Daniel J. Needleman
- Associate Professor of Applied Physics and of Molecular and Cellular Biology
The Needleman laboratory investigates how the cooperative behaviors of molecules give rise to the architecture and dynamics of self-organizing subcellular structures. These collective effects are not only directly relevant to cellular organization, they also raise a number of fascinating questions concerning the mechanics and statistical physics of these highly non-equilibrium systems. Our long term goal is to use our knowledge of subcellular structures to quantitatively predict biological behaviors and to determine if there are general principles which govern these non-equilibrium steady-state systems.
Our work currently focuses on studying the spindle, the self-organizing molecular machine that segregates chromosomes during cell division. The spindle is a dynamic steady-state structure composed of a plethora of molecules, most notably DNA, which is compacted into chromosomes, and the protein tubulin, which forms long fibers, called microtubules, which are oriented into a bipolar array that constitutes the bulk of the spindle. Even though the overall structure of the spindle can remain unchanged for hours, the molecules that make up the spindle undergo rapid turnover with a half-life of tens of seconds or less, and if the spindle is damaged, or even totally destroyed, it can repair itself. While many of the individual components of the spindle have been studied in detail, it is still unclear how these molecular constituents self-organize into this structure and how this leads to the internal balance of forces that are harnessed to divide the chromosomes.
Research in the Needleman laboratory uses three complementary approaches:
- We are using a range of methods, from single molecule tracking, to magnetic tweezers, to high resolution fluorescence and polarized light microscopy, to study microtubule nucleation, polymerization, and translocation throughout spindles, as well as the activity of motors and other proteins. These quantitative measurements are combined with biochemical and genetic perturbations, and theoretical analysis, to relate the underlying protein dynamics to spindle architecture and, finally, chromosome motion.
- We are developing novel experimental techniques to collect data that is currently inaccessible. This work includes the development of a massively parallel form of fluorescence correlation spectroscopy which will be able to measure the concentration, dynamics, and interactions of soluble proteins at hundreds of points in and around spindles. We are also working on new image analysis methods for optical and electron microscopy.
- We will study self-organization in simple model systems of highly purified cytoskeletal components designed to mimic specific aspects of spindle assembly. Experiments performed on in vitro systems reconstituted from purified components can be highly controlled and therefore provide the ability to test theories in a more rigorous manner than is possible in vivo.