An Atypical Tropomyosin in Drosophila with Intermediate Filament-like Properties

Abstract

A longstanding mystery has been the absence of cytoplasmic intermediate filaments (IFs) from Drosophila, despite their importance in other organisms. In the course of characterizing the in vivo expression and functions of Drosophila Tropomyosin (Tm) isoforms, we discovered an essential but unusual product of the Tm1 locus, Tm1-I/C, which resembles an IF protein in some respects. Like IFs, Tm1-I/C spontaneously forms filaments in vitro, which are intermediate in diameter between F-actin and microtubules. Like IFs, but unlike canonical Tms, Tm1-I/C contains N- and C-terminal low complexity domains flanking a central coiled coil. In vivo, Tm1-I/C forms cytoplasmic filaments that do not associate with F-actin or canonical Tms. Tm1-I/C is essential for collective border cell migration, in epithelial cells for proper cytoarchitecture, and in the germline for formation of germ plasm. These results suggest that flies have evolved a distinctive type of cytoskeletal filament from Tm.

A new isoform of Drosophila non-muscle Tropomyosin 1 interacts with Kinesin-1 and functions in oskar mRNA localization

“…Under in vitro conditions, Tm1C was able to form filamentous structures. In addition, when ovaries were incubated with a PIPES pH 6.8 buffer, mCherry-Tm1C formed filaments in vivo that colocalized with microtubules (Cho et al, 2016). We obtained similar results using our GFP-Tm1C strain (Fig.…”

“…Furthermore, these authors demonstrate that Tm1C shares some properties with intermediate filaments (Cho et al, 2016). Under in vitro conditions, Tm1C was able to form filamentous structures.…”

“…While our manuscript was in revision, Cho et al independently identified a role for Tm1C in border cell migration (Cho et al, 2016). Furthermore, these authors demonstrate that Tm1C shares some properties with intermediate filaments (Cho et al, 2016).…”

“…The samples were then stained with DAPI, washed in PBST, and mounted onto slides using Aqua Poly mount (Polysciences, Inc., Warrington, PA). In order to detect filaments of GFP-Tm1C and Khc, ovaries expressing the transgene were processed as previously described (Cho et al, 2016).…”

A common framework for EMT and collective cell migration

“…However, many of the mesenchymal markers expressed in human cells are not expressed in lower species (e.g. Brown, 2011;Cho et al, 2016). Indeed, epithelial and mesenchymal cells possess a range of distinct features (Fig.…”