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熔断丝调节果蝇环形内脏肌的伸展和生长,但不调节成肌细胞融合。

Blown fuse regulates stretching and outgrowth but not myoblast fusion of the circular visceral muscles in Drosophila.

作者信息

Schröter Roxane H, Buttgereit Detlev, Beck Lothar, Holz Anne, Renkawitz-Pohl Renate

机构信息

Philipps-Universität Marburg, Fachbereich Biologie, Entwicklungsbiologie, 35043 Marburg, Germany.

出版信息

Differentiation. 2006 Dec;74(9-10):608-21. doi: 10.1111/j.1432-0436.2006.00080.x.

Abstract

Circular visceral muscles of Drosophila are binuclear syncytia arising from fusion of two different kinds of myoblasts: a circular visceral founder cell and one visceral fusion-competent myoblast. In contrast to fusion leading to the somatic body-wall musculature, myoblast fusion for the circular visceral muscles does not result in massive syncytia but instead in syncytia interconnected with multiple cytoplasmic bridges, which differentiate into large web-shaped muscles. Here, we show that these syncytial circular visceral muscles build a gut-enclosing network with the interwoven longitudinal visceral muscles. At the ultrastructural level, during circular visceral myoblast fusion and the first step of somatic myoblast fusion prefusion complexes and electron-dense plaques were not detectable which was surprising as these structures are characteristic for the second step of somatic myoblast fusion. Moreover, we demonstrate that Blown fuse (Blow), a cytoplasmic protein essential for the second step of somatic myoblast fusion, plays a different role in circular visceral myogenesis. Blow is known to be essential for progression beyond the prefusion complex in the somatic mesoderm; however, analysis of blow mutants established that it has a restricted role in stretching and outgrowth of the syncytia in the circular visceral muscles. Furthermore, we also found that in the visceral mesoderm, Blow is expressed in both the fusion-competent myoblasts and circular visceral founders, while expression in the somatic mesoderm is initially restricted to fusion-competent myoblasts. We also demonstrate that different enhancer elements in the first intron of blow are responsible for this distinct expression pattern. Thus, we propose a model for Blow in which this protein is involved in at least two clearly differing processes during Drosophila muscle formation, namely somatic myoblast fusion on the one hand and stretching and outgrowth of circular visceral muscles on the other.

摘要

果蝇的环形内脏肌是双核合胞体,由两种不同类型的成肌细胞融合而成:一个环形内脏起始细胞和一个具有融合能力的内脏成肌细胞。与形成体壁肌肉组织的融合不同,环形内脏肌的成肌细胞融合不会产生大量合胞体,而是形成通过多个细胞质桥相互连接的合胞体,这些合胞体分化为大的网状肌肉。在这里,我们表明这些合胞体环形内脏肌与交织的纵向内脏肌构建了一个包围肠道的网络。在超微结构水平上,在环形内脏成肌细胞融合以及体壁成肌细胞融合的第一步过程中,未检测到预融合复合体和电子致密斑,这令人惊讶,因为这些结构是体壁成肌细胞融合第二步的特征。此外,我们证明了Blown fuse(Blow),一种体壁成肌细胞融合第二步所必需的细胞质蛋白,在环形内脏肌生成中发挥不同作用。已知Blow对于体壁中胚层中预融合复合体之后的进程至关重要;然而,对blow突变体的分析表明,它在环形内脏肌合胞体的伸展和生长中作用有限。此外,我们还发现在内脏中胚层中,Blow在具有融合能力的成肌细胞和环形内脏起始细胞中均有表达,而在体壁中胚层中的表达最初仅限于具有融合能力的成肌细胞。我们还证明了blow第一个内含子中的不同增强子元件负责这种不同的表达模式。因此,我们提出了一个关于Blow的模型,其中该蛋白在果蝇肌肉形成过程中至少参与两个明显不同的过程,一方面是体壁成肌细胞融合,另一方面是环形内脏肌的伸展和生长。

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