The making of "transgenic spermatozoa"

From Ancient to Emerging Infections: The Odyssey of Viruses in the Male Genital Tract

The male genital tract (MGT) is the target of a number of viral infections that can have deleterious consequences at the individual, offspring, and population levels. These consequences include infertility, cancers of male organs, transmission to the embryo/fetal development abnormalities, and sexual dissemination of major viral pathogens such as human immunodeficiency virus (HIV) and hepatitis B virus. Lately, two emerging viruses, Zika and Ebola, have additionally revealed that the human MGT can constitute a reservoir for viruses cleared from peripheral circulation by the immune system, leading to their sexual transmission by cured men. This represents a concern for future epidemics and further underlines the need for a better understanding of the interplay between viruses and the MGT. We review here how viruses, from ancient viruses that integrated the germline during evolution through old viruses (e.g., papillomaviruses originating from Neanderthals) and more modern sexually transmitted infections (e.g., simian zoonotic HIV) to emerging viruses (e.g., Ebola and Zika) take advantage of genital tract colonization for horizontal dissemination, viral persistence, vertical transmission, and endogenization. The MGT immune responses to viruses and the impact of these infections are discussed. We summarize the latest data regarding the sources of viruses in semen and the complex role of this body fluid in sexual transmission. Finally, we introduce key animal findings that are relevant for our understanding of viral infection and persistence in the human MGT and suggest future research directions.

Evaluating bovine sperm transfection using a high-performance polymer reagent and assessing the fertilizing capacity of transfected spermatozoa using an in vitro fertilization technique

Abstract. Sperm-mediated gene transfer (SMGT) has been considered as an innovative device for transgenesis on a mass scale by taking advantage of live spermatozoa to transfer exogenous DNA. However, the fertilizing ability of transfected sperm cells and the poor reproducibility of this method are still matters of controversy. Hence, the current study was conducted to evaluate transfecting the enhanced green fluorescent protein (EGFP) as the source of exogenous DNA into bovine spermatozoa using a high-performance polymer reagent as well as assessing the fertilizing capacity of transfected sperm cells by in vitro fertilization (IVF). In the first experiment, three different concentrations of rhodamine-labeled DNA and high-performance polymer transfection reagent, X-tremeGENE HP, were used to transfect bovine spermatozoa. In the second experiment, IVF and fluorescence microscopy methods were utilized to assess the fertilizing capacity of sperm cells carrying exogenous DNA when X-tremeGENE HP was used either alone or with dimethyl sulfoxide (DMSO) treatment. Findings revealed that at 1 µL X-tremeGENE HP and 1 µg of DNA concentration, approximately one-third of total spermatozoa were transfected. However, following IVF and fluorescence microscopy, no EGFP expression was detected in zygotes and morula-stage embryos. Results of this study showed that, although X-tremeGENE HP could transfer EGFP to bovine spermatozoa, transfected sperm cells were unable to transfer foreign DNA to matured bovine oocytes. Under our experimental conditions, we hypothesized that the absence of the EGFP fluorescence signal in embryos could be due to the detrimental effects of transfection treatments on sperm cells' fertility performance as well as incompetency of IVF to produce transgenic embryos using transfected sperm cells.

First study of sperm mediated gene transfer in Egyptian river buffalo

The present study was carried out to find the best treatments for enhancing the ration of insertion of a desired gene construct (pEGFP-N1) onto the sperm of buffalo as the first step for the production of transgenic buffalo using sperm mediated gene transfer (SMGT). The tested conditions were plasmid DNA concentration, sperm concentration, transfecting agent concentration: Dimethyle sulphoxide (DMSO) and time of transfection. The study proved that the best conditions for producing transgenic embryos were incubation sperm solution its concentration is 107/ml sperm with 3% DMSO: with 20 µg/ml from the linarized DNA, for 15 min at 4 °C are the best conditions to produce transgenic buffalo embryo using sperm mediated gene transfer.

Progress and biotechnological prospects in fish transgenesis

The history of transgenesis is marked by milestones such as the development of cellular transdifferentiation, recombinant DNA, genetic modification of target cells, and finally, the generation of simpler genetically modified organisms (e.g. bacteria and mice). The first transgenic fish was developed in 1984, and since then, continuing technological advancements to improve gene transfer have led to more rapid, accurate, and efficient generation of transgenic animals. Among the established methods are microinjection, electroporation, lipofection, viral vectors, and gene targeting. Here, we review the history of animal transgenesis, with an emphasis on fish, in conjunction with major developments in genetic engineering over the past few decades. Importantly, spermatogonial stem cell modification and transplantation are two common techniques capable of revolutionizing the generation of transgenic fish. Furthermore, we discuss recent progress and future biotechnological prospects of fish transgenesis, which has strong applications for the aquaculture industry. Indeed, some transgenic fish are already available in the current market, validating continued efforts to improve economically important species with biotechnological advancements.

Generation of gene edited birds in one generation using sperm transfection assisted gene editing (STAGE)

Generating transgenic and gene edited mammals involves in vitro manipulation of oocytes or single cell embryos. Due to the comparative inaccessibility of avian oocytes and single cell embryos, novel protocols have been developed to produce transgenic and gene edited birds. While these protocols are relatively efficient, they involve two generation intervals before reaching complete somatic and germline expressing transgenic or gene edited birds. Most of this work has been done with chickens, and many protocols require in vitro culturing of primordial germ cells (PGCs). However, for many other bird species no methodology for long term culture of PGCs exists. Developing methodologies to produce germline transgenic or gene edited birds in the first generation would save significant amounts of time and resource. Furthermore, developing protocols that can be readily adapted to a wide variety of avian species would open up new research opportunities. Here we report a method using sperm as a delivery mechanism for gene editing vectors which we call sperm transfection assisted gene editing (STAGE). We have successfully used this method to generate GFP knockout embryos and chickens, as well as generate embryos with mutations in the doublesex and mab-3 related transcription factor 1 (DMRT1) gene using the CRISPR/Cas9 system. The efficiency of the method varies from as low as 0% to as high as 26% with multiple factors such as CRISPR guide efficiency and mRNA stability likely impacting the outcome. This straightforward methodology could simplify gene editing in many bird species including those for which no methodology currently exists.

Transgenic mouse offspring generated by ROSI

The production of transgenic animals is an important tool for experimental and applied biology. Over the years, many approaches for the production of transgenic animals have been tried, including pronuclear microinjection, sperm-mediated gene transfer, transfection of male germ cells, somatic cell nuclear transfer and the use of lentiviral vectors. In the present study, we developed a new transgene delivery approach, and we report for the first time the production of transgenic animals by co-injection of DNA and round spermatid nuclei into non-fertilized mouse oocytes (ROSI). The transgene used was a construct containing the human CMV immediate early promoter and the enhanced GFP gene. With this procedure, 12% of the live offspring we obtained carried the transgene. This efficiency of transgenic production by ROSI was similar to the efficiency by pronuclear injection or intracytoplasmic injection of male gamete nuclei (ICSI). However, ICSI required fewer embryos to produce the same number of transgenic animals. The expression of Egfp mRNA and fluorescence of EGFP were found in the majority of the organs examined in 4 transgenic lines generated by ROSI. Tissue morphology and transgene expression were not distinguishable between transgenic animals produced by ROSI or pronuclear injection. Furthermore, our results are of particular interest because they indicate that the transgene incorporation mediated by intracytoplasmic injection of male gamete nuclei is not an exclusive property of mature sperm cell nuclei with compact chromatin but it can be accomplished with immature sperm cell nuclei with decondensed chromatin as well. The present study also provides alternative procedures for transgene delivery into embryos or reconstituted oocytes.

Germline transformation of the silkworm Bombyx mori L. by sperm-mediated gene transfer

The domesticated silkworm Bombyx mori L. has important roles in basic biological research and applied science. To explore the practical use of transgenic technology in agricultural silkworm varieties, we fused the neomycin-resistance gene (Neo(R)) and the green fluorescent protein gene (gfp) into the piggyBac-based transposon vector and transduced it into silkworms by sperm-mediated gene transfer (SMGT). Fluorescence observation indicated the positive rate of G0 egg-batches is 72.7%. After screening against the antibiotic G418, development of individual larvae in the same brood showed significant size differences. PCR detection indicated the existence of gfp and Neo(R) and confirmed the positive rate of transgenesis as 0.47%. Southern blot analysis confirmed the presence of the exogenous genes in the genome of G7 larvae. These results show that our strategy is practical and markedly improves the efficiency of SMGT.

Transgenic nonhuman primate models for human diseases: approaches and contributing factors

Nonhuman primates (NHPs) provide powerful experimental models to study human development, cognitive functions and disturbances as well as complex behavior, because of their genetic and physiological similarities to humans. Therefore, NHPs are appropriate models for the study of human diseases, such as neurodegenerative diseases including Parkinson's, Alzheimer's and Huntington's diseases, which occur as a result of genetic mutations. However, such diseases afflicting humans do not occur naturally in NHPs. So transgenic NHPs need to be established to understand the etiology of disease pathology and pathogenesis. Compared to rodent genetic models, the generation of transgenic NHPs for human diseases is inefficient, and only a transgenic monkey model for Huntington's disease has been reported. This review focuses on potential approaches and contributing factors for generating transgenic NHPs to study human diseases.

Production of transgenic piglets using ICSI-sperm-mediated gene transfer in combination with recombinase RecA

Sperm-mediated gene transfer (SMGT) is a method for the production of transgenic animals based on the intrinsic ability of sperm cells to bind and internalize exogenous DNA molecules and to transfer them into the oocyte at fertilization. Recombinase-A (RecA) protein-coated exogenous DNA has been used previously in pronuclear injection systems increasing integration into goat and pig genomes. However, there are no data regarding transgene expression after ICSI. Here, we set out to investigate whether the expression of transgenic DNA in porcine embryos is improved by recombinase-mediated DNA transfer and if it is possible to generate transgenic animals using this methodology. Different factors which could affect the performance of this transgenic methodology were analyzed by studying 1) the effect of the presence of exogenous DNA and RecA protein on boar sperm functionality; 2) the effect of recombinase RecA on in vitro enhanced green fluorescent protein (EGFP)-expressing embryos produced by ICSI or IVF; and 3) the efficiency of generation of transgenic piglets by RecA-mediated ICSI. Our results suggested that 1) the presence of exogenous DNA and RecA-DNA complexes at 5 microg/ml did not affect sperm functionality in terms of motility, viability, membrane lipid disorder, or reactive oxygen species generation; 2) EGFP-expressing embryos were obtained with a high efficiency using the SMGT-ICSI technique in combination with recombinase; however, the use of IVF system did not result in any fluorescent embryos; and 3) transgenic piglets were produced by this methodology. To our knowledge, this is the first time that transgenic pigs have been produced by ICSI-SGMT and a recombinase.

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.

Bovine sperm cells viability during incubation with or without exogenous DNA

The aim of this study was to assess the effect of exogenous DNA and incubation time on the viability of bovine sperm. Sperm were incubated at a concentration of 5 × 106/ml with or without plasmid pEYFP–NUC. Fluorescent probes, propidium iodide/Hoechst 33342, FITC–PSA and JC-1, were used to assess plasma membrane integrity (PMI), acrosome membrane integrity (AMI) and mitochondrial membrane potential (MMP) respectively at 0, 1, 2, 3 and 4 h of incubation. Exogenous DNA addition did not affect sperm viability; however, incubation time was related to sperm deterioration. Simultaneous assessment of PMI, AMI and MMP showed a reduction in the number of sperm with higher viability (integrity of plasma and acrosome membranes and high mitochondrial membrane potential) from 58.7% at 0 h to 7.5% after 4 h of incubation. Lower viability sperm (damaged plasma and acrosome membranes and low mitochondrial membrane potential) increased from 4.6% at 0 h to 25.9% after 4 h of incubation. When PMI, AMI and MMP were assessed separately we noticed a reduction in plasma and acrosome membrane integrity and mitochondrial membrane potential throughout the incubation period. Therefore, exogenous DNA addition does not affect sperm viability, but the viability is reduced by incubation time.

Use of sperm plasmid DNA lipofection combined with REMI (restriction enzyme-mediated insertion) for production of transgenic chickens expressing eGFP (enhanced green fluorescent protein) or human follicle-stimulating hormone

Linearized p-eGFP (plasmid-enhanced green fluorescent protein) or p-hFSH (plasmid human FSH) sequences with the corresponding restriction enzyme were lipofected into sperm genomic DNA. Sperm transfected with p-eGFP were used for artificial insemination in hens, and in 17 out of 19 of the resultant chicks, the exogenous DNA was detected in their lymphocytes as determined by PCR and expressed in tissues as determined by (a) PCR, (b) specific emission of green fluorescence by the eGFP, and (c) Southern blot analysis. A complete homology was found between the Aequorea Victoria eGFP DNA and a 313-bp PCR product of extracted DNA from chick blood cells. Following insemination with sperm lipofected with p-hFSH, transgenic offspring were obtained for two generations as determined by detection of the transgene for human FSH (PCR) and expression of the gene (RT-PCR and quantitative real-time PCR) and the presence of the protein in blood (radioimmunoassay). Data demonstrate that lipofection of plasmid DNA with restriction enzyme is a highly efficient method for the production of transfected sperm to produce transgenic offspring by direct artificial insemination.

Genomic DNA damage in mouse transgenesis

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.

Animal transgenesis: state of the art and applications

There is a constant expectation for fast improvement of livestock production and human health care products. The advent of DNA recombinant technology and the possibility of gene transfer between organisms of distinct species, or even distinct phylogenic kingdoms, has opened a wide range of possibilities. Nowadays we can produce human insulin in bacteria or human coagulation factors in cattle milk. The recent advances in gene transfer, animal cloning, and assisted reproductive techniques have partly fulfilled the expectation in the field of livestock transgenesis. This paper reviews the recent advances and applications of transgenesis in livestock and their derivative products. At first, the state of art and the techniques that enhance the efficiency of livestock transgenesis are presented. The consequent reduction in the cost and time necessary to reach a final product has enabled the multiplication of transgenic prototypes around the world. We also analyze here some emerging applications of livestock transgenesis in the field of pharmacology, meat and dairy industry, xenotransplantation, and human disease modeling. Finally, some bioethical and commercial concerns raised by the transgenesis applications are discussed.

Improving the generation of genomic-type transgenic mice by ICSI

Transgenes included in genomic-type constructs, such as yeast artificial chromosomes (YAC), P1-derived artificial chromosomes, or bacterial artificial chromosomes (BAC), are normally correctly expressed, according to the endogenous expression pattern of the homologous locus, because their large size usually ensures the inclusion of all regulatory elements required for proper gene expression. The use of these large genomic-type transgenes is therefore the method of choice to overcome most position effects, commonly associated with standard-type transgenes, and to guarantee the faithful transgene expression. However, in spite of the different methods available, including pronuclear microinjection and the use of embryonic stem cells as vehicles for genomic transgenes, the generation of transgenic animals with BACs and, particularly, with YACs can be demanding, because of the low efficiencies requiring extensive microinjection sessions and/or higher number of oocytes. Recently, we have explored the use of intracytoplasmic sperm injection (ICSI) into metaphase II oocytes as an alternative method for the generation of YAC transgenic mice. Our results suggest that the use of transgenic strategies based on ICSI significantly enhances the efficiency of YAC transgenesis by at least one order of magnitude.

Transgenic animal production and animal biotechnology

Considerable progress has been made in methods for production of transgenic livestock; beginning with pronuclear microinjection over 20 years ago. New methods, including the use of viral vectors, sperm-mediated gene transfer and somatic cell cloning, have overcome many of the limitations of pronuclear microinjection. It is now possible to not only readily make simple insertional genetic modifications, but also to accomplish, more complex, homozygous gene targeting and artificial chromosome transfer in livestock.

Transgenic modifications of the rat genome

The laboratory rat (R. norvegicus) is a very important experimental animal in several fields of biomedical research. This review describes the various techniques that have been used to generate transgenic rats: classical DNA microinjection and more recently described techniques such as lentiviral vector-mediated DNA transfer into early embryos, sperm-mediated transgenesis, embryo cloning by nuclear transfer and germline mutagenesis. It will also cover techniques associated to transgenesis such as sperm cryopreservation, embryo freezing and determination of zygosity. The availability of several technologies allowing genetic manipulation in the rat coupled to genomic data will allow biomedical research to fully benefit from the rat as an experimental animal.

Efficient and simple production of transgenic mice and rabbits using the new DMSO-sperm mediated exogenous DNA transfer method

A high efficient and simple transgenic technology on mice and rabbits to transfect spermatozoa with exogenous DNA/DMSO complex to obtain transgenic offspring, which is namely called DMSO-sperm mediated gene transfer (SMGT). Mouse sperm could be either directly transfected via injection into testis or cultured in vitro with the plasmed DNA containing the enhanced green fluorescent protein (EGFP) that could be expressed in the embryos and offspring. Then, 36 living transgenic rabbits were produced using the same technology, and the transgenic ratio of 56.3% was detected using PCR and Southern blot. As the controls, the transgenic ratios of 39.6% and 47.8% have also been tested using the liposomes mediated technology of Tfx-50 Reagent or Lipefectamin-2000, respectively. The results show that the female transgenic rabbits, as the mammary gland bioreactor models, could express the human tissue plasminogen activator mutant (htPAm) in their mammary cells when they are adult.

Human lactoferrin transgenic rabbits produced efficiently using dimethylsulfoxide - sperm-mediated gene transfer

Transgenic animal mammary gland bioreactors are used to produce recombinant proteins. However, it is difficult to validate whether these transgenic domestic animals are able to express the recombinant protein efficiently in their mammary glands before the birth of transgenic offspring. In the present study, a simple and efficient method was established to evaluate the functionality of animal mammary gland tissue-expressed cassettes. The gene transfer vector pGBC2LF was constructed, and the expression of human lactoferrin (LF) gene was controlled by the goat β-casein gene 5′ flanking sequence. To obtain the most efficient transfection, the influence of DNA concentration, dimethylsulfoxide (DMSO) concentration, and the ratio of linear-to-circular DNA required for associating DNA with spermatozoa were evaluated. Transfection of exogenous DNA into rabbit spermatozoa was found to be efficient using 30 μg mL–1 DNA, DMSO at a final concentration of 3%, and a 3 : 1 ratio of linear-to-circular DNA, with 29 of 85 (34.1%) in vitro-fertilised embryos being transgenic. Using DMSO–sperm-mediated gene transfer (DMSO-SMGT), 89 rabbit offspring were produced, with 46 of these (57.1%) being transgenic. As mammary gland bioreactor models, 17 of 21 (81%) transgenic female rabbits could express human LF protein in their glands. During lactation of the transgenic rabbits, the highest level of human LF protein expressed was 153 ± 31 μg mL–1, and the mean expression level in all of the transgenic rabbits was 103 ± 20 μg mL–1 in the third week, declining gradually after this time. Our results demonstrate that transgenic rabbits produced by DMSO–SMGT were able to express human LF protein in the correct tissue.

Efficient generation of transgenic mice with intact yeast artificial chromosomes by intracytoplasmic sperm injection

The production of animals with large transgenes is an increasingly valuable tool in biotechnology and for genetic studies, including the characterization and manipulation of large genes and polygenic traits. In the present study, we describe an intracytoplasmic sperm injection (ICSI) method for the stable incorporation and phenotypic expression of large yeast artificial chromosomes (YAC) constructs of submegabase and megabase magnitude. By coinjecting spermatozoa and YACs into metaphase II oocytes, we were able to produce founders exhibiting germline transmission of an intact and functional transgene of 250 kilobases, carrying the mouse tyrosinase locus, used here as a reporter gene to rescue the albinism of recipient mice. More than 35% transgenesis was obtained for this YAC transgene. When compared with the pronuclear microinjection standard method, the efficiency of the ICSI-mediated YAC transfer system was significantly greater. In summary, we describe, for the first time, stable incorporation in the host genome and correct phenotypic expression of large DNA constructs mediated by ICSI.

Novel aspect of perinuclear theca assembly revealed by immunolocalization of non-nuclear somatic histones during bovine spermiogenesis

The perinuclear theca (PT) is an important accessory structure of the sperm head, yet its biogenesis is not well defined. To understand the developmental origins of PT-derived somatic histones during spermiogenesis, we used affinity-purified antibodies against somatic-type histones H3, H2B, H2A, and H4 to probe bovine testicular tissue using three different immunolocalization techniques. While undetectable in elongating spermatid nuclei, immunoperoxidase light microscopy showed all four somatic histones remained associated to the caudal head region of spermatids from steps 11 to 14 of the 14 steps in bovine spermiogenesis. Immunogold electron microscopy confirmed the localization of somatic histones on two nonnuclear structures, namely transient manchette microtubules of step-9 to step-11 spermatids and the developing postacrosomal sheath of step-13 and -14 spermatids. Immunofluorescence demonstrated somatic histone immunoreactivity in the developing postacrosomal sheath, and on anti-beta-tubulin decorated manchette microtubules of step-12 spermatids. Focal antinuclear pore complex labeling on the base of round spermatid nuclei was detected by electron microscopy and immunofluorescence, occurring before the nucleoprotein transition period during spermatid elongation. This indicated that, if nuclear histone export precedes their degradation, this process could only occur in this region, thereby questioning the proposed role of the manchette in nucleocytoplasmic trafficking. Somatic histone immunodetection on the manchette during postacrosomal sheath formation supports a role for the manchette in PT assembly, signifying that some PT components have origins in the distal spermatid cytoplasm. Furthermore, these findings suggest that somatic histones are de novo synthesized in late spermiogenesis for PT assembly.

Prepubertal propagation of transgenic cloned goats by laparoscopic ovum pick-up and in vitro embryo production

The use of laparoscopic ovum pick-up (LOPU) followed by in vitro embryo production was evaluated in the early propagation of cloned goats. Ten kinder goats produced by somatic cell nuclear transfer technology were used as oocyte donors. Half of the donor animals were subjected to LOPU at 2-3 months of age (prior to induction of lactation), whereas the other five goats were subjected to LOPU at 6-7 months of age (following induction to lactation). They were stimulated with 80 mg NIH-FSH-P1 (Folltropin, Vetrepharm, Canada) together with 300 IU eCG (Novormon, Vetrepharm, Canada) administered intramuscularly 36 h prior to LOPU. The number of follicles aspirated and oocytes recovered was higher in the younger group of donors (57 +/- 7 and 41 +/- 4 vs. 28 +/- 2 and 25.8 +/- 2, p < 0.05), however, oocytes from animals in the late prepubertal age showed higher developmental capacity resulting in higher transferable embryo yield (81.4% vs. 67.8%, p < 0.01), pregnancy rate (80% vs. 40%, p < 0.05) and total kids born (27 vs. 15, p < 0.01). In conclusion, LOPU in combination with in vitro embryo production techniques is an efficient method for the early propagation of valuable goats produced by somatic cell nuclear transfer.

State of the art in the production of transgenic goats

This review summarises recent advances in the field of transgenic goats for the purpose of producing recombinant proteins in their milk. Production of transgenic goats via pronuclear microinjection of DNA expression vectors has been the traditional method, but this results in low efficiencies. Somatic cell nuclear transfer has dramatically improved efficiencies in rates of transgenesis. Characterisation of transfected cells in vitro before use in nuclear transfer guarantees that kids born are transgenic and of predetermined gender. Using these platform technologies, several recombinant proteins of commercial interest have been produced, although none of them has yet gained marketing approval. Before these technologies are implemented in goat improvement programmes, efficiencies must be improved, costs reduced, and regulatory approval obtained for the marketing of food products derived from such animals.