Bensimon, David B.



Prof. David Bensimon a world-leading biophysicist and a 2007 Regent’s Professor in our department, has been appointed as professor in the Physical Chemistry Division and will be teaching and carrying out research at UCLA for one quarter each year. He received his Ph.D. from the University of Chicago in 1986, where he completed his thesis on the theory of Chaos and Pattern Formation under the guidance of Leo Kadanoff.  As a recipient of a Weizmann Fellowship, he pursued post-doctoral research at Bell Laboratories and then at the Ecole Normale Superieure (ENS), in Paris.  In 1988 he accepted a permanent position at the ENS in the French National Center for Scientific Research (CNRS), where he currently holds the position of  Directeur de Recherche.

At the ENS Prof. Bensimon established a small experimental team that investigated instabilities in hydrodynamics and phospholipid membranes. With his post-doc, M. Mutz, and his student, X. Michalet, he discovered a new class of phospholipid vesicles — vesicles of non-spherical topology, work for which they received the 1997 Vinci of Excellence Award.  At the same time he began investigations in biophysics and in 1992, he and his brother, Aaron focused on the study of the elastic properties of single DNA molecules. While attempting to bind DNA specifically to surfaces, they discovered Molecular Combing, the process by which DNA molecules anchored to a surface are aligned by a receding meniscus. The Bensimon brothers received the 1994 Jacques Monod Prize for this work, an award by the Fondation de France to young scientists who have made significant research advances in the early years of their careers.

In 1995 Prof. Bensimon shifted his research focus to the study of the elastic properties of DNA.  While a number of researchers had been pulling/stretching single DNA molecules, he recognized that since the structure of DNA is a double helix, twisting it should be biologically more informative and relevant.  To that purpose he invented the Magnetic Trap, a tool that allowed him to pull and twist individual DNA molecules.  This has enabled him to study, at the single-molecule level, the interactions between DNA and topoisomerases (enzymes that modify the topology of a DNA molecule, relieving torsional stress that builds up during transcription and replication).  This influential series of fundamental and ground-breaking experiments, carried out with his colleague V. Croquette, earned him the Special Prize of the French Physical Society.

Prof. Bensimon has since broadened his interests to study a variety of increasingly more biological systems: DNA  polymerases, helicases, regulation factors, and chromatin remodeling factors, etc. His group is presently engaged in forays in three novel directions: a coupling between single-molecule manipulation and fluorescent visualization, studies of evolution in bacteria, and the development of photo-activatable regulation factors. Very recently, he has made considerable progress towards optically controlling the activity of any protein/enzyme in a single cell of the zebra fish.  This work is poised to revolutionize the field of developmental biology.

Prof. Bensimon co-founded Depixus, which works on the sequencing and epigenetic analysis of nucleic acids (DNA and RNA).  He also wrote “The Unity of Science” and “Single Molecule Studies of Nucleic Acids and their Proteins” and the use of optogenetic tools to induce cancer at the single cell level with high probability.

In collaboration with Prof. Shimon Weiss, Prof. Bensimon and colleagues used a caged-cyclofen system to activate a Cre-ERT recombinase and turn on an oncogene (kRasG12V) in single-cells of a live zebrafish embryo. The goal was to address the following questions. What are the minimal necessary oncogenic mutations needed for tumorigenesis? How many neighboring cells need to carry such mutations for efficient tumorigenesis? Under what genetic background? His team discovered that transient activation of an oncogene (kRas) did not result in tumors, while permanent activation of the mutant kRas in isolated cells resulted in tumorigenesis. Furthermore, they recently discovered that activation of kRas in a de-differentiated cell (expressing VentX) increases the probability of tumorigenesis by two orders of magnitude. These results suggest that cancer might originate in undifferentiated cells (stem cells as opposed to somatic cells), opening the way for a study of the early stages of carcinogenesis and the development of drugs against these early stages of cancer.

Lastly, his team has most recently developed a photoactivatable version of Cas9 (a Cas9-ERT fusion called OptoCas9) which allows one to target specific genes in specific tissues down to the single cell.

Honors & Awards

  • UCLA Regent’s Professor
  • ICAM ICAM Fellow

Representative Publications

[Recent Publications, complete list here]