Compared with our extensive understanding of the cell cycle, we have limited knowledge of how the cell quiescence-proliferation decision is regulated. Using a zebrafish epithelial model, we report a novel signaling mechanism governing the cell quiescence-proliferation decision. Zebrafish Ca2+-transporting epithelial cells, or ionocytes, maintain high cytoplasmic Ca2+ concentration ([Ca2+]c) due to the expression of Trpv6. Genetic deletion or pharmacological inhibition of Trpv6, or reduction of external Ca2+ concentration, lowered the [Ca2+]c and reactivated these cells. The ionocyte reactivation was attenuated by chelating intracellular Ca2+ and inhibiting calmodulin (CaM), suggesting involvement of a Ca2+ and CaM-dependent mechanism. Long-term imaging studies showed that after an initial decrease, [Ca2+]c gradually returned to the basal levels. There was a concomitant decease in endoplasmic reticulum (ER) Ca2+ levels. Lowering the ER Ca2+ store content or inhibiting ryanodine receptors impaired ionocyte reactivation. Further analyses suggest that CaM-dependent protein kinase kinase (CaMKK) is a key molecular link between Ca2+ and Akt signaling. Genetic deletion or inhibition of CaMKK abolished cell reactivation, which could be rescued by expression of a constitutively active Akt. These results suggest that the quiescence-proliferation decision in zebrafish ionocytes is regulated by Trpv6-mediated Ca2+ and CaMKK-Akt signaling.

中文翻译：

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Ca2+-CaMKK-Akt 信号对细胞静止-增殖平衡的调节。

与我们对细胞周期的广泛了解相比，我们对细胞静止-增殖决定如何调节的了解有限。我们使用斑马鱼上皮模型报告了一种控制细胞静止-增殖决定的新信号机制。由于 Trpv6 的表达，斑马鱼 Ca2+ 转运上皮细胞或离子细胞保持高细胞质 Ca2+ 浓度 ([Ca2+]c)。Trpv6 的遗传缺失或药理学抑制，或外部 Ca2+ 浓度的降低，降低了 [Ca2+]c 并重新激活了这些细胞。通过螯合细胞内 Ca2+ 和抑制钙调蛋白 (CaM) 减弱了离子细胞的再激活，表明参与了 Ca2+ 和 CaM 依赖性机制。长期影像学研究表明，在最初下降后，[Ca2+]c 逐渐恢复到基础水平。内质网 (ER) Ca2+ 水平随之下降。降低 ER Ca2+ 储存量或抑制兰尼碱受体会损害离子细胞的再激活。进一步的分析表明，CaM 依赖性蛋白激酶激酶 (CaMKK) 是 Ca2+ 和 Akt 信号传导之间的关键分子链接。CaMKK 的基因缺失或抑制消除了细胞再激活，这可以通过一活性 Akt 的表达来挽救。这些结果表明斑马鱼离子细胞中的静止增殖决定受 Trpv6 介导的 Ca2+ 和 CaMKK-Akt 信号传导的调节。进一步的分析表明，CaM 依赖性蛋白激酶激酶 (CaMKK) 是 Ca2+ 和 Akt 信号传导之间的关键分子链接。CaMKK 的基因缺失或抑制消除了细胞再激活，这可以通过一活性 Akt 的表达来挽救。这些结果表明斑马鱼离子细胞中的静止增殖决定受 Trpv6 介导的 Ca2+ 和 CaMKK-Akt 信号传导的调节。进一步的分析表明，CaM 依赖性蛋白激酶激酶 (CaMKK) 是 Ca2+ 和 Akt 信号传导之间的关键分子链接。CaMKK 的基因缺失或抑制消除了细胞再激活，这可以通过一活性 Akt 的表达来挽救。这些结果表明斑马鱼离子细胞中的静止增殖决定受 Trpv6 介导的 Ca2+ 和 CaMKK-Akt 信号传导的调节。