Project Significance: The faithful segregation of genetic material during cell division is critical for sustaining life. This becomes apparent if one considers that a 70-year old adult has used on average 1000 trillion (1020) cells, which were generated by an equal number of successful cell divisions. In contrast, chromosome segregation and cell division errors can lead to aneuploidy, yielding non- viable cells, genetic disorders or cancer. Cell division is orchestrated by the mitotic spindle, which is composed of a plethora of microtubules (MT) and MT associated proteins (MAP). First, the mitotic spindle captures and aligns chromosomes at the spindle equator. This is achieved via a bundle of MTs, which form the kinetochore-fiber (K-fiber) and connect the kinetochore (KT) of each sister chromatid with opposite cell poles. Next, sister chromatids are split and K-fibers pull sister chromatids to opposite cell poles. Despite 130 years of research on mitosis, it is not clear how the mitotic spindle is assembled and how it obtains its characteristic bipolar shape that is critical for accurate chromosome segregation. Most importantly, it is not understood how KTs are captured in the vast volume of a cell and aligned at its center. It also remains unknown how a threshold force is reached and transmitted via K-fibers to split and segregate sister chromatids and how errors occur. Answers to these questions are needed to explain how cells divide and thus procreate life, and may provide new treatments for diseases that lie at the heart of cell proliferation, such as cancer and cell regeneration. Here, I devise a holistic approach to overcome these experimental limitations and advance our understanding of chromosome segregation and its errors to a biochemical level. I will achieve this by breaking down the problem into the individual MT nucleation pathways that are required for spindle assembly and characterize these pathways at the single molecule level in vitro. This leaves us in the unprecedented position to start combining MT nucleation pathways. Thereby, we will build the mitotic spindle in vitro to not only to determine the molecular organization of the mitotic spindle, but also to elucidate the mechanisms by which K-fibers capture and segregate chromosomes and the causes of segregation errors. Finally, my research will explain how hundreds of proteins can self-assemble on the nm scale into a complex molecular machine 1000-fold larger than its constituents, a challenge for the biochemistry of the 21st century.

Public Health Relevance

In order to divide, a cell needs to equally segregate its chromosomes into two daughter cells, a process which is coordinated by the microtubule-based mitotic spindle. Failure in this process is detrimental for a cell and a leading cause for cancer. While our understanding of these processes rested on a descriptive level, we will elucidate the exact way the mitotic spindle functions, which is not only important to explain life, but is also of medical importance and can be used as a new target for cancer therapy and cell regeneration.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
NIH Director’s New Innovator Awards (DP2)
Project #
Application #
Study Section
Special Emphasis Panel (ZRG1-MOSS-C (56)R)
Program Officer
Deatherage, James F
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Princeton University
Schools of Arts and Sciences
United States
Zip Code
Thawani, Akanksha; Kadzik, Rachel S; Petry, Sabine (2018) XMAP215 is a microtubule nucleation factor that functions synergistically with the ?-tubulin ring complex. Nat Cell Biol 20:575-585
Song, Jae-Geun; Petry, Sabine (2018) Dissecting Protein Complexes in Branching Microtubule Nucleation Using Meiotic Xenopus Egg Extracts. Cold Spring Harb Protoc 2018:pdb.prot100958
Song, Jae-Geun; King, Matthew R; Zhang, Rui et al. (2018) Mechanism of how augmin directly targets the ?-tubulin ring complex to microtubules. J Cell Biol 217:2417-2428
Rale, Michael J; Kadzik, Rachel S; Petry, Sabine (2018) Phase Transitioning the Centrosome into a Microtubule Nucleator. Biochemistry 57:30-37
Alfaro-Aco, Raymundo; Thawani, Akanksha; Petry, Sabine (2017) Structural analysis of the role of TPX2 in branching microtubule nucleation. J Cell Biol 216:983-997
Alfaro-Aco, Raymundo; Petry, Sabine (2017) How TPX2 helps microtubules branch out. Cell Cycle 16:1560-1561