Calcium aids chromosome condensation prior to cell division

December 26, 2016

 

Osaka, Japan - Before cell division when a parent cell divides into two daughter cells, each with an identical set of genetic information, replicated chromosomes become condensed and align along the spindle in the middle of the cell. This is the metaphase stage of mitosis. Chromosomes are made up of strands of DNA wrapped around histones, forming nucleosomes that resemble beads on a string. The chromosome structure is maintained by histone changes, chromosome scaffold proteins, and positively charged ions (cations). However, removal of scaffold proteins has no effect on chromosome condensation, suggesting that another factor causes the organization of metaphase chromosomes. Now, work led by Osaka University has revealed that calcium ions (Ca2+) play a crucial role in chromatin fiber compaction. The study was reported in Scientific Reports.

Calcium is a universal second messenger with many functions, including progression of the cell cycle. During mitosis, both Ca2+ and magnesium ions (Mg2+) are released from storage organelles to bind chromatin, though 6-8-fold more Ca2+ is bound than Mg2+ suggesting that it has a more important role. A research team led by Hideaki Takata, Kiichi Fukui and Rinyaporn Phengchat at Osaka University first confirmed that Ca2+ is necessary to prevent chromosome misalignment during mitosis, then used an imaging assessment of molecular interactions based on fluorescence decay (FLIM-FRET) to show that chromosomes were less compact in the absence of intracellular Ca2+.

This same imaging process also revealed that changes in Ca2+ levels of living HeLa cells altered the extent of chromosome compaction, with the re-addition of Ca2+ causing chromosome compaction. Ca2+ therefore appears to control the transition between condensation and decondensation. "Although previous studies have demonstrated nucleosome packaging using isolated chromatin" study first author Rinyaporn Phengchat says, "such findings should be confirmed in vivo as we have done using the sensitive FLIM-FRET technique which provides a high level of spatial resolution."

The team then used scanning electron microscopy to visualize chromosome structures at very high resolution. "Ca2+ has a concentration-dependent effect on chromosome structure," corresponding author Hideaki Takata explains, "causing chromosomes to change from expanded fibrous structures to compact globular structures with increasing levels of Ca2+."

The researchers propose that, in the absence of Ca2+, the negatively charged DNA is less well neutralized, preventing it from condensing and delaying entry into prometaphase of the cell cycle. "We think that a lack of Ca2+ disturbs the organization of chromosomes at the spindle, causing them to misalign," corresponding author Kiichi Fukui says. "Conversely, the normal rising levels of Ca2+ during mitosis promote chromosome condensation after breakdown of the nuclear envelope."
-end-


Osaka University

Related Chromosomes Articles from Brightsurf:

Cancer's dangerous renovations to our chromosomes revealed
Cancer remodels the architecture of our chromosomes so the disease can take hold and spread, new research reveals.

Y chromosomes of Neandertals and Denisovans now sequenced
An international research team led by Martin Petr and Janet Kelso of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, has determined Y chromosome sequences of three Neandertals and two Denisovans.

Female chromosomes offer resilience to Alzheimer's
Women live longer than men with Alzheimer's because their sex chromosomes give them genetic protection from the ravages of the disease.

New protein complex gets chromosomes sorted
Researchers from the University of Tsukuba have identified a novel protein complex that regulates Aurora B localization to ensure that chromosomes are correctly separated during cell division.

Breaking up is hard to do (especially for sex chromosomes)
A team of scientists at the Sloan Kettering Institute has discovered how the X and Y chromosomes find one another, break, and recombine during meiosis even though they have little in common.

Exchange of arms between chromosomes using molecular scissors
The CRISPR/Cas molecular scissors work like a fine surgical instrument and can be used to modify genetic information in plants.

How small chromosomes compete with big ones for a cell's attention
Scientists at the Sloan Kettering Institute have solved the puzzle of how small chromosomes ensure that they aren't skipped over during meiosis, the process that makes sperm and egg.

GPS for chromosomes: Reorganization of the genome during development
The spatial arrangement of genetic material within the cell nucleus plays an important role in the development of an organism.

Extra chromosomes in cancers can be good or bad
Extra copies of chromosomes are typical in cancerous tumor cells, but researchers taking a closer look find that some extra copies promote cancer growth while others actually inhibit cancer metastasis.

X marks the spot: recombination in structurally distinct chromosomes
A recent study from the laboratory of Stowers Investigator Scott Hawley, PhD, has revealed more details about how the synaptonemal complex performs its job, including some surprising subtleties in function.

Read More: Chromosomes News and Chromosomes Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.