Tubulobulbar complexes (TBCs) internalize intercellular junctions during sperm release. One of the characteristic features of TBCs is that they form 'bulbs' or swollen regions that have well defined membrane contact sites (MCS) with adjacent cisternae of endoplasmic reticulum. Previously, we have localized the IP3R calcium channel to the TBC bulb-ER contacts and have hypothesized that fluctuations in local calcium levels may facilitate the maturation of TBC bulbs into putative endosomes, or alter local actin networks that cuff adjacent tubular regions of the TBCs. To test this, we injected the testes of Sprague Dawley rats with siRNAs against IP3R1 and processed the tissues for either western blot, immunofluorescence, or electron microscopy. When compared to control testes injected with non-targeting siRNAs, Sertoli cells in knocked-down testes showed significant morphological alterations to the actin networks including a loss of TBC actin and the appearance of ectopic para-crystalline actin bundles in Sertoli cell stalks. There also was a change in the abundance and distribution of TBC-ER contact sites and large internalized endosomes. This disruption of TBCs resulted in delay of the withdrawal of apical processes away from spermatids and in spermiation. Together, these findings are consistent with the hypothesis that calcium exchange at TBC-ER contacts is involved both in regulating actin dynamics at TBCs and in the maturing of TBC bulbs into endosomes. The results are also consistent with the hypothesis that TBCs are part of the sperm release mechanism.

中文翻译：

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IP3R1 的敲低破坏了球管球复合体-外质网的接触位点和包裹晚期精子细胞的顶端突起的形态†。

Tubulobulbar 复合物 (TBC) 在精子释放过程中内化细胞间连接。TBC 的特征之一是它们形成“灯泡”或肿胀区域，这些区域与相邻的内质网池具有明确的膜接触位点 (MCS)。以前，我们已将 IP3R 钙通道定位到 TBC 球-ER 接触点，并假设局部钙水平的波动可能促进 TBC 球成熟为假定的内体，或改变将邻近 TBC 管状区域封套的局部肌动蛋白网络。为了测试这一点，我们向 Sprague Dawley 大鼠的睾丸注射了针对 IP3R1 的 siRNA，并对组织进行了蛋白质印迹、免疫荧光或电子显微镜检查。与注射非靶向 siRNA 的对照睾丸相比，击倒睾丸中的支持细胞对肌动蛋白网络显示出显着的形态学改变，包括 TBC 肌动蛋白的丢失和支持细胞茎中异位副结晶肌动蛋白束的出现。TBC-ER 接触位点和大的内化内体的丰度和分布也发生了变化。TBC 的这种破坏导致顶端突起从精子细胞和精子形成中撤出的延迟。总之，这些发现与 TBC-ER 接触处的钙交换参与调节 TBC 的肌动蛋白动力学和 TBC 球成熟为内体的假设一致。结果也与 TBC 是精子释放机制的一部分的假设一致。