title: What was the ancestral function of decidual stromal cells? A model for the evolution of eutherian pregnancy.
abstract: In human and mouse, decidual stromal cells (DSC) are necessary for the establishment (implantation) and the maintenance of pregnancy by preventing inflammation and the immune rejection of the semi-allograft conceptus. DSC originated along the stem lineage of eutherian mammals, coincidental with the origin of invasive placentation. Surprisingly, in many eutherian lineages decidual cells are lost after the implantation phase of pregnancy, making it unlikely that DSC are necessary for the maintenance of pregnancy in these animals. In order to understand this variation, we review the literature on the fetal-maternal interface in all major eutherian clades Euarchontoglires, Laurasiatheria, Xenarthra and Afrotheria, as well as the literature about the ancestral eutherian species. We conclude that maintaining pregnancy may not be a shared derived function of DSC among all eutherian mammals. Rather, we propose that DSC originated to manage the inflammatory reaction associated with invasive implantation. We envision that this happened in a stem eutherian that had invasive placenta but still a short gestation. We further propose that extended gestation evolved independently in the major eutherian clades explaining why the major lineages of eutherian mammals differ with respect to the mechanisms maintaining pregnancy.
authors.affiliation: Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT, 06511, USA; Yale Systems Biology Institute, Yale University, West Haven, CT, 06516, USA.
authors.forename: Arun Rajendra
authors.initials: AR
authors.lastname: Chavan
authors.affiliation: Department of Geology and Geophysics, Yale University, New Haven, CT, 06511, USA.
authors.forename: Bhart-Anjan S
authors.initials: BA
authors.lastname: Bhullar
authors.affiliation: Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT, 06511, USA; Yale Systems Biology Institute, Yale University, West Haven, CT, 06516, USA; Department of Obstetrics, Gynecology and Reproductive Sciences, Yale Medical School, USA; Department of Obstetrics and Gynecology, Wayne State University, Detroit, MI, USA. Electronic address: gunter.wagner@yale.edu.
authors.forename: Günter P
authors.initials: GP
authors.lastname: Wagner
mesh_terms: D000818:Animals; D005075:Biological Evolution; D003656:Decidua / Q000502:physiology*; D010064:Embryo Implantation; D005260:Female; D006801:Humans; D008322:Mammals; D011247:Pregnancy
keywords: Decidual stromal cells; Endometrial stromal cells; Eutheria; Extended gestation; Origin of placental mammals