Intercellular Communication in In Vivo- and In Vitro-Produced Bovine Embryos

Abstract

In vivo bovine embryos were obtained by nonsurgical flushing of uterine horns of cows submitted to superovulatory treatment, while in vitro embryos were generated from oocytes collected from slaughtered donors. Lucifer Yellow injected into single blastomeres did not diffuse into neighboring cells until the morula stage in in vivo embryos and the blastocyst stage in in vitro embryos. In both cases diffusion was limited to a few cells. In contrast, diffusion was extensive in microsurgically isolated inner cell mass (ICM) but absent in the trophectoderm (TE). At the blastocyst stage, diffusion was always more extensive in in vivo than in in vitro embryos. Ultrastructural analyses confirmed these functional observations, and gap junction-like structures were observed at the blastocyst stage. These structures were diffuse in the ICM of in vivo embryos, scarce in the ICM of in vitro embryos and in the TE of in vivo embryos, and not observed in the TE of in vitro embryos. Blastomeres at all stages of development from the 2-cell stage to the blastocyst stage in in vitro embryos and at the morula and blastocyst stage in in vivo embryos were electrically coupled, and the junctional conductance (Gj) decreased in in vitro embryos from 4.18 +/- 1.70 nS (2-cell stage) to 0.37 +/- 0.12 nS (blastocyst stage). At each developmental stage, in vivo embryos showed a significantly (P < 0. 05) higher Gj than in vitro-produced embryos. Moreover, a significantly (P < 0.01) higher Gj was found in isolated ICM than in the respective blastocyst in both in vivo- and in vitro-produced embryos (3.5 +/- 1.4 vs. 0.7 +/- 0.3 and 2.6 +/- 1.6 vs. 0.37 +/- 0. 12 nS, respectively). The electrical coupling in absence of dye coupling in the early bovine embryo agrees with observations for embryos from other phyla. The late and reduced expression of intercellular communicative devices in in vitro-produced embryos may be one of the factors explaining their developmental low efficiency.

Biological differences between in vitro produced bovine embryos and parthenotes

“…The intercellular structures are altered in the IVP embryos (Boni et al 1999), and the expression of genes responsible for compaction and cell-to-cell adhesion, such as GJA1 (CX43) and E-cadherin (CDH1), is diminished (Wrenzycki et al 1996, 2001, Rizos et al 2002. A low expression of GJA1 has been associated to low quality of IVP blastocysts (Lonergan et al 2003a, 2003b, Rizos et al 2003, low Development and gene expression in parthenotes developmental competence as oocytes (Nemcova et al 2006), and reduced survival to cryopreservation (Rizos et al 2002).…”

Factors influencing oocyte and embryo quality in cattle

“…These differences include darker cytoplasm, lower density [64], more lipids, specifically, more triglycerides and less lipids from other classes [1], swollen blastomeres [81], a more fragile zona pellucida [19], differences in intercellular communication [10], and a higher incidence of chromosomal abnormalities [72,82]. All of these factors may contribute to the higher sensitivity to cryoinjury exhibited by IVP embryos.…”

Suppressed expression of genes involved in transcription and translation in in vitro compared with in vivo cultured bovine embryos

“…It is well recognized that bovine embryos derived in vivo are of higher quality than those derived in vitro (Hasler et al 1995). In vitro-produced blastocysts tend to have darker cytoplasm and lower buoyant density (Pollard & Leibo 1994), due to their higher lipid content (Abd El Razek et al 2000), a more fragile zona pellucida (Duby et al 1997), reduced intracellular communication (Boni et al 1999), differences in metabolism (Khurana & Niemann 2000, Thompson 2000) and a higher incidence of chromosome abnormalities (Viuff et al 1999). In addition, many differences have been reported at the ultrastructural level (Crosier et al 2000, 2002, Fair et al 2001, Rizos et al 2002a, which reflect some of the differences noted above.…”