UV Irradiation: A Method to Integrate Extrachromosomal Arrays

- Creating extrachromosomal DNA arrays by microinjection-- the simplest method to generate transgenic worm strains-- results in genetic elements that are not stably transmitted during cell division and, therefore, exhibit variable inheritance rates and expression levels. The goal of integrating the array into a chromosome is to lessen this genetic instability and variability.

To do so, start with an age-synchronized population of L4 transgenic worms, which carry an extrachromosomal array previously introduced by microinjection and allow them to grow into gravid adults. Transfer these adults to new plates and allow them to lay eggs until there are at least 30 eggs on each plate. Remove the adults and allow the eggs to grow up until they reach the L4 stage. Then, irradiate the worms with UV light. This causes random double-strand breaks in the genomic DNA where the worms DNA repair machinery may arbitrarily incorporate the array.

After an overnight recovery period, count the number of surviving worms. A small percentage of dead worms indicates efficient irradiation. Observe subsequent generations to isolate homozygous integrated transgenic lines. In the example protocol, we will inte