Edited Mouse Gene May (Ironically) Explain Why Snakes Are Legless

The title of this article was what first caught my attention. The title is "CRISPR-Edited Mouse Genes Help Us Understand How Snakes Lost Their Legs," written by Ryan F. Mandelbaum. It had never occurred to me that snakes might have had legs at one point in their history. It then made me think how unfortunate it would be for them if they did indeed lose their legs. It was my sympathy for the snakes, as well as my interest in an idea that was new to me that prompted me to choose this article.

Mandelbaum bases his article in part on the work published by Axel Visel, a scientist from the Lawrence Berkley National Laboratory. Visel and his team wanted to study morphology (the study of the forms of things), and how it has evolved in animals. In my humble opinion, they chose the second best possible example of this, how snakes may have lost their legs. The first would have been how birds developed their wings.

Visel and his team approached their study from a genetics standpoint. They first studied the already documented genomes of several species of snakes. Upon further inspection, they focused on one particular enhancer that the snakes all had in common. The ZRS enhancer is present in most animals with vertebrae and is partially responsible for creating a protein that is essential to the development of limbs in embryos. They discovered that through millennia of copying this gene, it had degraded in snakes. When Visel spliced this ZRS enhancer into the genetic code of embryonic mice, their limbs would develop with severe deformities, or not at all.

Visel admits that this discovery does not provide evidence that snakes lost their legs, nor does it give a reason why it might have happened. It does, however, show that despite losing their legs through natural genetic mutation, they would have still been able to live and continue to reproduce.

Mandelbaum points out that studies like this have actually been carried out since 2005, but Visel’s use of CRISPR technology allows the mice genes to be replaced much faster and for less money.

The article then goes on to discuss the ethics of creating limbless mice for the experiments and how the development of this CRISPR technology is so exciting for many different fields.

I was taken aback by the sudden shift in this article’s main point. The title drew me in by promising a possible reason as to why or how snakes lost their legs, but that doesn’t turn out to be the case at all. The study by Visel only confirms that if snakes had lost their legs through mutation, the nonfunctional ZRS enhancer would not have prevented them from surviving.

Apart from the weird subject change and anti-climactic conclusion, the article was very interesting and informative. Using CRISPR, which is present in many prokaryotic cells, to modify the mouse genes is a great idea. Hopefully the reduced cost and greater accessibility to the technology will lead to more innovations and discoveries in this field in the future.

Written by Boston G.
Source: Scientific American