Synemin has three splice variants (α, β, and L) with identical head and rod domains but with tail domains of varying size. α- and β-
Synemin are larger than most
intermediate filament proteins (1565 and 1253
amino acids, respectively) but L-
synemin is shorter (339
amino acids).
Synemin isoforms do not self-assemble into filaments but can copolymerize with
vimentin and
desmin.
Synemin is present in all muscle cell types, in a few neural cell types, and in various other nonepithelial cell types.
Synemin expression is regulated, sometimes in an
isoform-specific manner, during development of the nervous system, in brain and
breast cancer cells and during
injuries to the brain and liver. Mice-lacking
synemin develop a myopathic phenotype, possibly due to
synemin role in linking
desmin filaments to costameres and sarcomeres.
Synemin may play this role through its demonstrated binding to costameric and sarcolemmal
proteins, such as α-
actinin,
vinculin, and members of the
dystroglycan complex. In
astrocytoma cells,
synemin regulates proliferation by interacting with PP2A to modulate Akt phosphorylation status. Methods to identify
synemin binding partners are central to understand the roles of this
protein in diverse cell types. Here, we describe how to use proximal
ligation assays (PLA) for this purpose. PLA
complement biochemical methods such as immunoprecipitation by relying on the use of
antibodies conjugated to
oligonucleotide probes to visualize by fluorescence microscopy
protein-
protein interactions in cells and tissues.