Growth of preimplantation bovine embryos

Differential gene expression and developmental competence in in vitro produced bovine embryos

The embryonic developmental block occurs at the 8-cell stage in cattle and is characterized by a lengthening of the cell cycle and an increased number of embryos that stop development. The maternal-embryonic transition arises at the same stage resulting in the transcription of many genes. Gene expression studies during this stage may contribute to the understanding of the physiological mechanisms involved in the maternal-embryonic transition. Herein we identified genes differentially expressed between embryos with high or low developmental competence to reach the blastocyst stage using differential display PCR. Embryos were analysed according to developmental kinetics: fast cleavage embryos showing 8 cells at 48 h post insemination (hpi) with high potential of development (F8), and embryos with slow cleavage presenting 4 cells at 48 hpi (S4) and 8 cells at 90 hpi (S8), both with reduced rates of development to blastocyst. The fluorescence DDPCR method was applied and allowed the recovery of 176 differentially expressed bands with similar proportion between high and low development potential groups (52% to F8 and 48% in S4 and S8 groups). A total of 27 isolated fragments were cloned and sequenced, confirming the expected primer sequences and allowing the identification of 27 gene transcripts. PI3KCA and ITM2B were chosen for relative quantification of mRNA using real-time PCR and showed a kinetic and a time-related pattern of expression respectively. The observed results suggest the existence of two different embryonic genome activation mechanisms: fast-developing embryos activate genes related to embryonic development, and slow-developing embryos activate genes related to cellular survival and/or death.

Chromatin modifying agents in the in vitro production of bovine embryos

The low efficiency observed in cloning by nuclear transfer is related to an aberrant gene expression following errors in epigenetic reprogramming. Recent studies have focused on further understanding of the modifications that take place in the chromatin of embryos during the preimplantation period, through the use of chromatin modifying agents. The goal of these studies is to identify the factors involved in nuclear reprogramming and to adjust in vitro manipulations in order to better mimic in vivo conditions. Therefore, proper knowledge of epigenetic reprogramming is necessary to prevent possible epigenetic errors and to improve efficiency and the use of in vitro fertilization and cloning technologies in cattle and other species.

Effects of histone hyperacetylation on the preimplantation development of male and female bovine embryos

Trichostatin A (TSA) induces histone hyperacetylation by inhibiting histone deacetylases and consequently increasing gene expression. The hypothesis was that TSA supplementation during the in vitro culture (IVC) of bovine embryos would increase the blastocyst rate, particularly in low-quality and female embryos. Oocytes were fertilised separately with X and Y spermatozoa and, 70 h after IVF, the IVC medium was supplemented with 5 nM and 15 nM TSA for 48 or 144 h. Incubation of female embryos with 5 nM and 15 nM TSA resulted in similar increases in acetylated histone H3K9 levels. However, to see comparable effects on acetylated histone H3K9 levels in male embryos, the culture medium needed to be supplemented with 15 nM TSA (as opposed to 5 nM TSA for female embryos). Treatment of male and female embryos with 5 nM TSA for 48 h or female embryos with 5 nM for 144 h had no effect on blastocyst rates, although 15 nM TSA compromised embryonic development. The terminal deoxyribonucleotidyl transferase-mediated dUTP–digoxigenin nick end-labelling (TUNEL) assay revealed increased apoptosis in female embryos treated with 5 nM TSA for 144 h, as well as in male and female embryos treated with 15 nM TSA for 48 h, but this increase in apoptosis was not observed in low-quality embryos. The results of the present study suggest that TSA treatment promotes histone hyperacetylation, but has no beneficial effects on the in vitro production of male and female bovine embryos during preimplantation development.

Rabies antibodies in vaccinated dogs

Forty-seven healthy, owned dogs were vaccinated with Madivak and 85 with Rabisin. Geometric mean titres of 17.40 and 1.03 IU/ml were measured by the rapid immunofluorescent focus inhibition test 30-40 and 350-370 days, respectively, after a single injection. Four out of 130 (3.1%) and 18 out of 106 (17%) dogs had a titre of less than 0.5 IU/ml in serum 30-40 and 350-370 days after vaccination. Twenty-one dogs (19.8%) had a titre of 0.5 IU/ml 350-370 days after vaccination. There was no significant difference in antibody levels between animals vaccinated with Rabisin or Madivak. Our results indicate that a booster is always necessary after a single injection to ensure that all dogs have a lasting antibody titre.