Yu Linlin, Zhou Qingxiang, Zhang Chuanxi, Pignoni Francesca
Ministry of Agriculture Key Laboratory of Molecular Biology of Crop Pathogens and Insects, Institute of Insect Science, Zhejiang University, Hangzhou 310029, China.
Genesis. 2012 May;50(5):393-403. doi: 10.1002/dvg.20816. Epub 2011 Dec 27.
The proneural genes are fundamental regulators of neuronal development in all metazoans. A critical role of the fly proneural factor Atonal (Ato(Dm)) is to induce photoreceptor neuron formation in Drosophila, whereas its murine homolog, Atonal7(Mm) (aka Ath5) is essential for the development of the ganglion cells of the vertebrate eye. Here, we identify the Bombyx mori ato homolog (ato(Bm) ). In a pattern strikingly reminiscent of ato(Dm), the ato(Bm) mRNA is expressed as a stripe in the silkworm eye disc. Its DNA-binding and protein-protein interaction domain is highly homologous to the Ato(Dm) bHLH. Targeted expression of Ato(Bm) in the endogenous ato(Dm) pattern rescues the eyeless phenotype of the fly ato(1) mutant and its ectopic expression induces similar gain-of-function phenotypes as Ato(Dm). Rescue experiments with chimeric proteins show that the non-bHLH portion of Ato(Bm) (N-region) can effectively substitute for the corresponding region of the fly transcription factor, even though no apparent conservation can be found at the amino acid level. On the contrary, the highly similar bHLH domain of Ato(Bm) cannot similarly substitute for the corresponding region of Ato(Dm). Thus, the bHLH(Bm) domain requires the Ato(Bm) N-region to function effectively, whereas the bHLH(Dm) domain can operate well with either N-region. These findings suggest a role for the non-bHLH portion of Ato proteins in modulating the function of the bHLH domain in eye neurogenesis and implicate specific aa residues of the bHLH in this process.
原神经基因是所有后生动物神经元发育的基本调节因子。果蝇原神经因子无调性（Ato(Dm)）的一个关键作用是在果蝇中诱导光感受器神经元的形成，而其小鼠同源物无调性7（Mm）（又名Ath5）对于脊椎动物眼睛神经节细胞的发育至关重要。在这里，我们鉴定了家蚕无调性同源物（ato(Bm)）。ato(Bm) mRNA在蚕眼盘中呈条带状表达，这种表达模式与ato(Dm)惊人地相似。其DNA结合和蛋白质-蛋白质相互作用结构域与Ato(Dm)的bHLH高度同源。以果蝇内源性ato(Dm)的模式靶向表达Ato(Bm)可挽救果蝇ato(1)突变体的无眼表型，其异位表达诱导出与Ato(Dm)相似的功能获得性表型。嵌合蛋白的拯救实验表明，尽管在氨基酸水平上没有明显的保守性，但Ato(Bm)的非bHLH部分（N区域）可以有效地替代果蝇转录因子的相应区域。相反，Ato(Bm)高度相似的bHLH结构域不能类似地替代Ato(Dm)的相应区域。因此，bHLH(Bm)结构域需要Ato(Bm)的N区域才能有效发挥作用，而bHLH(Dm)结构域与任何一个N区域都能很好地发挥作用。这些发现表明Ato蛋白的非bHLH部分在调节眼神经发生中bHLH结构域的功能方面发挥作用，并暗示了该过程中bHLH的特定氨基酸残基。
