First so close, then so far apart

At the phylotypic stage, shown in the above row, vertebrate animals are very similar. (image courtesy American Technion Society).
A paper in Nature Genetics sheds light on why all vertebrate animals look alike during a certain phase of embryonic development: it's because the same genes are turned on.

During the so called phylotypic stage embryos of birds, fish and even humans start to look the same - before they diverge again and become very different looking animals.

Led by researchers from the University of Western Australia (UWA), the study looked at mice from Madrid, zebrafish from Seville, and toads from Nijmegen

The study shows that certain chemical signposts in the DNA of these animals change in a wave that activates the same developmental pathways.

According to lead author Ozren Bogdanovic from the ARC Centre of Excellence in Plant Energy Biology (ACE-PEB), it is likely that the animals are also similar in the epigenetic control of their development during the phylotypic stage - that is similar patterns of transient gene modifications may take place.

The reason behind this may be that the animals are setting up a shared fundamental body structure.

Project leader Professor Ryan Lister (ACE-PEB) explained that "Correct establishment of the body plan and organ formation at that early stage is so critical to life that the molecular processes underlying it have remained very similar despite millions of years of divergence between these species."

However, species vary in the time it takes to reach the phylotypic stage: one to two days after fertilisation in fish and toads, four weeks after conception in humans.

Story based on a media release from the ARC Centre of Excellence in Plant Energy Biology;

A related study was published in Nature, and was led by a team from the Technion-Israel Institute of Technology with participation of researchers from the University of Queensland. The study also found a striking pattern of universality across very diverse species, with similar genes turned on at certain stages of development. A media release on this study can be found here

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