Distinct functions of human Numb isoforms revealed by misexpression in the neural stem cell lineage in the Drosophila larval brain
Distinct functions of human Numb isoforms revealed by misexpression in the neural stem cell lineage in the Drosophila larval brain
复制标题
DOI：
10.1159/000090760
复制
发表时间：
2006-01-01
影响因子：
2.9
通讯作者：
Okano, H
中科院分区：
文献类型：
--
作者：
Toriya, M;Tokunaga, A;Okano, H
哺乳动物麻木（mNumb）具有多种功能，在中枢神经系统（CNS）神经发育的调控中发挥重要作用，包括维持神经祖细胞和促进神经元分化。然而，Numb的不同功能背后的分子基础尚未阐明。mNumb具有四种剪接异构体，根据其c端亲线富集区（pro-line-rich region， PRR）中氨基酸插入的存在与否可分为两种类型。有人提出mNumb的不同功能可能归因于这两种不同类型的同工异构体。在这项研究中，我们使用果蝇幼虫大脑的外视基板（OOA）作为检测系统来分析这两种亚型在神经干细胞中的功能，因为神经上皮（NE）干细胞在OOA中的增殖模式与脊椎动物神经干/祖细胞的增殖模式非常相似。它们在早期神经发生时分裂扩大祖细胞池，在神经发生晚期分裂产生神经前体/神经元。OOA的克隆分析可以区分NE干细胞和胚胎后神经母细胞（pNBs），前者对称分裂以扩大祖细胞池，后者不对称分裂以产生神经前体（神经节母细胞），每个细胞分裂一次产生两个神经元。我们发现，在OOA中，具有长PRR结构域的人Numb亚型（hNumb- prrl）主要在小鼠中枢神经系统的早期神经发生过程中表达，促进NE细胞和pnb细胞的增殖而不影响神经元分化，而另一种具有短PRR结构域的hNumb亚型（hNumb- prrs）在小鼠胚胎中枢神经系统的整个神经发生过程中表达，抑制干细胞的增殖并促进神经元分化。我们还发现，hnnum - prrs作为麻蝇的功能同源物，比hnnum - prrl更强烈地减少了核Notch的数量，并可能通过内噬降解拮抗Notch功能，这表明两种不同类型的hnnum亚型可能在小鼠胚胎中枢神经系统的不同阶段参与神经发生。
Mammalian Numb (mNumb) has multiple functions and plays important roles in the regulation of neural development, including maintenance of neural progenitor cells and promotion of neuronal differentiation in the central nervous system (CNS). However, the molecular bases underlying the distinct functions of Numb have not yet been elucidated. mNumb, which has four splicing isoforms, can be divided into two types based on the presence or absence of an amino acid insert in the pro-line-rich region (PRR) in the C-terminus. It has been proposed that the distinct functions of mNumb may be attributable to these two different types of isoforms. In this study, we used the outer optic anlage (OOA) of the Drosophila larval brain as an assay system to analyze the functions of these two types of isoforms in the neural stem cells, since the proliferation pattern of neuroepithelial (NE) stem cells in the OOA closely resembles that of the vertebrate neural stem/progenitor cells. They divide to expand the progenitor cell pool during early neurogenesis and to produce neural precursors/neurons during late neurogenesis. Clonal analysis in the OOA allows one to discriminate between the NE stem cells, which divide symmetrically to expand the progenitor pool, and the postembryonic neuroblasts (pNBs), which divide asymmetrically to produce neural precursors (ganglion mother cells), each of which divides once to produce two neurons. We found that in the OOA, the human Numb isoform with a long PRR domain (hNumb-PRRL), which is mainly expressed during early neurogenesis in the mouse CNS, promotes proliferation of both NE cells and pNBs without affecting neuronal differentiation, while the other type of hNumb isoform with a short PRR domain (hNumb-PRRS), which is expressed throughout neurogenesis in the mouse embryonic CNS, inhibits proliferation of the stem cells and promotes neuronal differentiation. We also found that hNumb-PRRS, a functional homologue of Drosophila Numb, more strongly decreases the amount of nuclear Notch than hNumb-PRRL, and could antagonize Notch functions probably through endocytic degradation, suggesting that the two distinct types of hNumb isoforms could contribute to different phases of neurogenesis in the mouse embryonic CNS.