Blastocyst invasion and the stromal response in primates

One of the most remarkable processes associated with the establishment of p regnancy in the primate is the process of decidualization. This transformat ion of a stromal fibroblast to a fully differentiated decidual cell is requ ired for implantation and embryo survival in early pregnancy. Although the morphological and biochemical characteristics of the primate decidual cell have been extensively studied, the precise cellular, biochemical and molecu lar signals required for this transformation have yet to be elucidated, Dur ing decidualization, stromal cells first proliferate and then differentiate , Based on our extensive in-vivo and ongoing in-vitro studies, we have sugg ested that the process of decidualization in the baboon can be divided into two distinct phases. The initial proliferative phase is characterized by t he expression of the cytoskeletal protein alpha smooth muscle actin (alpha SMA) in the stromal fibroblasts and is independent of the presence of the c onceptus, The second phase of differentiation is characterized by the expre ssion of insulin-like growth factor binding protein-1 (IGFBP-1) and the dow nregulation of alpha SMA in the decidualized stromal fibroblast. The expres sion of IGFBP-1 is dependent on the presence of the conceptus in vivo and i s regulated by hormones and cAMP in vitro, We have postulated that, during the initial phase of stromal cell differentiation, alpha SMA expression is regulated by the interaction between stromal cell integrins with the secret ed extracellular matrix proteins (ECM), In response to pregnancy a trophobl ast 'factor', mediated by cAMP signal transduction, induces IGFBP-1 express ion in decidualizing stromal fibroblasts. This induction of IGFBP-1 is asso ciated with the disappearance of alpha SMA and denovo protein synthesis, Ou r comparative studies suggest that the process of decidualization in the hu man and baboon involve similar mechanisms, However, the metabolic pathways required for decidualization in the two species appear to differ in their d egree of sensitivity to external stimuli, This review focuses on the cellul ar events that may potentially regulate decidualization in the primate and its role in regulating trophoblast migration.