Gene expression analysis of the human and chimpanzee brain

The origin of humans was accompanied by the emergence of new behavioral and cognitive functions, including language and specialized forms of abstract representation. However, the molecular foundations of these human capabilities are poorly understood. Because of the extensive similarity between human and chimpanzee DNA sequences, it has been suggested that many of the key phenotypic differences between species result primarily from alterations in the regulation of genes rather than in their sequences. To characterize gene expression patterns accross the brain and investigate the genetic basis of human specializations in brain organization and cognition, we used microarrays to quantify the transcript levels of thousands of genes in tissue samples from different brain regions of several human and chimpanzee individuals. Our results indicated that the human brain displays a distinctive pattern of gene expression relative to non-human primates, with higher expression levels for many genes belonging to a wide variety of functional classes. The increased expression of these genes could provide the basis for extensive modifications of cerebral physiology and function in humans, and suggests that the human brain is characterized by elevated levels of neuronal activity. Keywords: Species comparative study Gene-expression profiling was performed on 32 tissue samples from different brain regions of a total of 7 humans and 4 chimpanzees. Most samples were hybridized to a single independent arrays, but in a few cases 2 replicates from the same sample were performed, totaling 37 different arrays.