Visualizing cholesterol (CL) fluctuation in plasma membranes is a crucially important yet challenging task in cell biology. Here, we proposed a new imaging strategy based on permeability changes of plasma membranes triggered by different CL contents to result in controllable spatial distribution of single fluorescent probes (SF-probes) in subcellular organelles. Three spatial distribution-controllable SF-probes (PMM-Me, PMM-Et, and PMM-Bu) for imaging CL fluctuation in plasma membranes were rationally developed. These SF-probes target plasma membranes and mitochondria at normal CL levels, while they display solely staining in plasma membranes and mitochondria at increased and decreased CL levels, respectively. These polarity-sensitive probes also show distinct emission colors with fluorescence peaks of 575 and 620 nm in plasma membranes and mitochondria, respectively. Thus, the CL fluctuation in plasma membranes can be clearly visualized by means of the spatially distributed and two-color emissive SF-probes.
Cooperation between organelles is essential to maintain
the normal
functions of cells. Lipid droplets (LDs) and nucleoli, as important
organelles, play an important role in the normal activities of cells.
However, due to the lack of appropriate tools, in situ observation
of the interaction between them has been rarely reported. In this
work, taking into full consideration the pH and charge differences
between LDs and nucleoli, a pH-triggered charge reversible fluorescent
probe (LD-Nu) was constructed based on a cyclization–ring-opening
mechanism. The in vitro pH titration experiment and 1H
NMR showed that LD-Nu gradually transferred from the charged form
to the electroneutral form with the increase of pH, and thus, the
conjugate plane was reduced and its fluorescence blue-shifted. Most
importantly, the physical contact between LDs and nucleoli was visualized
for the first time. Meanwhile, the relationship between LDs and nucleoli
was also further investigated, and the results showed that their interaction
was more liable to be affected by the abnormality of LDs than those
of nucleoli. Moreover, the cell imaging results displayed that the
LDs both in the cytoplasm and nucleus were observed using the probe
LD-Nu, and interestingly, the LDs in the cytoplasm were more susceptible
to external stimuli than those in the nucleus. In a word, the probe
LD-Nu can serve as a powerful tool for further exploration of the
interaction mechanism between LDs and nucleoli in living cells.
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