Albino lizards around the size of your index finger are the world’s most gene edited reptiles.
According to research published in Cell Reports, these reptiles can successfully pass gene edited alleles for albinism to their offspring.
“For quite some time we’ve been wrestling with how to modify reptile genomes and manipulate genes in reptiles, but we’ve been stuck in the mode of how gene editing is being done in the major model systems,” says corresponding author Doug Menke, associate professor at the University of Georgia. “We wanted to explore anole lizards to study the evolution of gene regulation, since they’ve experienced a series of speciation events on Caribbean islands, much like Darwin’s finches of the Galapagos.”
The gene editing is done by injecting CRISPR-Cas9 gene editing reagents into fertilized eggs or single-cell zygotes, but this technique is not feasible in the case of reptiles because lizards have internal fertilization and the time of fertilization cannot be predicted. But the Menkes team noticed that all the developing eggs could be seen through the transparent membrane including the eggs which are going to be ovulated and fertilized. This led them to inject CRISPR reagent into unfertilized eggs and see the possibilities of CRISPR to work.
“Because we are injecting unfertilized eggs, we thought that we would only be able to perform gene editing on the alleles inherited from the mother. Paternal DNA isn’t in these unfertilized oocytes,” Menke says. “We had to wait three months for the lizards to hatch, so it’s a bit like slow-motion gene editing. But it turns out that when we did this procedure, about half of the mutant lizards that we generated had gene-editing events on the maternal allele and the paternal allele.”
This suggests that in the unfertilized egg, the CRISPR components stay active for a day or even weeks. About 6% to 9% of the oocytes screened produced offspring which are gene-edited. The team selected albino lizards because when tyrosinase albinism gene is kicked out; it loses its pigmentation without being lethal to itself and also humans with albinism have vision problems, this study gives more inputs to how the loss of this gene impacts retina development.