Imamura Osamu, Satoh Yasushi, Endo Shogo, Takishima Kunio
Department of Biochemistry, National Defense Medical College, Namiki, Tokorozawa, Japan.
Stem Cells. 2008 Dec;26(12):3247-56. doi: 10.1634/stemcells.2008-0578. Epub 2008 Sep 25.
Extracellular signal-regulated kinase 2 (ERK2) is involved in a variety of cell fate decisions during development, but its exact role in this process remains to be determined. To specifically focus on the role of ERK2 in the brain, and to avoid early lethalities, we used a conditional gene-targeting approach to preferentially inactivate Erk2 in the embryonic mouse brain. The resulting mutant mice were viable and were relatively normal in overall appearance. However, the loss of Erk2 resulted in a diminished proliferation of neural stem cells in the embryonic ventricular zone (VZ), although the survival and differentiation of these cells was unaffected. The multipotent neural progenitor cells (NPCs) isolated from ERK2-deficient brains also showed impaired proliferation, reduced self-renewal ability, and increased apoptosis. By neurosphere differentiation analysis we further observed that lineage-restricted glial progenitors were increased in ERK2-deficient mice. The decline in the self-renewal ability and multipotency of NPCs resulting from the loss of ERK2 was found to be caused at least in part by upregulation of the JAK-STAT signaling pathway and reduced G1/S cell cycle progression. Furthermore, by global expression analysis we found that neural stem cell markers, including Tenascin C NR2E1 (Tlx), and Lgals1 (Galectin-1), were significantly downregulated, whereas several glial lineage markers were upregulated in neurospheres derived from ERK2-deficient mice. Our results thus suggest that ERK2 is required both for the proliferation of neural stem cells in the VZ during embryonic development and in the maintenance of NPC multipotency by suppressing the commitment of these cells to a glial lineage.
细胞外信号调节激酶2（ERK2）在发育过程中参与多种细胞命运的决定，但其在这一过程中的确切作用仍有待确定。为了专门研究ERK2在大脑中的作用，并避免早期致死情况，我们采用了条件性基因靶向方法，优先使胚胎小鼠大脑中的Erk2失活。产生的突变小鼠能够存活，并且整体外观相对正常。然而，Erk2的缺失导致胚胎脑室区（VZ）神经干细胞的增殖减少，尽管这些细胞的存活和分化未受影响。从ERK2缺陷型大脑中分离出的多能神经祖细胞（NPCs）也表现出增殖受损、自我更新能力降低和凋亡增加。通过神经球分化分析，我们进一步观察到ERK2缺陷型小鼠中谱系受限的神经胶质祖细胞增多。发现由于ERK2缺失导致的NPCs自我更新能力和多能性的下降至少部分是由JAK-STAT信号通路的上调和G1/S细胞周期进程的减少引起的。此外，通过全局表达分析我们发现，包括腱生蛋白C、NR2E1（Tlx）和Lgals1（半乳糖凝集素-1）在内的神经干细胞标志物在ERK2缺陷型小鼠来源的神经球中显著下调，而几种神经胶质谱系标志物上调。因此，我们的结果表明，ERK2在胚胎发育过程中对于VZ中神经干细胞的增殖以及通过抑制这些细胞向神经胶质谱系的分化来维持NPC的多能性都是必需的。
