Component of ubiquitin-positive inclusions in ALS

TAR DNA-binding protein of 43 kDa (TDP-43), a heterogeneous nuclear ribonucleoprotein that functions in regulating transcription and alternative splicing, was identified as a component of ubiquitin-positive tau-negative cytoplasimic inclusions in frontotemporal lobar degeneration (FTLD-U), and subsequently of ubiquitin-positive skein-like inclusions in amyotrophic lateral sclerosis (ALS). Dephosphorylation treatment of sarkosyl-insoluble fractions have suggested that abnormal phosphorylation takes place in the deposited TDP-43. The common occurrence of intracellular accumulations of TDP-43 supports the hypothesis that these disorders represent a clinicopathological entity of a single disease, and suggests that they can be newly classified as a proteinopathy of TDP-43. This article reviews the ubiquitin-positive inclusions in ALS and the recent discovery of TDP-43 in tau-negative inclusions in FTLD-U and ALS. We also discuss the biological implications of these findings for the pathogenesis of ALS.