Proteins are constructed from a string of amino acids, and the amino acid sequence is coded in a gene. But how does the cell know which of its many genes to use in synthesizing proteins? Gene regulation is accomplished via a number of complex mechanisms. For instance, methyl groups are used to tag both the DNA as well as the histone proteins about which the DNA is wrapped. You can read more about histones here and here. In addition to such methylation, histones can also vary by tiny differences in their amino acid sequence. Such histone variants serve as yet another type of tag used for gene regulation. Now new research is revealing the profound complexity of this mechanism.
Histone variants are not merely static sign posts that influence gene expression. These variants are moved, by other proteins, between different locations in the genome. The new research elucidates the migration patterns of a histone variant during mouse embryonic development. Cells differentiate over time in the growing embryo, and in this process the histone variant migrates to different genomic locations. And the research indicates these movements are orchestrated by three different proteins. As one researcher put it:
Our work shows that the regulation of histone variant localization -- the shape of the so-called epigenetic landscape at different regions of the genome -- is more complex than previously thought.
Or as one writer explained, these findings “hint at an unimagined complexity of the genome.” Nothing in biology makes sense in the light of evolution.
