Monday, February 16, 2009

A Still Point in Cell Motility Research

I study a group of single-cell organisms - the Foraminifera - that are incessantly busy. Within "foram" pseudopodia, which are the spiderweb-like projections seen in the photo below, one can watch (with a microscope) zillions of granules zipping to-and-fro; likewise, tiny particles picked up from the environment move back and forth along the pseudopodial surfaces. The rapid, bidirectional motion of these intracellular granules and surface-bound particles is a fascinating biological phenomenon I've been studying for a couple of decades now.

Watching this cellular hustle and bustle can make you feel frazzled and fried, particularly if you empathize with the foram. It has no still point in life as it prods and probes the environment for food and a mate. That is, no still point until a cell biologist enters its realm...

Phase contrast light micrograph of Allogromia with extended pseudopodia

I recall here a critical experiment performed as part of my dissertation research back in the early 80's. The question being asked was whether or not membrane surface motility, revealed by the movement of surface-bound latex spheres, was linked to a system of cytoskeletal elements called microtubules. (I'll blog about these miniscule protein tubes at a later time.) To find out, I was treating forams with various drugs that disassemble microtubules. The logic was simple: destroy microtubules and you stop cell processes that depend on them. My colleague Jeff Travis had already shown that these anti-microtubule drugs shut down intracellular transport in forams. Would they likewise stop the motion surface-bound particles? Late one night, alone in the lab, I was ready to find out.

Foram pseudopodia are a blur of activity. Seen here is a one-second exposure of pseudopodia imaged at high magnification. Because of the non-stop motion of intracellular granules, the 'pods appear smeared and uniformly dark; surface-bound latex spheres (1-micrometer in diameter) are seen as white streaks due to their movement along the 'pod surfaces.

It takes several hours to set up these experiments and, quite frankly, they're dangerous because they involve handling tiny amounts of some very potent compounds. It is not simple work, either: nimble hands, like those of an artist, are needed to seal perfusion chambers and assemble the intricate apparatus. Also like artists, an eye for the aesthetic is needed in order to record observations in ways that colleagues will appreciate. I remember my mentor Sam McGee-Russell saying "If it looks good, mate, the results will be more convincing." My other mentor, Conly Rieder, always said "Bowser, if you want to get a job in science, you better take pretty pictures!" We'll call it effective visual communication.

The stillness following drug treatment is manifest as sharp images. In this two-second exposure, the motionless granules inside the pseudopods are clearly seen. So, too, are the static, white latex spheres.

The result of this experiment was yes: take away microtubules and you stop membrane surface motility. Not to be too melodramatic, but the thrill of this discovery screamed in the silence of that evening, and I'll never forget its impact on my psyche. It was a still point for me (and literally for the foram) -- an "ah-hah!" moment shared with no one until the video recordings were shown to lab mates the following morning. The question I was addressing was based on the collective wisdom of hundreds of scientists over many decades, but this experiment was mine alone. Conducted alone, at night, just the way that science was "supposed" to be done. A still point indeed.

Few things are more beautiful than gleaning basic knowledge about the workings of the natural world. To me, it defines the sublime. And revealing that truth is art.


  1. Very cool, Sam! Is there chance you can post that video you mention?

  2. Sorry Steffi, those experiments were documented using an ancient 3/4-inch time lapse recorder. BUT - I'm currently making HDTV movies of normal pseudopodial transport, and will post them if/when another still point occurs ...

  3. Samuel - this is poetry, too. Lovely, thoughtful, distilled. Thank you, C.

  4. I'd love to extract certain elements of this post and compose a poem, Claire. Perhaps it is something else we can collaborate on? Sam

  5. Hello Sam,

    Just a quick note to say Thank Q! for providing a link to my blog via your sidebar. I have now set up a reciprocal link on a separate dalek blog here, and this blog can be accessed from the sidebar of the OBD Home Blog.

    All The Best!