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Brandeis professor Nelson Lau (BIO) and his lab published two studies on the P-Element Induced Wimpy testis pathway (PIWI) this September, a pathway that, when blocked in fruit flies, results in underdeveloped reproductive organs.

Fifty percent of the DNA serves no particular function. Jumping genes comprise 50 percent of the DNA and are genetic parasites, called transposable elements or transposons. When this DNA moves around the genome, it destroys genes. If the genes move around, they lead to a variety of mutations, causing symptoms such as infertility. Reproductive cells are particularly sensitive to transposons, or DNA that can change position and mutate within a genome, and rely on the PIWI pathway to keep the transposons in check.

Scientists have long wondered how the pathway works. Despite its checks and balances, transposons still make up such a large portion of the genome. Lau’s studies seek to understand the system in such a way that would help scientists study human infertility transposon-related diseases.
Lau conducted two studies on PIWI. In the first study, Lau and his team, led by graduate student Josef Clark and former technician Christina Post, observed that PIWI proteins are careful. The proteins waited until they had a good composite picture before clamping down on the transposon.
In the second, Lau and postdocs Yuliya Sytnikova, Reazur Rahman and bioinformatician Gung-wei Chirn observed that the movement of new transposable elements in the fruit fly cells to different areas of the genome affects nearby genes. “We all knew that the PIWI pathway was continuously active, so the conventional wisdom was that it was doing a decent job keeping these transposons under wraps,” Lau said. “We stood corrected.”

Results showed transposons are not easily subdued. Some transposons slipped past the PIWI system, landing on new genome spots and impacting surrounding genes. Some transposons could even disguise themselves. Long non-coding RNAs, Lau thinks, “are meant to trick the PIWI proteins.”
This may explain why transposons continue to make up such a large part of the genome, Lau said. “The PIWI pathway works just well enough to allow our germ cells to develop, but not well enough to keep all of the transposons fully redacted,” he says.
A bit of genetic mischief in the right places is good, according to Lau. It ensures genetic variation and diversity, which is important for a species to reproduce and evolve.