Ever have the sensation that your brain cells were suddenly turning into fat cells? Yeah, sure, but it never really happens. And why not? After all, brain cells, fat cells, blood cells, skin cells - they all have the same DNA, and therefore the same protein-coding genes.
It's because, early in development, different cell types get locked into different patterns of protein production, which those cells maintain more or less faithfully throughout their lifetimes. The evidence continues to pile up in favor of the notion that RNA - whose job many of us learned in biology textbooks was largely confined to ferrying protein-coding recipes stored as DNA on chromosomes to protein-making factories located elsewhere in the cell - is proving crucial to the maintainance of a cell's sense of purpose.
One important new addition to RNA's job description involves work it does much closer to home - along the chromosomes from which RNA is copied. And this line of work requires some serious gymnastics. Whereas RNA was once considered a bit of a stiff in comparison with the regal ruler, DNA, it turns out that RNA's single-stranded lifestyle allows it to perform calisthenics its more rigid double-stranded doppelganger can only dream of.
In a November 2010 post, I wrote about lincRNA, a class of molecules that, rather than code for proteins, can coil themselves up into complicated shapes that allow them to serve as combination adapter-plugs and chauffers. As Stanford's Howard Chang, MD, PhD, and his associates showed last year, at least one lincRNA molecule (out of the perhaps 10,000 different varieties of it now believed to be transcribed from vast stretches of DNA that separate one gene from another) can shuttle massive epigenetic-marking complexes to targeted genes, which those complexes then designate as "gone fishing" - silenced so that the proteins they encode don't get made.
Now, Chang and colleagues have demonstrated lincRNAs' ability to do the opposite: grab another set of gene-marking behemoths by the nose and steer them to genes that then get marked as "open for busines" - activated so that the proteins whose recipes they spell out are produced.
Lots of scientists think RNA was around even before DNA came along. That thinking is bolstered by a growing list of demonstrations that RNA not only carries "digital" information as a rather colorless copy of a gene, but "analog" info as well, in the form of the convoluted conformations its contortions allow it to assume.
Previously: The RNA Insurrection: Genes' "humble servant" rules from behind the scenes