Lyon Kevin, Adams Arlo, Piva Matthew, Asghari Parisa, Moore Edwin D, Vogl A Wayne
Department of Obstetrics and Gynaecology, Life Sciences Institute, University of British Columbia, Vancouver, British Columbia, Canada.
Department of Cellular and Physiological Sciences, Life Sciences Institute, University of British Columbia, Vancouver, British Columbia, Canada.
Biol Reprod. 2017 Jun 1;96(6):1288-1302. doi: 10.1093/biolre/iox042.
The endoplasmic reticulum (ER) in Sertoli cells is a component of unique adhesion junctions (ectoplasmic specializations-ESs) and is closely associated with structures termed tubulobulbar complexes (TBCs) that internalize intercellular junctions during sperm release and during the translocation of spermatocytes through the blood-testis barrier. A role for the ER in Ca2+ regulation at ESs and TBCs has been suspected, but evidence for this function has proved elusive. Using electron microscopy, we define two new ER-plasma membrane (PM) contact sites in apical Sertoli cell processes. One of these sites occurs at TBCs where flattened lamellar cisternae of ER envelope the swollen bulb regions of the complexes, and where the gap between adjacent membranes is 12 nm. The other is at the periphery of apical processes where the gap between membranes is 13-14 nm. Using immunolocalization at the light and electron microscopic levels, we demonstrate that Ca2+ regulatory machinery is present at the ESs attached to spermatid heads, and at ER-PM contacts. Sarco/endoplasmic reticulum Ca2+-ATPase 2 (ATP2A2, SERCA2) is present at ESs; transient receptor potential channel subfamily M member 6 (TRPM6), Homer1 (HOMER1), and inositol 1,4,5-trisphosphate receptor (ITPR, IP3R) are present at ER-PM contacts associated with TBC bulbs; and stromal interacting molecule 1 (STIM1), Orai1 (ORAI1), and ATP2A2 are present at the ER-PM contacts around the margins of Sertoli cell apical processes. In Sertoli cells, the molecular machinery associated with ER generated Ca2+ fluxes is present in regions and structures directly related to junction remodeling-a process necessary for sperm release.
支持细胞中的内质网（ER）是独特黏附连接（外质特化结构，ESs）的组成部分，并且与称为管球复合体（TBCs）的结构密切相关，后者在精子释放过程中以及精母细胞通过血睾屏障移位期间内化细胞间连接。内质网在ESs和TBCs处的Ca²⁺调节中的作用一直受到怀疑，但这一功能的证据却难以捉摸。利用电子显微镜，我们在支持细胞顶端突起中定义了两个新的内质网-质膜（PM）接触位点。其中一个位点出现在TBCs处，内质网扁平的板层状潴泡包裹着复合体肿胀的球茎区域，相邻膜之间的间隙为12nm。另一个位于顶端突起的周边，膜之间的间隙为13 - 14nm。利用光镜和电镜水平的免疫定位，我们证明Ca²⁺调节机制存在于附着于精子头部的ESs处以及内质网-质膜接触部位。肌浆/内质网Ca²⁺-ATP酶2（ATP2A2，SERCA2）存在于ESs处；瞬时受体电位通道亚家族M成员6（TRPM6）、Homer1（HOMER1）和肌醇1,4,5-三磷酸受体（ITPR，IP3R）存在于与TBC球茎相关的内质网-质膜接触部位；基质相互作用分子1（STIM1）、Orai1（ORAI1）和ATP2A2存在于支持细胞顶端突起边缘周围的内质网-质膜接触部位。在支持细胞中，与内质网产生的Ca²⁺通量相关的分子机制存在于与连接重塑直接相关的区域和结构中，连接重塑是精子释放所必需的过程。
