There are long stretches of DNA which are known not to code for any proteins, but which are ultra-conserved, meaning that they are almost identical, across all vertebrates. The paradigm has been that when a DNA sequence is conserved, and not mutated to be different during the millions of years that the animal lineages have been separated, that those DNA sequences must code for something vital to the organisms.
That paradigm was challenged in 2007 when researchers deleted some of those sequences from mice, but the mice appeared to be just fine.
Further just-published research using the precision CRISPR-Cas9 method to knock-out various ultraconserved non-coding regions of DNA, within chromosomic regions containing brain protein genes, has now shown that the resulting mice do indeed have anatomical abnormalities in their brains. In the wild these animals would probably not survive. Hence the regions are assumed to contain gene expression controls which are vital to the correct development of the brain, re-confirming the paradigm.