Lysosomes visualized via LAMP1

A. Z-stack

B. Timelapse (apical)

C. Timelapse (basal)

Figures. Z-stack and timelapse movies of lysosomes. A) Z-stack of live hiPS cells expressing mEGFP tagged LAMP1 imaged on a spinning-disk confocal microscope. Movie starts at the bottom of the cells and ends at the top. Scale bar = 5µm. B–C) Timelapse movie of live hiPS cells expressing mEGFP-tagged LAMP1. Images were taken as a single slice near the top (B) or bottom (C) of the cell every 1 sec for 100 sec on a spinning-disk confocal microscope. Images have had the ‘despeckle’ ImageJ filter applied. Movie sped up 10x real time. Scale bar = 5 µm.
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Observations

• Lysosomes are membrane-bound organelles responsible for breaking down unwanted cellular materials for reuse. They are often considered the “waste disposal” sites within cells. LAMP1 is a transmembrane glycoprotein, which together with LAMP2 is the most abundant protein present in the lysosomal membrane (~50% of membrane proteins), making it a great reporter protein for lysosomes.
• Lysosomes are classically known to form round vesicles of different sizes. However, they can also take on tubular morphologies, something that is less commonly known because these tubules are often lost upon fixation. In hiPS cells, lysosomal tubules are more visible in the bottom half of cells. Smaller vesicles are also predominant near the bottom while larger vesicles are mainly found at the top of the cells.
• Lysosomes are very dynamic. Round vesicular lysosomes move around the cell rapidly, sometimes with a stop and go motion. They also deform, most dramatically when one end is pinched into a tear-drop shape. This can also be associated with the pulling out of tubular lysosomes.
• Tubular lysosomes are also very dynamic, with branches being pulled out and fission and fusion dynamics altering their morphology.
• In recent literature, tubular lysosomes have been implicated as being structures connecting the lysosome to other intracellular compartments (e.g. late endosome) and being involved in the fusion process between these compartments. Tubular lysosomes have also been shown to be a precursor to lysosome formation via budding during cell starvation.