Formin3 is required for assembly of the F-actin structure that mediates tracheal fusion in Drosophila

During tracheal development in Drosophila, some branches join to form a continuous luminal network. Specialized cells at the branch tip, called fusion cells, extend filopodia to make contact and become doughnut shaped to allow passage of the lumen. These morphogenetic processes accompany the highly regulated cytoskeletal reorganization of fusion cells. We identified the Drosophila formin 3 (form 3) gene that encodes a novel formin and plays a role in tracheal fusion. Formins are a family of proteins characterized by highly conserved formin homology (FH) domains. The formin family functions in various actin-based processes, including cytokinesis and cell polarity. During embryogenesis, from 3 mRNA is expressed mainly in the tracheal system. In form 3 mutant embryos, the tracheal fusion does not occur at some points. This phenotype is rescued by the forced expression of form 3 in the trachea. We used live imaging of GFP-moesin during tracheal fusion to show that an F-actin structure that spans the adjoining fusion cells and mediates the luminal connection does not form at abnormal anastomosis sites in form mutants. These results suggested that Form 3 plays a role in the F-actin assembly, which is essential for cellular rearrangement during tracheal fusion. (C) 2004 Elsevier Inc. All rights reserved.

在果蝇气管发育过程中，一些分支连接形成一个连续的管腔网络。位于分支顶端的特化细胞，称为融合细胞，伸出丝状伪足进行接触，并变成环形以允许管腔通过。这些形态发生过程伴随着融合细胞高度受调控的细胞骨架重组。我们鉴定出果蝇成蛋白3（form 3）基因，它编码一种新型成蛋白，并在气管融合中起作用。成蛋白是一类以高度保守的成蛋白同源（FH）结构域为特征的蛋白质家族。成蛋白家族在各种基于肌动蛋白的过程中发挥作用，包括胞质分裂和细胞极性。在胚胎发生过程中，form 3 mRNA主要在气管系统中表达。在form 3突变体胚胎中，气管在某些部位不发生融合。这种表型可通过在气管中强制表达form 3来挽救。我们在气管融合过程中对绿色荧光蛋白 - 膜突蛋白（GFP - moesin）进行实时成像，结果表明在form突变体的异常吻合部位不会形成跨越相邻融合细胞并介导管腔连接的F - 肌动蛋白结构。这些结果表明Form 3在F - 肌动蛋白组装中起作用，而F - 肌动蛋白组装对于气管融合过程中的细胞重排至关重要。（C）2004爱思唯尔公司。保留所有权利。