Park Soochul
Department of Biological Science, Sookmyung Women's University, Seoul 140-742, Korea.
Exp Neurobiol. 2013 Sep;22(3):143-8. doi: 10.5607/en.2013.22.3.143. Epub 2013 Sep 30.
Eph receptors and their ligands, ephrins, are abundantly expressed in neuroepithelial cells of the early embryonic brain. Overstimulation of Eph signaling in vivo increases apoptotic cell death of neuroepithelial cells, whereas null mutation of the Eph gene leads to the development of a larger brain during embryogenesis. Thus, it appears that Eph-ephrin signaling plays a role in regulating apoptotic cell death of neuroepithelial cells, thereby influencing brain size during embryonic development. Interestingly, Eph-ephrin signaling is bi-directional, with forward signaling from ephrin- to Eph-expressing cells and reverse signaling from Eph- to ephrin-expressing cells. However, it is not clear whether this forward or reverse signaling plays a role in regulating the size of the neuroepithelial cell population during early brain development. Also, Eph receptors and their corresponding ligands are mutually exclusive in their expression domains, and they encounter each other only at interfaces between their expression domains. This expression pattern may be a critical mechanism for preventing overstimulation of Eph-ephrin signaling. Nevertheless, Eph receptors are co-expressed with their corresponding ligands in certain brain regions. Recently, two studies demonstrated that brain region-specific apoptosis may be triggered by the overlapping expression of Eph and ephrin, a theme that will be explored in this mini-review.
Eph受体及其配体（ephrin）在胚胎早期大脑的神经上皮细胞中大量表达。体内Eph信号的过度激活会增加神经上皮细胞的凋亡性细胞死亡，而Eph基因的无效突变会导致胚胎发育过程中大脑变大。因此，Eph-ephrin信号似乎在调节神经上皮细胞的凋亡性细胞死亡中发挥作用，从而影响胚胎发育期间的大脑大小。有趣的是，Eph-ephrin信号是双向的，从ephrin表达细胞向Eph表达细胞传递正向信号，从Eph表达细胞向ephrin表达细胞传递反向信号。然而，尚不清楚这种正向或反向信号在早期大脑发育过程中调节神经上皮细胞群体大小方面是否发挥作用。此外，Eph受体及其相应配体在其表达域中相互排斥，仅在其表达域之间的界面处相遇。这种表达模式可能是防止Eph-ephrin信号过度激活的关键机制。尽管如此，Eph受体在某些脑区与其相应配体共表达。最近，两项研究表明，Eph和ephrin的重叠表达可能触发脑区特异性凋亡，本综述将探讨这一主题。
