Featured Research

from universities, journals, and other organizations

A Closer Look At The Genome's "Black Holes"

Date:
August 10, 2001
Source:
Howard Hughes Medical Institute
Summary:
The centromeres of chromosomes -- considered by some to be the genomic equivalent of black holes -- may hold the answers to many scientific questions, according Howard Hughes Medical Institute investigator Steven Henikoff. For example, studies of the centromere may help in understanding the paradox that while centromeric DNA is evolving with extraordinary rapidity, it is still stable enough to perform its job during cell division.

The centromeres of chromosomes -- considered by some to be the genomic equivalent of black holes -- may hold the answers to many scientific questions, according Howard Hughes Medical Institute investigator Steven Henikoff. For example, studies of the centromere may help in understanding the paradox that while centromeric DNA is evolving with extraordinary rapidity, it is still stable enough to perform its job during cell division.

Related Articles


In a review article published in the August 10, 2001, issue of the journal Science, Henikoff and colleagues Kami Ahmad and Harmit S. Malik at the Fred Hutchinson Cancer Research Center theorize that the rapid evolution of centromeric DNA may provide a mechanism by which newly evolving species rapidly become genetically incompatible with one another.

Each chromosome possesses a centromere, which is the site at which sister chromatids are held together. During mitosis and meiosis, the chromatid pair separates, and the centromere is the point of attachment of spindle fibers that pull each chromosome to opposite poles of the dividing cell. "While the centromere is a locus on the chromosome, it is different than a gene, because it is a locus that is acted upon by the apparatus of cell division," said Henikoff.

And unlike genes, which are amenable to mapping and sequencing, probing the genetic makeup of the centromere has proved to be a dead end because of the centromere’s unusual structure. "The centromere has remained enigmatic ever since it was discovered that centromeric DNA is highly repetitive," said Henikoff. "Current methodology really doesn’t allow the sequencing of centromeric DNA. Thus, nobody has sequenced the centromeres of the human genome, the fly genome, or that of any other complex organism. They remain big black holes often millions of bases in length in every chromosome."

The wide variability of centromeric DNA across different species has led some researchers to dismiss its importance. According to Henikoff, the centromere shouldn’t be dismissed so casually. “Some believe that centromeric DNA sequence is not all that important, because it is not conserved in evolution," said Henikoff. "That lack of conservation has led to the centromere paradox where stable inheritance occurs despite rapidly evolving DNA. Normally, the elements of the mitotic segregation machinery would be expected to be highly conserved, as are other essential cellular machines, such as ribosomes. But the central question with centromeric DNA is why it hasn't found some optimal sequence and just stayed there.”

A key to stable centromere inheritance might be found in the proteins called histones, with which all DNA in the nucleus must associate in order for it to form beadlike structures called nucleosomes that bind DNA into compact packages. In the Science article, Henikoff and his colleagues suggest that the uniqueness of the centromeric histone H3 may teach researchers some interesting lessons about evolution.

"While histones are crucial, they are thought to be boring, because they are so highly conserved," said Henikoff. "Because the histones must interact reliably with the entire genome, there are few amino acid differences in these proteins between plants and animals." Centromeric histones, however, have evolved to be profoundly different among organisms.

"The idea that we explore in the Science review is that the centromeric histone and centromeric DNA are evolving rapidly, but in step, since the histone must interact with the centromeric DNA,” said Henikoff.

Analysis of centromeric histones has revealed that they seem to be adapting constantly to the changing centromeric DNA. These evolutionary changes are occurring in parts of the histone that interact with DNA, Henikoff says, "so that tells us that it's the interaction with the DNA that's driving the evolution of the protein.”

Henikoff and his colleagues theorize that this continuous evolution is being driven by a sort of competition among centromeric DNA that occurs during meiosis in the egg. Three of the four products of meiosis are discarded, and only one survives to become the oocyte nucleus. The "winning" centromeres are those whose chromosomes may show even a slight advantage in orienting themselves during meiosis, said Henikoff.

"What's important about this competitive process among centromeres is that it can result in fixation of winning centromeres. This process can be deleterious to the host genome, and so centromeric histones would evolve to restore parity between competing centromeres,” Henikoff said. Bringing together incompatible centromeres and histones in hybrids would lead to their sterility or inviability.

"Understanding the basis of the sterility of cross-species breeding has been a huge problem in evolution ever since Darwin," he said. "The rapidly evolving centromeric DNA and histones and their incompatibility with their counterparts in another species might account for this phenomenon. We can test these ideas by analyzing the centromeric histones in emerging species.”


Story Source:

The above story is based on materials provided by Howard Hughes Medical Institute. Note: Materials may be edited for content and length.


Cite This Page:

Howard Hughes Medical Institute. "A Closer Look At The Genome's "Black Holes"." ScienceDaily. ScienceDaily, 10 August 2001. <www.sciencedaily.com/releases/2001/08/010810065638.htm>.
Howard Hughes Medical Institute. (2001, August 10). A Closer Look At The Genome's "Black Holes". ScienceDaily. Retrieved December 18, 2014 from www.sciencedaily.com/releases/2001/08/010810065638.htm
Howard Hughes Medical Institute. "A Closer Look At The Genome's "Black Holes"." ScienceDaily. www.sciencedaily.com/releases/2001/08/010810065638.htm (accessed December 18, 2014).

Share This


More From ScienceDaily



More Health & Medicine News

Thursday, December 18, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Kids Die While Under Protective Services

Kids Die While Under Protective Services

AP (Dec. 18, 2014) As part of a six-month investigation of child maltreatment deaths, the AP found that hundreds of deaths from horrific abuse and neglect could have been prevented. AP's Haven Daley reports. (Dec. 18) Video provided by AP
Powered by NewsLook.com
UN: Up to One Million Facing Hunger in Ebola-Hit Countries

UN: Up to One Million Facing Hunger in Ebola-Hit Countries

AFP (Dec. 17, 2014) Border closures, quarantines and crop losses in West African nations battling the Ebola virus could lead to as many as one million people going hungry, UN food agencies said on Wednesday. Duration: 00:52 Video provided by AFP
Powered by NewsLook.com
When You Lose Weight, This Is Where The Fat Goes

When You Lose Weight, This Is Where The Fat Goes

Newsy (Dec. 17, 2014) Can fat disappear into thin air? New research finds that during weight loss, over 80 percent of a person's fat molecules escape through the lungs. Video provided by Newsy
Powered by NewsLook.com
Why Your Boss Should Let You Sleep In

Why Your Boss Should Let You Sleep In

Newsy (Dec. 17, 2014) According to research out of the University of Pennsylvania, waking up for work is the biggest factor that causes Americans to lose sleep. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Health & Medicine

Mind & Brain

Living & Well

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins