Sperm-mediated Gene Transfer Research Articles

319 VALIDATION OF THE CARBOXYFLUORESCEIN DIACETATE ASSOCIATED WITH PROPIDIUM IODIDE FOR MURINE SPERM ACROSOME AND PLASMA MEMBRANE INTEGRITY

The spermatozoa is an ideal vehicle for genetic modification, production of transgenic animals, as well as a biotechnological tool for sperm-mediated gene transfer. However, in order to achieve successful sperm fertilization and exogenous DNA integration, it is necessary for viable cells to remain intact, allowing the sperm to penetrate the oocyte. Fluorescent probes allow evaluation of morphological and functional characteristics of cells, which can be evaluated separately or simultaneously. Therefore, the aim of this study was to validate the simultaneous evaluation of the integrity of plasma and acrosomal membranes of murine sperm using the probes carboxyfluorescein diacetate (CF) and propidium iodide (PI). In order to validate, a standard curve was performed. Sperm were obtained from epididymis and vas deferens from CD-1 mice (8 to 16 weeks of age). Recovered samples were diluted in PBS and then divided into 2 aliquots: one prepared with fresh semen (FS) and the other submitted to Percoll gradient (45%/90%) followed by flash-freezing in liquid nitrogen and thawing (FTP) to induce acrosome damage. Samples were prepared with the following average of FS:FTP: 100:0 (T100), 50 : 50 (T50), and 0 : 100 (T0). Samples were stained using 2 μL Hoescht 33342 (40 μLmL-1 in Dulbecco’s phosphate buffered saline), 3 μL of PI (0.5 mg mL-1 in PBS), 3 μL of CF (0.46 mg mL-1 in DMSO), and were incubated for 8 min at room temperature. After staining, the samples were placed on a slide, coverslipped, and evaluated immediately by epifluorescent microscopy. The Hoescht, PI, and CF fluorescence was detected using a filter with excitation at 352, 538, and 495 nm and emission at 455, 617, and 517 nm, respectively. Approximately 200 sperm cells per slide were examined and classified based on the fluorescence emitted from each probe. Spermatozoa CF+/IP- were considered as intact membranes, CF+/PI+ as acrosome membrane intact and plasma damaged, CF-/PI+ as damaged membranes, and CF-/PI- as acrosome membrane damaged and plasma intact. Hoeschst was used as positive dye. This experiment was replicated 6 times per group, and for statistical analyses, the data of plasma and acrosomal membrane integrity (dependent variables) in the treatments T0, T50, and T100 (independent variables) were submitted to simple linear regression analysis by STATVIEW software (SAS Institute Inc., Cary, NC, USA). The CFDA/PI probes were suitable for the analysis of acrosomal and membrane status of murine sperm and showed a high determination coefficient to plasma membrane integrity (R2 = 0.81; Y = 0.5412x + 6.375) and acrosome integrity (R2 = 0.85; Y = 0.5653x + 11.653). The described protocol was efficient for the simultaneous evaluation of plasma and acrosomal membrane integrity of murine spermatozoa, proving that CFDA can be employed to access acrosomal integrity as an alternative to FITC-PSA. Financial support: FAPESP.

Expression of hIGF-I in the silk glands of transgenic silkworms and in transformed silkworm cells

To express human insulin-like growth factor-I (hIGF-I) in transformed Bombyx mori cultured cells and silk glands, the transgenic vector pigA3GFP-hIGF-ie-neo was constructed with a neomycin resistance gene driven by the baculovirus ie-1 promoter, and with the hIGF-I gene under the control of the silkworm sericin promoter Ser-1. The stably transformed BmN cells expressing hIGF-I were selected by using the antibiotic G418 at a final concentration of 700-800 microg/mL after the BmN cells were transfected with the piggyBac vector and the helper plasmid. The specific band of hIGF-I was detected in the transformed cells by Western blot. The expression level of hIGF-I, determined by ELISA, was about 7800 pg in 5x10(5) cells. Analysis of the chromosomal insertion sites by inverse PCR showed that exogenous DNA could be inserted into the cell genome randomly or at TTAA target sequence specifically for piggyBac element transposition. The transgenic vector pigA3GFP-hIGF-ie-neo was transferred into the eggs using sperm-mediated gene transfer. Finally, two transgenic silkworms were obtained after screening for the neo and gfp genes and verified by PCR and dot hybridization. The expression level of hIGF-I determined by ELISA was about 2440 pg/g of silk gland of the transgenic silkworms of the G1 generation.

The Effect of Retroviral Vector on Uptake of Human Lactoferrin DNA by Yak (Bos Grunniens) Spermatozoa and their Fertilizability In Vitro

The objectives of this study were to evaluate the transfection effectiveness of retroviral vector PLNCX2 in yak sperm-mediated gene transfer (SMGT) and the effect of SMGT on sperm motility and fertilizability. Human lactoferrin (hLF) DNA was ligated into PLNCX2 to construct recombinant plasmid PLNCX2-hLF, then, using PLNCX2-hLF+FuGene 6 to generate SMGT yak spermatozoa for fertilizing bovine oocytes. The result showed that DNA-binding rate increased with the extension of incubation period and DNA treatment did not decrease sperm motility. Oocytes inseminated with SMGT-spermatozoa had a lower (P < 0.05) cleavage rate (57.7%) than the control (73.4%), but development up to blastocyst stage was not different (26.8 vs. 31.7%). It appears that PLNCX2 is useful for generating transgenic yaks by SMGT.

Sperm-mediated gene transfer–treated spermatozoa maintain good quality parameters and in vitro fertilization ability in swine

A simple and efficient method for producing multitransgenic animals is required for medical and veterinary applications. Sperm-mediated gene transfer (SMGT) is an effective method for introducing multiple genes into pigs (Sus, Sus scrofa). The major benefits of this technique are the high efficiency, low cost, and ease of use compared with that of other methods: Sperm-mediated gene transfer does not require embryo handling or expensive equipment. The aim of this study was to investigate the influence of SMGT treatment and exogenous DNA uptake on sperm quality. Even after a coincubation with a 20-fold larger amount (100 μg/mL) of DNA than usual (5 μg/mL), sperm quality parameters were not significantly affected, confirming the hypothesis that the SMGT protocol itself or the amount of bound DNA do not compromise the possibility of an extended employment of SMGT. More importantly, we found that semen used for in vitro fertilization 24 h after DNA uptake gave good cleavage (60% vs. 58%, treated vs. control) and developmental rates definitely positive (41% vs. 48%, treated vs. control). These good results are connected to a competitive efficiency of transformation (62%) due to the numerous improvements in SMGT technique. We demonstrate that SMGT-treated spermatozoa retain good quality and fertilization potential for at least 24 h, expanding the possibility to apply transgenesis in field conditions in swine, where the greatest hurdles are fertilization timing and plain procedure.

Exogenous DNA Uptake of Boar Spermatozoa by a Magnetic Nanoparticle Vector System

The sperm-mediated gene transfer method is applicable to transgenesis in many species that use spermatozoa for reproduction recently, which has been shown various results. In the current study, we show that transgenic porcine embryos can be efficiently produced by employing a simple transfection method that uses magnetic nanoparticles (MNPs). The complexes formed between plasmid DNA and MNPs were bounded on ejaculated boar spermatozoa at a higher efficiency compared to methods using DNA alone or lipofection. Using confocal microscopy, rhodamine fluorophore-labelled MNPs were detected on external surfaces of the spermatozoa membrane, which were bounded on zona pellucida of in vitro maturated oocyte during in vitro fertilization. Electron microscopy revealed that clusters of MNPs were detected in inside of plasma membrane and nucleus of the spermatozoa head. Additionally, we found that magnetofected boar spermatozoa could be fertilized with oocytes in vitro and that the resulting gene of green fluorescent protein was detected in fertilized eggs by genomic PCR analysis. Taken together, these results suggest that MNPs can be used to efficiently introduce a transgene into embryo via spermatozoa.

Relationships of chemical composition, quantity of milt to fertility and hatchability of Clarias gariepinus (Burchell, 1822).

The biochemical composition of milt and the effect of its varying quantity on fertility and hatchability of Clarias gariepinus (African catfish) eggs were investigated. The study aimed at determining the right quantity of milt that can be used to fertilize certain quantity of eggs. The study further examined the effect of varying volume of milt on the water quality during the incubation of C. gariepinus eggs in order to provide baseline information on chemical composition, which can be used as a basis for sperm-mediated gene transfer. Result obtained from this study showed that 0,035ml of milt gave the best hatchability 2041±90.9, while 0.175ml of milt gave the least hatchability 1341± 384.2 .There was a positive significant correlation between the quantity of milt used and hatchability (P< 0.05) and there was a significant difference among the treatments and within the hour of the experiment (P< 0.05). The investigation revealed that the quantity of milt used for artificial reproduction in fish significantly affect water quality used for incubation (P

Sperm mediated human coagulation factor VIII gene transfer and expression in transgenic mice.

B-domain deleted human coagulation factor VIII cDNA (BDD-hFVIIIcDNA) transgenic mice were produced by using sperm mediated gene transfer (SMGT). The transcription and expression of human FVIII in transgenic mice were also investigated. Sperm were isolated from caudae epididymides of male C57BL/6 mice and transfected with linearized RC/RSV-BDDhFVIIIcDNA plasmid, and subsequently used to fertilize female mice via artificial insemination in vivo. After birth, F0 progeny were identified by PCR and Southern blotting for BDD-hFVIIIcDNA transgenic mice. F1 progeny were subsequently derived from a male transgenic F0 mouse and a normal C57BL/6 female mouse. The F1 progeny were then identified as BDD-hFVIIIcDNA transgenic mice by Southern blotting. The transcription and expression of BDDhFVIIIcDNA in transgenic mice were determined by northern blotting, western blotting and immunohistochemical staining. Blood was also collected from both F0 and F1 progeny to detect hFVIII:Ag and anti-hFVIII inhibitors. A total of 9 F0 and 8 F1 progeny were delivered, in which 3 F0 and 2 F1 progeny were identified to have BDD-hFVIIIcDNA. The transcription and expression of BDD-hFVIIIcDNA were found to exist in the liver and kidneys of all transgenic mice. HFVIII:Ag in plasma of the transgenic F0 progeny was 31.95 ng/ml, 23.52 ng/ml and 26.36 ng/ml respectively, whilst the F1 transgenic mice showed results of 18.82 ng/ml and 12.16 ng/ml. Anti-hFVIII inhibitors were negative in both F0 and F1 progeny. Human FVIII gene transgenic mice can be produced by the SMGT technique and express human FVIII protein in their bodies.

Sperm mediated human coagulation factor VIII gene transfer and expression in transgenic mice.

B-domain deleted human coagulation factor VIII cDNA (BDD-hFVIIIcDNA) transgenic mice were produced by using sperm mediated gene transfer (SMGT). The transcription and expression of human FVIII in transgenic mice were also investigated. Sperm were isolated from caudae epididymides of male C57BL/6 mice and transfected with linearized RC/RSV-BDDhFVIIIcDNA plasmid, and subsequently used to fertilize female mice via artificial insemination in vivo. After birth, F0 progeny were identified by PCR and Southern blotting for BDD-hFVIIIcDNA transgenic mice. F1 progeny were subsequently derived from a male transgenic F0 mouse and a normal C57BL/6 female mouse. The F1 progeny were then identified as BDD-hFVIIIcDNA transgenic mice by Southern blotting. The transcription and expression of BDDhFVIIIcDNA in transgenic mice were determined by northern blotting, western blotting and immunohistochemical staining. Blood was also collected from both F0 and F1 progeny to detect hFVIII:Ag and anti-hFVIII inhibitors. A total of 9 F0 and 8 F1 progeny were delivered, in which 3 F0 and 2 F1 progeny were identified to have BDD-hFVIIIcDNA. The transcription and expression of BDD-hFVIIIcDNA were found to exist in the liver and kidneys of all transgenic mice. HFVIII:Ag in plasma of the transgenic F0 progeny was 31.95 ng/ml, 23.52 ng/ml and 26.36 ng/ml respectively, whilst the F1 transgenic mice showed results of 18.82 ng/ml and 12.16 ng/ml. Anti-hFVIII inhibitors were negative in both F0 and F1 progeny. Human FVIII gene transgenic mice can be produced by the SMGT technique and express human FVIII protein in their bodies.

Effect of sperm treatment on efficiency of EGFP-expressing porcine embryos produced by ICSI-SMGT

Intracytoplasmic sperm injection–sperm-mediated gene transfer (ICSI-SMGT) is a useful tool for the production of transgenic mice but is still rather inefficient in farm animals. In the current study, we evaluated the effect of the sperm treatments on the efficiency for producing enhanced green fluorescent protein (EGFP)-expressing pig embryos by ICSI-SMGT. Four different sperm treatments were assayed: (1) fresh (control), (2) frozen-thawing (FT), (3) quick freezing without cryoprotectant agents (QF), and (4) Triton X-100 treatment (TX-100). First, we evaluated the DNA-binding ability and the viability of sperm under the different treatments coincubated with exogenous DNA (EGFP) by flow cytometry. Second, we evaluated the embryo production rate and the efficiency in transgene expression in embryos after using these spermatozoa to fertilize oocytes by ICSI. Sperm treatment significantly increased DNA-binding capacity but reduced sperm viability compared with that of the control group. Treatments damaging the spermatozoa's membranes (QF and TX-100) resulted in a greater capacity of sperm binding exogenous DNA than that after FT treatment (P < 0.01). Similar rates of EGFP-expressing embryos were obtained from the control, FT, and TX-100 groups (37.04 ± 3.52%, 43.54 ± 5.41%, and 29.03 ± 8.29%, respectively), but were significantly higher in the QF group (80.43 ± 5.91%). These results demonstrate that the integrity of the sperm plasma membrane plays a critical role in DNA interaction, and altered plasma membranes facilitate interactions between an injected exogenous DNA and the sperm chromatin. However, severe sperm treatments such as QF and TX-100 may damage the sperm nucleus, induce DNA fragmentation, and/or lead to chromosomal breakage with a detrimental effect on further embryonic development.

Exogenous DNA influencing fertilization of goat sperm cells and expression in early embryos

Our early study found that goat spermatozoa could spontaneously take up foreign DNA and vary in capabilities of spermatozoa from different donors to bind and internalize exogenous DNA. In this study, three goats with considerable differences of capability were used to investigate the effect of exogenous DNA on goat spermatozoa, and feasibility and efficiency of transgenic embryo production by sperm-mediated gene transfer method. The viability, acrosomal reaction frequencies and cleavages were decreased in the groups co-cultured with exogenous DNA, compared with the control groups, and the range of decrease was correlated with the capability of sperm cells up-take foreign DNA. After fertilizing with co-cultured spermatozoa, GFP gene was introduced into oocytes and expressed in early embryos. However, different efficiencies of transgenic embryos appeared in sperm donors (P<0.05). GFP gene was detected in 16.2% (25/154), 5.3% (4/76), and 0% (0/36) embryos, respectively, when high, middle and low capability of sperm donors were used. But only 6.5% (10/154) embryos from high capability sperm donor expressed GFP. Our results demonstrate that selecting high capability of sperm donor is a key step for improving efficiency of sperm mediated-gene transfer method. However, the adverse influence of foreign DNA on spermatozoa needs to be further studied.

Evaluation of swine fertilisation medium (SFM) efficiency in preserving spermatozoa quality during long-term storage in comparison to four commercial swine extenders

In pig production, artificial insemination is widely carried out and the use of fresh diluted semen is predominant. For this reason, there are increasing interests in developing new extenders and in establishing the optimal storage conditions for diluted spermatozoa. In the last few decades, we utilised a homemade diluent (swine fertilisation medium (SFM)) for spermatozoa manipulation and biotechnological application as the production of transgenic pigs utilising the sperm-mediated gene transfer technique. The purpose of the present study is therefore to analyse the ability of SFM, in comparison to four commercial extenders, in preserving the quality of diluted boar semen stored at 16.5°C till 15 days. We utilised some of the main predictive tests as objectively measured motility, acrosome and sperm membrane integrity, high mitochondrial membrane potential and pH. Based on our in vitro study, SFM could be declared as a good long-term extender, able to preserve spermatozoa quality as well as Androhep Enduraguard for up to 6 to 9 days and more.

303 EFFECT OF THE PRESENCE OF EXOGENOUS DNA AND RECOMBINASE-A PROTEIN ON THE BOAR SPERM FUNCTIONALITY

Since 1989, a new method for the production of transgenic animals has been available, namely sperm-mediated gene transfer based on the intrinsic ability of sperm cells to bind exogenous DNA molecules and to transfer them into the oocyte. It has been reported that coating exogenous DNA with recombinase-A protein (RecA) may improve the efficiency of transgenic embryo production (Garcia-Vazquez FA et al. 2006 Reprod. Domest. Anim. 41, 338). The objective of this study was to investigate the effect of the presence of DNA and DNA-RecA complex on the sperm functionality. Spermatozoa were incubated with linealized plasmid 5.7 kb enhanced green fluorescent protein (DNA) or RecA-DNA complexes (40:1 or 40:3 protein:DNA w/w) in a relation of 108 cells mL–1 and 5 to 15 μg of DNA mL–1. Sperm viability, membrane lipid disorder, reactive oxygen species (ROS) generation, and motion parameters were evaluated by flow cytometry and computer-assisted semen analysis (CASA) for control (no DNA), DNA (5 μg), RecA 5 (5 μg), and RecA 15 (15 μg). A total of 5 replicates were used. Data were analyzed by ANOVA. The sperm viability measured by propidium iodide staining was significantly reduced by the presence of RecA DNA complexes (viable cells 77.5a v. 69.4ab v. 55.6b v. 35.8c%; P &lt; 0.01). Lipid membrane disorder (measured by merocyanine 540 and Yopro 1 staining) were significantly reduced in the group with high exogenous DNA concentration (RecA 15 group), with a reduction of percentage of viable cells and low lipid disorder (67.4a v. 60.0a v. 51.5a v. 24.3b; P &lt; 0.01). However, the ROS generation (measured by 2′,5′-dichlorofluorescein diacetate) was not different in the different experimental groups (fluorescent units 20.3 v. 25.5 v. 26.2 v. 13.9; P = 0.36). The motion parameters measured by CASA were affected by the presence of DNA-RecA complexes with a significant reduction in percentage of motile and progressive motile cells in the group RecA 15 (% progressive motility 46.7a v. 43.9a v. 46.8a v. 20.3b; P &lt; 0.01). Also, it was detected a change in the pattern of motility with an increase in the sperm velocities (velocity average path, velocity straight line, and VCL) in groups DNA and RecA 5 and a reduction of these values when the concentration of DNA was 15 μg mL–1 (VCL μm s–1 97.5a v. 106.4b v. 109.1b v. 58.1c; P &lt; 0.01). The motions parameters (LIN, STR, WOB, ALH, BCF) showed significant lower values for the group RecA 15. These results shown that the presence of DNA and RecA-DNA complex modified the pattern of motility and reduced the viability and functionality of the boar sperm in a concentration dose way. It is necessary to select an adequate DNA and RecA concentration that would protect the sperm functionality and optimize the binding process. Supported by BIOCARM 10BIO2005/01-6463 and AGL2006-03495.

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.

Evaluation of DNase activity in seminal plasma and uptake of exogenous DNA by spermatozoa of the Brazilian flounder Paralichthys orbignyanus

Sperm mediated gene transfer (SMGT) has been successfully used in mammals, amphibians, birds, and some invertebrates. In fish, this methodology has failed or had poor efficiency for the production of transgenic specimens, presumably because the processes regulating the interaction between spermatozoa and exogenous DNA are not well understood. Therefore, the objective was to develop a SMGT protocol for the Brazilian flounder Paralichthys orbignyanus, with an emphasis on the role of seminal plasma DNase on exogenous DNA uptake by fish spermatozoa. In this study, there was strong DNase activity in the seminal plasma of P. orbignyanus; however, this DNase activity was decreased or eliminated by washing the spermatozoa with solutions containing EDTA (DNase activity was completely inhibited by 40 mM EDTA). Three washing solutions were tested, all of which maintained sperm quality. Moreover, it was determined that the no more than 50 ng of exogenous DNA/10 6 cells should be used for SMGT in fish. Finally, it was demonstrated that fish spermatozoa were capable of spontaneous uptake of exogenous DNA after elimination of DNase activity; this was confirmed by exogenous DNA amplification (PCR using sperm genomic DNA as a template) after DNase I treatment. We concluded that whereas DNase activity was an important obstacle for exogenous DNA uptake by fish spermatozoa; controlling this activity improved the efficiency of SMGT in fish.

The negative effects of exogenous DNA binding on porcine spermatozoa are caused by removal of seminal fluid

Sperm-mediated gene transfer (SMGT) might become the most efficient and cost effective technique to generate transgenic animals, which will significantly increase their application in biomedical research and in commercial production. Despite some successes, the technique has remained controversial for almost 20 years and despite number of studies the reasons for poor reproducibility of this promising technology has not been understood. We suggest that the reason for poor reproducibility is the presence of natural defences against exogenous DNA invasion acting in spermatozoa or in embryo. Based on previous reports we have investigated the effect of foreign DNA binding on spermatozoa by monitoring motility, viability and genomic DNA damage. Evaluation of DNA binding in sperm collected from 16 boars demonstrated that 28–45% of the added pEGFP plasmid was bound to spermatozoa with 9–32% being internalized in sperm nucleus. In agreement with previous reports, our results demonstrated that the pEGFP-treated sperm show an average a 2-fold decrease in motility ( p < 0.05), 5-fold decrease in progressive motility ( p < 0.05), and 1.4-fold increase in number of sperm with highly damaged DNA ( p < 0.05) as detected by Comet assay. In contrast with previous reports, we demonstrate that all such changes were associated with the removal of seminal plasma during the washing step and not with foreign DNA binding per se. We suggest that poor reproducibility of SMGT most likely result from selection against DNA-loaded sperm at later stages of fertilization.

Sperm-mediated 'reverse' gene transfer: a role of reverse transcriptase in the generation of new genetic information

Sperm-mediated gene transfer (SMGT) is a procedure through which new genetic traits are introduced in animals by exploiting the ability of spermatozoa to take up exogenous DNA molecules and deliver them to oocytes at fertilization. The interaction of exogenous DNA with sperm cells is a regulated process mediated by specific factors; among those, a reverse transcriptase (RT) activity plays a central role in SMGT. 'Retro-genes' are generated either through reverse transcription of exogenous RNA internalized in spermatozoa, or through sequential transcription, splicing and reverse transcription of exogenous DNA. The resulting retro-genes are delivered to oocytes and transmitted to embryos and born animals as low-copy, transcriptionally competent, extrachromosomal structures capable of determining new phenotypic traits. Retro-genes can be further transmitted through sexual reproduction from founders to their F1 progeny: new genetic and phenotypic features, unlinked to chromosomes, can thus be generated and inherited in a non-Mendelian ratio. We have called this phenomenon sperm-mediated 'reverse' gene transfer (SMRGT). Thus, a RT-mediated machinery operates in sperm cells and is responsible for the genesis and non-Mendelian propagation of new genetic information. The features of RT-generated traits elicited in SMRGT resemble those characterized in recent studies of RNA-mediated inheritance of extra-genomic information.

Liposome‐mediated uptake of exogenous DNA by equine spermatozoa and applications in sperm‐mediated gene transfer

Sperm-mediated gene transfer has been reported as a method for production of transgenic animals in a variety of species, and this technique represents a possible method for production of transgenic equids. To evaluate the uptake of exogenous DNA (enhanced green fluorescent protein; pEGFP) by equine spermatozoa and to assess the ability of transfected spermatozoa to introduce this transgene into early equine embryos. To evaluate incorporation of pEGFP into equine spermatozoa, washed spermatozoa were incubated with 32P-pEGFP, with or without lipofection. Spermatozoa were also transfected with fluorescently-labelled DNA (Alexa647-pEGFP) and changes in sperm viability and DNA uptake were assessed. Mares were inseminated with pEGFP-transfected spermatozoa and embryos recovered. Expression of pEGFP was assessed by epifluorescence microscopy of embryos, and the presence of pEGFP DNA and mRNA was assessed by PCR and RT-PCR, respectively. Liposome-mediated transfection increased the incorporation of 32P-pEGFP into spermatozoa compared to controls. Flow cytometric evaluation of spermatozoa after transfection with Alexa647-pEGFP revealed a linear increase in the proportion of live, Alexa647+ spermatozoa with increasing DNA concentrations. After insemination with transfected spermatozoa, 8 embryos were recovered. There was no evidence of EGFP expression in the recovered embryos; however, PCR analysis revealed evidence of the pEGFP transgene in 2 of 5 embryos analysed. The incorporation of exogenous DNA by equine spermatozoa was enhanced by liposome-mediated transfection and this did not adversely affect sperm viability, acrosomal integrity or fertility. Although the EGFP transgene was detected in a proportion of Day 7-10 embryos, there was no evidence of expression of EGFP in these embryos. Sperm-mediated gene transfer offers a potential technique for the generation of transgenic equids.

Sperm-mediated Gene Transfer in the Chinese Honeybee, Apis cerana cerana (Hymenoptera: Apidae)

Transgenic Apis cerana cerana were produced by sperm-mediated gene transfer (SMGT). In the experiment, the foreign DNA was linearized and introduced with sperm during the instrumental insemination of virgin queen. The descendants of the experimental colonies were analyzed. In the green fluorescent-positive offspring, green fluorescence was observed for 1- to 2-day-old larvae, the predicted fragment was isolated by means of PCR amplification of genomic DNA and the expression of transferred genes was confirmed at transcriptional level by reverse transcription-polymerase chain reaction. These results showed that the exogenous gene could be integrated in a fraction of the germ line cells of the queen Apis cerana cerana and transmitted to offspring by SMGT.

Genomic DNA Damage in Mouse Transgenesis1

Creating transgenic mammals is currently a very inefficient process. In addition to problems with transgene integration and unpredictable expression patterns of the inserted gene, embryo loss occurs at various developmental stages. In the present study, we demonstrate that this loss is due to chromosomal damage. We examined the integrity of chromosomes in embryos produced by microinjection of pronuclei, intracytoplasmic sperm injection (ICSI), and in vitro fertilization (IVF)-mediated transgenesis, and correlated these findings with the abilities of embryos to develop in vitro and yield transgenic morulas/blastocysts. Chromosomal analysis was performed after microinjection of the pronuclei in zygotes, as well as in parthenogenetic and androgenetic embryos. In all the pronuclei injection groups, significant oocyte arrest and increased incidence of chromosome breaks were observed after both transgenic DNA injection and sham injection. This indicates that the DNA damage is a transgene-independent effect. In ICSI-mediated transgenesis, there was no significant oocyte arrest. The observed chromosomal damage was lower than that after pronuclei microinjection in zygotes and was dependent upon the presence of exogenous DNA. The occurrence of DNA breaks, as measured by comet assay performed on the sperm prior to ICSI, showed that DNA damage was present in the sperm before fertilization. Embryonic development in vitro and transgene expression at the morula/blastocyst stage were higher in ICSI-mediated transgenesis than after microinjection of pronuclei into zygotes. Sperm-mediated gene transfer via IVF did not affect chromosome integrity, allowed good embryo development, but did not yield any transgenic embryos. The present study demonstrates that DNA damage occurs after both the microinjection of pronuclei and ICSI-mediated transgenesis, albeit through different mechanisms.

A Brief Overview of Transgenic Farm Animals

Transgenesis offers new possibilities to rapidly modify the genome of living organisms. The application of transgenesis to farm animals faces many problems, more than those observed in the transgenesis of laboratory animals, as there are currently many different techniques available to obtain transgenic animals, which all have problems regarding low efficiency and high costs. When these techniques are applied to farm animals the problems concerning transgenesis are multiplied. Two main techniques, male pronuclear microinjection and sperm mediated gene transfer, utilised in farm animal transgenesis, are briefly presented. The improvement of these techniques and the employment of other biotechnologies such as cloning, could expand the uses of transgenic farm animals for human health.