Bai Ting, Seebald Jamie L, Kim Kyu-Eui, Ding Hong-Mei, Szeto Daniel P, Chang Henry C
Department of Biological Sciences, Purdue University, 915 W, State St,, West Lafayette, Indiana 47907-2054, USA.
BMC Dev Biol. 2010 Jan 18;10:7. doi: 10.1186/1471-213X-10-7.
The J-domain-containing protein auxilin, a critical regulator in clathrin-mediated transport, has been implicated in Drosophila Notch signaling. To ask if this role of auxilin is conserved and whether auxilin has additional roles in development, we have investigated the functions of auxilin orthologs in zebrafish.
Like mammals, zebrafish has two distinct auxilin-like molecules, auxilin and cyclin G-associated kinase (GAK), differing in their domain structures and expression patterns. Both zebrafish auxilin and GAK can functionally substitute for the Drosophila auxilin, suggesting that they have overlapping molecular functions. Still, they are not completely redundant, as morpholino-mediated knockdown of the ubiquitously expressed GAK alone can increase the specification of neuronal cells, a known Notch-dependent process, and decrease the expression of Her4, a Notch target gene. Furthermore, inhibition of GAK function caused an elevated level of apoptosis in neural tissues, resulting in severe degeneration of neural structures.
In support of the notion that endocytosis plays important roles in Notch signaling, inhibition of zebrafish GAK function affects embryonic neuronal cell specification and Her4 expression. In addition, our analysis suggests that zebrafish GAK has at least two functions during the development of neural tissues: an early Notch-dependent role in neuronal patterning and a late role in maintaining the survival of neural cells.
含J结构域的蛋白辅助蛋白是网格蛋白介导转运中的关键调节因子，与果蝇Notch信号通路有关。为了探究辅助蛋白的这一作用是否保守，以及辅助蛋白在发育过程中是否还有其他作用，我们研究了斑马鱼中辅助蛋白直系同源物的功能。
与哺乳动物一样，斑马鱼有两种不同的辅助蛋白样分子，即辅助蛋白和细胞周期蛋白G相关激酶（GAK），它们的结构域结构和表达模式不同。斑马鱼的辅助蛋白和GAK在功能上都可以替代果蝇的辅助蛋白，这表明它们具有重叠的分子功能。然而，它们并非完全冗余，因为单独使用吗啉代介导的方法敲低普遍表达的GAK可以增加神经细胞的特化，这是一个已知的Notch依赖过程，同时降低Notch靶基因Her4的表达。此外，抑制GAK功能会导致神经组织中凋亡水平升高，导致神经结构严重退化。
为了支持内吞作用在Notch信号通路中起重要作用这一观点，抑制斑马鱼GAK功能会影响胚胎神经细胞的特化和Her4表达。此外，我们的分析表明，斑马鱼GAK在神经组织发育过程中至少有两个功能：在神经元模式形成中起早期Notch依赖作用，在维持神经细胞存活中起后期作用。
