Jaspreet Khurana, a PhD student in Theurkauf's lab, made the keen observation that as these flies aged the hybrids were gaining fertility. "Based on the observation that the flies recovered, it seemed likely that they were learning how to shut down transposons. We decided to use this system to look at the process of adaptation to a new transposable element," said Theurkauf.
Using a multi-disciplinary approach that included next generation sequencing, Theurkauf and colleagues were able to get complete genetic sequences of the sterile, hybrid flies at various stages of development. Jie Wang, PhD, a postdoc in the lab of Zhiping Weng, PhD, professor and director of the Program in Bioinformatics and Integrative Biology at UMass Medical School, analyzed the genetic information to see how the genome was responding to the introduction of the new transposon.
What they found was startling. In the hybrid off spring, the new transposon had triggered a response that disrupted the entire piRNA machinery. Not only was the newly introduced transposon jumping around the genome and causing a problem which was expected but most of the 120 plus transposons in the Drosophila genome had also become active. "This massive destabilization of the genome is probably why they're sterile," said Theurkauf.
As the hybrids aged, however, the new transposon and all the existing, resident transposons, got shut down and fertility was restored. "We found there were two mechanisms responsible for silencing the transposons," said Weng. "For P elements it turned out the flies learned to process the piRNA transcripts inherited from the father and turn them into mature piRNAs and silence the transposon. Resident transposons, by contrast, jump into piRNA c
|Contact: Jim Fessenden|
University of Massachusetts Medical School