Endoplasmic Reticulum Stress Signalling Induces Casein Kinase 1-Dependent Formation of Cytosolic TDP-43 Inclusions in Motor Neuron-Like Cells.

Motor neuron disease (MND) is a progressive neurodegenerative disease with no effective treatment. One of the principal pathological hallmarks is the deposition of TAR DNA binding protein 43 (TDP-43) in cytoplasmic inclusions. TDP-43 aggregation occurs in both familial and sporadic MND; however, the mechanism of endogenous TDP-43 aggregation in disease is incompletely understood. This study focused on the induction of cytoplasmic accumulation of endogenous TDP-43 in the motor neuronal cell line NSC-34. The endoplasmic reticulum (ER) stressor tunicamycin induced casein kinase 1 (CK1)-dependent cytoplasmic accumulation of endogenous TDP-43 in differentiated NSC-34 cells, as seen by immunocytochemistry. Immunoblotting showed that induction of ER stress had no effect on abundance of TDP-43 or phosphorylated TDP-43 in the NP-40/RIPA soluble fraction. However, there were significant increases in abundance of TDP-43 and phosphorylated TDP-43 in the NP-40/RIPA-insoluble, urea-soluble fraction, including high molecular weight species. In all cases, these increases were lowered by CK1 inhibition. Thus ER stress signalling, as induced by tunicamycin, causes CK1-dependent phosphorylation of TDP-43 and its consequent cytosolic accumulation.

Towards designer organelles by subverting the peroxisomal import pathway.

The development of 'designer' organelles could be a key strategy to enable foreign pathways to be efficiently controlled within eukaryotic biotechnology. A fundamental component of any such system will be the implementation of a bespoke protein import pathway that can selectively deliver constituent proteins to the new compartment in the presence of existing endogenous trafficking systems. Here we show that the protein-protein interactions that control the peroxisomal protein import pathway can be manipulated to create a pair of interacting partners that still support protein import in moss cells, but are orthogonal to the naturally occurring pathways. In addition to providing a valuable experimental tool to give new insights into peroxisomal protein import, the variant receptor-signal sequence pair forms the basis of a system in which normal peroxisomal function is downregulated and replaced with an alternative pathway, an essential first step in the creation of a designer organelle.Designer organelles could allow the isolation of synthetic biological pathways from endogenous components of the host cell. Here the authors engineer a peroxisomal protein import pathway orthogonal to the naturally occurring system.

Peroxisome biogenesis, protein targeting mechanisms and PEX gene functions in plants.

Peroxisomes play diverse and important roles in plants. The functions of peroxisomes are dependent upon their steady state protein composition which in turn reflects the balance of formation and turnover of the organelle. Protein import and turnover of constituent peroxisomal proteins are controlled by the state of cell growth and environment. The evolutionary origin of the peroxisome and the role of the endoplasmic reticulum in peroxisome biogenesis are discussed, as informed by studies of the trafficking of peroxisome membrane proteins. The process of matrix protein import in plants and its similarities and differences with peroxisomes in other organisms is presented and discussed in the context of peroxin distribution across the green plants.