Editing Intermediate filament (section)

== In other organisms ==
IF proteins are universal among animals in the form of a nuclear lamin. The Hydra has an additional "nematocilin" derived from the lamin. Cytoplasmic IFs (type I-IV) are only found in [[Bilateria]]; they also arose from a [[gene duplication]] event involving "type V" nuclear lamin. In addition, a few other diverse types of eukaryotes have lamins, suggesting an early origin of the protein.<ref name=Polyphyly>{{cite journal | vauthors = Kollmar M | title = Polyphyly of nuclear lamin genes indicates an early eukaryotic origin of the metazoan-type intermediate filament proteins | journal = Scientific Reports | volume = 5 | page = 10652 | date = May 2015 | pmid = 26024016 | pmc = 4448529 | doi = 10.1038/srep10652 | doi-access = free | bibcode = 2015NatSR...510652K }}</ref>

There was not really a concrete definition of an "intermediate filament protein", in the sense that the size or shape-based definition does not cover a [[monophyletic group]]. With the inclusion of unusual proteins like the network-forming beaded lamins (type VI), the current classification is moving to a clade containing nuclear lamin and its many descendants, characterized by sequence similarity as well as the exon structure. Functionally-similar proteins out of this clade, like [[crescentin]]s, alveolins, tetrins, and epiplasmins, are therefore only "IF-like". They likely arose through [[convergent evolution]].<ref name=Polyphyly/>