Nagasaka Arata, Miyata Takaki
Department of Anatomy and Cell Biology, Nagoya University Graduate School of Medicine, Nagoya, Japan.
Division of Anatomy, Meikai University of School of Dentistry, Sakado, Japan.
Front Cell Dev Biol. 2021 Jul 23;9:702068. doi: 10.3389/fcell.2021.702068. eCollection 2021.
The inner/apical surface of the embryonic brain wall is important as a major site for cell production by neural progenitor cells (NPCs). We compared the mechanical properties of the apical surfaces of two neighboring but morphologically distinct cerebral wall regions in mice from embryonic day (E) E12-E14. Through indentation measurement using atomic force microscopy (AFM), we first found that Young's modulus was higher at a concave-shaped apical surface of the pallium than at a convex-shaped apical surface of the ganglionic eminence (GE). Further AFM analysis suggested that contribution of actomyosin as revealed with apical surface softening by blebbistatin and stiffness of dissociated NPCs were both comparable between pallium and GE, not accounting for the differential apical surface stiffness. We then found that the density of apices of NPCs was greater, with denser F-actin meshwork, in the apically stiffer pallium than in GE. A similar correlation was found between the decreasing density between E12 and E14 of NPC apices and the declining apical surface stiffness in the same period in both the pallium and the GE. Thus, one plausible explanation for the observed difference (pallium > GE) in apical surface stiffness may be differential densification of NPC apices. In laser ablation onto the apical surface, the convex-shaped GE apical surface showed quicker recoils of edges than the pallial apical surface did, with a milder inhibition of recoiling by blebbistatin than in pallium. This greater pre-stress in GE may provide an indication of how the initially apically concave wall then becomes an apically convex "eminence."
胚胎脑壁的内/顶端表面作为神经祖细胞（NPCs）产生细胞的主要部位具有重要意义。我们比较了来自胚胎期（E）E12 - E14小鼠两个相邻但形态不同的脑壁区域顶端表面的力学特性。通过使用原子力显微镜（AFM）进行压痕测量，我们首先发现，与神经节隆起（GE）的凸形顶端表面相比，大脑皮质的凹形顶端表面的杨氏模量更高。进一步的AFM分析表明，肌动球蛋白的作用（如通过blebbistatin使顶端表面软化所揭示）以及解离的NPCs的硬度在大脑皮质和GE之间相当，无法解释顶端表面硬度的差异。然后我们发现，顶端较硬的大脑皮质中NPCs的顶端密度更大，F - 肌动蛋白网络更密集，而在GE中则不然。在大脑皮质和GE中，E12至E14期间NPC顶端密度的降低与同期顶端表面硬度的下降之间也发现了类似的相关性。因此，对于观察到的顶端表面硬度差异（大脑皮质>GE），一个合理的解释可能是NPC顶端的不同致密化。在对顶端表面进行激光消融时，凸形的GE顶端表面比大脑皮质顶端表面显示出更快的边缘回缩，且blebbistatin对回缩的抑制作用比在大脑皮质中更弱。GE中这种更大的预应力可能为最初顶端凹陷的壁如何变成顶端凸起的“隆起”提供了一个线索。
