Junk DNA not junk?

[Urban Ranger]

ONE piece of so-called "junk" DNA appears to have a surprising role. In voles at least, a particular stretch of non-coding DNA seems to control a male's fidelity.

Larry Young and Elizabeth Hammock at Emory University in Atlanta, Georgia, bred two strains of prairie voles. Each had different lengths of "microsatellite" DNA in a gene encoding a receptor for the hormone vasopressin. Microsatellites are repetitive DNA sequences which, like all junk DNA, do not code for proteins.

The strains differed in length by just 19 base pairs; a small difference, but enough to change the voles' behaviour. Males with the longer sequence were more attentive to their partners when offered a choice of another female, and spent more time with their pups (Science, vol 308, p 1630). In lab tests the researchers also found that the longer sequence increased enzyme activity.

Junk DNA makes up at least 95 per cent of the human genome. Young says that microsatellites in the regulatory regions of genes can create diversity in behavioural traits between individuals. "They can be a mechanism for rapid evolution and adaptation," he says.

New Scientist

This is getting interesting. DNA sequences not encoding for actual proteins may have other roles.

[Tattila the Hun]

Did they actually think, that million years of evolution would leave something unused to the DNA? Silly people.

[Combat Ingrid]

One of the main ways for a gene to be regulated is by proteins binding to DNA sequences outside the actual gene, thereby controlling how much protein will be produced from that gene.

[Kuciwalker]

Re: Junk DNA not junk?

Originally posted by Urban Ranger


New Scientist

This is getting interesting. DNA sequences not encoding for actual proteins may have other roles.

This is actually really old. We've known that this DNA was important for many years now.

[Last Conformist]

That's not junk DNA, it's a control sequence.

Junk DNA can't really have much of a function, since neither sequence nor length is conserved by natural selection. It may provide a function as bulk filler, but even that is doubtful in light of the great variability in junk DNA amounts among species.

[Urban Ranger]

CI - got a link to a bigger version of that image?

[Combat Ingrid]

No, sorry. Try to google it: http://images.google.com/images?hl=e...ion+regulation

[Kuciwalker]

Originally posted by Last Conformist
That's not junk DNA, it's a control sequence.

Junk DNA can't really have much of a function, since neither sequence nor length is conserved by natural selection. It may provide a function as bulk filler, but even that is doubtful in light of the great variability in junk DNA amounts among species.

No, junk DNA is that DNA that has not been identified as coding for a protein or rRNA, or tRNA. Many junk DNA segments are highly conserved, more so than coding DNA. What the whole fuss is* about is that many of these now** appear to have other functions, either structural or through transcribed mRNA.

*was

**years ago

[Combat Ingrid]

Here's a slightly longer discussion on the findings:

http://www.emoryhealthcare.org/press_room/ehc_news/2005/June/Junk_DNA_Shapes_Social_Behavio.html

ATLANTA - Why are some people shy while others are outgoing? A study in the current issue of Science demonstrates for the first time that social behavior may be shaped by differences in the length of seemingly non-functional DNA, sometimes referred to as junk DNA. The finding by researchers at the Yerkes National Primate Research Center of Emory University and the Atlanta-based Center for Behavioral Neuroscience (CBN) has implications for understanding human social behavior and disorders, such as autism.

In the study, Yerkes and former CBN graduate student Elizabeth A.D. Hammock, PhD, and Yerkes and CBN researcher Larry J. Young, PhD, also of the Department of Psychiatry and Behavioral Sciences at Emory University’s School of Medicine, examined whether the junk DNA, more formally known as microsatellite DNA, associated with the vasopressin receptor gene affects social behavior in male prairie voles, a rodent species. Previous studies, including Dr. Young’s gene-manipulation study reported in Nature’s June 17, 2004, issue, have shown the vasopressin receptor gene regulates social behaviors in many species.

The researchers bred two groups of prairie voles with short and long versions of the junk DNA. By comparing the behavior of male offspring after they matured, they discovered microsatellite length affects gene expression patterns in the brain. In the prairie voles, males with long microsatellites had higher levels of vasopressin receptors in brain areas involved in social behavior and parental care, particularly the olfactory bulb and lateral septum. These males spent more time investigating social odors and approached strangers more quickly. They also were more likely to form bonds with mates, and they spent more time nurturing their offspring.

"This is the first study to demonstrate a link between microsatellite length, gene expression patterns in the brain and social behavior across several species," said Young. "Because a significant portion of the human genome consists of junk DNA and due to the way microsatellite DNA expands and contracts over time, microsatellites may represent a previously unknown factor in social diversity."

Hammock and Young’s finding extends beyond social diversity in rodents to that in apes and humans. Chimpanzees and bonobos, humans’ closest relatives, have the vasopressin receptor gene, yet only the bonobo, which has been called the most empathetic ape, has a microsatellite similar to that of humans. According to Yerkes researcher Frans de Waal, PhD, "That this specific microsatellite is missing from the chimpanzee’s DNA may mean the last common ancestor of humans and apes was socially more like the bonobo and less like the relatively aggressive and dominance-oriented chimpanzee."

The researchers’ finding also has set a clear course for the next step. They want to build upon previous studies that identified a microsatellite sequence in the human vasopressin receptor that varies in length. "The variability in the microsatellite could account for some of the diversity in human social personality traits," explains Hammock. "For example, it may help explain why some people are naturally gregarious while others are shy." In particular, Young wants his research team to expound upon studies that have identified a link with autism.

[Last Conformist]

Originally posted by Kuciwalker


No, junk DNA is that DNA that has not been identified as coding for a protein or rRNA, or tRNA. Many junk DNA segments are highly conserved, more so than coding DNA. What the whole fuss is* about is that many of these now** appear to have other functions, either structural or through transcribed mRNA.

*was

**years ago

Well, I'm afraid the geneticist I was speaking with a couple weeks ago used my definition of junk DNA, not yours.

[Combat Ingrid]

Basically, any DNA that has no known function (yet) could be called "junk DNA". It's not really a good term. Most DNA probably has some function (essential or not), we just haven't figured it out yet.

[Provost Harrison]

Originally posted by Last Conformist
That's not junk DNA, it's a control sequence.

Junk DNA can't really have much of a function, since neither sequence nor length is conserved by natural selection. It may provide a function as bulk filler, but even that is doubtful in light of the great variability in junk DNA amounts among species.

Hmmm, well this, too, may not necessarily be true either. We're not talking in a direct coding way but regarding the structure that strings of particular bases can result in - a string of adenine followed by a string of thymine can result in a doubling up...I am wondering whether it is structural features of the DNA that could produce what they are describing...but promotors, transcription factors, origins of replication, etc are not junk although they are not coding either...

[Kuciwalker]

Originally posted by Last Conformist
Well, I'm afraid the geneticist I was speaking with a couple weeks ago used my definition of junk DNA, not yours.

Well, I'm afraid the geneticist I was speaking with last week used my definition of junk DNA, not yours.

[Kuciwalker]

Originally posted by Provost Harrison
Hmmm, well this, too, may not necessarily be true either. We're not talking in a direct coding way but regarding the structure that strings of particular bases can result in - a string of adenine followed by a string of thymine can result in a doubling up...I am wondering whether it is structural features of the DNA that could produce what they are describing...but promotors, transcription factors, origins of replication, etc are not junk although they are not coding either...

It could be structural, but it could also be a ribozyme, rather than an ORE or promoter.

[Last Conformist]

Originally posted by Kuciwalker


Well, I'm afraid the geneticist I was speaking with last week used my definition of junk DNA, not yours.

Isn't it wonderful when experts can't agree?

Still, my geneticist's definition is better than yours.