microRNAs are really, really important.

The first mouse knockouts for a microRNA (miRNA, short interfering RNA or siRNA [1]), has revealed that it has a important role in the immune system and for homeostasis.

In the work, by people at Cambridge University's Babraham and Sanger Institutes and published recently in Science [2], they knockout out bic/microRNA-155, and got immunodeficient mice that also had funky airways due to them (the airways) being remodelled more.

siRNAs are a fairly recent discovery, and we are only just getting our heads around that fact that they have an incredibly important role in how the genome is used by our cells.
The fact that such regulatory effects can have such a massive effect on the immune system and homoeostasis is really some thing.

All this makes me wonder if any of my own work, which looks at the roles of signalling molecules in the developing skeleton, means anything without knowledge of what siRNAs are doing. That's depressing.

[1] a small, single stranded sequence of RNA which, instead of coding to make a protein, acts to regulate expression of other genes.
[2] DOI: 10.1126/science.1139253