Effects of electropermeabilization on the association of foreign DNA with pig sperm

A Critical Review of Electroporation as A Plasmid Delivery System in Mouse Skeletal Muscle

The gene delivery to skeletal muscles is a promising strategy for the treatment of both muscular disorders (by silencing or overexpression of specific gene) and systemic secretion of therapeutic proteins. The use of a physical method like electroporation with plate or needle electrodes facilitates long-lasting gene silencing in situ. It has been reported that electroporation enhances the expression of the naked DNA gene in the skeletal muscle up to 100 times and decreases the changeability of the intramuscular expression. Coelectransfer of reporter genes such as green fluorescent protein (GFP), luciferase or beta-galactosidase allows the observation of correctly performed silencing in the muscles. Appropriate selection of plasmid injection volume and concentration, as well as electrotransfer parameters, such as the voltage, the length and the number of electrical pulses do not cause long-term damage to myocytes. In this review, we summarized the electroporation methodology as well as the procedure of electrotransfer to the gastrocnemius, tibialis, soleus and foot muscles and compare their advantages and disadvantages.

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.

The impact of exogenous DNA on the structure of sperm of olive flounder (Paralichthys olivaceus)

Sperm-mediated gene transfer (SMGT) is a promising transgenic technology that relies on the capability of sperm to internalize exogenous DNA. In marine fish, however, the interaction between sperm and exogenous DNA appears to be deficient. Here, we demonstrated significant DNase activity in the seminal plasma of the olive flounder. When incubated with naked-DNA, the spermatozoa lost their structural integrity, including the head, mitochondria and flagellum, in an incubation time-dependent manner. However, internalization of a liposome-DNA complex resulted in the structural integrity of the spermatozoa being maintained, even when using incubation times of up to 50min. We concluded that in the olive flounder, SMGT is possible by integrating liposome-DNA complexes, rather than naked-DNA alone, into the sperm. In brief, removal of the seminal plasma and packaging the exogenous DNA were necessary for successful SMGT in the olive flounder.

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.

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.

The making of "transgenic spermatozoa"

The processes of making transgenic animals by microinjecting DNA into the pronucleus of a fertilized oocyte or after the transfection of embryonic stem cells are now well established. However, attempts have also been made, with varying degrees of success, to use spermatozoa as a vector for transgenesis in mammals and other vertebrates during the last decade. A number of different approaches for making transgenic spermatozoa have been developed. These include directly incubating mature, isolated spermatozoa with DNA or pretreating mature, isolated spermatozoa before assisted fertilization. Microinjection procedures have also been established to transfect male germ cells directly in vivo within the seminiferous tubules or to reimplant previously isolated male germ cells submitted to in vitro transfection into a recipient testis. The latter two techniques present the advantage of being able to create transgenic progeny simply by mating with wild-type females, which avoids the possibility of interference or damage as a result of assisted fertilization or the manipulation of embryos. The different aspects of sperm-mediated transgenesis are presented.

Interaction of exogenous DNA with the nuclear matrix of live spermatozoa

Sperm chromatin is a highly organized array of protamines and DNA, with the protamines serving to tightly condense the DNA into a compact, defined structure. We have previously demonstrated that the sperm nucleus is an ordered library of DNA organized into functional zones, such as the nuclear matrix and nuclear annulus. Other laboratories have suggested that mouse spermatozoa can interact with exogenous pSV2CAT plasmid DNA. In this work, we explored this interaction and examined the subcellular localization of the exogenous DNA. We found a repeatable association of exogenous DNA with a specific region of the sperm nuclear matrix. This region of the nucleus correlates with the equatorial segment of the sperm head. This interaction requires only a defined fertilization media, transfection quality DNA, and incubation with spermatozoa.

Sperm-mediated gene transfer studies on zebrafish in Singapore

This paper describes the work conducted in the Department of Biological Sciences, National University of Singapore; on sperm-mediated gene transfer in zebrafish. This study began by carrying out direct interaction experiments of pUSVCAT reporter DNA with spermatozoa. Other constructs, including pXGH5, pMTL, pRSVL and pGEM-luc, were subsequently used. The different constructs were taken up by sperm cells with comparable efficiencies. In general, no reporter gene expression, Mendelian inheritance, or evidence of genomic integration of the foreign sequences were obtained. However, transmission of the reporter DNA through generations was observed. DNA uptake by sperm cells was shown using FISH and was enhanced by electroporation. The potential use of more recent approaches, such as REMI and ICSI are explored. Future research directions are discussed.

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.

Identification of capacitation-associated phosphoproteins in porcine sperm electroporated with ATP-gamma-(32)P

Our objectives were to incorporate ATP-gamma-(32)P into boar sperm to radiolabel endogenous phosphoproteins and compare phosphorylation patterns from sperm incubated in capacitating (CM) and non-capacitating conditions (NCM). Sperm were electroporated (1000 V/cm, 125 microF/cm, 65 Omega/cm, 0.3 msec) with ATP-gamma-(32)P which moderately decreased sperm viability (P < 0.01), but did not affect motility (P = 0.34) or the appearance of spontaneous acrosome reactions (P = 0.49). Sperm incubated in CM for 3 hr underwent capacitation, determined by the ability to undergo ionophore-induced acrosome reactions (P </= 0.05). Furthermore, more sperm in CM than in NCM exhibited chlortetracycline (CTC) pattern B (capacitated) fluorescence (P </= 0.01). SDS-PAGE, autoradiography and phosphoimagery of extracted, (32)P-labeled sperm proteins revealed a subset of phosphoproteins (Mr 28,000-60,000) from cells incubated in CM, whereas only two phosphorylated proteins were evident from sperm in NCM (44 and 57 kDa). The appearance of phosphoproteins increased concomitant with capacitation (P </= 0.05). In NCM, the 44 kDa protein was unaffected by time (P > 0.05) and the 57 kDa phosphoprotein increased after capacitation (P </= 0.05). Computer-assisted analysis revealed that the percentage of motile sperm in either medium decreased with time, and CM only transiently maintained motility over NCM (P >/= 0.02). ATP-gamma-(32)P can, therefore, be incorporated into porcine sperm to radiolabel endogenous phosphoproteins, and the different profiles from sperm incubated in NCM versus CM suggest that capacitation is mediated by signaling events involving protein phosphorylation.

Electric pulse-induced precipitation of biological macromolecules in electroporation

We found that electric discharge through solution of biological macromolecules (DNA, RNA and proteins) causes precipitation of significant portions of these macromolecules. This precipitation is a consequence of the interaction of biological macromolecules with the metal ions solubilized from the anode plate by the electric pulse, and occurs in both absence and presence of the cells in poration medium. Precipitated fractions of macromolecules sediments at the centrifugation speed used to pellet eukaryotic cells and does not dissolve when washed with buffer. Our data indicate a complication of the direct evaluation of electroporation efficiency based on the assumption that electroporated biological macromolecules which remain associated with the cells after several washes, are successfully electroinjected into the cytoplasm of cells.

Spermatozoa, DNA binding and transgenic animals

The idea that sperm cells could be used as an effective tool for introducing exogenous DNA into an oocyte at fertilization is generally regarded with scepticism. However, in recent years, several investigators have been working on different aspects of this intriguing research topic. In the present review, their results are summarised and discussed. Sections have been dedicated to the way DNA molecules bind to spermatozoa of different species, to the events regulating such binding, to the fate of the DNA within sperm cells, and to the attempts made to produce transgenic animals with this method. The data available on the interaction between DNA and spermatozoa begin to explain how this event takes place and how it is regulated. However, the stable integration of exogenous genes into the genome of adult animals mediated by sperm cells is a very rare event, although several reports describe forms of partial success. Available evidence suggests that changes to the DNA molecules, occurring mostly within the oocyte, represents the limiting step in the production of transgenic animals using spermatozoa as vectors of exogenous genes. At present there are not enough data to understand what happens to sperm-associated DNA upon its entrance into the oocyte at fertilization. Therefore, it has not yet been resolved whether sperm-mediated gene transfer is a possible way to manipulate the genome or if evolution has imposed some unsurpassible barriers to its use.

The fate of foreign DNA associated with pig sperm following the in vitro fertilization of zona-free hamster ova and zona-intact pig ova

The aim of this study was to determine the fate of foreign DNA molecules bound to porcine sperm that had been capacitated and acrosome reacted in vitro using calcium ionophore and then used in the in vitro fertilization of zona-free hamster ova and zona-intact pig ova. Fluoresceinated Pisum sativum agglutinin (PSA) labeling was used to differentiate between acrosome-intact and acrosome-reacted sperm. This revealed that up to 80% of the sperm treated with calcium ionophore were acrosome reacted. Up to 70% of these acrosome-reacted sperm were labeled with the foreign DNA at the post-acrosomal region. Following association of DNA with the acrosome-reacted sperm, insemination droplets were prepared and zona-free hamster oocytes or zona-intact pig oocytes were added. The gametes were allowed to interact and then fixed and stained to visualize decondensed sperm heads that had penetrated into the oocytes. The sperm were stained with streptavidin peroxidases to detect the biotinylated foreign DNA bound to the decondensed heads. These studies revealed that 54% of fertilized hamster and pig oocytes contained decondensed sperm that had retained the post-acrosomal pattern of bound foreign DNA. After incubation with DNA-associated sperm, the oocytes were washed and cultured for 15-17 h. After fixation, up to 30% of hamster oocytes and 10% of porcine oocytes were found to contain sperm pronuclei. However, using the streptavidin peroxidase detection system, it was not possible to determine if any of these pronuclei contained the foreign DNA.