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Trophoblast concept as applied to therian mammals
Author(s) -
Blackburn Daniel G.,
Taylor J. Mary,
Padykula Helen A.
Publication year - 1988
Publication title -
journal of morphology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.652
H-Index - 74
eISSN - 1097-4687
pISSN - 0362-2525
DOI - 10.1002/jmor.1051960203
Subject(s) - trophoblast , biology , conceptus , blastocyst , placentation , evolution of mammals , evolutionary biology , term (time) , placenta , microbiology and biotechnology , genetics , fetus , embryo , pregnancy , embryogenesis , gene , physics , quantum mechanics
Available evidence provides little support for a recent proposal that the term “trophoblast” be applied solely to eutherian mammals. Arguments for such a restricted usage are based on a dichotomous interpretation of therian reproduction that underestimates the developmental, structural, and functional diversity of trophoblastic tissues occurring within the infraclass Eutheria. The occurrence of developmental patterns that are phenotypically intermediate between those of commonly studied eutherians and metatherians suggests that blastocyst development is not fundamentally different in marsupials and eutherians. The trophoblast of marsupials accomplishes most or all of the major functions of the eutherian trophoblast, including maternal‐fetal physiological exchange, implantation, contribution to placental membranes, steroid metabolism, and possibly, immunological protection of the conceptus. Furthermore, application of the term “trophoblast” to marsupials is consistent with present and past usage, as well as with the original definition and etymological derivation of the term. Therefore, we recommend that the term “trophoblast” continue to be applied in a functional‐morphological sense to the appropriate extraembryonic tissues of marsupials. Such use of functional (rather than taxonomic) criteria for application of this term avoids biasing interpretations of mammalian reproductive evolution.