Analysis of the expression of putatively imprinted genes in bovine peri-implantation embryos.

The application of assisted reproductive technologies (ART) has been shown to induce changes in the methylation of the embryonic genome, leading to aberrant gene expression, including that of imprinted genes. Aberrant methylation and gene expression has been linked to the large offspring syndrome (LOS) in bovine embryos resulting in increased embryonic morbidity and mortality. In the bovine, limited numbers of imprinted genes have been studied and studies have primarily been restricted to pre-implantation stages. This study reports original data on the expression pattern of 8 putatively imprinted genes (Ata3, Dlk1, Gnas, Grb10, Magel2, Mest-1, Ndn and Sgce) in bovine peri-implantation embryos. Two embryonic developmental stages were examined, Day 14 and Day 21. The gene expression pattern of single embryos was recorded for in vivo, in vitro produced (IVP) and parthenogenetic embryos. The IVP embryos allow us to estimate the effect of in vitro procedures and the analysis of parthenogenetic embryos provides provisional information on maternal genomic imprinting. Among the 8 genes investigated, only Mest-1 showed differential expression in Day 21 parthenogenetic embryos compared to in vivo and IVP counterparts, indicating maternal imprinting of this gene. In addition, our expression analysis of single embryos revealed a more heterogeneous gene expression in IVP than in in vivo developed embryos, adding further to the hypothesis of transcriptional dysregulation induced by in vitro procedures, either by in vitro maturation, fertilization or culture. In conclusion, effects of genomic imprinting and of in vitro procedures for embryo production may influence the success of bovine embryo implantation.

Gene expression analysis of single preimplantation bovine embryos and the consequence for developmental potential.

Preimplantation embryo development typically involves sequential morphological events connecting embryonic cleavage, morula compaction and blastocyst formation, and occurs in parallel with transcriptional regulation, specifically, the maternal to embryonic transition. The underlying homeostatic and metabolic mechanisms governing embryo development are influenced by both genetic and epigenetic factors that respond to environmental stimuli and may impact development during later gestational and fetal growth. There is a renewed interest in the identification and characterization of developmentally important genes during embryonic and fetal development. Perturbations in gene expression, resulting from environmental conditions, can have serious consequences on further embryonic development, homeostasis and disease pathogenesis. The bovine embryo is, however, capable of tolerating and adapting to a wide range of conditions, although little is known of the molecular fingerprint required for oocyte maturation, fertilization and development to term. The genomic revolution united with promising new technologies offer greater opportunity to elucidate the mechanisms behind this well-orchestrated biological process. This paper reviews the current literature on gene expression in the bovine embryo with reference to environmental interference and the development of new technologies to observe this biological process. Defining the difference in molecular signalling between in vivo and in vitro systems will undoubtedly improve the safety and efficiency of assisted reproductive technologies. The future challenge is to devise culture conditions that mimic the changing environment required by developing embryos to allow the correct temporal and spatial expression of a cohort of developmental genes in a manner similar to that seen in

Birth of a cloned calf derived from a vitrified hand-made cloned embryo.

The hand-made cloning (HMC) technique describes a simplified nuclear transfer process without the need for micromanipulators. The technique involves manual bisection of zona-free oocytes, selection of cytoplasts by Hoechst staining and fusion of a single somatic cell and two cytoplasts. In this proof-of-principle experiment, the objective was to examine the developmental competence of HMC embryos following embryo transfer. Modifications to the original method include not selecting of matured oocytes and simultaneous fusion of cytoplasts and karyoplast. Blastocyst rates for embryos cultured in the glass oviduct system as singles (10.5%; 24/228) or in pairs (16.1%; 36/224) did not differ significantly. Fresh and vitrified-thawed blastocysts were transferred to 16 synchronised recipients (three to four embryos per recipient). Ultrasound examination on Days 35-45 showed an initial pregnancy rate of 43.8% (7/16) and a pregnancy rate >8 months of 12.5% (2/16). A male cloned calf (42 kg) derived from a vitrified HMC blastocyst was delivered by Caesarean section on Day 271. The birth and ongoing survival (15 months, 243 kg) of a healthy and apparently normal calf, combining both HMC and vitrification technologies, provides a 'proof of principle' of the technology and a promising alternative to traditional nuclear-transfer techniques.

Semen collection from mice: electroejaculation.

The effects of device type (electrostimulator, function generator or computer-generated waveforms), waveform (square, triangle or sine wave), probe type (ring or strip) and anaesthetic compound (ketamine/xylazine combination or pentobarbitone sodium) were investigated on electroejaculation (EEJ) responses of C57B1 x CBA and C57Bl/6J mice. Ejaculates were analysed for total sperm count and motility variables using computer-assisted sperm analyses. Automated computer-generated waveforms delivered through a sound card were more effective and reproducible compared with waveforms generated by function generator and electrostimulator. Sine waves and triangle waves were found to be more effective in producing ejaculate than square waves. As an anaesthetic, pentobarbitone sodium tended to outperform ketamine/xylazine across waveforms and strains. Strip probes failed to produce any ejaculate regardless of the device or waveform employed. Sperm obtained by EEJ exhibited poor motility and C5B1/6J mice had lower motility variables than C57BI x CBA mice.

Effects of electrical stimulation and seminal plasma on the motility of mouse sperm.

The effects of electric current (in vivo and in vitro) and seminal plasma on epididymal and ejaculated sperm obtained from C57BL x CBA and C57BL/6J mice were investigated by studying motility parameters, fertilization and embryo development. Electroejaculates were obtained by applying a series of computer-generated sinusoidal alternating currents (0.25-3.0 V at 50 Hz) delivered for 1, 2 and 3 s with 1-s rest periods using a four-electrode rectal probe for 4 min. Epididymal sperm obtained from the same mice were either subjected to electric current in vitro in a Plexiglass chamber or incubated in a medium containing seminal plasma for 2 h. In vitro electric current application and incubation in a medium containing seminal plasma significantly (P < 0.01) decreased sperm motility. Neither electroejaculates nor epididymal spermatozoa incubated with seminal plasma could fertilize oocytes by conventional IVF (P < 0.001), whereas sperm subjected to in vitro electric current had lost little of their ability to fertilize oocytes. Following transfer of embryos generated by intracytoplasmic sperm injection (ICSI), the number of live pups obtained from electroejaculated sperm (10.2%; 6/59) was significantly (P < 0.01) lower than from epididymal sperm (50.0%; 22/42). Electroejaculation using a rectal probe had little effect on motility and fertilization capacity of mouse epididymal sperm, whereas the presence of seminal plasma decreased motility and prevented fertilization.