently gene expression in the embryo

SummaryOne of the methods to generate transgenic animals is called sperm-mediated gene transfer (SMGT). Mature sperm cells can take up exogenous DNA molecules intrinsically and transfer them into the oocyte during fertilization. This study assessed the effect of dimethyl sulfoxide (DMSO) and electrolyte-free medium (EFM) on DNA uptake (EGFP-N1plasmid) in mouse sperm. Sperms cells cultured in human tubular fluid (HTF) without any treatment were considered as the control group. Sperms cells that were incubated in EFM and HTF with DNA/DMSO at 4°C were classified into EFM and HTF groups. Sperm motility and viability were assessed following treatment. In vitro fertilization (IVF) with sperm in all groups was performed. Fertilization, embryo development and GFP-positive blastocyst rates were analyzed and compared. The result showed that sperm motility and viability in EFM were better than those in the HTF group. The rate of development to reach the blastocyst stage and GFP-positive blastocysts was significantly higher in the EFM group compared with the HTF group (P<0.05). Our data demonstrate that sperm stored in the EFM group can improve the efficiency of SMGT for the generation of GFP-positive blastocysts.

Comparison between electroporation and polyfection in pig sperm: efficiency and cell viability implications

The aim of this study was to optimize protocols for electroporation (EP) and polyfection (PLF) using polyethyleneimine (PEI) for pig sperm transfection and to determine which method was the most efficient. For EP standardization, different voltages, amounts and times of electric pulses were tested using propidium iodide (PI) as reporter. For PLF standardization, different concentrations of fluorescein isothiocyanate (FITC)-labelled PEI (PEI/FITC) were incubated with sperm for different periods of time. Flow cytometry was performed to evaluate the best protocol in terms of cell viability, including cytoplasmic membrane, acrosome, chromatin integrities and mitochondrial potential using the FITC probe, PI, acridine orange (AO) and JC1. Transfections with the plasmid pmhyGENIE-5 were carried out under optimum conditions for each procedure (EP: 500 volts, 500 μs and two pulses; PLF: PEI 0.5 mg/ml and incubation time 10 min). Transfection efficacy was assessed by fluorescence in situ hybridization (FISH). A lower transfection rate was observed for sperm in the control group (17.8%) compared with EP (36.7%), with PLF (76.8%) being the most efficient. These results suggest that the EP and PEI could be an efficient and low cost transfection method for swine sperm. Notably, treated cells showed higher plasmatic the membrane damage (PMD) and/or acrosome damage (AD) indexes, therefore the combination of this procedure with biotechniques that facilitate fecundation (i.e. in vitro fertilization or intracytoplasmic sperm injection) or even inclusion of antioxidant or anti-apoptotic drugs to improve spermatozoa viability would be important.

Flow cytometric sex sorting affects CD4 membrane distribution and binding of exogenous DNA on bovine sperm cells

Bovine sex-sorted sperm have been commercialized and successfully used for the production of transgenic embryos of the desired sex through the sperm-mediated gene transfer (SMGT) technique. However, sex-sorted sperm show a reduced ability to internalize exogenous DNA. The interaction between sperm cells and the exogenous DNA has been reported in other species to be a CD4-like molecule-dependent process. The flow cytometry-based sex-sorting process subjects the spermatozoa to different stresses causing changes in the cell membrane. The aim of this study was to elucidate the relationship between the redistribution of CD4-like molecules and binding of exogenous DNA to sex-sorted bovine sperm. In the first set of experiments, the membrane phospholipid disorder and the redistribution of the CD4 were evaluated. The second set of experiments was conducted to investigate the effect of CD4 redistribution on the mechanism of binding of exogenous DNA to sperm cells and the efficiency of lipofection in sex-sorted bovine sperm. Sex-sorting procedure increased the membrane phospholipid disorder and induced the redistribution of CD4-like molecules. Both X-sorted and Y-sorted sperm had decreased DNA bound to membrane in comparison with the unsorted sperm; however, the binding of the exogenous DNA was significantly increased with the addition of liposomes. Moreover, we demonstrated that the number of sperm-bound exogenous DNA was decreased when these cells were preincubated with anti-bovine CD4 monoclonal antibody, supporting our hypothesis that CD4-like molecules indeed play a crucial role in the process of exogenous DNA/bovine sperm cells interaction.

Effect of transfection and co-incubation of bovine sperm with exogenous DNA on sperm quality and functional parameters for its use in sperm-mediated gene transfer

Sperm-mediated gene transfer (SMGT) is based on the capacity of sperm to bind exogenous DNA and transfer it into the oocyte during fertilization. In bovines, the progress of this technology has been slow due to the poor reproducibility and efficiency of the production of transgenic embryos. The aim of the present study was to evaluate the effects of different sperm transfection systems on the quality and functional parameters of sperm. Additionally, the ability of sperm to bind and incorporate exogenous DNA was assessed. These analyses were carried out by flow cytometry and confocal fluorescence microscopy, and motility parameters were also evaluated by computer-assisted sperm analysis (CASA). Transfection was carried out using complexes of plasmid DNA with Lipofectamine, SuperFect and TurboFect for 0.5, 1, 2 or 4 h. The results showed that all of the transfection treatments promoted sperm binding and incorporation of exogenous DNA, similar to sperm incorporation of DNA alone, without affecting the viability. Nevertheless, the treatments and incubation times significantly affected the motility parameters, although no effect on the integrity of DNA or the levels of reactive oxygen species (ROS) was observed. Additionally, we observed that transfection using SuperFect and TurboFect negatively affected the acrosome integrity, and TurboFect affected the mitochondrial membrane potential of sperm. In conclusion, we demonstrated binding and incorporation of exogenous DNA by sperm after transfection and confirmed the capacity of sperm to spontaneously incorporate exogenous DNA. These findings will allow the establishment of the most appropriate method [intracytoplasmic sperm injection (ICSI) or in vitro fertilization (IVF)] of generating transgenic embryos via SMGT based on the fertilization capacity of transfected sperm.

X and Y chromosome-bearing spermatozoa are equally able to uptake and internalize exogenous DNA by sperm-mediated gene transfer in swine

Since proteomic differences between male X/Y chromosome-bearing gametes have recently been described, a question has been raised: could these differences be responsible for different behavior between X and Y chromosome-bearing spermatozoa during the binding and internalization of exogenous DNA in the swine species? In order to investigate this hypothesis, our group studied the process of the uptake and internalization of exogenous DNA in X and Y chromosome-bearing sperm sub-populations. No significant differences were found between sperm types in both the uptake and internalization of exogenous DNA. The quantity of internalized exogenous DNA was significantly lower than that of the uptaken DNA. In conclusion, our results showed that X and Y chromosomes-bearing spermatozoa have the same binding capacity and internalization of DNA, and the proteomic differences between them do not seem to interfere with these complex processes.

Intracytoplasmic sperm injection (ICSI)-mediated transgenesis in mice

Over the years many well-described techniques for the introduction of transgene DNA into host organisms have been used, including pronuclear injection, in vitro fertilization-mediated transgenesis, transfection of ES and spermatogenic cells, nuclear transfer of somatic cell nuclei, and lentiviral vectors. The application of these techniques has been limited however either by the time and effort to be executed or by their narrow efficiency with large transgenes. The greatest advantage of intracytoplasmic sperm injection (ICSI)-mediated transgenesis is precisely its ability to stably introduce large DNA molecules into the genome of host organisms with relatively high efficiency, as compared to alternative procedures. In mice, this procedure has been shown to be a reproducible method to generate transgenic offspring with a high efficiency. Recently, it proved also to be a viable method to generate transgenic rats and pigs, and as such, it is foreseen with great interest for the production of transgenic farm animals, where it would constitute an important tool for the production of recombinant proteins and livestock improvement.

Methods for sperm-mediated gene transfer

The transgenic technologies represent potent biotechnological tools that allow the generation of genetically modified animals useful for basic research and for biomedical, veterinary, and agricultural applications. Among transgenic techniques, we describe here the sperm-mediated gene transfer methods that is gene transfer based on the spontaneous ability of sperm cells to bind and internalize exogenous DNA and to carry it to oocyte during fertilization, producing genetically modified animals with high efficiency.

Sperm DNA Fragmentation: Origin and Impact on Human Reproduction

Sperm DNA can be damaged due to a multitude of different noxae, which include disease, and occupational and environmental factors. Depending on the magnitude of the damage, such lesions may be repaired by the oocyte or the embryo. If this is not possible, a permanent damage can be manifested leading to mutations of the male genome. In cases where the oocyte or the embryo does not counter these damages to the male genome in terms of repair or an early abortion, sperm DNA damage and fragmentation can be a cause of numerous diseases including childhood cancer.

MtDNA typing of single-sperm cells isolated by micromanipulation

Some sexual assault crimes constitute a problem for the legal institutions confronted with the DNA analysis of such cases. Often, sperm cells are found in the victim's vaginal tract during medical examination but their successful genotyping is compromised by the huge excess of the victim's epithelial cells as well as by the degradation of genomic DNA present in sperm cells as a consequence of female immune response. Mitochondrial DNA present in the mid-piece of sperm cells might be useful in some specific cases in order to differentiate the donors of a semen sample. The high number of copies per cell and its circular nature that may confer some protection from the action of exonucleases make it more suitable for cases where few cells are available and/or the DNA is degraded. We have developed a novel strategy for typing mtDNA from single-sperm cells. Specific amplification of male mitochondrial DNA is ensured by use of sequence specific primers designed on the basis of mitochondrial single nucleotide polymorphisms existent throughout the control region. The strategy was applied to single-sperm cells isolated by micromanipulation from slides smeared with vaginal swabs taken immediately after sexual intercourse of voluntary couples. After sequencing the PCR products, it was possible to obtain a match between the DNA sequence from the buccal swab and the DNA sequence of the single sperm-cell, for each voluntary man. With this new strategy, the problem of contamination with DNA from the victim observed when using universal primers was completely overtaken. This method will probably allow the resolution of multiple-rapist crimes, where the collected sperm cells can be separately typed.

Sperm and testis mediated DNA transfer as a means of gene therapy

Assisted reproductive technologies (ART) have revolutionized the treatment of infertility. However, many types of infertility may still not be addressable by ART. With recent successes in identifying many of the genetic factors responsible for male infertility and the future prospect of whole individual human genome sequencing to identify disease causing genes, the possible use of gene therapy for treating infertility deserves serious consideration. Gene therapy in the sperm and testis offers both opportunities and obstacles. The opportunities stem from the fact that numerous different approaches have been developed for introducing transgenes into the sperm and testis, mainly because of the interest in using sperm mediated gene transfer and testis mediated gene transfer as ways to generate transgenic animals. The obstacles arise from the fact that it may be very difficult to carry out gene therapy of the testis and sperm without also affecting the germline. Here we consider new developments in both sperm and testis mediated gene transfer, including the use of viral vectors, as well as the technical and ethical challenges facing those who would seek to use these approaches for gene therapy as a way to treat male infertility.

Transgene transmission in South American catfish (Rhamdia quelen) larvae by sperm-mediated gene transfer

The silver catfish (Rhamdia quelen) is an endemic American fish species. The sperm of each species has its own peculiarities and biological characteristics, which influence the success of mass DNA transfer methods. Our objective in this study was to evaluate different sperm-mediated gene transfer (SMGT) methods to obtain transgenic silver catfish. Different treatments for the incorporation of a foreign pEGFP plasmid group were used: (1) dehydrated/rehydrated (DR), (2) dehydrated/rehydrated/electroporated (DRE), (3) electroporated (E), (4) incubated with seminal plasma (INC); and (5) incubated in the absence of seminal plasma (INCSP). Sperm motility, time of activity duration (TAD), fertilization rate (FR), hatching rate (HR) and sperm morphology were also evaluated. The polymerase chain reaction (PCR) positivity rates for the presence of the transgene were: DRE 60%; DR 40%; E 25%; INC 5% and INCSP 25%. The rates of embryo EGFP expression were: DRE 63%; DR 44%; E 34%; INC 8% and INCSP 38%. The fertilization rate in the control and DRE treatments groups were higher than in the DR group, but the E,INC and INCSP treatment groups had the lowest rate. The hatching rates of the DRE, DR and control groups were higher than in the INCSP, INC and E treatment groups (P>0.05). There were no differences among the DRE and DR, E and DR, E and INCSP groups in expression and PCR positivity rates of enhanced green fluorescent protein (EGFP) in embryos. Scanning electron microscopy also did not show any change in sperm morphology among treatment groups. To the best of our knowledge, this is the first report on transgene transmission of exogenous DNA into silver catfish larvae through SMGT technology.

Production of transgenic rabbit embryos through intracytoplasmic sperm injection

The objective of this study was to test if intracytoplasmic sperm injection (ICSI)-mediated gene transfer was an effective method in the production of transgenic rabbit embryos. Rabbit sperm diluted in different media with various pH were treated by freezing without cryoprotectant, and their ability for DNA uptake was determined. In these experiments using production of transgenic rabbit embryos by ICSI, exogenous genes at three concentrations and of two conformation types were used. The rate of DNA association to the sperm seen by rhodamine-tagged DNA encoding green fluorescent protein (GFP) was 90.0%, 92.7%, 91.0%, 91.7%, and 92.3%, respectively in TCM199, DM, DPBS, CZB, and HCZB media. The DNA attachment to sperm was not affected by media pH within the range of 5.4-9.4 (p > 0.05). Expression of GFP first occurred at the 2-cell stage and continued to blastocyst formation. DNA concentration (between 5, 10, and 20 ng/μl) or conformation (linear and circular) had no effect on the production rate of transgenic embryos. These results indicated that genetically modified rabbit blastocysts can be efficiently produced by ICSI technique.

An efficient method for generating transgenic mice using NaOH-treated spermatozoa

Transgenic (Tg) animals are widely used in researching the characteristics of exogenous genes. Intracytoplasmic sperm injection (ICSI)-mediated transgenesis (ICSI-Tr) has been a useful method for generating Tg animals, especially in the mouse. However, the original methods using freeze-thawed spermatozoa showed severe chromosomal damage and low offspring rates after embryo transfer. Herein, we describe an improved method to generate Tg mice efficiently using a simple pretreatment of spermatozoa with 10 mM NaOH. These spermatozoa lost their plasma membrane and tail, while still maintaining nuclear integrity. Sperm heads were mixed with 0.5-5 ng/microl of the transgene for enhanced green fluorescent protein (EGFP) for 3 min to 1 h at room temperature and were then microinjected into oocytes by ICSI. The best results were obtained when treated spermatozoa were incubated with 2 ng/microl of EGFP for 10 min; 55.6% of injected embryos developed to the blastocyst stage, and more than half (56.9%) of them displayed EGFP fluorescence. Under these conditions, 12 pups of 34 offspring were positive for the transgene after transfer at the 2-cell stage into pseudopregnant recipient mice (a high rate [10.2%] from manipulated embryos). This method was found to be suitable for hybrid and inbred strains of mouse such as C57BL/6 and 129X1/Sv. Thus, a simple sperm pretreatment with NaOH before ICSI-Tr resulted in an efficient insertion of an exogenous gene into the host genome. This method allows for easy production of Tg mice, requiring fewer oocytes for micromanipulation than classical methods.

In vivoGene Transfer into Testis and Sperm: Developments and Future Application

Despite significant advances in the treatment of infertility via assisted reproductive technology (ART), the underlying causes of idiopathic male infertility still remain unclear. Accumulating evidence suggests that disorders associated with testicular gene expression may play an important role in male infertility. To be able to fully study the molecular mechanisms underlying spermatogenesis and fertilization, it is necessary to manipulate gene expression in male germ cells. Since there is still no reliable method of recapitulating spermatogenesis culture, the development of alternative transgenic approaches is paramount in the study of gene function in testis and sperm. Established methods of creating transgenic animals rely heavily upon injection of DNA into the pronucleus or the injection of transfected embryonic stem cells into blastocysts to form chimeras. Despite the success of these two approaches for making transgenic and knockout animals, concerns remain over costs and the efficiency of transgene integration. Consequently, efforts are in hand to evaluate alternative methodologies. At present, there is much interest in developing approaches that utilize spermatozoa as vectors for gene transfer. These approaches, including testis mediated gene transfer (TMGT) and sperm mediated gene transfer (SMGT), have great potential as tools for infertility research and in the creation of transgenic animals. The aim of this short review is to briefly describe developments in this field and discuss how these gene transfer methods might be used effectively in future research and clinical arenas.

Progress in gene transfer by germ cells in mammals

Use of germ cells as vectors for transgenesis in mammals has been well developed and offers exciting prospects for experimental and applied biology, agricultural and medical sciences. Such approach is referred to as either male germ cell mediated gene transfer (MGCMGT) or female germ cell mediated gene transfer (FGCMGT) technique. Sperm-mediated gene transfer (SMGT), including its alternative method, testis-mediated gene transfer (TMGT), becomes an established and reliable method for transgenesis. They have been extensively used for producing transgenic animals. The newly developed approach of FGCMGT, ovary-mediated gene transfer (OMGT) is also a novel and useful tool for efficient transgenesis. This review highlights an overview of the recent progress in germ cell mediated gene transfer techniques, methods developed and mechanisms of nucleic acid uptake by germ cells.

Efficient generation of transgenic mice by direct intraovarian injection of plasmid DNA

We established a rapid procedure for obtaining transgenic mice by directly injecting an enhanced green fluorescent protein (EGFP)-expressing plasmid (pIRES-EGFP) into the ovaries of fertile mice. The frequency of transgenic mouse production was determined by pair-mating, and by polymerase chain reaction (PCR) and sequence analysis of DNA taken from the tails of the offspring. The mice that received the EGFP gene transmitted it to their offspring (F(1)). Genetic and PCR analyses of F(1) progeny confirmed that the inserted EGFP was stably inherited. Of six female F(1) mice, all were able to pass the foreign DNA on to the next generation (F(2)). In situ hybridization using paraffin-embedded sections of ovarian and testicular tissues from the F(1) and F(2) progeny showed that the introduced gene was expressed in the gonads of the animals. The chromosomal location of the injected DNA was determined by fluorescence in situ hybridization, and the frequency of multiple site versus single site insertions is 85.71% (18/21) analyzed by FISH. We anticipate great progress in murine genetic engineering using this technique.

Proteins involved in binding and cellular uptake of nucleic acids

The study of mechanisms of nucleic acid transport across the cell membrane is valuable both for understanding the biological function of extracellular nucleic acids and the practical use of nucleic acids in gene therapy. It has been clearly demonstrated that cell surface proteins are necessary for transport of nucleic acids into cells. A large amount of data has now been accumulated about the proteins that participate in nucleic acid transport. The methods for revealing and identification of these proteins, possible mechanisms of protein-mediated transport of nucleic acids, and cellular functions of these proteins are described.

Spontaneous uptake of exogenous DNA by bull spermatozoa

Sperm-mediated DNA transfer can be used to transfer exogenous DNA into the oocyte for the production of transgenic animals. In spite of controversy in the literature, sperm-mediated DNA transfer is a simple and quick technique that can be used in routine breeding programs (AI, embryo transfer and IVF). The main objective of this study was to determine the factors affecting the spontaneous uptake of exogenous DNA by bull spermatozoa. For this purpose, fresh and frozen spermatozoa (0.25 x 10(6)), from the same ejaculate from each of four bulls were co-incubated with fluorescent-labeled green fluorescent protein (GFP) and chloremphenicol acetyltransferase (CAT) plasmids at 37 degrees C for 30 min. Neither bull nor plasmid significantly affected the uptake of exogenous DNA. However, transfection efficiency was higher in frozen-thawed versus fresh spermatozoa (P<0.001). Regardless of whether transfected spermatozoa were alive or dead, all transfected spermatozoa were immotile. It can be concluded that a population of spermatozoa is present in bull semen which has the ability to uptake exogenous DNA spontaneously. There is tremendous scope to improve transfection efficiency of spermatozoa while maintaining motility; this needs to be achieved in order to more easily use this technique in transgenesis. However, live-transfected bull spermatozoa clearly can incorporate exogenous DNA and should be usable in intracytoplasmic sperm injection protocols.

Sperm-mediated gene transfer

Since 1989, a new method for the production of transgenic animals has been available, namely sperm-mediated gene transfer (SMGT), based on the intrinsic ability of sperm cells to bind and internalise exogenous DNA molecules and to transfer them into the oocyte at fertilisation. We first described the SMGT procedure in a small animal model, with high efficiency reported in the mouse. In addition, we successfully adapted and optimised the technique for use in large animals; it was, in fact, highly efficient in the generation of human decay accelerating factor transgenic pig lines, as well as multigene transgenic pigs in which three different reporter genes, namely enhanced green fluorescent protein, enhanced blue fluorescent protein and red fluorescent protein, were introduced. The major benefits of the SMGT technique were found to be its high efficiency, low cost and ease of use compared with other methods. Furthermore, SMGT does not require embryo handling or expensive equipment. Sperm-mediated gene transfer could also be used to generate multigene transgenic pigs that would be of benefit as large animal models for medical research, for agricultural and pharmaceutical applications and, in particular, for xenotransplantation, which requires extensive genetic manipulation of donor pigs to make them suitable for grafting to humans.

Multi-transgenic pigs expressing three fluorescent proteins produced with high efficiency by sperm mediated gene transfer

Multi-gene transgenic pigs would be of benefit for large animal models in medical, agricultural, and pharmaceutical applications; in particular for xenotransplantation, where extensive genetic manipulation of donor pigs is required to make them suitable for organ grafting to humans. We used the sperm mediated gene transfer (SMGT) method to produce with high efficiency multi-gene transgenic pigs using three genes coding for fluorescent proteins: enhanced blue (EBFP), green (EGFP), and red (DsRed2). All three fluorescent proteins were expressed in 171 out of 195 normally developed morula/blastocysts examined at day 6 post insemination (88%). Genomic DNA of 18 piglets born from two litters was screened by PCR, showing that all piglets were transgenic with at least one gene, 7/18 piglets were triple transgenic, 7/18 double transgenic, and 4/18 single transgenic. Fluorescence in situ hybridization (FISH) analysis revealed multiple sites of integration of the transgenes. RNA and protein expression was found in muscle, heart, liver, hair, and peripheral blood mononuclear cells (PBMCs). These results show that SMGT is an effective method for introducing multiple genes into pigs as shown by the simultaneous expression of three fluorescent proteins.

Sperm-mediated gene transfer: applications and implications

Recent developments in studies of sperm-mediated gene transfer (SMGT) now provide solid ground for the notion that sperm cells can act as vectors for exogenous genetic sequences. A substantive body of evidence indicates that SMGT is potentially useable in animal transgenesis, but also suggests that the final fate of the exogenous sequences transferred by sperm is not always predictable. The analysis of SMGT-derived offspring has shown the existence of integrated foreign sequences in some cases, while in others stable modifications of the genome are difficult to detect. The appearance of SMGT-derived modified offspring on the one hand and, on the other hand, the rarity of actual modification of the genome, suggest inheritance as extrachromosomal structures. Several specific factors have been identified that mediate distinct steps in SMGT. Among those, a prominent role is played by an endogenous reverse transcriptase of retrotransposon origin. Mature spermatozoa are naturally protected against the intrusion of foreign nucleic acid molecules; however, particular environmental conditions, such as those occurring during human assisted reproduction, can abolish this protection. The possibility that sperm cells under these conditions carry genetic sequences affecting the integrity or identity of the host genome should be critically considered. These considerations further suggest the possibility that SMGT events may occasionally take place in nature, with profound implications for evolutionary processes.

Telomeres and telomerase activity in pig tissues

The current state of the art concerning telomeres and telomerase stems almost exclusively from the analysis of protozoa, yeast, and a small number of mammals. In the present study, we confirm that the pig telomeric sequence is indeed T(2)AG(3), as previously suggested. By making use of sequence analysis of pig telomeric DNA variant telomeric repeats in the medial region of the telomeres, interspersed with canonical T(2)AG(3) repeats, were identified. This telomere organization is similar to the one present in humans. Analysis of terminal restriction fragments showed that the majority of telomeres from different pig tissues are longer than in humans but shorter than in Mus musculus. Telomeres from spermatozoa were found to be longer, ranging in size between 13 and 44 kb. Most of the somatic pig tissues expressed significant levels of telomerase activity, a situation more similar to mouse and that contrasts with the one in humans and dog. Moreover, the analysis of sperm cells from different epididymal compartments of an adult animal showed that telomerase activity is absent in maturing spermatozoa, suggesting that sperm telomere elongation is restricted during spermatogenesis.

Gene Therapy: The Potential Applicability of Gene Transfer Technology to the Human Germline

The theoretical possibility of applying gene transfer methodologies to the human germline is explored. Transgenic methods for genetically manipulating embryos may in principle be applied to humans. In particular, microinjection of retroviral vector appears to hold the greatest promise, with transgenic primates already obtained from this approach. Sperm-mediated gene transfer offers potentially the easiest route to the human germline, however the requisite methodology is presently underdeveloped. Nuclear transfer (cloning) offers an alternative approach to germline genetic modification, however there are major health concerns associated with current nuclear transfer methods. It is concluded that human germline gene therapy remains for all practical purposes a future possibility that must await significant and important advances in gene transfer technology.

Human seminal plasma antibody-binding proteins

PROBLEM

The physiological role of antibody-binding proteins in human seminal plasma and the potential role of these proteins in infertility is relatively unknown.

METHOD OF STUDY

Literature on antibody-binding proteins.

RESULTS

Human seminal plasma has a diverse effect on immune function of the reproductive tracts. This review describes (1) the presence of receptors like proteins that can react with monoclonal antibodies against Fcgamma receptors III (Fcgamma RIII) but are distinctly different from Fcgamma RIII; (2) IgG binding factors (IgGBF), a group of low molecular weight proteins that are capable of binding human IgG; (3) other proteins that can bind antibodies, such as prolactin-inducible protein and three other novel proteins that we have discovered. These proteins potentially all have the ability to reduce the interactions between antisperm antibodies and effector components of the immune system, such as phagocytic cells.

CONCLUSIONS

Human seminal plasma contains proteins that can bind antibodies. However, to date our knowledge of these proteins especially, whether they have a physiological role in either the male and female reproductive tracts is limited.

Sperm mediated gene transfer in pig: Selection of donor boars and optimization of DNA uptake

Transgenic animals are produced primarily by microinjecting exogenous DNA into the male pronuclei of a zygote. Microinjection is successful in mice but not efficient in farm animals, limiting its general utility. We have pursued an alternative technology for producing transgenic animals: Sperm Mediated Gene Transfer (SMGT). Based on our finding that sperm cells bind and internalize exogenous DNA, we used sperm as a vector for transmitting, not only their own DNA, but also, the exogenously-introduced gene of interest to the zygote. SMGT is highly efficient (up to greater than 80%) and relatively inexpensive; it can be used in species refractory to microinjection, whenever reproduction is mediated by gametes. In this report, we describe the procedure for selection of sperm donors and optimization of DNA uptake that are the key steps for the successful outcome of SMGT. We found that the nominal parameters that boar sperm should possess to serve as a good vector for exogenous DNA are the quality of semen based on standard parameters used in conventional animal breeding programs (volume, concentration, presence of abnormal sperm cells, motility at time of collection, and high progressive motility after 2 hr) and the ability of the sperm cells to take up and internalize exogenous DNA. The results described provide significant advances in SMGT technology applied to pigs, so that transgenic pigs can be efficiently obtained. Mol.

Efficient production by sperm-mediated gene transfer of human decay accelerating factor (hDAF) transgenic pigs for xenotransplantation

A large number of hDAF transgenic pigs to be used for xenotransplantation research were generated by using sperm-mediated gene transfer (SMGT). The efficiency of transgenesis obtained with SMGT was much greater than with any other method. In the experiments reported, up to 80% of pigs had the transgene integrated into the genome. Most of the pigs carrying the hDAF gene transcribed it in a stable manner (64%). The great majority of pigs that transcribed the gene expressed the protein (83%). The hDAF gene was transmitted to progeny. Expression was stable and found in caveolae as it is in human cells. The expressed gene was functional based on in vitro experiments performed on peripheral blood mononuclear cells. These results show that our SMGT approach to transgenesis provides an efficient procedure for studies involving large animal models.

Viruses in the mammalian male genital tract and their effects on the reproductive system

This review describes the various viruses identified in the semen and reproductive tracts of mammals (including humans), their distribution in tissues and fluids, their possible cell targets, and the functional consequences of their infectivity on the reproductive and endocrine systems. The consequences of these viral infections on the reproductive tract and semen can be extremely serious in terms of organ integrity, development of pathological and cancerous processes, and transmission of diseases. Furthermore, of essential importance is the fact that viral infection of the testicular cells may result not only in changes in testicular function, a serious risk for the fertility and general health of the individual (such as a fall in testosteronemia leading to cachexia), but also in the possible transmission of virus-induced mutations to subsequent generations. In addition to providing an exhaustive account of the data available in these domains, this review focuses attention on the fact that the interface between endocrinology and virology has so far been poorly explored, particularly when major health, social and economical problems are posed. Our conclusions highlight the research strategies that need to be developed. Progress in all these domains is essential for the development of new treatment strategies to eradicate viruses and to correct the virus-induced dysfunction of the endocrine system.

Regulation of foreign DNA uptake by mouse spermatozoa

We have studied some features of DNA uptake in both mature and immature mammalian spermatozoa. Mature sperm collected from the cauda epididymis are able to incorporate foreign DNA in a buffer containing only salts and calcium. Immature spermatozoa, however, are unable to bind DNA. This seems to be caused by the lack of a functional receptor in the sperm membrane since once this membrane is disrupted by sonication, DNA can be detected in the postacrosome region of the sperm nucleus, matching the distribution of the mature spermatozoa. Comparison between the DNA binding proteins of mature and immature spermatozoa allowed us to identify two bands that could be part of the putative membrane receptor for the DNA. On the other hand, DNA uptake in mature sperm is prevented by the seminal plasma. We have identified two components of the seminal plasma, a calcium-dependent DNase present in the seminal vesicle fluid and several DNA binding proteins secreted by the ventral prostate, that could account for the inhibitory activity. Taken as a whole, our results indicate that DNA uptake by the mammalian spermatozoa is a very specific and highly regulated phenomenon.

Nucleosomal domains of mouse spermatozoa chromatin as potential sites for retroposition and foreign DNA integration

Exogenous DNA molecules are spontaneously taken up by sperm cells, internalized in nuclei, and eventually integrated in the sperm genome. The actual occurrence of the integration suggests that the sperm chromosomal DNA is not uniformly and tightly packed with protamines, implying the existence of genomic sites where the chromosomal DNA is accessible to foreign molecules. We have characterized a hypersensitive, nucleosomal subfraction of mouse sperm chromatin that is highly enriched in unmethylated retroposon DNA from a variety of families. Here we propose that both the integration of exogenous DNA molecules, and the endogenous retroposition activity, occur in the same site(s) of sperm chromatin.

Sperm-mediated DNA transfer to cells of the uterus and embryo

There is a paucity of information about sperm-mediated transmission of exogenous DNA to implanting embryos and cells of the reproductive tract. Preliminary experiments established that sperm has the capacity to actively take in exogenous DNA derived from HPV. In addition, blastocysts also take up exogenous HPV DNA, but in contrast to sperm, the process appears passive. DNA-carrying sperm migrating in an artificial glass tube or excised mouse bicornuate uteri transfected the blastocysts at the remote position using a flip-flop mechanism. There were preferential transmission of the types of HPV DNA but this was not attributed to the gene sequence or the size of the DNA fragments. The internalized DNA became undetectable unless continuous sperm bombardment or pricking took place. Mycoplasma vectors offer a novel way to enhance the transfection of blastocyst with exogenous DNA.

Sperm cell mediated transgenesis: a review

Transgenesis would be greatly streamlined if sperm cells could be used as transgene vectors. Attempts to 'force' sperm cells to take up transgenes may be more worthy of further study than 'autouptake' attempts. However, thorough proof of its effectiveness will be required if sperm cell-mediated gene transfer is to be accepted, given the evolutionary implications associated with the possibility of sperm cells being able to transfer exogenous DNA.

Sperm-mediated transgenesis

The idea of using a sperm cell for introducing exogenous DNA into an oocyte at the time of fertilization would be brilliant if only we were sure that it can be done. Since 1989, contradictory reports have appeared in the literature and, at present, no consensus has been reached on the topic. Given the potential impact of this method for the generation of transgenic animals, for both mammalian and non-mammalian species, this review summarizes what has been achieved in this field. While some aspects, such as the binding of DNA molecules to spermatozoa, have now a solid experimental base, others, such as the generation of real transgenic individuals, are still based on disputed evidence. A critical analysis of the most relevant data will be presented in order to provide the tools for an objective evaluation of the efficiency of this method.