seminar: bianxiao cui

January 23, 2007 at 9:30 pm | | seminars, single molecules

Bianxiao Cui, a postdoc in Steve Chu‘s lab here at Stanford, gave a job talk in the Chemistry Department last week. The title was approximately “Single-Molecule Analysis of NGF in Live Neurons (Using Quantum Dots).” Anyway, that gets the point of the talk. It was pretty cool. Here are my notes:

cui_seminar_1.jpg     cui_seminar_2.jpg     cui_seminar_3.jpg

Summary: Nerve-growth factor (NGF) is transported down the axon from the distal end near a target to the nerve cell body, and this tells the axon to grow. To image this transport in live cells, they labeled NGF with quantum dots (QDs) using a biotin/streptavidin linkage and tracked the labeled molecules using “pseudo TIRF”—somewhere between TIR illumination and columnated epi so that the excitation extended a little more into the sample than TIR, but kept background low. They used special compartmented sample containers (and later, microfluidic cells) in order to separate the cell body from the axon (because the labeled NGF nonspecifically labels the entire cell body and makes it too difficult to image).

Cui showed some beautiful (false-color) movies of individual QD-NGF-endosome complexes being actively transported down microtubules toward the cell body. Also found were instances where endosomes moved backward (toward distal axon) and endosomes allegedly passed over each other (although it was unclear to me how they proved that the two endosomes were on the same microtubule and if they actually passed over, because each diffraction-limited spot is indistinguishable). She made some claims about only one NGF per endosome (i.e. the endosome does not wait for more passengers), but that part was a little fuzzy to me (although it was probably the point of the talk). Also, they found that labeled NGF co-localized with signaling molecules in the cell body. Cool.

By fitting the point-spread function of the QDs, they were able to localize each endosome to individual microtubules (imaging below the diffraction limit). This was very cool, and Cui showed tracks of endosomes switching microtubules and then changing speed or direction. Finally, she even did a mouse study, but this seemed tacked on. The real results were the imaging and single-particle tracking.

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  1. I am happy to hear that someone other than me is using bastardized-TIR as an imaging tool. I wasn’t calling it pseudo-TIR though.
    speaking of job talks, a guy from your lab gave a talk at Harvard (Cohen?), i think it was quite good.
    although I wasn’t so impressed by the electrical trap idea.

    Comment by nick — February 4, 2007 #

  2. Yeah, Adam Cohen was a grad student/is a postdoc in my lab and he’s on the job-talk circuit. Glad you liked his talk, I’ll let him know.
    .
    I understand your lack of excitement about his trap mechanism: it’s sorta still in the theoretically-exciting phase, I suppose. (See this link to learn what we’re talking about.) I wonder if you’d be more impressed if he’d done any real measurement on single biomolecules. Are you unimpressed by the concept, the applicability, or what? I do like the idea of measuring single nano objects without attaching them to a surface!
    .
    So “pseudo”-TIR is working for you? Do you use it because you have some large objects on the surface or because you have some passivation layer? Wouldn’t it be cool to use some super-lens or negative-index material and shift the evanescent decay up a quarter micron? Granted, I know very little about the theory, but I want it!

    Comment by sam — February 7, 2007 #

  3. pseudo-TIR works great.
    indeed a lot of people are using it either they don’t bother to deal with having real TIR or they don’t know how to allign TIR. For example, I saw people imaging kinesins on axonyms (thickness of axonyms is ~250-300 nm), and they still claim that they use TIR. Funny! I use it for my E Coli experiments and works great. I guess there can be alternative ways of increasing the range, such as wave guides or surface plasmons. But buying a box of precleaned coverslips from the store room is the easiest.

    I wouldn’t say that I am unimpressed with ABEL trap. It is cool, but I am not sure about the applicability of the work. I remember there was a dutch or german group separating nanotubes with the same idea(on an APS meeting 4-5 years ago). Actually I am curious to see whether you can really get some useful biology out of it. There are microfluidic devices as well for the same purpose. Isn’t Steve Quake’s stuff bad ass?
    lab on a chip!
    or if your point is really getting rid of brownian noise, just stick your bacteria to the surface as everyone does. But I should admit that I find the patience and the endurance of single molecule people outstanding. BTW someone told that Adam pulled his application back. is that true?

    Comment by nick — February 9, 2007 #

  4. Quake’s stuff always impresses me. I go to talks from his lab whenever I can!
    .
    I don’t know anything about Adam’s applications, etc. He hasn’t said anything and I haven’t asked. I figure we’ll just have a champagne-cork-shooting contest when he accepts a job!

    Comment by sam — February 9, 2007 #

  5. […] 刚刚google到的一个有趣的网站,关于polymer Chemistry。只可惜我不做化学,:P http://blog.everydayscientist.com/?p=403   […]

    Pingback by 一花一世界: 8一个高中校友Bianxiao Cui — April 27, 2007 #

  6. It is probably more accurate to call it leaky TIRF rather than “Pseudo-TIRF.”

    Comment by Axicon — January 14, 2008 #

  7. ooo, i like that description!

    Comment by sam — January 15, 2008 #

  8. […] 刚刚google到的一个有趣的网站,关于polymer Chemistry。只可惜我不做化学,:P http://blog.everydayscientist.com/?p=403   […]

    Pingback by 8一个高中校友Bianxiao Cui | 一花一世界 — October 24, 2010 #

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