Carson D D, DeSouza M M, Regisford E G
Department of Biochemistry and Molecular Biology, University of Texas M.D. Anderson Cancer Center, Houston 77030, USA.
Bioessays. 1998 Jul;20(7):577-83. doi: 10.1002/(SICI)1521-1878(199807)20:7<577::AID-BIES9>3.0.CO;2-H.
Embryo implantation is a complex series of events that involves changes in pattern of expression of embryonic as well as uterine cell surface components. In the case of the embryo, these changes are driven by the developmental program. In the case of the uterus, these changes are triggered by both maternal hormonal influences as well as embryo-derived factors. Aspects of the implantation process vary among species; however, interaction between the external surface of the embryonic trophectoderm and the apical surface of the lumenal uterine epithelium is a common event. Progress is being made in defining the molecular players in these cell surface interactions. Large-molecular-weight mucin glycoproteins such as MUC1 are present at the apical surface of the uterine epithelium under most conditions. Under most circumstances, these mucins appear to protect the mucosal surface from infection and the action of degradative enzymes. These mucins are antiadhesive and also appear to represent a barrier to embryo attachment. Consistent with this model, reduction of mucin expression is observed in uterine lumenal epithelia in many species. Nonetheless, mucin expression persists in the human uterus during the proposed receptive phase. It is possible that mucin loss is localized to implantation sites in humans. Alternatively, mucins may function differently within the context of human implantation than in other species. Studies primarily performed in mice indicate that heparan sulfate proteoglycans, in particular, perlecan, appears on the exterior trophectodermal surface coincident with the acquisition of attachment competence. Various in vitro studies indicate that heparan sulfate proteoglycans support embryo attachment activity that may represent an early event in embryo-uterine interaction. Uterine epithelia cells express several complementary heparan sulfate-binding proteins that may participate in these attachment processes. Use of molecular genetic approaches in mouse models, as well as careful studies of the expression and function of these molecules in the context of implantation in various species are beginning to shed light on the key molecular events of implantation.
胚胎着床是一系列复杂的事件，涉及胚胎以及子宫细胞表面成分表达模式的变化。就胚胎而言，这些变化由发育程序驱动。就子宫而言，这些变化是由母体激素影响以及胚胎衍生因子共同触发的。着床过程的各个方面在不同物种间存在差异；然而，胚胎滋养外胚层的外表面与子宫腔上皮的顶端表面之间的相互作用是一个常见现象。在确定这些细胞表面相互作用中的分子参与者方面正在取得进展。在大多数情况下，诸如MUC1等大分子粘蛋白糖蛋白存在于子宫上皮的顶端表面。在大多数情况下，这些粘蛋白似乎可保护粘膜表面免受感染和降解酶的作用。这些粘蛋白具有抗粘附性，似乎也构成了胚胎附着的障碍。与该模型一致，在许多物种的子宫腔上皮中观察到粘蛋白表达减少。尽管如此，在人类子宫中，在所提出的着床期粘蛋白表达仍然持续。有可能在人类中粘蛋白的缺失局限于着床部位。或者，粘蛋白在人类着床过程中的功能可能与在其他物种中的不同。主要在小鼠中进行的研究表明，硫酸乙酰肝素蛋白聚糖，特别是基底膜聚糖，在获得附着能力的同时出现在滋养外胚层的外表面。各种体外研究表明，硫酸乙酰肝素蛋白聚糖支持胚胎附着活性，这可能是胚胎与子宫相互作用中的早期事件。子宫上皮细胞表达几种互补的硫酸乙酰肝素结合蛋白，它们可能参与这些附着过程。在小鼠模型中使用分子遗传学方法，以及在各种物种的着床背景下对这些分子的表达和功能进行仔细研究，开始揭示着床的关键分子事件。
