Isomin: a novel cytoplasmic intermediate filament protein from an arthropod species

Abstract

BackgroundThe expression of intermediate filaments (IFs) is a hallmark feature of metazoan cells. IFs play a central role in cell organization and function, acting mainly as structural stress-absorbing elements. There is growing evidence to suggest that these cytoskeletal elements are also involved in the integration of signalling networks. According to their fundamental functions, IFs show a widespread phylogenetic expression, from simple diblastic animals up to mammals, and their constituent proteins share the same molecular organization in all species so far analysed. Arthropods represent a major exception in this scenario. Only lamins, the nuclear IF proteins, have so far been identified in the model organisms analysed; on this basis, it has been considered that arthropods do not express cytoplasmic IFs.ResultsHere, we report the first evidence for the expression of a cytoplasmic IF protein in an arthropod - the basal hexapod Isotomurus maculatus. This new protein, we named it isomin, is a component of the intestinal terminal web and shares with IFs typical biochemical properties, molecular features and reassembly capability. Sequence analysis indicates that isomin is mostly related to the Intermediate Filament protein C (IFC) subfamily of Caenorhabditis elegans IF proteins, which are molecular constituents of the nematode intestinal terminal web. This finding is coherent with, and provides further support to, the most recent phylogenetic views of arthropod ancestry. Interestingly, the coil 1a domain of isomin appears to have been influenced by a substantial molecular drift and only the aminoterminal part of this domain, containing the so-called helix initiation motif, has been conserved.ConclusionsOur results set a new basis for the analysis of IF protein evolution during arthropod phylogeny. In the light of this new information, the statement that the arthropod phylum lacks cytoplasmic IFs is no longer tenable.See commentary article: http://www.biomedcentral.com/1741-7007-9-16.

An Atypical Tropomyosin in Drosophila with Intermediate Filament-like Properties

“…Despite the prevalence of IFs in metazoans, they are lacking from the largest phylum, the arthropods, with one known exception (Mencarelli et al, 2011). It has been suggested that some of the mechanical support provided by IFs, such as the protection from skin blistering by epidermal keratins, might be unnecessary in animals with an exoskeleton, whereas other IF functions might have been subsumed by distinct proteins (Herrmann and Strelkov, 2011).…”

“…It has been suggested that other types of proteins might perform crucial functions of IFs (Herrmann and Strelkov, 2011; Mencarelli et al, 2011), however the identities of such proteins if they exist are unknown. Reasonable candidates would be proteins that possess similar domains.…”

Proteomic analysis of secreted saliva from Russian Wheat Aphid (Diuraphis noxia Kurd.) biotypes that differ in virulence to wheat

“…It functions as a cytoplasmic intermediate filament protein in nuclear and chromatin organization, mechanical stress mitigation, and cytoplasmic organization and cellular polarity [94][95][96]. The presence of vesicle-associated proteins in D. noxia saliva suggests protein carry-over from the secretory pathway into the salivary solution.…”

History and phylogeny of intermediate filaments: Now in insects

“…This notion has now been challenged by the discovery of a protein in the hexapod Isotomurus maculatus , that resembles cytoplasmic IF proteins from other invertebrates quite distinctly [4]. When the primary sequence of isomin is aligned to a Drosophila lamin D m0 (the B-type lamin), coil 1B and coil 2 match quite well in length (Figure 2).…”