mortality/aging
• death between E9.5-12.5
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embryo
• by examining for the presence of numerous developmental molecular markers, it appears that the epiblast no longer has a distinct polarity and instead seems to have defaulted to an entire posterior character
• the anterior region which normally develops into neuroectoderm is diverted to posterior mesoderm, demonstrating a role for Smad2 in establishing proper anteroposterior polarity
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• at E8.5, the extraembryonic tissues (ectoplacental cone, Reicherts membrane, allantois, and visceral yolk sac) are present and normal, but the embryo proper is absent
• no node tissue nor axial mesoderm derivatives can be detected
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• epiblast lacks a uniform morphology
• epiblast exclusively forms extraembryonic mesoderms and fails to give rise to the three primary germ layers
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• epiblast fails to give rise to the ectoderm
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• epiblast fails to give rise to the definitive endoderm
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• epiblast fails to give rise to the mesoderm
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• no node tissue can be detected
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• chorion appears highly folded and misplaced, situated laterally and distally instead of proximally, however at later stages, chorion assumes a more normal location
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