by Roberto
Fig.1. L. olor cellular features. Top: the long "neck" of L. olor. Source Middle: the distinct cell morphologies between active contracted and active elongated states in live cells imaged using differential interference contrast (DIC) microscopy. Scale bar, 40 μm. Source Bottom: confocal fluorescence z-stack projection of an α-tubulin–stained fixed cell reveals the helically arranged cortical cytoskeleton. Source.
I was recently made aware of one of Earth's "most interesting living beings owing primarily to its power of elongation, its wonderful elasticity and its great freedom of movement." Thus begins a captivating 1911 article by S. O. Mast, describing the amazing features of the ciliate Lacrymaria olor. Its name already hints at its shape: a cell body in the form of a tear (Latin lacryma) out of which protrudes a long proboscis reminiscent of a swan's neck (Latin olor).
It is difficult to know exactly when L. olor got its name; I found a source pointing back to the Danish naturalist O.F. Müller. If you are curious and can read Latin, you might want to browse his 1876 treatise on fluvial and marine protists (infusoria). I'll admit, I was not up to the task. In any case, naturalists have gazed (through microscopes) at L. olor in wonderment for centuries.
What makes L. olor so utterly special and captivating? Just look at the thing! In its search for food, it can stretch its proboscis to many times the length of its cell body. Amazingly, this reversible stretching can go from completely withdrawn to longer than thirty body lengths in thirty seconds. You get a sense of the speed of the process from the two middle panels in the figure: all that stretching in the span of a second! In addition, you get a sense of the dynamics of the cellular processes underlying the "neck stretches" from the dramatic changes in the cytoskeleton revealed in the bottom panel of the figure. Of course, the ideal way to visualize L. olor is in "real time." So, have a look at this video.
Fig. 2. Membrane-microtubule unspooling, curved crease origami in a living cell. A: schematic of the membrane pleats along the cell during extension. 1 to 3: zoom-ins of the membrane and cortical cytoskeleton folds in the body, transition zone, and neck (respectively) of an elongated cell. B: folded origami structures (Lacrygami) are pulled to elongate, demonstrating d-cone singularity propagation through sequential opening of the curved crease pleats. Scale bars, 25 mm. Source
How does L. olor accomplish this behavior? A recent paper by Elliot Flaum and Manu Prakash from Stanford University reveals the underlying mechanism. The entire potential length of the neck is stored, folded in helical layers of membrane and cytoskeleton. The authors refer to this geometry as a "curved crease origami" or "Lacrygami." As the forces generated by the beating cilia along the neck and around the mouth pull, the Lacrygami quickly and easily unfolds (Fig. 2A). Realizing that geometry is scale-free, the authors tested the features of this mechanism in a scaled-up model of paper origami (Fig. 2B). It took me a bit of time, but I finally was able to fold a piece of paper. It was certainly thrilling to get a sense of how quickly and easily it is to unfold and refold the pleats. If you have some time to spare after reading the paper, I encourage you to try it. The solutions of evolution will never cease to amaze me!
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