Aussie Suzuki

Visualize and Analyze “Force” at Kinetochores
Accurate cell division, which transmits replicated chromosomes equally into daughter cells, is an essential process to maintain life in all organisms. In order to achieve faithful chromosome segregation, microtubules must be properly attached to the kinetochore. The kinetochore is a macro-molecular protein architecture on centromere chromatin and serves as a platform for the microtubule assembly. The kinetochore structure is built by at least 26 different kinds of core-kinetochore proteins, with their multiple copies.

Important kinetochore functions are: 1) serving as a platform for microtubule binding on chromosome 2) force production and transmission, 3) mitotic checkpoint (SAC: Spindle Assembly Checkpoint) control, and 4) mitotic error correction. Force at kinetochore is critical for dynamic chromosome movements as well as kinetochore deformation in chromosome segregation process, but it requires technical advance to detect cellular tension when studying functions of force at kinetochores. We have recently succeeded in developing a sensitive device to detect tension at the Ndc80 complex in budding yeast kinetochores. Our next question is how human kinetochore generates and transmits forces for faithful chromosome segregation. We are trying to build a human Ndc80 tension biosensor in order to study functions of “force” at human kinetochores.

Kinetochore Functions in Faithful Chromosome Segregation
Kinetochore is a macro-molecular protein complex built by at least 26 different core-kinetochore proteins during metaphase and additional corona proteins, also known as SAC proteins, which are contributed during prometaphase or at unattached kinetochores. All kinetochore proteins have multiple copies. Are these multiple copies of kinetochore proteins randomly mixed, like a salad bowl, at the kinetochore? The answer is No. It may be surprising, but the core-kinetochore proteins systematically build a kinetochore architecture within a diffraction limited spot (~200 nm dimensions) at centromeric chromatin on the chromosome.

In order to resolve these spatial and temporal difficulties, we use a calibrated confocal microscope, light-sheet microscopy, and super-resolution microscopy including SIM, STED, and 2D/3D fluorescence co-localization methods we recently developed for the following projects:

(1) How kinesin contributes to proper kinetochore functions.

(2) Kinetochore deformation in mitotic progression.

(3) SAC protein architecture.

Kinetochore/Centromere Integrity and Cancer
Failure of accurate chromosome segregation causes CIN (Chromosomal INstability), which includes occurrences of aneuploidy, chromosome breakage, and micronuclei. CIN leads to cancer, various birth defects, as well as up to one third of miscarriage, lethality, and infertility cases.

Aneuploidy is particularly important because it is a hallmark of cancer, especially poor prognosis cancer, as ~90 % of solid tumors show aneuploidy. A major cause of aneuploidy is kinetochore-microtubule attachment errors. One of these errors is lagging chromosome, a kind of “Tug of War” within a sister kinetochore pair by improper microtubule assembly and is often found during anaphase.

Important kinetochore functions include monitoring mitotic errors and error corrections; thus, it is critical to study how the kinetochore ensures the integrity of chromosome segregation. We are studying the mechanism of how the loss of kinetochore integrity causes cancer with a focus on the kinetochore size, the architectural integrity of kinetochores, and the regulation of kinetochore proteins/genes with a focus on colon, breast, and neck cancer.