Universités de Montpellier, 34293, Montpellier, France.
CRBM, CNRS, UMR 5237, 1919 Route de Mende, 34293, Montpellier, France.
BMC Biol. 2018 Oct 18;16(1):116. doi: 10.1186/s12915-018-0584-6.
Upon maturation in the bone marrow, polyploid megakaryocytes elongate very long and thin cytoplasmic branches called proplatelets. Proplatelets enter the sinusoids blood vessels in which platelets are ultimately released. Microtubule dynamics, bundling, sliding, and coiling, drive these dramatic morphological changes whose regulation remains poorly understood. Microtubule properties are defined by tubulin isotype composition and post-translational modification patterns. It remains unknown whether microtubule post-translational modifications occur in proplatelets and if so, whether they contribute to platelet formation.
Here, we show that in proplatelets from mouse megakaryocytes, microtubules are both acetylated and polyglutamylated. To bypass the difficulties of working with differentiating megakaryocytes, we used a cell model that allowed us to test the functions of these modifications. First, we show that α2bβ3integrin signaling in D723H cells is sufficient to induce β1tubulin expression and recapitulate the specific microtubule behaviors observed during proplatelet elongation and platelet release. Using this model, we found that microtubule acetylation and polyglutamylation occur with different spatio-temporal patterns. We demonstrate that microtubule acetylation, polyglutamylation, and β1tubulin expression are mandatory for proplatelet-like elongation, swelling formation, and cytoplast severing. We discuss the functional importance of polyglutamylation of β1tubulin-containing microtubules for their efficient bundling and coiling during platelet formation.
We characterized and validated a powerful cell model to address microtubule behavior in mature megakaryocytes, which allowed us to demonstrate the functional importance of microtubule acetylation and polyglutamylation for platelet release. Furthermore, we bring evidence of a link between the expression of a specific tubulin isotype, the occurrence of microtubule post-translational modifications, and the acquisition of specific microtubule behaviors. Thus, our findings could widen the current view of the regulation of microtubule behavior in cells such as osteoclasts, spermatozoa, and neurons, which express distinct tubulin isotypes and display specific microtubule activities during differentiation.
在骨髓中成熟后，多倍体巨核细胞伸长非常长而细的细胞质分支，称为前血小板。前血小板进入窦状血管，血小板最终从其中释放。微管动力学、束集、滑动和卷曲驱动这些剧烈的形态变化，但其调节仍知之甚少。微管的性质由微管蛋白同工型组成和翻译后修饰模式定义。目前尚不清楚前血小板中是否存在微管翻译后修饰，如果存在，它们是否有助于血小板形成。
在这里，我们表明，在来自小鼠巨核细胞的前血小板中，微管既乙酰化又多聚谷氨酸化。为了绕过分化巨核细胞的工作困难，我们使用了一种细胞模型，使我们能够测试这些修饰的功能。首先，我们表明，D723H 细胞中的 α2bβ3 整联蛋白信号足以诱导β1 微管蛋白表达，并重现前血小板伸长和血小板释放过程中观察到的特定微管行为。使用该模型，我们发现微管乙酰化和多聚谷氨酸化发生具有不同的时空模式。我们证明微管乙酰化、多聚谷氨酸化和β1 微管蛋白表达对于前血小板样伸长、肿胀形成和胞质体切割是必需的。我们讨论了β1 微管蛋白包含的微管多聚谷氨酸化对其在血小板形成过程中有效束集和卷曲的功能重要性。
我们对成熟巨核细胞中的微管行为进行了表征和验证，建立了一个强大的细胞模型，该模型使我们能够证明微管乙酰化和多聚谷氨酸化对血小板释放的功能重要性。此外，我们提供了证据表明特定微管蛋白同工型的表达、微管翻译后修饰的发生与特定微管行为的获得之间存在联系。因此，我们的发现可以拓宽当前对细胞中微管行为调节的认识，例如表达不同微管蛋白同工型并在分化过程中表现出特定微管活动的破骨细胞、精子和神经元。
