The shape of chromosomes is determined by the relative levels of key protein complexes, research conducted by Keishi Shintomi and Tatsuya Hirano of the RIKEN Advanced Science Institute has shown.
Figure 1: Mitotic chromosomes assembled in the Xenopus cell-free system. Condensin I (green) and II (magenta) display distinct localizations within the chromosomes.
Copyright : 2011 Tatsuya Hirano
As a cell prepares to divide via the process called mitosis, chromatin—the material in which DNA is packaged—condenses to form discrete rod-shaped structures called chromosomes. Each chromosome contains duplicated chromatids—sister chromatids—that are aligned in parallel. After ‘mitotic chromosome condensation’ is complete, the paired chromatids segregate such that each daughter cell receives one of each pair.
“For well over a century, biologists have noticed that the shape of condensed chromosomes is highly characteristic, but varies among different organisms or among different developmental stages in a single organism,” explains Hirano. “We are interested in understanding how the shape of chromosomes is determined at a molecular level.”
Hirano’s group previously discovered that mitotic chromosome condensation requires the action of two protein complexes, known as condensins I and II. This group and others have shown that a third protein complex called cohesin is responsible for the pairing of sister chromatids within a chromosome.
To test exactly how condensins and cohesin may contribute to shaping of chromosomes, Shintomi and Hirano turned to a cell-free system based on extracts prepared from the eggs of the frog Xenopus laevis. “The Xenopus system perfectly suited our purposes because it enables us to recapitulate many chromosomal events, including chromosome condensation, in a test tube in a cell-cycle regulated manner (Fig. 1),” says Hirano.
To achieve their goal, the researchers then had to develop a series of sophisticated experimental protocols to precisely manipulate the levels of condensins I and II and cohesin present in the extracts.
Under the standard condition, chromosomes assembled in this cell-free system tended to be long and thin, which are general characteristics of chromosomes observed in early embryos. Strikingly, however, when the ratio of condensin I to II was reduced, they became shorter and thicker, being reminiscent of chromosomes observed in later stages of development. Further experiments revealed that cohesin works with condensin I and counteracts condensin II to properly place sister chromatids within a chromosome. Thus, their actions can be likened to a molecular ‘tug-of-war’.
“Our findings demonstrated that chromosome shape is achieved by an exquisite balance between condensin I and II and cohesin,” says Hirano. “Such a concept had been suspected for a long time, but has never been demonstrated so beautifully and convincingly until now.”
The corresponding author for this highlight is based at the Chromosome Dynamics Laboratory, RIKEN Advanced Science Institute
Shintomi, K. & Hirano, T. The relative ratio of condensin I to II determines chromosome shapes. Genes & Development 25, 1464–1469 (2011).
Researchers identify potentially druggable mutant p53 proteins that promote cancer growth
09.12.2016 | Cold Spring Harbor Laboratory
Plant-based substance boosts eyelash growth
09.12.2016 | Fraunhofer-Institut für Angewandte Polymerforschung IAP
Physicists of the University of Würzburg have made an astonishing discovery in a specific type of topological insulators. The effect is due to the structure of the materials used. The researchers have now published their work in the journal Science.
Topological insulators are currently the hot topic in physics according to the newspaper Neue Zürcher Zeitung. Only a few weeks ago, their importance was...
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
09.12.2016 | Life Sciences
09.12.2016 | Ecology, The Environment and Conservation
09.12.2016 | Health and Medicine