title: Specific epiblast loss and hypoblast impairment in cattle embryos sensitized to survival signalling by ubiquitous overexpression of the proapoptotic gene BAD.
abstract: Early embryonic lethality is common, particularly in dairy cattle. We made cattle embryos more sensitive to environmental stressors by raising the threshold of embryo survival signaling required to overcome the deleterious effects of overexpressing the proapoptotic protein BAD. Two primary fibroblast cell lines expressing BAD and exhibiting increased sensitivity to stress-induced apoptosis were used to generate transgenic Day 13/14 BAD embryos. Transgenic embryos were normal in terms of retrieval rates, average embryo length or expression levels of the trophectoderm marker ASCL2. However both lines of BAD-tg embryos lost the embryonic disc and thus the entire epiblast lineage at significantly greater frequencies than either co-transferrred IVP controls or LacZ-tg embryos. Embryos without epiblast still contained the second ICM-derived lineage, the hypopblast, albeit frequently in an impaired state, as shown by reduced expression of the hypoblast markers GATA4 and FIBRONECTIN. This indicates a gradient of sensitivity (epiblast > hypoblast > TE) to BAD overexpression. We postulate that the greater sensitivity of specifically the epiblast lineage that we have seen in our transgenic model, reflects an inherent greater susceptibility of this lineage to environmental stress and may underlie the epiblast-specific death seen in phantom pregnancies.
authors.affiliation: Animal Productivity, AgResearch, Hamilton, Waikato, New Zealand; Department of Biological Sciences, University of Waikato, Hamilton, Waikato, New Zealand.
authors.forename: Jessica
authors.initials: J
authors.lastname: van Leeuwen
authors.affiliation: Animal Productivity, AgResearch, Hamilton, Waikato, New Zealand.
authors.forename: Debra K
authors.initials: DK
authors.lastname: Berg
authors.affiliation: Animal Productivity, AgResearch, Hamilton, Waikato, New Zealand; School of Medicine, University of Notre Dame, Sydney, New South Wales, Australia.
authors.forename: Craig S
authors.initials: CS
authors.lastname: Smith
authors.affiliation: Animal Productivity, AgResearch, Hamilton, Waikato, New Zealand.
authors.forename: David N
authors.initials: DN
authors.lastname: Wells
authors.affiliation: Animal Productivity, AgResearch, Hamilton, Waikato, New Zealand.
authors.forename: Peter L
authors.initials: PL
authors.lastname: Pfeffer
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified / Q000235:genetics / Q000378:metabolism; D017209:Apoptosis / Q000235:genetics; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism; D002417:Cattle; D046149:Embryo Culture Techniques; D004622:Embryo, Mammalian; D047108:Embryonic Development / Q000235:genetics*; D005353:Fibronectins / Q000378:metabolism; D050991:GATA4 Transcription Factor / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D005855:Germ Layers / Q000378:metabolism*; D051025:bcl-Associated Death Protein / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D005353:Fibronectins; D050991:GATA4 Transcription Factor; D051025:bcl-Associated Death Protein