Wikimedia, Unknown SourceWhile most organisms use methyl marks on the genome to stake out gene expression, the fresh-water protozoan Oxytricha trifallax use the tags to kick junk DNA—95 percent of its genome—to the curb, according to a new study in Genome Biology published today (October 17). The finding refutes previous studies that concluded the ciliated single-cell critters—which usually carry four nuclei—have methylation-free DNA.
“It’s actually surprising that there is methylation, because it wasn't reported to be there—a lot of studies in the 80s and 90s looked for it and didn't find it,” said John R. Bracht, a postdoctoral researcher at Princeton University, and lead author of the study. “And what's kind of fun about this, is that it’s the exact same modification that you'll find in humans,” he added, “but it may be playing a different role.”
Oxytricha has a particularly peculiar life-cycle, with each organism containing two types of nuclei: a germ-line micronucleus that houses the entirety of the genome, but is transcriptionally silent, and a transcriptionally active macronucleus, which contains just 5 percent of the genome, explained senior author Laura Landweber, an evolutionary geneticist at Princeton. ...
