Friday, February 15, 2008

splicing - or how we generate more than 150,000 different proteins from about 25,000 genes

Even though the human genome contains only about 25,000 genes, these can produce more than 150,000 different proteins, making the immense human complexity possible. One of the explanations for this contradiction is splicing, a molecular phenomenon that five research groups at the PRBB are studying.

And what is it about? It helps reading the genes. Genes, the instructions to create an organism, are formed by some bits that make sense (full sentences or exons), and bits that are nonsense (random words or introns). Splicing eliminates introns, facilitating the reading of the instructions. Understanding splicing is fundamental, because without it, having the sequence of all genes, (the human genome) would be like having a book and not being able to read it.

And how does splicing help increasing protein diversity? Thanks to alternative splicing. Different cells, or the same cell in different conditions, can decide to include or not a specific exon (sentence) in the final instructions of a gene, the protein. And this decision modifies proteins giving them different actions, even opposite ones. The fact is that we know that nearly 30% of genetic diseases, such as neurofibromatosis, are due to splicing problems.

It is still a mystery how and why cells decide whether to include or not a specific exon in a protein. What is known is that each gene can generate between 2 and 5 different proteins – the most extreme case known is the Dscam gene from Drosophila, which can generate up to 32,000 different proteins.

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