San Raffaele-Vita-Salute University and San Raffaele Scientific institute, Cell Adhesion Unit, Division of Neuroscience, Milano, Italy.
PLoS One. 2019 Aug 1;14(8):e0220496. doi: 10.1371/journal.pone.0220496. eCollection 2019.
The Rac1 and Rac3 GTPases are co-expressed in the developing nervous system, where they are involved in different aspects of neuronal development, including the formation of synapses. The deletion of both Rac genes determines a stronger reduction of dendritic spines in vitro compared to the knockout of either gene, indicating that Rac1 and Rac3 play a synergistic role in the formation of these structures. Here, we have addressed the role of each GTPase in the formation of dendritic spines by overexpressing either Rac1 or Rac3 in wildtype neurons, or by re-expressing either GTPase in double knockout hippocampal cultures. We show that the Rac3 protein is expressed with Rac1 in developing hippocampal neurons. Overexpression of either GTPase in WT neurons increases the density of dendritic spines, suggesting the involvement of both GTPases in their formation. We also found that the re-expression of either Rac1 or Rac3 in double knockout neurons is sufficient to restore spinogenesis. Rac1 is significantly more efficient than Rac3 in restoring the formation of spines. On the other hand the quantitative analysis in neurons overexpressing or re-expressing either GTPase shows that Rac3 induces a more pronounced increase in the size of the spines compared to Rac1. These enlarged spines form morphological synapses identified by the juxtaposition of postsynaptic and presynaptic markers. Thus, while Rac1 appears more efficient in inducing the formation of mature spines, Rac3 is more efficient in promoting their enlargement. Our study highlights specific roles of Rac1 and Rac3, which may be functionally relevant also to synaptic plasticity.
Rac1 和 Rac3 GTPases 在发育中的神经系统中共同表达，它们参与神经元发育的不同方面，包括突触的形成。与敲除单个基因相比，敲除这两个 Rac 基因会导致体外树突棘的减少更为明显，这表明 Rac1 和 Rac3 在这些结构的形成中发挥协同作用。在这里，我们通过在野生型神经元中过表达 Rac1 或 Rac3，或在双敲除海马培养物中重新表达这两种 GTPase 中的任何一种，来研究每种 GTPase 在树突棘形成中的作用。我们发现 Rac3 蛋白与 Rac1 在发育中的海马神经元中共同表达。在 WT 神经元中过表达任一种 GTPase 都会增加树突棘的密度，这表明这两种 GTPase 都参与了它们的形成。我们还发现，在双敲除神经元中重新表达任一种 Rac1 或 Rac3 足以恢复 spinogenesis。Rac1 在恢复棘突形成方面比 Rac3 更有效。另一方面，在过表达或重新表达任一种 GTPase 的神经元中的定量分析表明，Rac3 比 Rac1 更能显著增加棘突的大小。这些增大的棘突形成形态学突触，由突触后和突触前标志物的并置来识别。因此，虽然 Rac1 似乎更有效地诱导成熟棘突的形成，但 Rac3 更有效地促进它们的增大。我们的研究强调了 Rac1 和 Rac3 的特定作用，这些作用在突触可塑性方面可能也具有功能相关性。
