Abstract
We investigated lysosome dynamics during neuronal stem cell (NSC) differentiation by two quantitative and complementary biophysical methods based on fluorescence: imaging-derived mean square displacement (iMSD) and single-particle tracking (SPT). The former extracts the average dynamics and size of the whole population of moving lysosomes directly from imaging, with no need to calculate single trajectories; the latter resolves the finest heterogeneities and dynamic features at the single-lysosome level, which are lost in the iMSD analysis. In brief, iMSD analysis reveals that, from a structural point of view, lysosomes decrement in size during NSC differentiation, from 1 μm average diameter in the embryonic cells to approximately 500 nm diameter in the fully differentiated cells. Concomitantly, iMSD analysis highlights modification of key dynamic parameters, such as the average local organelle diffusivity and anomalous coefficient, which may parallel cytoskeleton remodeling during the differentiation process. From average to local, SPT allows mapping heterogeneous dynamic responses of single lysosomes in different districts of the cells. For instance, a dramatic decrease of lysosomal transport in the soma is followed by a rapid increase of transport in the projections at specific time points during neuronal differentiation, an observation compatible with the hypothesis that lysosomal active mobilization shifts from the soma to the newborn projections. Our combined results provide new insight into the lysosome size and dynamics regulation throughout NSC differentiation, supporting new functions proposed for this organelle.
Highlights
Lysosomes and lysosome-related organelles, which comprise early and late endosomes, constitute a dynamic network of vesicles that traffic and process substrates coming from inside and outside the cell through the connection with autophagy and endocytosis processes, respectively
We investigated lysosome dynamics during neuronal stem cell (NSC) differentiation by two quantitative and complementary biophysical methods based on fluorescence: imaging-derived mean square displacement and single-particle tracking (SPT)
We investigated the lysosome dynamics during the differentiation of neuronal stem cells (NSCs), obtained from mouse embryonic stem cells differentiated using a protocol that mimics cortical development in vitro [19]
Summary
Lysosomes and lysosome-related organelles, which comprise early and late endosomes, constitute a dynamic network of vesicles that traffic and process substrates coming from inside and outside the cell through the connection with autophagy and endocytosis processes, respectively. A better comprehension of lysosomal biophysics could shed new light on the relationship between gene expression and synaptic activity
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