Lin-28 is Master of Let-7 miRNA Processing

In yet another report from the incredibly boring and slow-paced field of microRNA research, Viswanathan et al. report on the biochemical purification of a factor that controls the processing of the let7 miRNA. For those of you who have wisely been ignoring recent developments in this mundane field, the Let7s are a group of pretty much useless miRNA genes. All they seem to do is control the fate of stem cells, which intelligent people know are mythical entities invented by people from Canada. Oh, and they're underexpressed in cancer and **may** act as tumor suppressors. Whatever.

Anyway these guys pulled out an interesting protein called Lin-28 in a screen for regulators of Let-7 processing in embryonic stem cells. In stem cells, and presumably cancer cells as well, the idea is that Lin28 binds to the primary Let-7 transcript and prevents processing to the active form. Genes that would otherwise be regulated by Let-7 can therefore be expressed and pluripotency/proliferation carries on. In differentiated cells, Lin-28 is down-regulated, freeing Let-7 to go about it's business repressing it's targets. Or so the story goes.

We already knew that Lin-28 was an RNA-binding protein of developmental significance, so this new finding makes a lot of sense. Palazzo has been drooling all over this paper, and he's particularly worked up about the fact the Lin-28 was also recently identified as one of the magic factors that can reprogram adult somatic cells into pluripotent, embryonic-like stem cells. Read what he has to say for more on this. I find it interesting to note that Lin-28 can be found in P-bodies, cytoplasmic sites of RNA processing that seem to be part of the whole miRNA game (see also here for recent developments in the miRNA-P-body connection).

Anyway, that's enough blathering for now on the clearly trivial research that is being done over at the Harvard Medical School.