Frise E, Knoblich J A, Younger-Shepherd S, Jan L Y, Jan Y N
Howard Hughes Medical Institute, University of California, San Francisco 94143-0724, USA.
Proc Natl Acad Sci U S A. 1996 Oct 15;93(21):11925-32. doi: 10.1073/pnas.93.21.11925.
Specification of unequal daughter cell fates in the Drosophila external sense organ lineage requires asymmetric localization of the intrinsic determinant Numb as well as cell-cell interactions mediated by the Delta ligand and Notch receptor. Previous genetic studies indicated that numb acts upstream of Notch, and biochemical studies revealed that Numb can bind Notch. For a functional assay of the action of Numb on Notch signaling, we expressed these proteins in cultured Drosophila cells and used nuclear translocation of Suppressor of Hairless [Su(H)] as a reporter for Notch activity. We found that Numb interfered with the ability of Notch to cause nuclear translocation of Su(H); both the C-terminal half of the phosphotyrosine binding domain and the C terminus of Numb are required to inhibit Notch. Overexpression of Numb during wing development, which is sensitive to Notch dosage, revealed that Numb is also able to inhibit the Notch receptor in vivo. In the external sense organ lineage, the phosphotyrosine binding domain of Numb was found to be essential for the function but not for asymmetric localization of Numb. Our results suggest that Numb determines daughter cell fates in the external sense organ lineage by inhibiting Notch signaling.
果蝇外周感觉器官谱系中不等的子细胞命运特化需要内在决定因子Numb的不对称定位以及由Delta配体和Notch受体介导的细胞间相互作用。先前的遗传学研究表明，numb在Notch上游起作用，生化研究揭示Numb能与Notch结合。为了对Numb作用于Notch信号传导进行功能分析，我们在培养的果蝇细胞中表达这些蛋白，并使用无毛抑制因子[Su(H)]的核转位作为Notch活性的报告物。我们发现Numb干扰了Notch引起Su(H)核转位的能力；磷酸酪氨酸结合结构域的C端一半和Numb的C端对于抑制Notch都是必需的。在对Notch剂量敏感的翅发育过程中过表达Numb，表明Numb在体内也能够抑制Notch受体。在外周感觉器官谱系中，发现Numb的磷酸酪氨酸结合结构域对于其功能是必需的，但对于Numb的不对称定位并非必需。我们的结果表明，Numb通过抑制Notch信号传导决定外周感觉器官谱系中的子细胞命运。
