Genetically encoded lysine photocage for spatiotemporal control of TDP-43 nuclear import.

Intracellular aggregation of transactive response DNA binding protein of 43 kDa (TDP-43) is a hallmark of neurodegenerative diseases such as amyotrophic lateral sclerosis. While primarily a nuclear protein, TDP-43 translocates to the cytosol during cellular stress. Consequences of cytosolic accumulation of TDP-43 is difficult to evaluate in the absence of exogenous toxins. Here, we demonstrate spatiotemporal control over the nuclear import of TDP-43 by installing a photocage (ortho-nitrobenzyl ester) on a single lysine residue (K84) through amber codon suppression in HEK293T cells. Translocation of this cytosolic construct is photo-triggerable in a dose-dependent manner with 355 nm light. Interestingly, both fluid- and solid-like puncta were found based on fluorescence recovery after photobleaching experiments, similar to what is expected of stress granules and intracellular aggregates, respectively. This optogenetic method is advantageous as it is minimally perturbative and broadly applicable to other studies of protein translocation between cellular compartments.