Snakes have not always been legless, but have lost their limbs through evolution. Professor Laura Elo from the University of Turku is part of an international research project that investigates the reasons why snakes lost their limbs.
The ancestors of snakes were tetrapods—vertebrates whose basic body plan included four limbs. Over evolutionary time, snakes lost their limbs, while simultaneously developing extraordinarily elongated bodies.
The University of Turku is part of the research project coordinated by the Gulbenkian Institute for Molecular Medicine (GIMM) in Portugal and joined by the University of Florida in the United States. The research project aims to address the question “How snakes lost their limbs”. GIMM will lead the experiments in mice, including genetic manipulation. The research team at the University of Florida will lead the experiments in reptiles, working with snakes and lizards.
Professor of Computational Medicine Laura Elo leads the bioinformatics and computational analysis to interpret the extensive molecular data on mice and reptiles generated by GIMM and the University of Florida.
“The challenge is not simply to identify which genes differ between snakes, lizards, and mice, but to understand how cells change their molecular state, how they communicate with each other, and how these processes may have changed during evolution,” says Laura Elo.
The Human Frontier Science Program has granted the research project 1.2 million USD (approximately €1.1 million) in funding, of which the share of the University of Turku is 400,000 USD (approximately €351,000). The funding covers a period of three years.
This project is the only funded project by the Human Frontier Science Program this year involving a research group based in Finland. HFSP funding is highly competitive international research funding, and only around 3% of the submitted applications worldwide were funded this year.
Monitoring the development of embryos can provide answers
The research team will compare snakes with lizards that still have legs as well as with limbless lizards and mice. They will monitor the development of embryos in particular.
As an embryo grows, cells at its posterior end progressively build the trunk and then the tail. The transition between these two developmental programmes is tightly regulated by networks of genes that determine what kind of body structures can form and where.
The researchers hypothesise that the loss of limbs in snakes is not simply a matter of switching off the genes that make legs. Instead, it may be connected to when and where the embryo stops making trunk and starts making tail.
“In this transition from making the trunk to making the tail is when there are the inducing signals that make the limb and the genitalia,” explains Moisés Mallo who leads the research at GIMM.
According to the researchers’ hypothesis, the changes in the timing of this transition could disrupt the signals or separate them from the tissues that respond to these signals to initiate the limbs. To test the hypothesis, the researchers will investigate which genes are active in developing embryos and which regions of the genome are accessible to the molecular machinery that controls gene activity. They will compare these patterns across species, searching for the regulatory changes that accompany the evolution of a long, limbless body.
