Why has the bodyplan of vertebrates remained so conservative through evolution?
- Reuse of genes and constraints on diversification –
Overview of the press release
Researchers at the University of Tokyo have found a possible reason for why the basic bodyplan of vertebrates has remained conserved for over 500 million years of evolution. Their findings show that the reuse of genes may have constrained its diversification.
Vertebrates, a group of animals that have vertebrae in their back, emerged more than 500 million years ago and diversified into species with a variety of shapes, including human beings. However, the reason why vertebrates retained their basic anatomical architecture through such a long evolutionary time scale remains to be clarified. Studies so far have attributed this to the embryonic phase when vertebrates’ basic architecture develops, and recent studies have particularly highlighted the evolutionary conservation of this phase compared to earlier and later stages (known as the developmental hourglass model). Nonetheless, it is still unknown why this embryonic phase has remained conserved for millions of years.
An international collaboration called the EXPANDE Consortium, led by Associate Professor Naoki Irie, tackled this problem by comparing the embryogenesis of eight chordate species, including vertebrates, at the molecular level. By identifying and comparing massive gene expression data in these species, they found that most of the genes acting around the developmental phase that shape vertebrates’ basic architecture were repeatedly recruited (pleiotropic genes). Notably, the repeatedly recruited genes showed a strong correlation towards evolutionary conservation. One plausible scenario is that through evolution, pleiotropic genes constrained the diversification of the embryonic phase that develops vertebrates’ basic architecture.
Since gene recruitment is commonly observed during the evolution of various organisms, the current findings would provide a basis for better understanding what kind of trait is more (or less) likely to evolve.
Figure 1: Possible constraint by pleiotropic genes was found at the mid-embryonic phase.
According to the recently supported developmental hourglass model (middle), development proceeds from the bottom to the top, and embryos pass through a phase when vertebrates’ basic architecture is established (left). However, it was unclear why animal embryos follow this model. The present research clarified that there may be a possible contribution of pleiotropic constraints by repeatedly recruited genes (pleiotropic genes) that are also used in variety of other developmental processes. In the image on the right, the small circles represent genes and the vertical lines indicate their repeated usage in other developmental stages.
Journal Nature Ecology & Evolution Title Constrained vertebrate evolution by pleiotropic genes Authors Haiyang Hu, Masahiro Uesaka, Song Guo, Kotaro Shimai, Tsai-Ming Lu, Fang Li, Satoko Fujimoto, Masato Ishikawa, Shiping Liu, Yohei Sasagawa, Guojie Zhang, Shigeru Kuratani, Jr-Kai Yu, Takehiro G Kusakabe, Philipp Khaitovich, Naoki Irie*, EXPANDE Consortium DOI 10.1038/s41559-017-0318-0 Paper link https://www.nature.com/articles/s41559-017-0318-0
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