Proteoglycan as modulators of embryo-uterine interactions

The process by which mammalian embryos attach to and invade the uterine endometrium is both fascinating and complex. From early conception until parturition, embryonal and maternal tissues must exist symbiotically without imposing detrimental effects on the other. It remains unclear why the immunologically competent mother fails to reject the embryo in spite of histocompatibility differences. It also is unclear why the highly invasive trophoblast tissue of the embryo normally halts its progress within the endometrium although it clearly has the capacity to invade a wide range of tissues (1, 2). In this regard, the interesting feature of the uterus may not be that it supports embryo implantation, but that it has the unique ability to prevent and limit embryo invasion.