Aberrant neural activity in prefrontal pyramidal neurons lacking TDP-43 precedes neuron loss.

Mislocalization of TAR DNA binding protein 43 kDa (TARDBP, or TDP-43) is a principal pathological hallmark identified in cases of neurodegenerative disorders such as amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). As an RNA binding protein, TDP-43 serves in the nuclear compartment to repress non-conserved cryptic exons to ensure the normal transcriptome. Multiple lines of evidence from animal models and human studies support the view that loss of TDP-43 leads to neuron loss, independent of its cytosolic aggregation. However, the underlying pathogenic pathways driven by the loss-of-function mechanism are still poorly defined. We employed a genetic approach to determine the impact of TDP-43 loss in pyramidal neurons of the prefrontal cortex (PFC). Using a custom-built miniscope imaging system, we performed repetitive in vivo calcium imaging from freely behaving mice for up to 7 months. By comparing calcium activity in PFC pyramidal neurons between TDP-43 depleted and TDP-43 intact mice, we demonstrated remarkably increased numbers of pyramidal neurons exhibiting hyperactive calcium activity after short-term TDP-43 depletion, followed by rapid activity declines prior to neuron loss. Our results suggest aberrant neural activity driven by loss of TDP-43 as the pathogenic pathway at early stage in ALS and FTD.

Chromosome-condensed G1 phase yeast cells are tolerant to desiccation stress.

The budding yeast Saccharomyces cerevisiae is capable of surviving extreme water loss for a long time. However, less is known about the mechanism of its desiccation tolerance. In this study, we revealed that in an exponential culture, all desiccation tolerant yeast cells were in G1 phase and had condensed chromosomes. These cells share certain features of stationary G0 cells, such as low metabolic level. They were also replicatively young, compared to the desiccation sensitive G1 cells. A similar percentage of chromosome-condensed cells were observed in stationary phase but the condensation level was much higher than that of the log-phase cells. These chromosome-condensed stationary cells were also tolerant to desiccation. However, the majority of the desiccation tolerant cells in stationary phase do not have condensed chromosomes. We speculate that the log-phase cells with condensed chromosome might be a unique feature developed through evolution to survive unpredicted sudden changes of the environment.