The conundrum has centred on DNA sequences that do not encode proteins, and yet remain identical across a broad range of animals.
By deleting some of these ‘ultraconserved elements’, researchers have found that these sequences guide brain development by fine-tuning the expression of protein-coding genes.
Bejerano and his colleagues originally noticed ultraconserved elements when they compared the human genome to those of mice, rats and chickens, and found 481 stretches of DNA that were incredibly similar across the species.
In mice, they deleted four ultraconserved elements – individually and in various combinations – that lie within regions of DNA that also contain genes important in brain development.
Mice lacking certain sequences had abnormally low numbers of brain cells that have been implicated in the progression of Alzheimer’s disease.
Variations in these ultraconserved regions would not spread through a population, because afflicted individuals would be less successful at reproducing than those who were unaffected.
Although the functions of many other ultraconserved sequences remain unknown, Bejerano feels confident that they, too, will prove essential.