How did we first acquire the limbs that allowed us to crawl onto dry land? Could the fins of our fishy ancestors hold previously undiscovered clues? A recent research article by Denis Duboule and colleagues published in PLOS Biology (and an accompanying Synopsis), attempted to shed more light on this fascinating topic.
The authors found that the genes and regulatory architecture necessary for digit patterning are present in fish (and therefore presumably in our last common ancestor); however some essential elements for actually forming digits are missing, and this functionality has been subsequently “retrofitted” in land-dwellers. The article has received over 7000 views since it was first published on January 21st, so here we take a look at some of the accompanying media interest.
LA Times science writer Geoffrey Mohan gave some background to the debate of how fish could have evolved to walk on land, mentioning previous discoveries which have provided some pieces to the puzzle. “There have been tantalizing finds, including Tiktaalik, a prehistoric fish with shoulder and pelvis characteristics of a tetrapod, or four-legged animal. Modern genetics since has added evidence to supplement the fossil record.”
BBC science reporter Melissa Hogenboom provided a detailed summary of the study, but also sought some expert opinions on whether the model organism used in the study (the zebrafish) is really the right fish for the job. Professor Jenny Clack, of the University of Cambridge explained “We know that this animal, and by inference its relatives… lack some of the developmental stages that make digits in tetrapods”. Prof. Clack suggests that zebrafish were not the best choice for this experiment, calling into question what can really be inferred from the study.
Phys.org discussed the Hox genes which are necessary for both fins and limbs to form, but which Duboule and colleagues found behave differently in fish and land animals. “When inserted into transgenic mouse embryos, the fish Hox genes were only active in the mouse arm but not in the digits, showing that the fish DNA lacks essential genetic elements for digit formation”.