Nobody knows what it does yet but a section of DNA that codes for DUF1220 has become heavily duplicated in humans as compared to other species.
The team compared the DNA sequences of humans, chimpanzees and monkeys, and looked for genes that were repeated more often in human DNA than in the other primate genomes. One gene that codes for a piece of protein called DUF1220 stood out. Humans carry 212 copies of DUF1220, whereas chimps have 37 copies, and monkeys have only 30 copies, the researchers found. Mice and rats each had a paltry single copy of the protein-coding region. When the team looked for the protein in the human body, they found it in many places, including in neurons in the brain.
It probably does stuff in the brain and we probably became smarter as a result of having many DUF1220 segments in the human genome.
Extreme gene duplication is a major source of evolutionary novelty. A genome-wide survey of gene copy number variation among human and great ape lineages revealed that the most striking human lineage–specific amplification was due to an unknown gene, MGC8902, which is predicted to encode multiple copies of a protein domain of unknown function (DUF1220). Sequences encoding these domains are virtually all primate-specific, show signs of positive selection, and are increasingly amplified generally as a function of a species' evolutionary proximity to humans, where the greatest number of copies (212) is found. DUF1220 domains are highly expressed in brain regions associated with higher cognitive function, and in brain show neuron-specific expression preferentially in cell bodies and dendrites.
Do humans differ in how many copies of MGC8902 and DUF1220 we have?
So there are two stories here. One is about the multiple duplication of MGC8902 on the human lineage. The draft human genome has 49 copies of it, chimpanzees have only 10.
A seperate story is about the proliferation of this DUF1220 domain, which occurs in many proteins. This domain increased in copy number on the human lineage compared to chimpanzees, the African ape lineage compared to orangutans, and primates compared to other mammals.
To me the DUF1220 story is the fascinating part. Not only one gene, but apparently many genes that contain this domain have been proliferating; additionally some genes apparently have acquired this domain during human evolution. In at least one gene, the DUF1220 domain shows evidence of positive selection, but the rest of the coding sequence doesn't.
In the next 10 years we will learn the identity of most of the genes that make us smarter than other specices. We will also learn which genetic variations make some humans smarter than others.
|Share |||Randall Parker, 2006 September 05 10:59 PM Brain Evolution|