Totipotency and lineage segregation in the human embryo.
During human preimplantation development the totipotent zygote divides and undergoes a number of changes that lead to the first lineage differentiation in the blastocyst displaying trophectoderm (TE) and inner cell mass (ICM) on Day 5. The TE is a differentiated epithelium needed for implantation and the ICM forms the embryo proper and serves as a source for pluripotent embryonic stem cells (ESCs). The blastocyst implants around Day 7. The second lineage differentiation occurs in the ICM after implantation resulting in specification of primitive endoderm and epiblast. Knowledge on human preimplantation development is limited due to ethical and legal restrictions on embryo research and scarcity of materials. Studies in the human are mainly descriptive and lack functional evidence. Most information on embryo development is obtained from animal models and ESC cultures and should be extrapolated with caution. This paper reviews totipotency and the molecular determinants and pathways involved in lineage segregation in the human embryo, as well as the role of embryonic genome activation, cell cycle features and epigenetic modifications.
Research Group Reproduction and Genetics (REGE), Vrije Universiteit Brussel (VUB), Laarbeeklaan 103, B-1090 Brussel, Belgium.
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De Paepe
Research Group Reproduction and Genetics (REGE), Vrije Universiteit Brussel (VUB), Laarbeeklaan 103, B-1090 Brussel, Belgium.
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Krivega
Research Group Reproduction and Genetics (REGE), Vrije Universiteit Brussel (VUB), Laarbeeklaan 103, B-1090 Brussel, Belgium Centre for Reproductive Medicine (CRG), Universitair Ziekenhuis Brussel (UZ Brussel), Laarbeeklaan 101, B-1090 Brussel, Belgium.
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Cauffman
Research Group Reproduction and Genetics (REGE), Vrije Universiteit Brussel (VUB), Laarbeeklaan 103, B-1090 Brussel, Belgium.
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Geens
Research Group Reproduction and Genetics (REGE), Vrije Universiteit Brussel (VUB), Laarbeeklaan 103, B-1090 Brussel, Belgium Centre for Reproductive Medicine (CRG), Universitair Ziekenhuis Brussel (UZ Brussel), Laarbeeklaan 101, B-1090 Brussel, Belgium hilde.vandevelde@uzbrussel.be.
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Van de Velde
D001755:Blastocyst / Q000166:cytology*; D019070:Cell Lineage / Q000502:physiology*; D047108:Embryonic Development / Q000502:physiology*; D053595:Embryonic Stem Cells / Q000166:cytology*; D044127:Epigenesis, Genetic; D005260:Female; D006801:Humans; D011247:Pregnancy; D039901:Totipotent Stem Cells / Q000166:cytology*
epigenetic modifications; human embryonic stem cells; human preimplantation embryo; lineage segregation; totipotency