Although they're commonly known as brown anoles, there are now four Anolis sagrei lizards at a University of Georgia lab that are actually a pale pink color. They're albinos, and are the result of what is reportedly the world's first successful attempt at producing a genetically modified reptile. The research could have implications for human medicine.
Lead scientist Douglas Menke chose brown anoles for the study because isolated populations of the lizards are known for independently evolving distinctive traits, on various islands in the Caribbean. Genetically modifying reptiles of any type does pose some challenges, however.
Ordinarily, when utilizing the CRISPR gene-editing tool, scientists inject gene-editing solutions into an animal's freshly-fertilized egg, or into a single-cell embryo. This causes a mutation in the DNA, which gets reproduced in all of the subsequently-developed cells.
In reptiles, though, females are capable of storing sperm in their oviducts for a long time after mating – this makes it hard to determine when fertilization of the egg has actually occurred. Additionally, once an egg has been fertilized, its pliable shell and lack of an internal air space make it difficult to manipulate the embryo without damaging it.
In order to get around these challenges, Menke and colleagues used the CRISPR-Cas9 tool to micro-inject CRISPR proteins into immature eggs (aka oocytes) which were still located in the anoles' ovaries. They then simply waited for those eggs to be naturally fertilized. All told, the scientists injected 146 eggs in 21 of the reptiles, targeting the tyrosinase gene – when this gene is inactivated, albinism results. After a few weeks, the end result was the four pink lizards.
As an interesting side note, these anoles displayed the manipulated tyrosinase in gene copies inherited from both their mother and father. According to the scientists, this suggests that the CRISPR proteins remained active in the mother longer than was anticipated, mutating the paternal genes after fertilization had occurred.
"That was a surprise," says Menke. "It enabled us to see the functional requirements of the gene without having to breed mutated animals to produce offspring who inherit the mutated gene from both parents. It's a big time-saver."
Additionally, the research could lead to improved treatments for eye problems in humans. While tyrosinase is required for eye development in both people and anoles, it isn't present in commonly-studied animals such as mice. Now, it's possible that anoles could be utilized in ocular health studies.
Source: University of Georgia