Effects of time of deoxyribonucleic acid microinjection on gene detection and in vitro development of bovine embryos

Collection of tubal stage bovine embryos by means of endoscopy. A technique report

Here we describe the development and optimization of endoscopy-mediated transvaginal access for collecting ova and embryos from the bovine oviduct. The novel technique was developed in three experimental setups: In Experiment 1 embryos were collected unilaterally from nonstimulated heifers. We flushed the oviducts of superovulated heifers unilaterally (Experiment 2) and bilaterally (Experiment 3). In Experiment 1 the oviducts of 18 heifers were successfully cannulated, which resulted in the collection of twelve 1-cell to 8-cell embryos and one empty zona. Unilateral flushing of 13 animals (Experiment 2) resulted in 84 ova with 6.3 +/- 3.2 observed ovulation sites. Bilateral flushing of 25 animals (Experiment 3) resulted in 293 ova plus 10 empty zonae from 11.8 +/- 5.4 ovulation sites. Given our experience from these studies we optimized the technical equipment by improving the flushing metal catheter (Experiment 4). The novel catheter hermetically sealed the lumen of the ampulla at the moment, the medium was flushed through the oviduct. This resulted in a visible flow of medium via oviducts toward the embryo filter connected to an embryo flushing catheter that was fixed in the uterine horns. Our endoscopy-guided method is minimally invasive and facilitates the flushing of tubal stage embryos.

The use of embryo genotyping in the propagation of genes involved in the immune response

Multiple ovulation and embryo transfer (MOET) now enables researchers to produce identical twin animals, to obtain progeny from pre-pubertal females and to obtain more offspring from valuable animals. MOET and sexed semen have produced genetic progress of up to 60% of milk production. The oestrous cycles of animals are synchronized with progestagens before superovulation with gonadal hormones, pregnant mare serum gonadotrophin and follicle stimulating hormone. Surgical, non-surgical and laparoscopic methods are applied to recover and transfer embryos. Sexing and genotyping of the pre-implantation embryos is a key step in improving the management and breeding programmes for livestock, as well as in the human for the prenatal diagnosis of genetic disorders. Several serological and physiological methods have been used to determine the sex of the pre-implantation embryos; none has had satisfactory results in terms of time and accuracy. Sexing by polymerase chain reaction (PCR) using male-specific chromosome sequences alone or with female-specific chromosomal DNA probes simultaneously has been sufficient to identify the sex of the embryos with 100% accuracy. However, caution should be taken against sources of the contamination. The MHC class I, class II and background genes have been implicated in resistance to internal parasites in animals. Biotechnological methods such as screening of embryos prior to transfer using PCR and primer extension pre-amplification have already made it possible to detect transgenic or genetically disordered embryos and could be applied to select those embryos bearing immunological genotypes of interest, such as resistance to internal parasites. Ultimately, cloning and nuclear transplantation would provide the possibility of isolating these resistance genes and to transfer them to livestock pre-implantation embryos to propagate these desirable traits.

In vitro embryo production after microinjection and ovarian dynamics following transvaginal follicular oocyte aspiration

Ultrasound-guided transvaginal follicular aspiration of oocytes from live cows combined with IVM, IVF and in vitro culture (IVC) is a procedure for producing preimplantation-stage bovine embryos and a source of oocytes for pronuclear microinjection of DNA for producing transgenic cattle. This experiment was designed to compare in vitro embryo development rates between oocytes derived from transvaginal follicular aspiration and those obtained from cows at slaughter. Nine cows were subject to a twice-weekly aspiration. Oocytes were aspirated with a 5 MHz ultrasound transducer packaged in a vaginal probe equipped with a dorsal-mounted needle guide (16-ga). All visible follicles (>2 mm) were punctured with a 17-ga, 55-cm needle at each aspiration session and the contents removed under vacuum suction. Oocytes underwent IVM/IVF/IVC. Microinjection of DNA was performed during the pronuclear stage of development, and the zygotes were co-cultured on Buffalo Rat Liver (BRL) cells in modified M199 at 39 degrees C in 5% CO2 and air. After 7 d in culture, embryos were removed and scored for development. A Chi-square analysis was used to compare transvaginal follicular-derived oocytes (microinjected and not) and slaughterhouse-derived, matured in transit oocytes (SHDMT; microinjected and not). Nonmicroinjected embryos resulting from IVF of transvaginal aspiration-derived oocytes developed to blastocysts at a higher rate than SHDMT oocytes (40.0 vs 30.8%; P < 0.05). There was no difference in development rates between the microinjected groups (aspiration = 15.9% vs SHDMT = 12.8%). Higher proportions of the embryos generated from the aspirated oocytes were of excellent or good quality following culture (P < 0.05). In the present experiments the effects of microinjection may overshadow some effects of ova source, but transvaginal follicular aspiration may provide a more consistent, synchronous population of oocytes than those derived from commercial slaughter house sources for use with in vitro systems.