Organisms are made up of cells, and in each of those cells, a genome encodes the instructions for that organism to grow and survive. The human genome has at least 20,000 genes, and the expression of all of those genes has to be very carefully controlled; they must be active in the right places at the right times, or major problems could arise. There are many genetic features that help control gene expression, like sequences known as enhancers. Genetic enhancers do what their name implies: they can help modulate and raise the expression of certain genes. Some genes are affected by multiple enhancers, and their effects might depend on the tissue where the gene is being expressed.
Enhancers were also thought to occupy their own region of DNA. But new research conducted in fruit flies has shown otherwise. The findings have been reported in Science Advances.
In this study, the researchers focused on a gene known as yellow that is expressed in Drosophila, or fruit flies, and yellow's enhancers. The gene is related to the production of the pigment melanin. Several enhancers can influence the expression of the yellow gene.
One enhancer can control the coloration of the fly abdomen, head, and thorax, while another enhancer is related to coloration patterns on fly wings.
This study revealed that the enhancer that influences yellow expression in the body is not in a different genomic location than the enhancer that relates to wing pigmentation. Some of the same extensive parts of the fly genome are related to both enhancers. The researchers suggested that regulatory sequences in the genome may actually be much more complex than we knew.
The findings may change how we view the role of enhancers in evolution. For example, certain genes that may control to very basic processes, such as the shape of a fly's body, do not change much throughout evolution. But mutations in enhancer regions can alter the expression of genes in more subtle ways than direct gene mutations.
“The cost of mutating an enhancer is therefore often lower than the cost of mutating the gene directly," explained first study author and graduate student Mariam Museridze, of the University of Bonn. It's therefore easier for novel traits to develop.
Museridze noted that this could also enable mutations in enhancers to have more extensive impacts.
The researchers also added that some enhancers may still be acting independently and more specifically. More research will be needed to decipher all of the effects that enhancers may have in different organisms, tissues, and cell types.
Sources: University of Bonn, Science Advances