Random mutagenesis typically deletes only 300 to 500 base pairs at a time only part of a gene, Frkjr-Jensen says.
A Knockout with Benefits
At the same time the DNA repair process is used to delete a targeted worm gene, the scientists also use it to give the mutant worms a "positive selection marker."
That is because "it's easier to find a moderately sick worm among dying worms than to find one sick worm among a whole lot of healthy worms," Frkjr-Jensen says.
So the researchers began with worms lacking a gene named unc-119. Without it, their nerves degenerate and they die. But when the scientists used the DNA repair process to knock out a targeted gene, that process also inserts a working unc-119 gene.
Because worms without unc-119 die, the worms that live are alive because the unc-119 was reinserted at the same time a targeted gene was deleted. So the knockout worms can be identified because they are alive, even if they are ill or abnormal because of whatever targeted gene was knocked out.
The researchers tested the method on 10 genes they targeted for knocking out, including one named dumpy-13. "We knocked out dumpy-13," Frkjr-Jensen says. "It made the worms short and fat, so they were easy to distinguish."
Knocking out genes in worms is advantageous because it is faster and more efficient than other methods. Genes can be knocked out completely, not partially, ensuring that researchers can see what happens without them. Adjacent genes can be deleted, making it easier to learn the combined effects of genes with similar functions.
Frkjr-Jensen says it might be possible to use the new method to study genes in other animals that serve as models for humans, including flatworms and zebrafish. But the method probably would not work in mammals because
|Contact: Lee Siegel|
University of Utah