Evolution: It's all in how you splice it

When genes were first discovered, the canonical view was that each gene encodes a unique protein. However, biologists later found that segments of genes can be combined in different ways, giving rise to many different proteins.

This phenomenon, known as alternative RNA splicing, often alters the outputs of signalling networks in different tissues and may contribute disproportionately to differences between species, according to a new study from MIT biologists.

After analysing vast amounts of genetic data, the researchers found that the same genes are expressed in the same tissue types, such as liver or heart, across mammalian species. However, alternative splicing patterns - which determine the segments of those genes included or excluded - vary from species to species.

''The core things that make a heart a heart are mostly determined by a heart-specific gene expression signature. But the core things that make a mouse a mouse may disproportionately derive from splicing patterns that differ from those of rats or other mammals'' says Chris Burge, an MIT professor of biology and biological engineering, and senior author of a paper on the findings in the 20 December online edition of Science.

Lead author of the paper is MIT biology graduate student Jason Merkin. Other authors are Caitlin Russell, a former technician in Burge's lab, and Ping Chen, a visiting grad student at MIT.

A variety of proteins
Alternative RNA splicing (a discovery for which MIT Institute Professor Phillip Sharp shared the 1993 Nobel Prize in medicine or physiology), controls the composition of proteins encoded by a gene.