Biology of implantation

Despite the availability of many null mutations in the mouse, the molecular mechanisms underlying embryonic implantation remain poorly understood. Alt hough carbohydrates are clearly involved at the initial stage of implantati on (apposition) and integrins participate in later stages (attachment and p enetration), the prevaling idea is that several independent parallel system s operate at all times. That remarkably different cellular strategies of im plantation are used among different mammalian species might account for the existence and maintenance of redundant molecular mechanisms. In any case, conclusions drawn from the study of implantation in the mouse will have to be carefully examined before extrapolating to other species.