Department of Oncology, Cross Cancer Institute, University of Alberta, Edmonton, Alberta, Canada.
PLoS One. 2011;6(12):e28579. doi: 10.1371/journal.pone.0028579. Epub 2011 Dec 6.
The Reelin-Dab1 signaling pathway plays a critical role in the positioning of migrating neurons, dendrite formation and lamination in the developing central nervous system. We have previously identified two alternatively spliced forms of Dab1 in the developing chick retina: an early form, Dab1-E, expressed in retinal progenitor cells, and a late form, Dab1 or Dab1-L, expressed in amacrine and ganglion cells. Compared to Dab1-L, Dab1-E lacks two exons that encode two Src family kinase (SFK) phosphorylation sites.
Both Dab1-L and Dab1-E-like transcripts were identified in human fetal retina. Expression of human Dab1-L in primary chick retinal cultures resulted in Reelin-mediated induction of SFK phosphorylation and formation of neurite-like processes. In contrast, human Dab1-E-expressing cells retained an undifferentiated morphology. The human Dab1 gene is located within a common fragile site, and it has been postulated that it may function as a tumor suppressor. Analysis of Dab1 splice forms in retinoblastoma and neuroblastoma tumor cells revealed relative enrichment of Dab1-L-like (includes exons 7 and 8) and Dab1-E-like (excludes exons 7 and 8) transcripts in retinoblastoma and neuroblastoma, respectively. Treatment of retinoblastoma cell line RB522A with Reelin resulted in increased tyrosine phosphorylation of Dab1. As Nova2 has previously been implicated in the exclusion of exons 9B and 9C in Dab1, we examined the expression of this splicing factor in neuroblastoma and retinoblastoma cell lines. Nova2 was only detected in neuroblastoma cells, suggesting a correlation between Nova2 expression and increased levels of Dab1-E-like splice forms in neuroblastoma.
These results indicate that alternative splicing of Dab1 is conserved in avian and mammalian species, with Dab1-L driving SFK phosphorylation in both species. Dab1-E- and Dab-L-like isoforms are also expressed in childhood neural tumors, with preferential enrichment of Dab1-L-like and Dab1-E-like isoforms in retinoblastoma and neuroblastoma, respectively.
Reelin-Dab1 信号通路在迁移神经元的定位、树突形成和发育中的中枢神经系统分层中起着关键作用。我们之前在发育中的鸡视网膜中鉴定出 Dab1 的两种选择性剪接形式：一种早期形式 Dab1-E，在视网膜祖细胞中表达，一种晚期形式 Dab1 或 Dab1-L，在无长突细胞和节细胞中表达。与 Dab1-L 相比，Dab1-E 缺失两个编码两个Src 家族激酶（SFK）磷酸化位点的外显子。
在人胎视网膜中均鉴定出 Dab1-L 和 Dab1-E 样转录本。在原代鸡视网膜培养物中表达人 Dab1-L 导致 Reelin 介导的 SFK 磷酸化和神经突样过程的形成。相比之下，表达人 Dab1-E 的细胞保持未分化的形态。人 Dab1 基因位于常见的脆性位点内，据推测它可能作为肿瘤抑制因子发挥作用。在视网膜母细胞瘤和神经母细胞瘤肿瘤细胞中分析 Dab1 剪接形式时，发现相对富含视网膜母细胞瘤和神经母细胞瘤中的 Dab1-L 样（包含外显子 7 和 8）和 Dab1-E 样（排除外显子 7 和 8）转录本。用 Reelin 处理视网膜母细胞瘤细胞系 RB522A 导致 Dab1 的酪氨酸磷酸化增加。由于 Nova2 先前被牵连到 Dab1 中外显子 9B 和 9C 的排除，我们在神经母细胞瘤和视网膜母细胞瘤细胞系中检查了这种剪接因子的表达。仅在神经母细胞瘤细胞中检测到 Nova2，表明 Nova2 表达与神经母细胞瘤中 Dab1-E 样剪接形式水平升高之间存在相关性。
这些结果表明，Dab1 的选择性剪接在禽类和哺乳动物物种中是保守的，Dab1-L 在两种物种中都驱动 SFK 磷酸化。Dab1-E- 和 Dab1-L 样异构体也在儿童神经肿瘤中表达，Dab1-L 样和 Dab1-E 样异构体分别优先富集在视网膜母细胞瘤和神经母细胞瘤中。
