title: The mammalian blastocyst.
abstract: The blastocyst is a mammalian invention that carries the embryo from cleavage to gastrulation. For such a simple structure, it exhibits remarkable diversity in its mode of formation, morphology, longevity, and intimacy with the uterine endometrium. This review explores this diversity in the light of the evolution of viviparity, comparing the three main groups of mammals: monotremes, marsupials, and eutherians. The principal drivers in blastocyst evolution were loss of yolk coupled with evolution of the placenta. An important outcome of blastocyst development is differentiation of two extraembryonic lineages (trophoblast and hypoblast) that contribute to the placenta. While in many species trophoblast segregation is often coupled with blastocyst formation, in marsupials and at least some Afrotherians, these events do not coincide. Thus, many questions regarding the conservation of molecular mechanisms controlling these events are of great interest but currently unresolved. For further resources related to this article, please visit the WIREs website.
authors.affiliation: School of BioSciences, University of Melbourne, Victoria, Australia.
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Frankenberg
authors.affiliation: Program in Developmental and Stem Cell Biology, Peter Gilgan Centre for Research and Learning, Hospital for Sick Children, Toronto, Canada.|Department of Molecular Genetics, University of Toronto, Toronto, Canada.
authors.forename: Flavia R O
authors.initials: FR
authors.lastname: de Barros
authors.affiliation: Program in Developmental and Stem Cell Biology, Peter Gilgan Centre for Research and Learning, Hospital for Sick Children, Toronto, Canada.|Department of Molecular Genetics, University of Toronto, Toronto, Canada.
authors.forename: Janet
authors.initials: J
authors.lastname: Rossant
authors.affiliation: School of BioSciences, University of Melbourne, Victoria, Australia.
authors.forename: Marilyn B
authors.initials: MB
authors.lastname: Renfree
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001755:Blastocyst / Q000166:cytology* / Q000378:metabolism; D019070:Cell Lineage; D018507:Gene Expression Regulation, Developmental; D008322:Mammals / Q000196:embryology / Q000235:genetics