Evolution treats transcription factors differently than DNA

People with reddish hair have genes for that, but what gets the job done – that is, growing reddish hair – isn’t the DNA or gene, it’s the transcription of the genes by molecules of protein, mainly RNA polymerase transcribing into messenger RNA (mRNA), which takes the designs coded in DNA and guides the production of relevant proteins in the cell. This is called gene regulation in the process of gene expression. (The red hair is the final expression.)

It’s been long assumed that like DNA, evolution is strongly conservative of the details of gene transcription. That is, it seemed that making sure DNA was accurately copied from generation to generation would also be applied to the methods of transcription, especially the gene locations for triggering transcription and the gene sequences used for the transcription. A new study by a European team of researchers indicates this may not be so. Evolution protects the copying of DNA but is more flexible about the details of gene transcription.

The study followed the evolution of five vertebrate species: Human, dog, mouse, short-tailed opossum, and chicken – over a span of 300 million years. Specifically, they were looking at the preservation of two transcription factors (protein complexes called CEBPA and HNF4A) for liver-specific genes. They mapped how these transcription factors bound to the genome of each species (the site of trigger genes, and the sequence copied).

What they found was somewhat surprising. In most cases neither the trigger site nor the copy sequence was maintained by evolution. They varied over time and between species. Nevertheless, the transcription factors managed to do what they are coded to do – carry out the expression and function of liver tissue.

Paul Flicek, leader of the Vertebrate Genomics Team at EMBL-EBI, an outstation of the European Molecular Biology Laboratory, and coauthor on the paper said “The evolutionary changes in transcription factor binding in the five species have left clues that we can use to explain how function is preserved but not necessarily sequence. What we have learnt is that although the transcription factors regulate similar target genes in all five species, the binding events underpinning this regulation have not been conserved as the species diverged.”

[Source: EurekAlert]

In the beginning for molecular biologists there was and is DNA. DNA is the master plan, copied (more or less) intact from generation to generation. However, it’s becoming clear that the long and highly complex process of taking the DNA plan and implementing it in the building blocks of life (proteins) has a much more fluid and potentially decisive role in gene expression. This study ‘merely’ points out that over 300 million years and five species, although the transcription factors remain the same, where they read and what they read from the DNA changes. Therein, probably, lie some of the mechanisms of speciation – how different species are formed and how groups or even individuals can express the same type of DNA in different ways.

Lurking in all this are proteomics (the systematic study of protein structures and functions) and epigenetics (the study of inherited changes in gene expression caused by mechanisms other than DNA), but the picture at this point is murky. However, it’s an extremely important and fascinating murk.

Research Spectrum

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