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MEK signalling pathway is required for hypoblast differentiation in mouse embryos, but its role in ungulate embryos remains controversial. This paper demonstrates that MEK is required for hypoblast specification in the inner cell mass of the ovine blastocyst and that it plays a role during the hypoblast migration occurring following blastocyst hatching.

Developmental failures occurring shortly after blastocyst hatching from the zona pellucida constitute a major cause of pregnancy losses in both humans and farm ungulates. The developmental events occurring following hatching in ungulates include the proliferation and maturation of extra-embryonic membranes - trophoblast and hypoblast - and the formation of a flat embryonic disc, similar to that found in humans, which initiates gastrulation prior to implantation. Unfortunately, our understanding of these key processes for embryo survival is limited because current culture systems cannot sustain ungulate embryo development beyond hatching. Here, we report a culture system that recapitulates most developmental landmarks of gastrulating ovine embryos: trophoblast maturation, hypoblast migration, embryonic disc formation, disappearance of the Rauber's layer, epiblast polarization and mesoderm differentiation. Our system represents a highly valuable platform for exploring the cell differentiation, proliferation and migration processes governing gastrulation in a flat embryonic disc and for understanding pregnancy failures during the second week of gestation. This article has an associated 'The people behind the papers' interview.

The effect of lactose and glycerol concentration, as well as the equilibration time with glycerol was studied on motility, normal apical ridge (NAR), and chromatin state of boar spermatozoa after the freezing and thawing process. In the first experiment, samples were frozen in first and second extenders containing different concentrations of lactose (11, 12 and 14%). In the second experiment samples were frozen using second extenders with different concentrations of glycerol (4, 6, 8 and 10%) and were incubated at 5 °C for 0 and 30 min. Motility, motility after caffeine treatment, NAR, chromatin condensation and stability (susceptibility to decondense after heparin treatment) were evaluated. The results indicated that freezing spermatozoa in extenders with increasing concentrations of lactose adversely affected motility but provided a protective effect on acrosomes. Increased lactose concentration induced higher chromatin condensation but maintained the same stability. Increasing the glycerol concentration in the second extender from 4-6 to 8% led to higher motility and NAR as well as lower chromatin condensation and stability. When 30 min equilibration time was allowed after dilution with the same extenders, spermatozoa showed higher NAR and lower chromatin condensation and stability. The longer equilibration time was detrimental for motility when freezing in the 8% glycerol extender but favourable when using the 4% glycerol extender. Compared to the 8% glycerol, spermatozoa frozen in the 10% glycerol extender showed similar motility and increased chromatin condensation and stability, as well as low values of NAR that did not improve by longer incubation time. © 2007 Elsevier Inc. All rights reserved.