New biophysical strategies for uncovering how dividing cells accurately segregate their chromosomes

Synopsis

An exquisite molecular machine, the mitotic spindle, separates duplicated chromosomes during cell division.  To uncover how it operates, we are reconstituting spindle activities using purified components and developing biophysical tools to directly manipulate and track their dynamics at the single molecule level.  The accuracy of eukaryotic chromosome segregation is astounding and depends critically on kinetochores, which are protein complexes that maintain strong yet dynamic attachments between chromosomes and spindle microtubules in order to produce force and move the chromosomes.  Kinetochores also carry out vital regulatory activities such as distinguishing and selectively stabilizing proper attachments, releasing erroneous attachments, and generating diffusible ‘wait’ signals to delay mitosis until proper attachments are achieved.  Our reconstitution-based approach has enabled the first direct measurements of many fundamental kinetochore activities and direct tests of long-standing hypotheses, proving for example that tension stabilizes kinetochore attachments in at least two different ways.  Our new data now reveal another striking and previously unrecognized behavior:  yeast kinetochores grip the sides of microtubules with directionally asymmetric strength – much more strongly when pulled toward plus ends than when pulled toward minus ends.  In my talk, I will describe how we discovered this phenomenon and how it might promote proper attachments during early mitosis, thus helping to explain the incredible fidelity of mitotic chromosome segregation, on which all eukaryotic life depends.