Many studies attribute decreased Cdk kinase activity in quiescent or differentiating cells to an increase in the expression of Cdk-inhibitory proteins (reviewed in ) including p27Kipl. Expression of p27KiP* gene and protein was apparent in freshly isolated trophoblasts, yet significantly decreased within the first 24 h after culture (Figs. 6b and 2c, respectively). Subsequently, expression of p27Kipi protein increased to levels 4-fold above those in freshly isolated trophoblast. birth control pills
Mononuclear cytotrophoblasts isolated from term placentae are classified as postmitotic (reviewed in ) and as such might be expected to express p27Ripi Placement of the cytotrophoblasts into our culture system, which is rich in mitogenic factors (epidermal growth factor, insulin, and serum) required for differentiation, might induce the initial loss of p27KlP1 protein analogous to that described previously upon mitogen restimulation of cells arrested by growth factor deprivation. However, terminal differentiation of cytotrophoblasts into syncytiotrophoblast appears to coincide with increased p27KiP’.