EXPRESSION OF DECIDUAL PROLACTIN-RELATED PROTEIN IN THE RAT DECIDUA

It is well established that rat decidual tissue produces a PRL-like ho rmone(s) that binds to the PRL receptor on both the corpus luteum and the decidual cells and initiates profound changes in the endocrine mil ieu required for the establishment of pregnancy. The recent cloning of a decidual PRL-related. protein (dPRP) prompted us 1) to determine wh ether the expression of this gene is triggered by decidualization of t he endometrial stromal cells, 2) to examine the temporal and cell spec ific pattern of its expression, and 3) to examine the role of both dec idual signals and PRL on levels of its messenger RNA (mRNA). Total RNA was isolated from uteri of either nonpseudopregnant rats or pseudopre gnant rats with or without decidual tissue. A 1-kilobase mRNA species hybridizing strongly with the dPRP probe was present in decidualized u teri. No dPRP mRNA could be detected in uteri not subjected to decidua lization. Developmental studies indicated a constant high level of dPR P mRNA in the decidual tissue until day 12 of pseudopregnancy, followe d by a marked decline at a time when extensive cell death occurs in th e decidua, suggesting that dPRP is constitutively expressed in this ti ssue. To examine the cell-specific expression of dPRP, antimesometrial decidua was separated from mesometrial decidua, and the large antimes ometrial cell population was separated from the small mesometrial cell s by elutriation. The results of Northern analysis revealed clearly th at dPRP is abundantly and solely expressed in the large antimesometria l cells. No dPRP mRNA could be detected in the mesometrial cells and i n numerous other endocrine and nonen docrine tissues. A faint signal w as observed, however, in the trophoblast. Despite the very strong para crine regulation between the antimesometrial and mesometrial cells and the high levels of PRL receptor expression in these cells, both in vi vo and coculture experiments revealed no regulation of dPRP gene expre ssion by either PRL or mesometrial cell signal, adding further support to the possibility that once induced, dPRP remains constitutively exp ressed. In summary, the results of this investigation revealed that th e expression of dPRP in endometrial stromal cells is triggered by the induction of decidualization and that this gene is selectively and abu ndantly expressed in a defined cell population located in the antimeso metrial region of the uterus. Thus, dPRP is not only a useful indicato r of decidualization, but is also an excellent marker for the differen tiated antimesometrial cells.