Human nervous system cells with more FOXP2 show up red or orange
A gene that has long been implicated in the evolution of speech and language has given up more of its secrets.
A study of the effects of two versions of the FOXP2 gene, one from chimpanzees and one from humans, showed marked differences in their effects.
Human FOXP2 triggered changes in genes known to affect the growth of brain areas related to language and also, more generally, to higher thought.
The findings, published in Nature, could aid diagnosis of mental diseases.
The exact genetic basis of language is mysterious. But the FOXP2 gene was first implicated as a contributor when, in 1990, a family with an inherited language disorder was found to have a mutation in the gene.
A structurally very similar "version" of the gene is found in a wide number of species of vertebrates.
And ancient DNA, extracted from Neanderthal remains, shows the same version of the gene found in humans.
But the form in chimpanzees is slightly different. The gene provides instructions for a protein of the same name that varies by just two amino acids - proteins' building blocks - from the chimpanzees' version.
"Two doesn't sound like a lot but given how highly conserved the gene is across species and how close we are in evolutionary time to chimps, that was a pretty big change," said Daniel Geschwind of the University of California, Los Angeles, who led this study.
The implication is that our non-vocal cousins, the chimpanzees, might be non-vocal because of the effects of those two amino acids.
Chimps' and humans' nearly identical FOXP2 genes have different effects
The FOXP2 gene produces a protein of the same name. This protein is a transcription factor - it acts as a dimmer switch for a number of other genes, switching them on or off or regulating their activity.
Dr Geschwind and his team put the chimp version and the human version of the gene into human nervous system cells.
They then profiled all of the genes that had been switched on.
What they found was that the human version had effects on some genes that were unaffected by the chimp version.
While earlier studies made it relatively certain that FOXP2 was involved in the development of the fine motor control that is needed for speech, it was not clear whether it had anything to do with parts of the brain that are specifically involved with language.
But among those 116 genes "tied" to the human FOXP2 gene, Dr Geschwind told BBC News, there is at least one "that is involved in the development of brain regions that are part of a critical circuit we know is important for higher cognition".
In other words, the FOXP2 gene may be more than just a "language gene". It could be involved in a number of aspects of higher thought that we attribute to humans.
Further work is needed to pin down all the genes and molecules at work in speech and language.
Dr Geschwind said that the new array of genes specific to the human version of FOXP2 must now be investigated, to assess the role of each one.
FOXP2 could prove to be a crucial part of all "higher thought"
Simon Fisher, a molecular neuroscientist at the Wellcome Trust Centre for Human Genetics called the results "intriguing", and explained that FOXP2 itself is expressed to varying degrees in different types of neurons in the brain.
"It will be exciting in future to directly examine the in vivo impacts of FOXP2... in each distinct neuronal subpopulation," he told BBC News.
But he said that the initial results needed to be considered carefully.
"A large number of genetic differences distinguish the brains of these two species, not just the substitutions in FOXP2," he said.
"While a few of the genes have been linked to aspects of central nervous system development, we are still some way off from describing how differences in FOXP2 alter the properties and behaviour of neurons in the living brain."