Li Nan, Mruk Dolores D, Wong Chris K C, Han Daishu, Lee Will M, Cheng C Yan
Center for Biomedical Research (N.L., D.D.M., C.Y.C.), Population Council, New York, New York 10065; Department of Biology (C.K.C.W.), Hong Kong Baptist University, Hong Kong, China; Department of Cell Biology (D.H.), Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, Peking Union Medical College, Beijing 100005, China; and School of Biological Sciences (W.M.L.), University of Hong Kong, Hong Kong, China.
Endocrinology. 2015 Aug;156(8):2969-83. doi: 10.1210/en.2015-1161. Epub 2015 Apr 22.
During spermatogenesis, developing spermatids and preleptotene spermatocytes are transported across the adluminal compartment and the blood-testis barrier (BTB), respectively, so that spermatids line up near the luminal edge to prepare for spermiation, whereas preleptotene spermatocytes enter the adluminal compartment to differentiate into late spermatocytes to prepare for meiosis I/II. These cellular events involve actin microfilament reorganization at the testis-specific, actin-rich Sertoli-spermatid and Sertoli-Sertoli cell junction called apical and basal ectoplasmic specialization (ES). Formin 1, an actin nucleation protein known to promote actin microfilament elongation and bundling, was expressed at the apical ES but limited to stage VII of the epithelial cycle, whereas its expression at the basal ES/BTB stretched from stage III to stage VI, diminished in stage VII, and was undetectable in stage VIII tubules. Using an in vitro model of studying Sertoli cell BTB function by RNA interference and biochemical assays to monitor actin bundling and polymerization activity, a knockdown of formin 1 in Sertoli cells by approximately 70% impeded the tight junction-permeability function. This disruptive effect on the tight junction barrier was mediated by a loss of actin microfilament bundling and actin polymerization capability mediated by changes in the localization of branched actin-inducing protein Arp3 (actin-related protein 3), and actin bundling proteins Eps8 (epidermal growth factor receptor pathway substrate 8) and palladin, thereby disrupting cell adhesion. Formin 1 knockdown in vivo was found to impede spermatid adhesion, transport, and polarity, causing defects in spermiation in which elongated spermatids remained embedded into the epithelium in stage IX tubules, mediated by changes in the spatiotemporal expression of Arp3, Eps8, and palladin. In summary, formin 1 is a regulator of ES dynamics.
在精子发生过程中，发育中的精子细胞和前细线期精母细胞分别穿过管腔隔和血睾屏障（BTB），使得精子细胞排列在管腔边缘附近为精子释放做准备，而前细线期精母细胞进入管腔隔分化为晚期精母细胞为减数分裂I/II做准备。这些细胞事件涉及在睾丸特异性、富含肌动蛋白的支持细胞 - 精子细胞和支持细胞 - 支持细胞连接（分别称为顶端和基底外质特化，ES）处的肌动蛋白微丝重组。Formin 1是一种已知可促进肌动蛋白微丝伸长和成束的肌动蛋白成核蛋白，在顶端ES表达，但仅限于上皮周期的VII期，而其在基底ES/BTB的表达从III期延伸至VI期，在VII期减少，在VIII期小管中无法检测到。使用RNA干扰和生化分析来监测肌动蛋白成束和聚合活性的体外模型研究支持细胞BTB功能，支持细胞中Formin 1敲低约70%会阻碍紧密连接通透性功能。对紧密连接屏障的这种破坏作用是由肌动蛋白微丝成束和肌动蛋白聚合能力的丧失介导的，这是由分支肌动蛋白诱导蛋白Arp3（肌动蛋白相关蛋白3）以及肌动蛋白成束蛋白Eps8（表皮生长因子受体途径底物8）和palladin的定位变化引起的，从而破坏细胞黏附。体内研究发现，Formin 1敲低会阻碍精子细胞黏附、运输和极性，导致精子释放缺陷，即IX期小管中的长形精子细胞仍嵌入上皮中，这是由Arp3、Eps8和palladin的时空表达变化介导的。总之，Formin 1是ES动态变化的调节因子。
