Division of Anatomy and Neurobiology, Department of Physiology and Cell Biology, Kobe University Graduate School of Medicine, Kobe 650-0017, Japan.
Dev Growth Differ. 2012 Feb;54(2):253-63. doi: 10.1111/j.1440-169X.2012.01327.x.
The brain morphology of vertebrates exhibits huge evolutionary diversity, but one of the shared morphological features unique to vertebrate brain is laminar organization of neurons. Because the Reelin signal plays important roles in the development of the laminar structures in mammalian brain, investigation of Reelin signal in lower vertebrates will give some insights into evolution of vertebrate brain morphogenesis. Although zebrafish homologues of Reelin, the ligand, and Dab1, a cytoplasmic component of the signaling pathway, have been reported, the Reelin receptor molecules of zebrafish are not reported yet. Here, we sought cDNA sequence of zebrafish homologue of the receptors, vldlr and apoer2, and examined their expression patterns by in situ hybridization. Developmental gene expression pattern of reelin, dab1, vldlr, and apoer2 in the central nervous system of zebrafish was compared, and their remarkable expression was detected in the developing laminar structures, such as the tectum and the cerebellum, and also non-laminated structures, such as the pallium. The Reelin receptors exhibited different spatial and temporal gene expression. These results suggest a possibility that duplication and subsequent functional diversity of Reelin receptors contributed to the morphological and functional evolution of vertebrate brain.
脊椎动物的大脑形态表现出巨大的进化多样性，但神经元层状组织是脊椎动物大脑所共有的形态特征之一。由于 Reelin 信号在哺乳动物大脑层状结构的发育中发挥着重要作用，因此研究低等脊椎动物中的 Reelin 信号将有助于深入了解脊椎动物大脑形态发生的进化。虽然已经报道了 Reelin 的配体（如 zebrafish 的 Reelin 配体）和信号通路的细胞质成分 Dab1 的斑马鱼同源物，但斑马鱼的 Reelin 受体分子尚未报道。在这里，我们试图寻找斑马鱼 vldlr 和 apoer2 同源物的 cDNA 序列，并通过原位杂交技术来检测它们的表达模式。比较了 Reelin、Dab1、vldlr 和 apoer2 在斑马鱼中枢神经系统中的发育基因表达模式，它们在发育中的层状结构（如顶盖和小脑）和非层状结构（如大脑皮层）中都有显著表达。Reelin 受体表现出不同的时空基因表达。这些结果表明，Reelin 受体的复制和随后的功能多样性可能有助于脊椎动物大脑的形态和功能进化。
