A possible genetic mechanism in the evolution of birds from dinosaurs

Scheme of the genetic research on birds (Image courtesy Koji Tamura (Tohoku University), Ryohei Seki (National Institute of Genetics), and Naoki Irie (University of Tokyo))
Scheme of the genetic research on birds (Image courtesy Koji Tamura (Tohoku University), Ryohei Seki (National Institute of Genetics), and Naoki Irie (University of Tokyo))

An article published in the journal “Nature Communications” describes a research showing a possible genetic mechanism that determined the evolution of birds from dinosaurs. A team of researchers from the Japanese Tohoku University that includes international collaborators provided what the scientists believe are evidence of the connection of certain genetic sequences to the evolution of bird traits such as feathers.

The discovery in the course of the last decades of new species of dinosaurs with various bird characteristics allowed to understand a part of evolution from the former to the latter but fossil studies show the anatomical changes in dinosaurs and not the genetic ones. Dinosaur extinction prevents biologists from comparing their DNA with that of birds so from this point of view there are various hypotheses but verifying them could be impossible at least in a direct way.

A possible evolutionary mechanism is given by cis-regulatory elements (CSEs), DNA regions that don’t encode proteins and control various organism traits by regulating the transcription of neighbor genes. To understand which ones concerned bird’s traits, it was first necessary to try to understand which genetic regions were inherited from dinosaurs.

The research conducted by the team led by the Tohoku University compared the genome of 48 bird species with that of other vertebrates to identify avian-specific genetic sequences. Many sequences connected to avian-specific characteristics are common to all the species examined and probably were inherited from dinosaurs because they are not present in other vertebrates.

This research made it possible to find millions of genetic regions with cis-regulatory element functions called avian-specific highly conserved elements (ASHCEs). The researchers found some changes in proteins called histones associated with ASHCEs, changes known to indicate active and repressed states of corresponding DNA regions.

In some cases, there are avian-specific genes that contain ASHCEs that appear to be connected to their evolution. For example, a gene called Sim1 may be associated with the evolution of flight feathers in birds. The ASHCE works as a regulator of that gene’s expression in an avian-specific way.

ASHCEs in genes such as Sim1 are very similar in the various bird species showing that they have changed very little in the course of their evolution. This suggests that this type of cis-regulatory elements was crucial in the development of avian-specific traits.

This research proposes a possible mechanism that regulated bird evolution and provides tools for further studies. The integration of analytical tools that bring together paleontology, developmental biology and genomics could allow to reconstruct the evolution of other bird anatomical traits and organs to better understand their evolution from dinosaurs.

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