Decidual prolactin-related protein (dPRP) is a member of the prolactin gene family and is abundantly expressed in the rat deciduum. Previously, dPRP was shown to associate with heparincontaining molecules and was found to reside, at least in part, within the decidual extracellular matrix, where it was postulated to influence decidual cells and other cell types. The purpose of this investigation was to identify the cellular origin and the temporal and regional characteristics of dPRP expression

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... n the rat uterus during pregnancy. Protein expression was evaluated by Western blot analysis, immunoprecipitation, and immunocytochemistry; dPRP mRNA expression was assessed by reverse transcriptase polymerase chain reaction and in situ hybridization. Decidual PRP was first detected at Day 6 of pregnancy or pseudopregnancy. Expression increased with the growth of the deciduum and then declined coincident with regression of decidual tissue. Throughout the first half of pregnancy or pseudopregnancy, dPRP and mRNA were predominantly localized to the antimesometrial deciduum of the developing conceptus. During the second half of gestation, expression also appeared in the chorioallantoic placenta. Trophoblast giant cells and spongiotrophoblast cells within the junctional zone of the chorioallantoic placenta expressed dPRP, as did the Rcho-1 trophoblast cell line. In conclusion, dPRP production is elevated from implantation until parturition through the participation of decidual (early pregnancy) and trophoblastic (late pregnancy) tissues.