Guttman Julian A, Takai Yoshimi, Vogl A Wayne
Department of Anatomy and Cell Biology, Faculty of Medicine, The University of British Columbia, 313-2177 Wesbrook Mall, Vancouver, British Columbia, Canada V6T 1Z3.
Biol Reprod. 2004 Aug;71(2):548-59. doi: 10.1095/biolreprod.104.028803. Epub 2004 Apr 14.
Tubulobulbar complexes may be part of the mechanism by which intercellular adhesion junctions are internalized by Sertoli cells during sperm release. These complexes develop in regions where Sertoli cells are attached to adjacent cells by intercellular adhesion junctions termed ectoplasmic specializations. At sites where Sertoli cells are attached to spermatid heads, tubulobulbar complexes consist of fingerlike processes of the spermatid plasma membrane, corresponding invaginations of the Sertoli cell plasma membrane, and a surrounding cuff of modified Sertoli cell cytoplasm. At the terminal ends of the complexes occur clusters of vesicles. Here we show that tubulobulbar complexes develop in regions previously occupied by ectoplasmic specializations and that the structures share similar molecular components. In addition, the adhesion molecules nectin 2 and nectin 3, found in the Sertoli cell and spermatid plasma membranes, respectively, are concentrated at the distal ends of tubulobulbar complexes. We also demonstrate that double membrane bounded vesicles are associated with the ends of tubulobulbar complexes and nectin 3 is present on spermatids, but is absent from spermatozoa released from the epithelium. These results are consistent with the conclusion that Sertoli cell and spermatid membrane adhesion domains are internalized together by tubulobulbar complexes. PKCalpha, a kinase associated with endocytosis of adhesion domains in other systems, is concentrated at tubulobulbar complexes, and antibodies to endosomal and lysosomal (LAMP1, SGP1) markers label the cluster of vesicles associated with the ends of tubulobulbar complexes. Our results are consistent with the conclusion that tubulobulbar complexes are involved with the disassembly of ectoplasmic specializations and with the internalization of intercellular membrane adhesion domains during sperm release.
球管状复合体可能是支持细胞在精子释放过程中将细胞间黏附连接内化的机制的一部分。这些复合体在支持细胞通过称为外质特化的细胞间黏附连接与相邻细胞相连的区域形成。在支持细胞与精子细胞头部相连的部位，球管状复合体由精子细胞质膜的指状突起、支持细胞质膜的相应内陷以及周围一圈经过修饰的支持细胞细胞质组成。在复合体的末端出现囊泡簇。我们在此表明，球管状复合体在先前被外质特化占据的区域形成，并且这些结构共享相似的分子成分。此外，分别在支持细胞和精子细胞质膜中发现的黏附分子nectin 2和nectin 3集中在球管状复合体的远端。我们还证明，双膜包被的囊泡与球管状复合体的末端相关联，并且nectin 3存在于精子细胞上，但在上皮释放的精子中不存在。这些结果与支持细胞和精子细胞膜黏附结构域通过球管状复合体一起内化的结论一致。PKCalpha是一种在其他系统中与黏附结构域内吞作用相关的激酶，它集中在球管状复合体上，并且针对内体和溶酶体（LAMP1、SGP1）标志物的抗体标记了与球管状复合体末端相关的囊泡簇。我们的结果与球管状复合体参与外质特化的解体以及精子释放过程中细胞间膜黏附结构域内化的结论一致。
