Van Praet Oliver, Argraves W Scott, Morales Carlos R
Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada.
Mol Reprod Dev. 2003 Feb;64(2):129-35. doi: 10.1002/mrd.10245.
Cubilin is a peripheral membrane protein that cooperates with the endocytic receptor megalin to mediate endocytosis of ligands in various polarized epithelia. Megalin is expressed in the male reproductive tract where it has been implicated in the process of sperm membrane remodeling. A potential role for cubilin in the male reproductive tract has not been explored. Using RT-PCR, we found that cubilin and megalin mRNAs are expressed in the efferent ducts, corpus and cauda epididymis, and proximal and distal vas deferens. Immunohistological analysis revealed that cubilin was expressed in nonciliated cells of the efferent ducts, principal cells of the corpus and cauda epididymis and vas deferens. Immunogold EM showed cubilin in endocytic pits, endocytic vesicles, and endosomes of these cells. The expression profile of cubilin in the male reproductive tract was coincident with that of megalin except in principal cells of the caput epididymis. Double immunogold labeling showed that cubilin and megalin co-localized within the endocytic apparatus and recycling vesicles of efferent duct cells. Neither protein was found in lysosomes. Injection of RAP, an antagonist of megalin interaction with cubilin, reduced the level of intracellular cubilin in cells of the efferent ducts and vas deferens. In conclusion, cubilin and megalin are co-expressed in cells of the epididymis and vas deferens and the endocytosis of cubilin in these tissues is dependent on megalin. Together, these findings highlight the potential for a joint endocytic role for cubilin and megalin in the male reproductive tract.
cubilin是一种外周膜蛋白，它与内吞受体巨蛋白协同作用，介导各种极化上皮细胞中配体的内吞作用。巨蛋白在雄性生殖道中表达，它与精子膜重塑过程有关。cubilin在雄性生殖道中的潜在作用尚未得到探索。通过逆转录聚合酶链反应（RT-PCR），我们发现cubilin和巨蛋白的信使核糖核酸（mRNA）在输出小管、附睾体和附睾尾以及输精管的近端和远端均有表达。免疫组织学分析显示，cubilin在输出小管的非纤毛细胞、附睾体和附睾尾的主细胞以及输精管中表达。免疫金电子显微镜显示cubilin存在于这些细胞的内吞小窝、内吞囊泡和内体中。除了附睾头的主细胞外，cubilin在雄性生殖道中的表达谱与巨蛋白的表达谱一致。双重免疫金标记显示，cubilin和巨蛋白在输出小管细胞的内吞装置和回收囊泡中共定位。在溶酶体中均未发现这两种蛋白。注射巨蛋白与cubilin相互作用的拮抗剂RAP可降低输出小管和输精管细胞内cubilin的水平。总之，cubilin和巨蛋白在附睾和输精管细胞中共同表达，并且这些组织中cubilin的内吞作用依赖于巨蛋白。这些发现共同凸显了cubilin和巨蛋白在雄性生殖道中联合内吞作用的潜力。
