Researchers at the Yale School of Medicine have published a study hypothesising that during human evolution (when the cerebral cortex was developing), thousands of regulatory elements, described by the researchers as ‘genetic dimmer switches’, were highly active.
The switches show that the human brain developed very differently from those of other animals, in the case of this study, mice and rhesus monkeys. Moreover, it also shows it that was much more active and may have even developed the genes in region of the brain involved in language and conscious thought, the cerebral cortex.
The study was published in the Journal of Science and has created a detailed catalogue of human-specific changes in gene regulation and has also pinpointed several biological processes guided by these switches which are crucial to the development of the human brain.
The Factors Needed to Create a More Complex Cerebral Cortex
Creating a more complex cortex involves several factors. The making of more cells, the modifying of cortical area functions, and making changes to the connections that neurons make with one another.
Over the years, scientists have become proficient at genome comparisons between different species with the aim of identifying the DNA sequence changes that underlie those differences. But as many of our genes resemble those of other primates, it’s believed that changes in the way our genes are regulated, along with changes in the genes themselves, are what sets human biology apart from those of similar species.
Until this study, it’s been difficult for researchers to measure the changes in genes and work out the exact impact of those changes, especially when studying a brain in development.
How Changes Are Measured
To measure changes, Yale researchers used a variety of new computational and experimental tools to identify the DNA sequences in the human cortex which switch genes on or off (at particular times and in particular cell types) and study the effects.
After mapping the active regulatory elements in the developing human genome and those of rhesus monkeys and mice, the researchers then compared the three maps to identify elements exhibiting the greatest activity in the developing human brain.
The results were overwhelming, with several thousand regulatory elements showing increased activity in the human brain, but that still didn’t help them to understand the biological impact of those regulatory changes.
To achieve this, the Yale researchers used BrainSpan, described as a ‘digital atlas of gene expression in the brain throughout the human lifespan’. Using BrainSpan, they used the data accumulated to identify gene groups within the cerebral cortex that show coordinated expression, then overlaid the regulatory changes to identify several biological processes.
It’s these biological processes which are associated with the regulatory changes in the human brain that have made us unique by setting our biological evolution on a very different course to those of similar species.