Human neural progenitor cells (hNPCs) are self-renewing cells of neural lineage that can be differentiated into neurons of different subtypes. Here we show that SEPT7, a member of the family of filament-forming GTPases called septins, prevents constitutive Ca²⁺ entry through the store-operated Ca²⁺ entry channel, Orai in hNPCs and in differentiated neurons and is thus required for neuronal calcium homeostasis. Previous work in Drosophila neurons has shown that loss of one copy of the evolutionarily-conserved dSEPT7 gene leads to elevated Ca²⁺ entry via Orai, in the absence of ER-Ca²⁺ store depletion. We have identified an N-terminal polybasic region of SEPT7, known to interact with membrane-localized phospholipids, as essential for spontaneous calcium entry through Orai in hNPCs, whereas the GTPase domain of dSEPT7 is dispensable for this purpose. Re-organisation of Orai1 and the ER-Ca²⁺ sensor STIM1 observed near the plasma membrane in SEPT7 KD hNPCs, supports the idea that Septin7 containing heteromers prevent Ca²⁺ entry through a fraction of STIM-Orai complexes. Possible mechanisms by which SEPT7 reduction leads to opening of Orai channels in the absence of store-depletion are discussed.

人类神经祖细胞 (hNPC) 是神经谱系的自我更新细胞，可以分化为不同亚型的神经元。在这里，我们展示了 SEPT7 是称为 septins 的丝状 GTP 酶家族的成员，它阻止组成性 Ca ²⁺通过存储操作的 Ca ²⁺进入通道进入 hNPC 和分化神经元中的 Orai，因此是神经元钙所必需的体内平衡。先前在果蝇神经元中的研究表明，在没有 ER-Ca ²⁺的情况下，进化保守的dSEPT7基因的一个副本的丢失会导致通过 Orai 进入的Ca ²⁺升高存储耗尽。我们已经确定了 SEPT7 的 N 端多碱基区域，已知与膜定位的磷脂相互作用，对于自发钙进入 hNPC 中的 Orai 至关重要，而 dSEPT7 的 GTPase 域对于此目的是可有可无的。在SEPT7 KD hNPC 的质膜附近观察到的 Orai1 和 ER-Ca ²⁺传感器 STIM1 的重组，支持含有异聚体的 Septin7 阻止 Ca ²⁺通过一小部分 STIM-Orai 复合物进入的观点。讨论了在没有存储耗尽的情况下 SEPT7 减少导致 Orai 通道打开的可能机制。